Transplanckian censorship and global cosmic strings

NASA Astrophysics Data System (ADS)

Dolan, Matthew J.; Draper, Patrick; Kozaczuk, Jonathan; Patel, Hiren

2017-04-01

Large field excursions are required in a number of axion models of inflation. These models also possess global cosmic strings, around which the axion follows a path mirroring the inflationary trajectory. Cosmic strings are thus an interesting theoretical laboratory for the study of transplanckian field excursions. We describe connections be-tween various effective field theory models of axion monodromy and study the classical spacetimes around their supercritical cosmic strings. For small decay constants f < M p and large winding numbers n > M p /f , the EFT is under control and the string cores undergo topological inflation, which may be either of exponential or power-law type. We show that the exterior spacetime is nonsingular and equivalent to a decompactifying cigar geometry, with the radion rolling in a potential generated by axion flux. Signals are able to circumnavigate infinite straight strings in finite but exponentially long time, t ˜ e Δ a/ M p . For finite loops of supercritical string in asymptotically flat space, we argue that if topological inflation occurs, then topological censorship implies transplanckian censorship, or that external observers are forbidden from threading the loop and observing the full excursion of the axion.

Evolution of cosmic string networks

NASA Technical Reports Server (NTRS)

Albrecht, Andreas; Turok, Neil

1989-01-01

Results on cosmic strings are summarized including: (1) the application of non-equilibrium statistical mechanics to cosmic string evolution; (2) a simple one scale model for the long strings which has a great deal of predictive power; (3) results from large scale numerical simulations; and (4) a discussion of the observational consequences of our results. An upper bound on G mu of approximately 10(-7) emerges from the millisecond pulsar gravity wave bound. How numerical uncertainties affect this are discussed. Any changes which weaken the bound would probably also give the long strings the dominant role in producing observational consequences.

Cosmic strings and superconducting cosmic strings

NASA Technical Reports Server (NTRS)

Copeland, Edmund

1988-01-01

The possible consequences of forming cosmic strings and superconducting cosmic strings in the early universe are discussed. Lecture 1 describes the group theoretic reasons for and the field theoretic reasons why cosmic strings can form in spontaneously broken gauge theories. Lecture 2 discusses the accretion of matter onto string loops, emphasizing the scenario with a cold dark matter dominated universe. In lecture 3 superconducting cosmic strings are discussed, as is a mechanism which leads to the formation of structure from such strings.

Type-I cosmic-string network

NASA Astrophysics Data System (ADS)

Hiramatsu, Takashi; Sendouda, Yuuiti; Takahashi, Keitaro; Yamauchi, Daisuke; Yoo, Chul-Moon

2013-10-01

We study the network of Type-I cosmic strings using the field-theoretic numerical simulations in the Abelian-Higgs model. For Type-I strings, the gauge field plays an important role, and thus we find that the correlation length of the strings is strongly dependent upon the parameter β, the ratio between the masses of the scalar field and the gauge field, namely, β=mφ2/mA2. In particular, if we take the cosmic expansion into account, the network becomes densest in the comoving box for a specific value of β for β<1.

First LIGO search for gravitational wave bursts from cosmic (super)strings

NASA Astrophysics Data System (ADS)

Abbott, B. P.; Abbott, R.; Adhikari, R.; Ajith, P.; Allen, B.; Allen, G.; Amin, R. S.; Anderson, S. B.; Anderson, W. G.; Arain, M. A.; Araya, M.; Armandula, H.; Armor, P.; Aso, Y.; Aston, S.; Aufmuth, P.; Aulbert, C.; Babak, S.; Baker, P.; Ballmer, S.; Barker, C.; Barker, D.; Barr, B.; Barriga, P.; Barsotti, L.; Barton, M. A.; Bartos, I.; Bassiri, R.; Bastarrika, M.; Behnke, B.; Benacquista, M.; Betzwieser, J.; Beyersdorf, P. T.; Bilenko, I. A.; Billingsley, G.; Biswas, R.; Black, E.; Blackburn, J. K.; Blackburn, L.; Blair, D.; Bland, B.; Bodiya, T. P.; Bogue, L.; Bork, R.; Boschi, V.; Bose, S.; Brady, P. R.; Braginsky, V. B.; Brau, J. E.; Bridges, D. O.; Brinkmann, M.; Brooks, A. F.; Brown, D. A.; Brummit, A.; Brunet, G.; Bullington, A.; Buonanno, A.; Burmeister, O.; Byer, R. L.; Cadonati, L.; Camp, J. B.; Cannizzo, J.; Cannon, K. C.; Cao, J.; Cardenas, L.; Caride, S.; Castaldi, G.; Caudill, S.; Cavaglià, M.; Cepeda, C.; Chalermsongsak, T.; Chalkley, E.; Charlton, P.; Chatterji, S.; Chelkowski, S.; Chen, Y.; Christensen, N.; Chung, C. T. Y.; Clark, D.; Clark, J.; Clayton, J. H.; Cokelaer, T.; Colacino, C. N.; Conte, R.; Cook, D.; Corbitt, T. R. C.; Cornish, N.; Coward, D.; Coyne, D. C.; Creighton, J. D. E.; Creighton, T. D.; Cruise, A. M.; Culter, R. M.; Cumming, A.; Cunningham, L.; Danilishin, S. L.; Danzmann, K.; Daudert, B.; Davies, G.; Daw, E. J.; Debra, D.; Degallaix, J.; Dergachev, V.; Desai, S.; Desalvo, R.; Dhurandhar, S.; Díaz, M.; Dietz, A.; Donovan, F.; Dooley, K. L.; Doomes, E. E.; Drever, R. W. P.; Dueck, J.; Duke, I.; Dumas, J.-C.; Dwyer, J. G.; Echols, C.; Edgar, M.; Effler, A.; Ehrens, P.; Espinoza, E.; Etzel, T.; Evans, M.; Evans, T.; Fairhurst, S.; Faltas, Y.; Fan, Y.; Fazi, D.; Fehrmann, H.; Finn, L. S.; Flasch, K.; Foley, S.; Forrest, C.; Fotopoulos, N.; Franzen, A.; Frede, M.; Frei, M.; Frei, Z.; Freise, A.; Frey, R.; Fricke, T.; Fritschel, P.; Frolov, V. V.; Fyffe, M.; Galdi, V.; Garofoli, J. A.; Gholami, I.; Giaime, J. A.; Giampanis, S.; Giardina, K. D.; Goda, K.; Goetz, E.; Goggin, L. M.; González, G.; Gorodetsky, M. L.; Goßler, S.; Gouaty, R.; Grant, A.; Gras, S.; Gray, C.; Gray, M.; Greenhalgh, R. J. S.; Gretarsson, A. M.; Grimaldi, F.; Grosso, R.; Grote, H.; Grunewald, S.; Guenther, M.; Gustafson, E. K.; Gustafson, R.; Hage, B.; Hallam, J. M.; Hammer, D.; Hammond, G. D.; Hanna, C.; Hanson, J.; Harms, J.; Harry, G. M.; Harry, I. W.; Harstad, E. D.; Haughian, K.; Hayama, K.; Heefner, J.; Heng, I. S.; Heptonstall, A.; Hewitson, M.; Hild, S.; Hirose, E.; Hoak, D.; Hodge, K. A.; Holt, K.; Hosken, D. J.; Hough, J.; Hoyland, D.; Hughey, B.; Huttner, S. H.; Ingram, D. R.; Isogai, T.; Ito, M.; Ivanov, A.; Johnson, B.; Johnson, W. W.; Jones, D. I.; Jones, G.; Jones, R.; Ju, L.; Kalmus, P.; Kalogera, V.; Kandhasamy, S.; Kanner, J.; Kasprzyk, D.; Katsavounidis, E.; Kawabe, K.; Kawamura, S.; Kawazoe, F.; Kells, W.; Keppel, D. G.; Khalaidovski, A.; Khalili, F. Y.; Khan, R.; Khazanov, E.; King, P.; Kissel, J. S.; Klimenko, S.; Kokeyama, K.; Kondrashov, V.; Kopparapu, R.; Koranda, S.; Kozak, D.; Krishnan, B.; Kumar, R.; Kwee, P.; Lam, P. K.; Landry, M.; Lantz, B.; Lazzarini, A.; Lei, H.; Lei, M.; Leindecker, N.; Leonor, I.; Li, C.; Lin, H.; Lindquist, P. E.; Littenberg, T. B.; Lockerbie, N. A.; Lodhia, D.; Longo, M.; Lormand, M.; Lu, P.; Lubiński, M.; Lucianetti, A.; Lück, H.; Machenschalk, B.; Macinnis, M.; Mageswaran, M.; Mailand, K.; Mandel, I.; Mandic, V.; Márka, S.; Márka, Z.; Markosyan, A.; Markowitz, J.; Maros, E.; Martin, I. W.; Martin, R. M.; Marx, J. N.; Mason, K.; Matichard, F.; Matone, L.; Matzner, R. A.; Mavalvala, N.; McCarthy, R.; McClelland, D. E.; McGuire, S. C.; McHugh, M.; McIntyre, G.; McKechan, D. J. A.; McKenzie, K.; Mehmet, M.; Melatos, A.; Melissinos, A. C.; Menéndez, D. F.; Mendell, G.; Mercer, R. A.; Meshkov, S.; Messenger, C.; Meyer, M. S.; Miller, J.; Minelli, J.; Mino, Y.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Miyakawa, O.; Moe, B.; Mohanty, S. D.; Mohapatra, S. R. P.; Moreno, G.; Morioka, T.; Mors, K.; Mossavi, K.; Mowlowry, C.; Mueller, G.; Müller-Ebhardt, H.; Muhammad, D.; Mukherjee, S.; Mukhopadhyay, H.; Mullavey, A.; Munch, J.; Murray, P. G.; Myers, E.; Myers, J.; Nash, T.; Nelson, J.; Newton, G.; Nishizawa, A.; Numata, K.; O'Dell, J.; O'Reilly, B.; O'Shaughnessy, R.; Ochsner, E.; Ogin, G. H.; Ottaway, D. J.; Ottens, R. S.; Overmier, H.; Owen, B. J.; Pan, Y.; Pankow, C.; Papa, M. A.; Parameshwaraiah, V.; Patel, P.; Pedraza, M.; Penn, S.; Perreca, A.; Pierro, V.; Pinto, I. M.; Pitkin, M.; Pletsch, H. J.; Plissi, M. V.; Postiglione, F.; Principe, M.; Prix, R.; Prokhorov, L.; Punken, O.; Quetschke, V.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raics, Z.; Rainer, N.; Rakhmanov, M.; Raymond, V.; Reed, C. M.; Reed, T.; Rehbein, H.; Reid, S.; Reitze, D. H.; Riesen, R.; Riles, K.; Rivera, B.; Roberts, P.; Robertson, N. A.; Robinson, C.; Robinson, E. L.; Roddy, S.; Röver, C.; Rollins, J.; Romano, J. D.; Romie, J. H.; Rowan, S.; Rüdiger, A.; Russell, P.; Ryan, K.; Sakata, S.; Sancho de La Jordana, L.; Sandberg, V.; Sannibale, V.; Santamaría, L.; Saraf, S.; Sarin, P.; Sathyaprakash, B. S.; Sato, S.; Satterthwaite, M.; Saulson, P. R.; Savage, R.; Savov, P.; Scanlan, M.; Schilling, R.; Schnabel, R.; Schofield, R.; Schulz, B.; Schutz, B. F.; Schwinberg, P.; Scott, J.; Scott, S. M.; Searle, A. C.; Sears, B.; Seifert, F.; Sellers, D.; Sengupta, A. S.; Sergeev, A.; Shapiro, B.; Shawhan, P.; Shoemaker, D. H.; Sibley, A.; Siemens, X.; Sigg, D.; Sinha, S.; Sintes, A. M.; Slagmolen, B. J. J.; Slutsky, J.; Smith, J. R.; Smith, M. R.; Smith, N. D.; Somiya, K.; Sorazu, B.; Stein, A.; Stein, L. C.; Steplewski, S.; Stochino, A.; Stone, R.; Strain, K. A.; Strigin, S.; Stroeer, A.; Stuver, A. L.; Summerscales, T. Z.; Sun, K.-X.; Sung, M.; Sutton, P. J.; Szokoly, G. P.; Talukder, D.; Tang, L.; Tanner, D. B.; Tarabrin, S. P.; Taylor, J. R.; Taylor, R.; Thacker, J.; Thorne, K. A.; Thorne, K. S.; Thüring, A.; Tokmakov, K. V.; Torres, C.; Torrie, C.; Traylor, G.; Trias, M.; Ugolini, D.; Ulmen, J.; Urbanek, K.; Vahlbruch, H.; Vallisneri, M.; van den Broeck, C.; van der Sluys, M. V.; van Veggel, A. A.; Vass, S.; Vaulin, R.; Vecchio, A.; Veitch, J.; Veitch, P.; Veltkamp, C.; Villar, A.; Vorvick, C.; Vyachanin, S. P.; Waldman, S. J.; Wallace, L.; Ward, R. L.; Weidner, A.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Wen, S.; Wette, K.; Whelan, J. T.; Whitcomb, S. E.; Whiting, B. F.; Wilkinson, C.; Willems, P. A.; Williams, H. R.; Williams, L.; Willke, B.; Wilmut, I.; Winkelmann, L.; Winkler, W.; Wipf, C. C.; Wiseman, A. G.; Woan, G.; Wooley, R.; Worden, J.; Wu, W.; Yakushin, I.; Yamamoto, H.; Yan, Z.; Yoshida, S.; Zanolin, M.; Zhang, J.; Zhang, L.; Zhao, C.; Zotov, N.; Zucker, M. E.; Zur Mühlen, H.; Zweizig, J.; Robinet, F.

2009-09-01

We report on a matched-filter search for gravitational wave bursts from cosmic string cusps using LIGO data from the fourth science run (S4) which took place in February and March 2005. No gravitational waves were detected in 14.9 days of data from times when all three LIGO detectors were operating. We interpret the result in terms of a frequentist upper limit on the rate of gravitational wave bursts and use the limits on the rate to constrain the parameter space (string tension, reconnection probability, and loop sizes) of cosmic string models. Many grand unified theory-scale models (with string tension Gμ/c2≈10-6) can be ruled out at 90% confidence for reconnection probabilities p≤10-3 if loop sizes are set by gravitational back reaction.

Cosmic strings and the large-scale structure

NASA Technical Reports Server (NTRS)

Stebbins, Albert

1988-01-01

A possible problem for cosmic string models of galaxy formation is presented. If very large voids are common and if loop fragmentation is not much more efficient than presently believed, then it may be impossible for string scenarios to produce the observed large-scale structure with Omega sub 0 = 1 and without strong environmental biasing.

CMB temperature trispectrum of cosmic strings

NASA Astrophysics Data System (ADS)

Hindmarsh, Mark; Ringeval, Christophe; Suyama, Teruaki

2010-03-01

We provide an analytical expression for the trispectrum of the cosmic microwave background (CMB) temperature anisotropies induced by cosmic strings. Our result is derived for the small angular scales under the assumption that the temperature anisotropy is induced by the Gott-Kaiser-Stebbins effect. The trispectrum is predicted to decay with a noninteger power-law exponent ℓ-ρ with 6<ρ<7, depending on the string microstructure, and thus on the string model. For Nambu-Goto strings, this exponent is related to the string mean square velocity and the loop distribution function. We then explore two classes of wave number configuration in Fourier space, the kite and trapezium quadrilaterals. The trispectrum can be of any sign and appears to be strongly enhanced for all squeezed quadrilaterals.

Stochastic gravitational wave background from light cosmic strings

DOE Office of Scientific and Technical Information (OSTI.GOV)

DePies, Matthew R.; Hogan, Craig J.

2007-06-15

Spectra of the stochastic gravitational wave backgrounds from cosmic strings are calculated and compared with present and future experimental limits. Motivated by theoretical expectations of light cosmic strings in superstring cosmology, improvements in experimental sensitivity, and recent demonstrations of large, stable loop formation from a primordial network, this study explores a new range of string parameters with masses lighter than previously investigated. A standard 'one-scale' model for string loop formation is assumed. Background spectra are calculated numerically for dimensionless string tensions G{mu}/c{sup 2} between 10{sup -7} and 10{sup -18}, and initial loop sizes as a fraction of the Hubble radiusmore » {alpha} from 0.1 to 10{sup -6}. The spectra show a low frequency power-law tail, a broad spectral peak due to loops decaying at the present epoch (including frequencies higher than their fundamental mode, and radiation associated with cusps), and a flat (constant energy density) spectrum at high frequencies due to radiation from loops that decayed during the radiation-dominated era. The string spectrum is distinctive and unlike any other known source. The peak of the spectrum for light strings appears at high frequencies, significantly affecting predicted signals. The spectra of the cosmic string backgrounds are compared with current millisecond pulsar limits and Laser Interferometer Space Antenna (LISA) sensitivity curves. For models with large stable loops ({alpha}=0.1), current pulsar-timing limits exclude G{mu}/c{sup 2}>10{sup -9}, a much tighter limit on string tension than achievable with other techniques, and within the range of current models based on brane inflation. LISA may detect a background from strings as light as G{mu}/c{sup 2}{approx_equal}10{sup -16}, corresponding to field theory strings formed at roughly 10{sup 11} GeV.« less

Non-Abelian cosmic string in the Starobinsky model of gravity

NASA Astrophysics Data System (ADS)

Morais Graça, J. P.; de Pádua Santos, A.; Bezerra de Mello, Eugênio R.; Bezerra, V. B.

In this paper, we analyze numerically the behavior of the solutions corresponding to a non-Abelian cosmic string in the framework of the Starobinsky model, i.e. where f(R) = R + ζR2. We perform the calculations for both an asymptotically flat and asymptotically (anti)-de Sitter spacetimes. We found that the angular deficit generated by the string decreases as the parameter ζ increases, in the case of a null cosmological constant. For a positive cosmological constant, we found that the cosmic horizon is affected in a nontrivial way by the parameter ζ.

Edge detection, cosmic strings and the south pole telescope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stewart, Andrew; Brandenberger, Robert, E-mail: stewarta@physics.mcgill.ca, E-mail: rhb@physics.mcgill.ca

2009-02-15

We develop a method of constraining the cosmic string tension G{mu} which uses the Canny edge detection algorithm as a means of searching CMB temperature maps for the signature of the Kaiser-Stebbins effect. We test the potential of this method using high resolution, simulated CMB temperature maps. By modeling the future output from the South Pole Telescope project (including anticipated instrumental noise), we find that cosmic strings with G{mu} > 5.5 Multiplication-Sign 10{sup -8} could be detected.

Cosmic archaeology with gravitational waves from cosmic strings

NASA Astrophysics Data System (ADS)

Cui, Yanou; Lewicki, Marek; Morrissey, David E.; Wells, James D.

2018-06-01

Cosmic strings are generic cosmological predictions of many extensions of the standard model of particle physics, such as a U (1 )' symmetry-breaking phase transition in the early Universe or remnants of superstring theory. Unlike other topological defects, cosmic strings can reach a scaling regime that maintains a small fixed fraction of the total energy density of the Universe from a very early epoch until today. If present, they will oscillate and generate gravitational waves with a frequency spectrum that imprints the dominant sources of total cosmic energy density throughout the history of the Universe. We demonstrate that current and future gravitational wave detectors, such as LIGO and LISA, could be capable of measuring the frequency spectrum of gravitational waves from cosmic strings and discerning the energy composition of the Universe at times well before primordial nucleosynthesis and the cosmic microwave background where standard cosmology has yet to be tested. This work establishes a benchmark case that gravitational waves may provide an unprecedented, powerful tool for probing the evolutionary history of the very early Universe.

CMB temperature trispectrum of cosmic strings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hindmarsh, Mark; Ringeval, Christophe; Suyama, Teruaki

2010-03-15

We provide an analytical expression for the trispectrum of the cosmic microwave background (CMB) temperature anisotropies induced by cosmic strings. Our result is derived for the small angular scales under the assumption that the temperature anisotropy is induced by the Gott-Kaiser-Stebbins effect. The trispectrum is predicted to decay with a noninteger power-law exponent l{sup -{rho}}with 6<{rho}<7, depending on the string microstructure, and thus on the string model. For Nambu-Goto strings, this exponent is related to the string mean square velocity and the loop distribution function. We then explore two classes of wave number configuration in Fourier space, the kite andmore » trapezium quadrilaterals. The trispectrum can be of any sign and appears to be strongly enhanced for all squeezed quadrilaterals.« less

Construction of cosmic string induced temperature anisotropy maps with CMBFAST and statistical analysis

NASA Astrophysics Data System (ADS)

Simatos, N.; Perivolaropoulos, L.

2001-01-01

We use the publicly available code CMBFAST, as modified by Pogosian and Vachaspati, to simulate the effects of wiggly cosmic strings on the cosmic microwave background (CMB). Using the modified CMBFAST code, which takes into account vector modes and models wiggly cosmic strings by the one-scale model, we go beyond the angular power spectrum to construct CMB temperature maps with a resolution of a few degrees. The statistics of these maps are then studied using conventional and recently proposed statistical tests optimized for the detection of hidden temperature discontinuities induced by the Gott-Kaiser-Stebbins effect. We show, however, that these realistic maps cannot be distinguished in a statistically significant way from purely Gaussian maps with an identical power spectrum.

Resurrecting hot dark matter - Large-scale structure from cosmic strings and massive neutrinos

NASA Technical Reports Server (NTRS)

Scherrer, Robert J.

1988-01-01

These are the results of a numerical simulation of the formation of large-scale structure from cosmic-string loops in a universe dominated by massive neutrinos (hot dark matter). This model has several desirable features. The final matter distribution contains isolated density peaks embedded in a smooth background, producing a natural bias in the distribution of luminous matter. Because baryons can accrete onto the cosmic strings before the neutrinos, the galaxies will have baryon cores and dark neutrino halos. Galaxy formation in this model begins much earlier than in random-phase models. On large scales the distribution of clustered matter visually resembles the CfA survey, with large voids and filaments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lizarraga, Joanes; Urrestilla, Jon; Daverio, David

We present cosmic microwave background (CMB) power spectra from recent numerical simulations of cosmic strings in the Abelian Higgs model and compare them to CMB power spectra measured by Planck . We obtain revised constraints on the cosmic string tension parameter G μ. For example, in the ΛCDM model with the addition of strings and no primordial tensor perturbations, we find G μ < 2.0 × 10{sup −7} at 95% confidence, about 20% lower than the value obtained from previous simulations, which had 1/64 of the spatial volume. The increased computational volume also makes it possible to simulate fully themore » physical equations of motion, in which the string cores shrink in comoving coordinates. We find however that this, and the larger dynamic range, changes the amplitude of the power spectra by only about 10%. The main cause of the stronger constraints on G μ is instead an improved treatment of the string evolution across the radiation-matter transition.« less

On the large-scale structures formed by wakes of open cosmic strings

NASA Technical Reports Server (NTRS)

Hara, Tetsuya; Morioka, Shoji; Miyoshi, Shigeru

1990-01-01

Large-scale structures of the universe have been variously described as sheetlike, filamentary, cellular, bubbles or spongelike. Recently cosmic strings became one of viable candidates for a galaxy formation scenario, and some of the large-scale structures seem to be simply explained by the open cosmic strings. According to this scenario, sheets are wakes which are traces of moving open cosmic strings where dark matter and baryonic matter have accumulated. Filaments are intersections of such wakes and high density regions are places where three wakes intersect almost orthogonally. The wakes formed at t sub eq become the largest surface density among all wakes, where t sub eq is the epoch when matter density equals to radiation density. If we assume that there is one open cosmic string per each horizon, then it can be explained that the typical distances among wakes, filaments and clusters are also approx. 10(exp 2) Mpc. This model does not exclude a much more large scale structure. Open cosmic string may move even now and accumulate cold dark matter after its traces. However, the surface density is much smaller than the ones formed at t sub eq. From this model, it is expected that the typical high density region will have extended features such as six filaments and three sheets and be surrounded by eight empty regions (voids). Here, the authors are mainly concerned with such structures and have made numerical simulations for the formation of such large scale structures.

Cosmic Strings Stabilized by Quantum Fluctuations

NASA Astrophysics Data System (ADS)

Weigel, H.

2017-03-01

Fermion quantum corrections to the energy of cosmic strings are computed. A number of rather technical tools are needed to formulate this correction, and isospin and gauge invariance are employed to verify consistency of these tools. These corrections must also be included when computing the energy of strings that are charged by populating fermion bound states in its background. It is found that charged strings are dynamically stabilized in theories similar to the standard model of particle physics.

CMB temperature bispectrum induced by cosmic strings

NASA Astrophysics Data System (ADS)

Hindmarsh, Mark; Ringeval, Christophe; Suyama, Teruaki

2009-10-01

The cosmic microwave background (CMB) bispectrum of the temperature anisotropies induced by a network of cosmic strings is derived for small angular scales, under the assumption that the principal cause of temperature fluctuations is the Gott-Kaiser-Stebbins effect. We provide analytical expressions for all isosceles triangle configurations in Fourier space. Their overall amplitude is amplified as the inverse cube of the angle and diverges for flat triangles. The isosceles configurations generically lead to a negative bispectrum with a power-law decay ℓ-6 for large multipole ℓ. However, collapsed triangles are found to be associated with a positive bispectrum whereas the squeezed triangles still exhibit negative values. We then compare our analytical estimates to a direct computation of the bispectrum from a set of 300 statistically independent temperature maps obtained from Nambu-Goto cosmic string simulations in a Friedmann-Lemaître-Robertson-Walker universe. We find good agreement for the overall amplitude, the power-law behavior, and the angle dependency of the various triangle configurations. At ℓ˜500 the cosmic string Gott-Kaiser-Stebbins effect contributes approximately the same equilateral CMB bispectrum amplitude as an inflationary model with |fNLloc|≃103, if the strings contribute about 10% of the temperature power spectrum at ℓ=10. Current bounds on fNL are not derived using cosmic string bispectrum templates, and so our fNL estimate cannot be used to derive bounds on strings. However it does suggest that string bispectrum templates should be included in the search of CMB non-Gaussianities.

Gravitational-wave stochastic background from cosmic strings.

PubMed

Siemens, Xavier; Mandic, Vuk; Creighton, Jolien

2007-03-16

We consider the stochastic background of gravitational waves produced by a network of cosmic strings and assess their accessibility to current and planned gravitational wave detectors, as well as to big bang nucleosynthesis (BBN), cosmic microwave background (CMB), and pulsar timing constraints. We find that current data from interferometric gravitational wave detectors, such as Laser Interferometer Gravitational Wave Observatory (LIGO), are sensitive to areas of parameter space of cosmic string models complementary to those accessible to pulsar, BBN, and CMB bounds. Future more sensitive LIGO runs and interferometers such as Advanced LIGO and Laser Interferometer Space Antenna (LISA) will be able to explore substantial parts of the parameter space.

CMB power spectrum contribution from cosmic strings using field-evolution simulations of the Abelian Higgs model

NASA Astrophysics Data System (ADS)

Bevis, Neil; Hindmarsh, Mark; Kunz, Martin; Urrestilla, Jon

2007-03-01

We present the first field-theoretic calculations of the contribution made by cosmic strings to the temperature power spectrum of the cosmic microwave background (CMB). Unlike previous work, in which strings were modeled as idealized one-dimensional objects, we evolve the simplest example of an underlying field theory containing local U(1) strings, the Abelian Higgs model. Limitations imposed by finite computational volumes are overcome using the scaling property of string networks and a further extrapolation related to the lessening of the string width in comoving coordinates. The strings and their decay products, which are automatically included in the field theory approach, source metric perturbations via their energy-momentum tensor, the unequal-time correlation functions of which are used as input into the CMB calculation phase. These calculations involve the use of a modified version of CMBEASY, with results provided over the full range of relevant scales. We find that the string tension μ required to normalize to the WMAP 3-year data at multipole ℓ=10 is Gμ=[2.04±0.06(stat.)±0.12(sys.)]×10-6, where we have quoted statistical and systematic errors separately, and G is Newton’s constant. This is a factor 2 3 higher than values in current circulation.

Bianchi-V string cosmological model with dark energy anisotropy

NASA Astrophysics Data System (ADS)

Mishra, B.; Tripathy, S. K.; Ray, Pratik P.

2018-05-01

The role of anisotropic components on the dark energy and the dynamics of the universe is investigated. An anisotropic dark energy fluid with different pressures along different spatial directions is assumed to incorporate the effect of anisotropy. One dimensional cosmic strings aligned along x-direction supplement some kind of anisotropy. Anisotropy in the dark energy pressure is found to evolve with cosmic expansion at least at late times. At an early phase, the anisotropic effect due to the cosmic strings substantially affect the dynamics of the accelerating universe.

Large-scale structure from cosmic-string loops in a baryon-dominated universe

NASA Technical Reports Server (NTRS)

Melott, Adrian L.; Scherrer, Robert J.

1988-01-01

The results are presented of a numerical simulation of the formation of large-scale structure in a universe with Omega(0) = 0.2 and h = 0.5 dominated by baryons in which cosmic strings provide the initial density perturbations. The numerical model yields a power spectrum. Nonlinear evolution confirms that the model can account for 700 km/s bulk flows and a strong cluster-cluster correlation, but does rather poorly on smaller scales. There is no visual 'filamentary' structure, and the two-point correlation has too steep a logarithmic slope. The value of G mu = 4 x 10 to the -6th is significantly lower than previous estimates for the value of G mu in baryon-dominated cosmic string models.

Scaling properties of cosmic (super)string networks

NASA Astrophysics Data System (ADS)

Martins, C. J. A. P.

2014-10-01

I use a combination of state-of-the-art numerical simulations and analytic modelling to discuss the scaling properties of cosmic defect networks, including superstrings. Particular attention is given to the role of extra degrees of freedom in the evolution of these networks. Compared to the 'plain vanilla' case of Goto-Nambu strings, three such extensions play important but distinct roles in the network dynamics: the presence of charges/currents on the string worldsheet, the existence of junctions, and the possibility of a hierarchy of string tensions. I also comment on insights gained from studying simpler defect networks, including Goto-Nambu strings themselves, domain walls and semilocal strings.

Detection of low tension cosmic superstrings

NASA Astrophysics Data System (ADS)

Chernoff, David F.; Tye, S.-H. Henry

2018-05-01

Cosmic superstrings of string theory differ from conventional cosmic strings of field theory. We review how the physical and cosmological properties of the macroscopic string loops influence experimental searches for these relics from the epoch of inflation. The universe's average density of cosmic superstrings can easily exceed that of conventional cosmic strings having the same tension by two or more orders of magnitude. The cosmological behavior of the remnant superstring loops is qualitatively distinct because the string tension is exponentially smaller than the string scale in flux compactifications in string theory. Low tension superstring loops live longer, experience less recoil (rocket effect from the emission of gravitational radiation) and tend to cluster like dark matter in galaxies. Clustering enhances the string loop density with respect to the cosmological average in collapsed structures in the universe. The enhancement at the Sun's position is ~ 105. We develop a model encapsulating the leading order string theory effects, the current understanding of the string network loop production and the influence of cosmological structure formation suitable for forecasting the detection of superstring loops via optical microlensing, gravitational wave bursts and fast radio bursts. We evaluate the detection rate of bursts from cusps and kinks by LIGO- and LISA-like experiments. Clustering dominates rates for G μ < 10‑11.9 (LIGO cusp), G μ<10‑11.2 (LISA cusp), G μ < 10‑10.6 (LISA kink); we forecast experimentally accessible gravitational wave bursts for G μ>10‑14.2 (LIGO cusp), G μ>10‑15 (LISA cusp) and G μ>10‑ 14.1 (LISA kink).

CMB temperature bispectrum induced by cosmic strings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hindmarsh, Mark; Ringeval, Christophe; Suyama, Teruaki

2009-10-15

The cosmic microwave background (CMB) bispectrum of the temperature anisotropies induced by a network of cosmic strings is derived for small angular scales, under the assumption that the principal cause of temperature fluctuations is the Gott-Kaiser-Stebbins effect. We provide analytical expressions for all isosceles triangle configurations in Fourier space. Their overall amplitude is amplified as the inverse cube of the angle and diverges for flat triangles. The isosceles configurations generically lead to a negative bispectrum with a power-law decay l{sup -6} for large multipole l. However, collapsed triangles are found to be associated with a positive bispectrum whereas the squeezedmore » triangles still exhibit negative values. We then compare our analytical estimates to a direct computation of the bispectrum from a set of 300 statistically independent temperature maps obtained from Nambu-Goto cosmic string simulations in a Friedmann-Lemaitre-Robertson-Walker universe. We find good agreement for the overall amplitude, the power-law behavior, and the angle dependency of the various triangle configurations. At l{approx}500 the cosmic string Gott-Kaiser-Stebbins effect contributes approximately the same equilateral CMB bispectrum amplitude as an inflationary model with |f{sub NL}{sup loc}|{approx_equal}10{sup 3}, if the strings contribute about 10% of the temperature power spectrum at l=10. Current bounds on f{sub NL} are not derived using cosmic string bispectrum templates, and so our f{sub NL} estimate cannot be used to derive bounds on strings. However it does suggest that string bispectrum templates should be included in the search of CMB non-Gaussianities.« less

Constraints on Cosmic Strings from the LIGO-Virgo Gravitational-Wave Detectors

NASA Astrophysics Data System (ADS)

Aasi, J.; Abadie, J.; Abbott, B. P.; Abbott, R.; Abbott, T.; Abernathy, M. R.; Accadia, T.; Acernese, F.; Adams, C.; Adams, T.; Adhikari, R. X.; Affeldt, C.; Agathos, M.; Aggarwal, N.; Aguiar, O. D.; Ajith, P.; Allen, B.; Allocca, A.; Amador Ceron, E.; Amariutei, D.; Anderson, R. A.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Araya, M. C.; Arceneaux, C.; Areeda, J.; Ast, S.; Aston, S. M.; Astone, P.; Aufmuth, P.; Aulbert, C.; Austin, L.; Aylott, B. E.; Babak, S.; Baker, P. T.; Ballardin, G.; Ballmer, S. W.; Barayoga, J. C.; Barker, D.; Barnum, S. H.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barton, M. A.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J.; Bauchrowitz, J.; Bauer, Th. S.; Bebronne, M.; Behnke, B.; Bejger, M.; Beker, M. G.; Bell, A. S.; Bell, C.; Belopolski, I.; Bergmann, G.; Berliner, J. M.; Bersanetti, D.; Bertolini, A.; Bessis, D.; Betzwieser, J.; Beyersdorf, P. T.; Bhadbhade, T.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Bitossi, M.; Bizouard, M. A.; Black, E.; Blackburn, J. K.; Blackburn, L.; Blair, D.; Blom, M.; Bock, O.; Bodiya, T. P.; Boer, M.; Bogan, C.; Bond, C.; Bondu, F.; Bonelli, L.; Bonnand, R.; Bork, R.; Born, M.; Boschi, V.; Bose, S.; Bosi, L.; Bowers, J.; Bradaschia, C.; Brady, P. R.; Braginsky, V. B.; Branchesi, M.; Brannen, C. A.; Brau, J. E.; Breyer, J.; Briant, T.; Bridges, D. O.; Brillet, A.; Brinkmann, M.; Brisson, V.; Britzger, M.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brückner, F.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cadonati, L.; Cagnoli, G.; Calderón Bustillo, J.; Calloni, E.; Camp, J. B.; Campsie, P.; Cannon, K. C.; Canuel, B.; Cao, J.; Capano, C. D.; Carbognani, F.; Carbone, L.; Caride, S.; Castiglia, A.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C.; Cesarini, E.; Chakraborty, R.; Chalermsongsak, T.; Chao, S.; Charlton, P.; Chassande-Mottin, E.; Chen, X.; Chen, Y.; Chincarini, A.; Chiummo, A.; Cho, H. S.; Chow, J.; Christensen, N.; Chu, Q.; Chua, S. S. Y.; Chung, S.; Ciani, G.; Clara, F.; Clark, D. E.; Clark, J. A.; Cleva, F.; Coccia, E.; Cohadon, P.-F.; Colla, A.; Colombini, M.; Constancio, M.; Conte, A.; Conte, R.; Cook, D.; Corbitt, T. R.; Cordier, M.; Cornish, N.; Corsi, A.; Costa, C. A.; Coughlin, M. W.; Coulon, J.-P.; Countryman, S.; Couvares, P.; Coward, D. M.; Cowart, M.; Coyne, D. C.; Craig, K.; Creighton, J. D. E.; Creighton, T. D.; Crowder, S. G.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dahl, K.; Canton, T. Dal; Damjanic, M.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Dattilo, V.; Daudert, B.; Daveloza, H.; Davier, M.; Davies, G. S.; Daw, E. J.; Day, R.; Dayanga, T.; De Rosa, R.; Debreczeni, G.; Degallaix, J.; Del Pozzo, W.; Deleeuw, E.; Deléglise, S.; Denker, T.; Dent, T.; Dereli, H.; Dergachev, V.; DeRosa, R.; DeSalvo, R.; Dhurandhar, S.; Di Fiore, L.; Di Lieto, A.; Di Palma, I.; Di Virgilio, A.; Díaz, M.; Dietz, A.; Dmitry, K.; Donovan, F.; Dooley, K. L.; Doravari, S.; Drago, M.; Drever, R. W. P.; Driggers, J. C.; Du, Z.; Dumas, J.-C.; Dwyer, S.; Eberle, T.; Edwards, M.; Effler, A.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Endrőczi, G.; Essick, R.; Etzel, T.; Evans, K.; Evans, M.; Evans, T.; Factourovich, M.; Fafone, V.; Fairhurst, S.; Fang, Q.; Farinon, S.; Farr, B.; Farr, W.; Favata, M.; Fazi, D.; Fehrmann, H.; Feldbaum, D.; Ferrante, I.; Ferrini, F.; Fidecaro, F.; Finn, L. S.; Fiori, I.; Fisher, R.; Flaminio, R.; Foley, E.; Foley, S.; Forsi, E.; Fotopoulos, N.; Fournier, J.-D.; Franco, S.; Frasca, S.; Frasconi, F.; Frede, M.; Frei, M.; Frei, Z.; Freise, A.; Frey, R.; Fricke, T. T.; Fritschel, P.; Frolov, V. V.; Fujimoto, M.-K.; Fulda, P.; Fyffe, M.; Gair, J.; Gammaitoni, L.; Garcia, J.; Garufi, F.; Gehrels, N.; Gemme, G.; Genin, E.; Gennai, A.; Gergely, L.; Ghosh, S.; Giaime, J. A.; Giampanis, S.; Giardina, K. D.; Giazotto, A.; Gil-Casanova, S.; Gill, C.; Gleason, J.; Goetz, E.; Goetz, R.; Gondan, L.; González, G.; Gordon, N.; Gorodetsky, M. L.; Gossan, S.; Goßler, S.; Gouaty, R.; Graef, C.; Graff, P. B.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greenhalgh, R. J. S.; Gretarsson, A. M.; Griffo, C.; Groot, P.; Grote, H.; Grover, K.; Grunewald, S.; Guidi, G. M.; Guido, C.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Hall, B.; Hall, E.; Hammer, D.; Hammond, G.; Hanke, M.; Hanks, J.; Hanna, C.; Hanson, J.; Harms, J.; Harry, G. M.; Harry, I. W.; Harstad, E. D.; Hartman, M. T.; Haughian, K.; Hayama, K.; Heefner, J.; Heidmann, A.; Heintze, M.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hoak, D.; Hodge, K. A.; Holt, K.; Holtrop, M.; Hong, T.; Hooper, S.; Horrom, T.; Hosken, D. J.; Hough, J.; Howell, E. J.; Hu, Y.; Hua, Z.; Huang, V.; Huerta, E. A.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh, M.; Huynh-Dinh, T.; Iafrate, J.; Ingram, D. R.; Inta, R.; Isogai, T.; Ivanov, A.; Iyer, B. R.; Izumi, K.; Jacobson, M.; James, E.; Jang, H.; Jang, Y. J.; Jaranowski, P.; Jiménez-Forteza, F.; Johnson, W. W.; Jones, D.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; Haris, K.; Kalmus, P.; Kalogera, V.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Kasprzack, M.; Kasturi, R.; Katsavounidis, E.; Katzman, W.; Kaufer, H.; Kaufman, K.; Kawabe, K.; Kawamura, S.; Kawazoe, F.; Kéfélian, F.; Keitel, D.; Kelley, D. B.; Kells, W.; Keppel, D. G.; Khalaidovski, A.; Khalili, F. Y.; Khazanov, E. A.; Kim, B. K.; Kim, C.; Kim, K.; Kim, N.; Kim, W.; Kim, Y.-M.; King, E. J.; King, P. J.; Kinzel, D. L.; Kissel, J. S.; Klimenko, S.; Kline, J.; Koehlenbeck, S.; Kokeyama, K.; Kondrashov, V.; Koranda, S.; Korth, W. Z.; Kowalska, I.; Kozak, D.; Kremin, A.; Kringel, V.; Królak, A.; Kucharczyk, C.; Kudla, S.; Kuehn, G.; Kumar, A.; Kumar, P.; Kumar, R.; Kurdyumov, R.; Kwee, P.; Landry, M.; Lantz, B.; Larson, S.; Lasky, P. D.; Lawrie, C.; Lazzarini, A.; Le Roux, A.; Leaci, P.; Lebigot, E. O.; Lee, C.-H.; Lee, H. K.; Lee, H. M.; Lee, J.; Lee, J.; Leonardi, M.; Leong, J. R.; Leroy, N.; Letendre, N.; Levine, B.; Lewis, J. B.; Lhuillier, V.; Li, T. G. F.; Lin, A. C.; Littenberg, T. B.; Litvine, V.; Liu, F.; Liu, H.; Liu, Y.; Liu, Z.; Lloyd, D.; Lockerbie, N. A.; Lockett, V.; Lodhia, D.; Loew, K.; Logue, J.; Lombardi, A. L.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J.; Luan, J.; Lubinski, M. J.; Lück, H.; Lundgren, A. P.; Macarthur, J.; Macdonald, E.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magana-Sandoval, F.; Mageswaran, M.; Mailand, K.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; Manca, G. M.; Mandel, I.; Mandic, V.; Mangano, V.; Mantovani, M.; Marchesoni, F.; Marion, F.; Márka, S.; Márka, Z.; Markosyan, A.; Maros, E.; Marque, J.; Martelli, F.; Martin, I. W.; Martin, R. M.; Martinelli, L.; Martynov, D.; Marx, J. N.; Mason, K.; Masserot, A.; Massinger, T. J.; Matichard, F.; Matone, L.; Matzner, R. A.; Mavalvala, N.; May, G.; Mazumder, N.; Mazzolo, G.; McCarthy, R.; McClelland, D. E.; McGuire, S. C.; McIntyre, G.; McIver, J.; Meacher, D.; Meadors, G. D.; Mehmet, M.; Meidam, J.; Meier, T.; Melatos, A.; Mendell, G.; Mercer, R. A.; Meshkov, S.; Messenger, C.; Meyer, M. S.; Miao, H.; Michel, C.; Mikhailov, E. E.; Milano, L.; Miller, J.; Minenkov, Y.; Mingarelli, C. M. F.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moe, B.; Mohan, M.; Mohapatra, S. R. P.; Mokler, F.; Moraru, D.; Moreno, G.; Morgado, N.; Mori, T.; Morriss, S. R.; Mossavi, K.; Mours, B.; Mow-Lowry, C. M.; Mueller, C. L.; Mueller, G.; Mukherjee, S.; Mullavey, A.; Munch, J.; Murphy, D.; Murray, P. G.; Mytidis, A.; Nagy, M. F.; Nanda Kumar, D.; Nardecchia, I.; Nash, T.; Naticchioni, L.; Nayak, R.; Necula, V.; Nelemans, G.; Neri, I.; Neri, M.; Newton, G.; Nguyen, T.; Nishida, E.; Nishizawa, A.; Nitz, A.; Nocera, F.; Nolting, D.; Normandin, M. E.; Nuttall, L. K.; Ochsner, E.; O'Dell, J.; Oelker, E.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Oppermann, P.; O'Reilly, B.; Ortega Larcher, W.; O'Shaughnessy, R.; Osthelder, C.; Ott, C. D.; Ottaway, D. J.; Ottens, R. S.; Ou, J.; Overmier, H.; Owen, B. J.; Padilla, C.; Pai, A.; Palomba, C.; Pan, Y.; Pankow, C.; Paoletti, F.; Paoletti, R.; Papa, M. A.; Paris, H.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Pedraza, M.; Peiris, P.; Penn, S.; Perreca, A.; Phelps, M.; Pichot, M.; Pickenpack, M.; Piergiovanni, F.; Pierro, V.; Pinard, L.; Pindor, B.; Pinto, I. M.; Pitkin, M.; Poeld, J.; Poggiani, R.; Poole, V.; Poux, C.; Predoi, V.; Prestegard, T.; Price, L. R.; Prijatelj, M.; Principe, M.; Privitera, S.; Prix, R.; Prodi, G. A.; Prokhorov, L.; Puncken, O.; Punturo, M.; Puppo, P.; Quetschke, V.; Quintero, E.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Rácz, I.; Radkins, H.; Raffai, P.; Raja, S.; Rajalakshmi, G.; Rakhmanov, M.; Ramet, C.; Rapagnani, P.; Raymond, V.; Re, V.; Reed, C. M.; Reed, T.; Regimbau, T.; Reid, S.; Reitze, D. H.; Ricci, F.; Riesen, R.; Riles, K.; Robertson, N. A.; Robinet, F.; Rocchi, A.; Roddy, S.; Rodriguez, C.; Rodruck, M.; Roever, C.; Rolland, L.; Rollins, J. G.; Romano, R.; Romanov, G.; Romie, J. H.; Rosińska, D.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Ryan, K.; Salemi, F.; Sammut, L.; Sandberg, V.; Sanders, J.; Sannibale, V.; Santiago-Prieto, I.; Saracco, E.; Sassolas, B.; Sathyaprakash, B. S.; Saulson, P. R.; Savage, R.; Schilling, R.; Schnabel, R.; Schofield, R. M. S.; Schreiber, E.; Schuette, D.; Schulz, B.; Schutz, B. F.; Schwinberg, P.; Scott, J.; Scott, S. M.; Seifert, F.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sergeev, A.; Shaddock, D.; Shah, S.; Shahriar, M. S.; Shaltev, M.; Shapiro, B.; Shawhan, P.; Shoemaker, D. H.; Sidery, T. L.; Siellez, K.; Siemens, X.; Sigg, D.; Simakov, D.; Singer, A.; Singer, L.; Sintes, A. M.; Skelton, G. R.; Slagmolen, B. J. J.; Slutsky, J.; Smith, J. R.; Smith, M. R.; Smith, R. J. E.; Smith-Lefebvre, N. D.; Soden, K.; Son, E. J.; Sorazu, B.; Souradeep, T.; Sperandio, L.; Staley, A.; Steinert, E.; Steinlechner, J.; Steinlechner, S.; Steplewski, S.; Stevens, D.; Stochino, A.; Stone, R.; Strain, K. A.; Straniero, N.; Strigin, S.; Stroeer, A. S.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Susmithan, S.; Sutton, P. J.; Swinkels, B.; Szeifert, G.; Tacca, M.; Talukder, D.; Tang, L.; Tanner, D. B.; Tarabrin, S. P.; Taylor, R.; ter Braack, A. P. M.; Thirugnanasambandam, M. P.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thorne, K. S.; Thrane, E.; Tiwari, V.; Tokmakov, K. V.; Tomlinson, C.; Toncelli, A.; Tonelli, M.; Torre, O.; Torres, C. V.; Torrie, C. I.; Travasso, F.; Traylor, G.; Tse, M.; Ugolini, D.; Unnikrishnan, C. S.; Vahlbruch, H.; Vajente, G.; Vallisneri, M.; van den Brand, J. F. J.; Van Den Broeck, C.; van der Putten, S.; van der Sluys, M. V.; van Heijningen, J.; van Veggel, A. A.; Vass, S.; Vasúth, M.; Vaulin, R.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Verkindt, D.; Verma, S.; Vetrano, F.; Viceré, A.; Vincent-Finley, R.; Vinet, J.-Y.; Vitale, S.; Vlcek, B.; Vo, T.; Vocca, H.; Vorvick, C.; Vousden, W. D.; Vrinceanu, D.; Vyachanin, S. P.; Wade, A.; Wade, L.; Wade, M.; Waldman, S. J.; Walker, M.; Wallace, L.; Wan, Y.; Wang, J.; Wang, M.; Wang, X.; Wanner, A.; Ward, R. L.; Was, M.; Weaver, B.; Wei, L.-W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Welborn, T.; Wen, L.; Wessels, P.; West, M.; Westphal, T.; Wette, K.; Whelan, J. T.; Whitcomb, S. E.; White, D. J.; Whiting, B. F.; Wibowo, S.; Wiesner, K.; Wilkinson, C.; Williams, L.; Williams, R.; Williams, T.; Willis, J. L.; Willke, B.; Wimmer, M.; Winkelmann, L.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Worden, J.; Yablon, J.; Yakushin, I.; Yamamoto, H.; Yancey, C. C.; Yang, H.; Yeaton-Massey, D.; Yoshida, S.; Yum, H.; Yvert, M.; ZadroŻny, A.; Zanolin, M.; Zendri, J.-P.; Zhang, F.; Zhang, L.; Zhao, C.; Zhu, H.; Zhu, X. J.; Zotov, N.; Zucker, M. E.; Zweizig, J.; LIGO Scientific Collaboration; Virgo Collaboration

2014-04-01

Cosmic strings can give rise to a large variety of interesting astrophysical phenomena. Among them, powerful bursts of gravitational waves (GWs) produced by cusps are a promising observational signature. In this Letter we present a search for GWs from cosmic string cusps in data collected by the LIGO and Virgo gravitational wave detectors between 2005 and 2010, with over 625 days of live time. We find no evidence of GW signals from cosmic strings. From this result, we derive new constraints on cosmic string parameters, which complement and improve existing limits from previous searches for a stochastic background of GWs from cosmic microwave background measurements and pulsar timing data. In particular, if the size of loops is given by the gravitational backreaction scale, we place upper limits on the string tension Gμ below 10-8 in some regions of the cosmic string parameter space.

Constraints on Cosmic Strings from the LIGO-Virgo Gravitational-Wave Detectors

NASA Technical Reports Server (NTRS)

Aasi, J.; Abadie, J.; Abbott, B.P.; Abbott, R.; Abbott, T.; Abernathy, M.R.; Accadia, T.; Adams, C.; Adams, T.; Adhikari, R.X.;

Constraints on cosmic strings from the LIGO-Virgo gravitational-wave detectors.

PubMed

Aasi, J; Abadie, J; Abbott, B P; Abbott, R; Abbott, T; Abernathy, M R; Accadia, T; Acernese, F; Adams, C; Adams, T; Adhikari, R X; Affeldt, C; Agathos, M; Aggarwal, N; Aguiar, O D; Ajith, P; Allen, B; Allocca, A; Amador Ceron, E; Amariutei, D; Anderson, R A; Anderson, S B; Anderson, W G; Arai, K; Araya, M C; Arceneaux, C; Areeda, J; Ast, S; Aston, S M; Astone, P; Aufmuth, P; Aulbert, C; Austin, L; Aylott, B E; Babak, S; Baker, P T; Ballardin, G; Ballmer, S W; Barayoga, J C; Barker, D; Barnum, S H; Barone, F; Barr, B; Barsotti, L; Barsuglia, M; Barton, M A; Bartos, I; Bassiri, R; Basti, A; Batch, J; Bauchrowitz, J; Bauer, Th S; Bebronne, M; Behnke, B; Bejger, M; Beker, M G; Bell, A S; Bell, C; Belopolski, I; Bergmann, G; Berliner, J M; Bersanetti, D; Bertolini, A; Bessis, D; Betzwieser, J; Beyersdorf, P T; Bhadbhade, T; Bilenko, I A; Billingsley, G; Birch, J; Bitossi, M; Bizouard, M A; Black, E; Blackburn, J K; Blackburn, L; Blair, D; Blom, M; Bock, O; Bodiya, T P; Boer, M; Bogan, C; Bond, C; Bondu, F; Bonelli, L; Bonnand, R; Bork, R; Born, M; Boschi, V; Bose, S; Bosi, L; Bowers, J; Bradaschia, C; Brady, P R; Braginsky, V B; Branchesi, M; Brannen, C A; Brau, J E; Breyer, J; Briant, T; Bridges, D O; Brillet, A; Brinkmann, M; Brisson, V; Britzger, M; Brooks, A F; Brown, D A; Brown, D D; Brückner, F; Bulik, T; Bulten, H J; Buonanno, A; Buskulic, D; Buy, C; Byer, R L; Cadonati, L; Cagnoli, G; Calderón Bustillo, J; Calloni, E; Camp, J B; Campsie, P; Cannon, K C; Canuel, B; Cao, J; Capano, C D; Carbognani, F; Carbone, L; Caride, S; Castiglia, A; Caudill, S; Cavaglià, M; Cavalier, F; Cavalieri, R; Cella, G; Cepeda, C; Cesarini, E; Chakraborty, R; Chalermsongsak, T; Chao, S; Charlton, P; Chassande-Mottin, E; Chen, X; Chen, Y; Chincarini, A; Chiummo, A; Cho, H S; Chow, J; Christensen, N; Chu, Q; Chua, S S Y; Chung, S; Ciani, G; Clara, F; Clark, D E; Clark, J A; Cleva, F; Coccia, E; Cohadon, P-F; Colla, A; Colombini, M; Constancio, M; Conte, A; Conte, R; Cook, D; Corbitt, T R; Cordier, M; Cornish, N; Corsi, A; Costa, C A; Coughlin, M W; Coulon, J-P; Countryman, S; Couvares, P; Coward, D M; Cowart, M; Coyne, D C; Craig, K; Creighton, J D E; Creighton, T D; Crowder, S G; Cumming, A; Cunningham, L; Cuoco, E; Dahl, K; Dal Canton, T; Damjanic, M; Danilishin, S L; D'Antonio, S; Danzmann, K; Dattilo, V; Daudert, B; Daveloza, H; Davier, M; Davies, G S; Daw, E J; Day, R; Dayanga, T; De Rosa, R; Debreczeni, G; Degallaix, J; Del Pozzo, W; Deleeuw, E; Deléglise, S; Denker, T; Dent, T; Dereli, H; Dergachev, V; DeRosa, R; DeSalvo, R; Dhurandhar, S; Di Fiore, L; Di Lieto, A; Di Palma, I; Di Virgilio, A; Díaz, M; Dietz, A; Dmitry, K; Donovan, F; Dooley, K L; Doravari, S; Drago, M; Drever, R W P; Driggers, J C; Du, Z; Dumas, J-C; Dwyer, S; Eberle, T; Edwards, M; Effler, A; Ehrens, P; Eichholz, J; Eikenberry, S S; Endrőczi, G; Essick, R; Etzel, T; Evans, K; Evans, M; Evans, T; Factourovich, M; Fafone, V; Fairhurst, S; Fang, Q; Farinon, S; Farr, B; Farr, W; Favata, M; Fazi, D; Fehrmann, H; Feldbaum, D; Ferrante, I; Ferrini, F; Fidecaro, F; Finn, L S; Fiori, I; Fisher, R; Flaminio, R; Foley, E; Foley, S; Forsi, E; Fotopoulos, N; Fournier, J-D; Franco, S; Frasca, S; Frasconi, F; Frede, M; Frei, M; Frei, Z; Freise, A; Frey, R; Fricke, T T; Fritschel, P; Frolov, V V; Fujimoto, M-K; Fulda, P; Fyffe, M; Gair, J; Gammaitoni, L; Garcia, J; Garufi, F; Gehrels, N; Gemme, G; Genin, E; Gennai, A; Gergely, L; Ghosh, S; Giaime, J A; Giampanis, S; Giardina, K D; Giazotto, A; Gil-Casanova, S; Gill, C; Gleason, J; Goetz, E; Goetz, R; Gondan, L; González, G; Gordon, N; Gorodetsky, M L; Gossan, S; Goßler, S; Gouaty, R; Graef, C; Graff, P B; Granata, M; Grant, A; Gras, S; Gray, C; Greenhalgh, R J S; Gretarsson, A M; Griffo, C; Groot, P; Grote, H; Grover, K; Grunewald, S; Guidi, G M; Guido, C; Gushwa, K E; Gustafson, E K; Gustafson, R; Hall, B; Hall, E; Hammer, D; Hammond, G; Hanke, M; Hanks, J; Hanna, C; Hanson, J; Harms, J; Harry, G M; Harry, I W; Harstad, E D; Hartman, M T; Haughian, K; Hayama, K; Heefner, J; Heidmann, A; Heintze, M; Heitmann, H; Hello, P; Hemming, G; Hendry, M; Heng, I S; Heptonstall, A W; Heurs, M; Hild, S; Hoak, D; Hodge, K A; Holt, K; Holtrop, M; Hong, T; Hooper, S; Horrom, T; Hosken, D J; Hough, J; Howell, E J; Hu, Y; Hua, Z; Huang, V; Huerta, E A; Hughey, B; Husa, S; Huttner, S H; Huynh, M; Huynh-Dinh, T; Iafrate, J; Ingram, D R; Inta, R; Isogai, T; Ivanov, A; Iyer, B R; Izumi, K; Jacobson, M; James, E; Jang, H; Jang, Y J; Jaranowski, P; Jiménez-Forteza, F; Johnson, W W; Jones, D; Jones, D I; Jones, R; Jonker, R J G; Ju, L; K, Haris; Kalmus, P; Kalogera, V; Kandhasamy, S; Kang, G; Kanner, J B; Kasprzack, M; Kasturi, R; Katsavounidis, E; Katzman, W; Kaufer, H; Kaufman, K; Kawabe, K; Kawamura, S; Kawazoe, F; Kéfélian, F; Keitel, D; Kelley, D B; Kells, W; Keppel, D G; Khalaidovski, A; Khalili, F Y; Khazanov, E A; Kim, B K; Kim, C; Kim, K; Kim, N; Kim, W; Kim, Y-M; King, E J; King, P J; Kinzel, D L; Kissel, J S; Klimenko, S; Kline, J; Koehlenbeck, S; Kokeyama, K; Kondrashov, V; Koranda, S; Korth, W Z; Kowalska, I; Kozak, D; Kremin, A; Kringel, V; Królak, A; Kucharczyk, C; Kudla, S; Kuehn, G; Kumar, A; Kumar, P; Kumar, R; Kurdyumov, R; Kwee, P; Landry, M; Lantz, B; Larson, S; Lasky, P D; Lawrie, C; Lazzarini, A; Le Roux, A; Leaci, P; Lebigot, E O; Lee, C-H; Lee, H K; Lee, H M; Lee, J; Lee, J; Leonardi, M; Leong, J R; Leroy, N; Letendre, N; Levine, B; Lewis, J B; Lhuillier, V; Li, T G F; Lin, A C; Littenberg, T B; Litvine, V; Liu, F; Liu, H; Liu, Y; Liu, Z; Lloyd, D; Lockerbie, N A; Lockett, V; Lodhia, D; Loew, K; Logue, J; Lombardi, A L; Lorenzini, M; Loriette, V; Lormand, M; Losurdo, G; Lough, J; Luan, J; Lubinski, M J; Lück, H; Lundgren, A P; Macarthur, J; Macdonald, E; Machenschalk, B; MacInnis, M; Macleod, D M; Magana-Sandoval, F; Mageswaran, M; Mailand, K; Majorana, E; Maksimovic, I; Malvezzi, V; Man, N; Manca, G M; Mandel, I; Mandic, V; Mangano, V; Mantovani, M; Marchesoni, F; Marion, F; Márka, S; Márka, Z; Markosyan, A; Maros, E; Marque, J; Martelli, F; Martin, I W; Martin, R M; Martinelli, L; Martynov, D; Marx, J N; Mason, K; Masserot, A; Massinger, T J; Matichard, F; Matone, L; Matzner, R A; Mavalvala, N; May, G; Mazumder, N; Mazzolo, G; McCarthy, R; McClelland, D E; McGuire, S C; McIntyre, G; McIver, J; Meacher, D; Meadors, G D; Mehmet, M; Meidam, J; Meier, T; Melatos, A; Mendell, G; Mercer, R A; Meshkov, S; Messenger, C; Meyer, M S; Miao, H; Michel, C; Mikhailov, E E; Milano, L; Miller, J; Minenkov, Y; Mingarelli, C M F; Mitra, S; Mitrofanov, V P; Mitselmakher, G; Mittleman, R; Moe, B; Mohan, M; Mohapatra, S R P; Mokler, F; Moraru, D; Moreno, G; Morgado, N; Mori, T; Morriss, S R; Mossavi, K; Mours, B; Mow-Lowry, C M; Mueller, C L; Mueller, G; Mukherjee, S; Mullavey, A; Munch, J; Murphy, D; Murray, P G; Mytidis, A; Nagy, M F; Nanda Kumar, D; Nardecchia, I; Nash, T; Naticchioni, L; Nayak, R; Necula, V; Nelemans, G; Neri, I; Neri, M; Newton, G; Nguyen, T; Nishida, E; Nishizawa, A; Nitz, A; Nocera, F; Nolting, D; Normandin, M E; Nuttall, L K; Ochsner, E; O'Dell, J; Oelker, E; Ogin, G H; Oh, J J; Oh, S H; Ohme, F; Oppermann, P; O'Reilly, B; Ortega Larcher, W; O'Shaughnessy, R; Osthelder, C; Ott, C D; Ottaway, D J; Ottens, R S; Ou, J; Overmier, H; Owen, B J; Padilla, C; Pai, A; Palomba, C; Pan, Y; Pankow, C; Paoletti, F; Paoletti, R; Papa, M A; Paris, H; Pasqualetti, A; Passaquieti, R; Passuello, D; Pedraza, M; Peiris, P; Penn, S; Perreca, A; Phelps, M; Pichot, M; Pickenpack, M; Piergiovanni, F; Pierro, V; Pinard, L; Pindor, B; Pinto, I M; Pitkin, M; Poeld, J; Poggiani, R; Poole, V; Poux, C; Predoi, V; Prestegard, T; Price, L R; Prijatelj, M; Principe, M; Privitera, S; Prix, R; Prodi, G A; Prokhorov, L; Puncken, O; Punturo, M; Puppo, P; Quetschke, V; Quintero, E; Quitzow-James, R; Raab, F J; Rabeling, D S; Rácz, I; Radkins, H; Raffai, P; Raja, S; Rajalakshmi, G; Rakhmanov, M; Ramet, C; Rapagnani, P; Raymond, V; Re, V; Reed, C M; Reed, T; Regimbau, T; Reid, S; Reitze, D H; Ricci, F; Riesen, R; Riles, K; Robertson, N A; Robinet, F; Rocchi, A; Roddy, S; Rodriguez, C; Rodruck, M; Roever, C; Rolland, L; Rollins, J G; Romano, R; Romanov, G; Romie, J H; Rosińska, D; Rowan, S; Rüdiger, A; Ruggi, P; Ryan, K; Salemi, F; Sammut, L; Sandberg, V; Sanders, J; Sannibale, V; Santiago-Prieto, I; Saracco, E; Sassolas, B; Sathyaprakash, B S; Saulson, P R; Savage, R; Schilling, R; Schnabel, R; Schofield, R M S; Schreiber, E; Schuette, D; Schulz, B; Schutz, B F; Schwinberg, P; Scott, J; Scott, S M; Seifert, F; Sellers, D; Sengupta, A S; Sentenac, D; Sergeev, A; Shaddock, D; Shah, S; Shahriar, M S; Shaltev, M; Shapiro, B; Shawhan, P; Shoemaker, D H; Sidery, T L; Siellez, K; Siemens, X; Sigg, D; Simakov, D; Singer, A; Singer, L; Sintes, A M; Skelton, G R; Slagmolen, B J J; Slutsky, J; Smith, J R; Smith, M R; Smith, R J E; Smith-Lefebvre, N D; Soden, K; Son, E J; Sorazu, B; Souradeep, T; Sperandio, L; Staley, A; Steinert, E; Steinlechner, J; Steinlechner, S; Steplewski, S; Stevens, D; Stochino, A; Stone, R; Strain, K A; Straniero, N; Strigin, S; Stroeer, A S; Sturani, R; Stuver, A L; Summerscales, T Z; Susmithan, S; Sutton, P J; Swinkels, B; Szeifert, G; Tacca, M; Talukder, D; Tang, L; Tanner, D B; Tarabrin, S P; Taylor, R; ter Braack, A P M; Thirugnanasambandam, M P; Thomas, M; Thomas, P; Thorne, K A; Thorne, K S; Thrane, E; Tiwari, V; Tokmakov, K V; Tomlinson, C; Toncelli, A; Tonelli, M; Torre, O; Torres, C V; Torrie, C I; Travasso, F; Traylor, G; Tse, M; Ugolini, D; Unnikrishnan, C S; Vahlbruch, H; Vajente, G; Vallisneri, M; van den Brand, J F J; Van Den Broeck, C; van der Putten, S; van der Sluys, M V; van Heijningen, J; van Veggel, A A; Vass, S; Vasúth, M; Vaulin, R; Vecchio, A; Vedovato, G; Veitch, J; Veitch, P J; Venkateswara, K; Verkindt, D; Verma, S; Vetrano, F; Viceré, A; Vincent-Finley, R; Vinet, J-Y; Vitale, S; Vlcek, B; Vo, T; Vocca, H; Vorvick, C; Vousden, W D; Vrinceanu, D; Vyachanin, S P; Wade, A; Wade, L; Wade, M; Waldman, S J; Walker, M; Wallace, L; Wan, Y; Wang, J; Wang, M; Wang, X; Wanner, A; Ward, R L; Was, M; Weaver, B; Wei, L-W; Weinert, M; Weinstein, A J; Weiss, R; Welborn, T; Wen, L; Wessels, P; West, M; Westphal, T; Wette, K; Whelan, J T; Whitcomb, S E; White, D J; Whiting, B F; Wibowo, S; Wiesner, K; Wilkinson, C; Williams, L; Williams, R; Williams, T; Willis, J L; Willke, B; Wimmer, M; Winkelmann, L; Winkler, W; Wipf, C C; Wittel, H; Woan, G; Worden, J; Yablon, J; Yakushin, I; Yamamoto, H; Yancey, C C; Yang, H; Yeaton-Massey, D; Yoshida, S; Yum, H; Yvert, M; Zadrożny, A; Zanolin, M; Zendri, J-P; Zhang, F; Zhang, L; Zhao, C; Zhu, H; Zhu, X J; Zotov, N; Zucker, M E; Zweizig, J

2014-04-04

Cosmic strings can give rise to a large variety of interesting astrophysical phenomena. Among them, powerful bursts of gravitational waves (GWs) produced by cusps are a promising observational signature. In this Letter we present a search for GWs from cosmic string cusps in data collected by the LIGO and Virgo gravitational wave detectors between 2005 and 2010, with over 625 days of live time. We find no evidence of GW signals from cosmic strings. From this result, we derive new constraints on cosmic string parameters, which complement and improve existing limits from previous searches for a stochastic background of GWs from cosmic microwave background measurements and pulsar timing data. In particular, if the size of loops is given by the gravitational backreaction scale, we place upper limits on the string tension Gμ below 10(-8) in some regions of the cosmic string parameter space.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ciuca, Razvan; Hernández, Oscar F., E-mail: razvan.ciuca@mail.mcgill.ca, E-mail: oscarh@physics.mcgill.ca

There exists various proposals to detect cosmic strings from Cosmic Microwave Background (CMB) or 21 cm temperature maps. Current proposals do not aim to find the location of strings on sky maps, all of these approaches can be thought of as a statistic on a sky map. We propose a Bayesian interpretation of cosmic string detection and within that framework, we derive a connection between estimates of cosmic string locations and cosmic string tension G μ. We use this Bayesian framework to develop a machine learning framework for detecting strings from sky maps and outline how to implement this frameworkmore » with neural networks. The neural network we trained was able to detect and locate cosmic strings on noiseless CMB temperature map down to a string tension of G μ=5 ×10{sup −9} and when analyzing a CMB temperature map that does not contain strings, the neural network gives a 0.95 probability that G μ≤2.3×10{sup −9}.« less

Level crossing analysis of cosmic microwave background radiation: a method for detecting cosmic strings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Movahed, M. Sadegh; Khosravi, Shahram, E-mail: m.s.movahed@ipm.ir, E-mail: khosravi@ipm.ir

2011-03-01

In this paper we study the footprint of cosmic string as the topological defects in the very early universe on the cosmic microwave background radiation. We develop the method of level crossing analysis in the context of the well-known Kaiser-Stebbins phenomenon for exploring the signature of cosmic strings. We simulate a Gaussian map by using the best fit parameter given by WMAP-7 and then superimpose cosmic strings effects on it as an incoherent and active fluctuations. In order to investigate the capability of our method to detect the cosmic strings for the various values of tension, Gμ, a simulated puremore » Gaussian map is compared with that of including cosmic strings. Based on the level crossing analysis, the superimposed cosmic string with Gμ∼>4 × 10{sup −9} in the simulated map without instrumental noise and the resolution R = 1' could be detected. In the presence of anticipated instrumental noise the lower bound increases just up to Gμ∼>5.8 × 10{sup −9}.« less

Superconducting cosmic string loops as sources for fast radio bursts

NASA Astrophysics Data System (ADS)

Cao, Xiao-Feng; Yu, Yun-Wei

2018-01-01

The cusp burst radiation of superconducting cosmic string (SCS) loops is thought to be a possible origin of observed fast radio bursts with the model-predicted radiation spectrum and the redshift- and energy-dependent event rate, we fit the observational redshift and energy distributions of 21 Parkes fast radio bursts and constrain the model parameters. It is found that the model can basically be consistent with the observations, if the current on the SCS loops has a present value of ˜1016μ179 /10 esu s-1 and evolves with redshift as an empirical power law ˜(1 +z )-1.3 , where μ17=μ /1017 g cm-1 is the string tension. This current evolution may provide a clue to probe the evolution of the cosmic magnetic fields and the gathering of the SCS loops to galaxy clusters.

PhD Thesis: String theory in the early universe

NASA Astrophysics Data System (ADS)

Gwyn, Rhiannon

2009-11-01

The intersection of string theory with cosmology is unavoidable in the early universe, and its exploration may shine light on both fields. In this thesis, three papers at this intersection are presented and reviewed, with the aim of providing a thorough and pedagogical guide to their results. First, we address the longstanding problem of finding a string theory realisation of the axion. Using warped compactifications in heterotic string theory, we show that the axion decay constant can be lowered to acceptable values by the warp factor. Next, we move to the subject of cosmic strings, whose network evolution could have important consequences for astrophysics and cosmology. In particular, there are quantitative differences between cosmic superstring networks and GUT cosmic string networks. We investigate the properties of cosmic superstring networks in warped backgrounds, giving the tension and properties of three-string junctions in these backgrounds. Finally, we examine the possibility that cosmic strings in heterotic string theory could be responsible for generating the galactic magnetic fields that seeded those observed today.

Effect of the cosmological constant on the deflection angle by a rotating cosmic string

NASA Astrophysics Data System (ADS)

Jusufi, Kimet; Övgün, Ali

2018-03-01

We report the effect of the cosmological constant and the internal energy density of a cosmic string on the deflection angle of light in the spacetime of a rotating cosmic string with internal structure. We first revisit the deflection angle by a rotating cosmic string and then provide a generalization using the geodesic equations and the Gauss-Bonnet theorem. We show there is an agreement between the two methods when employing higher-order terms of the linear mass density of the cosmic string. By modifying the integration domain for the global conical topology, we resolve the inconsistency between these two methods previously reported in the literature. We show that the deflection angle is not affected by the rotation of the cosmic string; however, the cosmological constant Λ strongly affects the deflection angle, which generalizes the well-known result.

Semianalytic calculation of cosmic microwave background anisotropies from wiggly and superconducting cosmic strings

NASA Astrophysics Data System (ADS)

Rybak, I. Yu.; Avgoustidis, A.; Martins, C. J. A. P.

2017-11-01

We study how the presence of world-sheet currents affects the evolution of cosmic string networks, and their impact on predictions for the cosmic microwave background (CMB) anisotropies generated by these networks. We provide a general description of string networks with currents and explicitly investigate in detail two physically motivated examples: wiggly and superconducting cosmic string networks. By using a modified version of the CMBact code, we show quantitatively how the relevant network parameters in both of these cases influence the predicted CMB signal. Our analysis suggests that previous studies have overestimated the amplitude of the anisotropies for wiggly strings. For superconducting strings the amplitude of the anisotropies depends on parameters which presently are not well known—but which can be measured in future high-resolution numerical simulations.

Self-force on an electric dipole in the spacetime of a cosmic string

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muniz, C.R., E-mail: celiomuniz@yahoo.com; Bezerra, V.B., E-mail: valdir@ufpb.br

2014-01-15

We calculate the electrostatic self-force on an electric dipole in the spacetime generated by a static, thin, infinite and straight cosmic string. The electric dipole is held fixed in different configurations, namely, parallel, perpendicular to the cosmic string and oriented along the azimuthal direction around this topological defect, which is stretched along the z axis. We show that the self-force is equivalent to an interaction of the electric dipole with an effective dipole moment which depends on the linear mass density of the cosmic string and on the configuration. The plots of the self-forces as functions of the parameter whichmore » determines the angular deficit of the cosmic string are shown for those different configurations. -- Highlights: •Review of regularized Green’s function applied to the problem. •Self-force on an electric dipole in the string spacetime for some orientations. •Representation via graphs of the self-forces versus angular parameter of the cosmic string. •Self-force induced by the string seen as an interaction between two dipoles. •Discussion about the superposition principle in this non-trivial background.« less

Closed timelike curves produced by pairs of moving cosmic strings - Exact solutions

NASA Technical Reports Server (NTRS)

Gott, J. Richard, III

1991-01-01

Exact solutions of Einstein's field equations are presented for the general case of two moving straight cosmic strings that do not intersect. The solutions for parallel cosmic strings moving in opposite directions show closed timelike curves (CTCs) that circle the two strings as they pass, allowing observers to visit their own past. Similar results occur for nonparallel strings, and for masses in (2+1)-dimensional spacetime. For finite string loops the possibility that black-hole formation may prevent the formation of CTCs is discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anthonisen, Madeleine; Brandenberger, Robert; Laguë, Alex

Cosmic string loops contain cusps which decay by emitting bursts of particles. A significant fraction of the released energy is in the form of photons. These photons are injected non-thermally and can hence cause spectral distortions of the Cosmic Microwave Background (CMB). Under the assumption that cusps are robust against gravitational back-reaction, we compute the fractional energy density released as photons in the redshift interval where such non-thermal photon injection causes CMB spectral distortions. Whereas current constraints on such spectral distortions are not strong enough to constrain the string tension, future missions such as the PIXIE experiment will be ablemore » to provide limits which rule out a range of string tensions between G μ ∼ 10{sup −15} and G μ ∼ 10{sup −12}, thus ruling out particle physics models yielding these kind of intermediate-scale cosmic strings.« less

Effects of cosmic string velocities and the origin of globular clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Ling; Yamanouchi, Shoma; Brandenberger, Robert, E-mail: ling.lin2@mail.mcgill.ca, E-mail: shoma.yamanouchi@mail.mcgill.ca, E-mail: rhb@physics.mcgill.ca

2015-12-01

With the hypothesis that cosmic string loops act as seeds for globular clusters in mind, we study the role that velocities of these strings will play in determining the mass distribution of globular clusters. Loops with high enough velocities will not form compact and roughly spherical objects and can hence not be the seeds for globular clusters. We compute the expected number density and mass function of globular clusters as a function of both the string tension and the peak loop velocity, and compare the results with the observational data on the mass distribution of globular clusters in our Milkymore » Way. We determine the critical peak string loop velocity above which the agreement between the string loop model for the origin of globular clusters (neglecting loop velocities) and observational data is lost.« less

Scattering of Cosmic Strings by Black Holes:. Loop Formation

NASA Astrophysics Data System (ADS)

Dubath, Florian; Sakellariadou, Mairi; Viallet, Claude Michel

We study the deformation of a long cosmic string by a nearby rotating black hole. We examine whether the deformation of a cosmic string, induced by the gravitational field of a Kerr black hole, may lead to the formation of a string loop. The segment of the string which enters the ergo-sphere of a rotating black hole gets deformed and, if it is sufficiently twisted, it can self-intersect, chopping off a loop. We find that the formation of a loop, via such a mechanism, is a rare event. It will only arise in a small region of the collision phase space, which depends on the string velocity, the impact parameter and the black hole angular momentum. We conclude that, generically, a long cosmic string is simply scattered, or captured, by a nearby rotating black hole.

Black holes as beads on cosmic strings

NASA Astrophysics Data System (ADS)

Ashoorioon, Amjad; Mann, Robert B.

2014-11-01

We consider the possibility of the formation of cosmic strings with black holes as beads. We focus on the simplest setup where two black holes are formed on a long cosmic string. It turns out that in the absence of a background magnetic field and for observationally viable values for cosmic string tensions, μ \\lt 2× {{10}-7}, the tension of the strut in between the black holes has to be less than the ones that run into infinity. This result does not change if a cosmological constant is present. However, if a background magnetic field is turned on, we can have stable setups where the tensions of all cosmic strings are equal. We derive the equilibrium conditions in each of these setups depending on whether the black holes are extremal or non-extremal. We obtain cosmologically acceptable solutions with solar mass black holes and an intragalactic-strength cosmic magnetic field.

Geometric phase for a static two-level atom in cosmic string spacetime

NASA Astrophysics Data System (ADS)

Cai, Huabing; Ren, Zhongzhou

2018-05-01

We investigate the geometric phase of a static two-level atom immersed in a bath of fluctuating vacuum electromagnetic field in the background of a cosmic string. Our results indicate that due to the existence of the string, the geometric phase depends crucially on the position and the polarizability of the atom relative to the string. This can be ascribed to the fact that the presence of the string profoundly modify the distribution of electric field in Minkowski spacetime. So in principle, we can detect the cosmic string by experiments involving geometric phase.

Cosmic R-string, R-tube and vacuum instability

NASA Astrophysics Data System (ADS)

Eto, Minoru; Hamada, Yuta; Kamada, Kohei; Kobayashi, Tatsuo; Ohashi, Keisuke; Ookouchi, Yutaka

2013-03-01

We show that a cosmic string associated with spontaneous U(1) R symmetry breaking gives a constraint for supersymmetric model building. In some models, the string can be viewed as a tube-like domain wall with a winding number interpolating a false vacuum and a true vacuum. Such string causes inhomogeneous decay of the false vacuum to the true vacuum via rapid expansion of the radius of the tube and hence its formation would be inconsistent with the present Universe. However, we demonstrate that there exist metastable solutions which do not expand rapidly. Furthermore, when the true vacua are degenerate, the structure inside the tube becomes involved. As an example, we show a "bamboo"-like solution, which suggests a possibility observing an information of true vacua from outside of the tube through the shape and the tension of the tube.

D-term inflation, cosmic strings, and consistency with cosmic microwave background measurements.

PubMed

Rocher, Jonathan; Sakellariadou, Mairi

2005-01-14

Standard D-term inflation is studied in the framework of supergravity. D-term inflation produces cosmic strings; however, it can still be compatible with cosmic microwave background (CMB) measurements without invoking any new physics. The cosmic strings contribution to the CMB data is not constant, nor dominant, contrary to some previous results. Using current CMB measurements, the free parameters (gauge and superpotential couplings, as well as the Fayet-Iliopoulos term) of D-term inflation are constrained.

A Search for Cosmic String Loops Using GADGET-2 Cosmological N-Body Simulator

NASA Astrophysics Data System (ADS)

Braverman, William; Cousins, Bryce; Jia, Hewei

2018-01-01

Cosmic string loops are an extremely elusive hypothetical entity that have eluded the grasp of physicists and astronomers since their existence was postulated in the 1970’s. Finding evidence of their existence could be the first empirical evidence of string theory.Simulating their basic motion in a cold dark matter background using GADGET-2 allows us to predict where they may cluster during large scale structure formation (if they cluster at all). Here, we present our progress in placing cosmic strings into GADGET-2 with their basic equations of motion to lay a ground work for more complex simulations to find where these strings cluster. Ultimately, these simulations could lay a groundwork as to where future microlensing and gravitational wave observatories should look for cosmic strings.

Propagation of cosmic rays through the atmosphere in the quark-gluon strings model

NASA Technical Reports Server (NTRS)

Erlykin, A. D.; Krutikova, N. P.; Shabelski, Y. M.

1985-01-01

The quark-gluon strings model succeeds in the description of multiple hadron production in the central rapidity region of nucleon-nucleon interctions. This model was developed for hadron-nucleus interactions and used for calculation of the cosmic ray propagation through the atmosphere. It is shown that at energies 10 to the 11th power to the 12th power eV, this model gives a satisfactory description of experimental data. But with the increase of the energy up to approximately 10 to the 14th power eV, results of calculations and of experiments begin to differ and this difference rises with the energy. It may indicate that the scaling violation in the fragmentation region of inclusive spectra for hadron-nucleus interactions is stronger than in the quark-gluon strings model.

Patterns of the cosmic microwave background from evolving string networks

NASA Technical Reports Server (NTRS)

Bouchet, Francois R.; Bennett, David P.; Stebbins, Albert

1988-01-01

A network of cosmic strings generated in the early universe may still exist today. As the strings move across the sky, they produce, by gravitational lensing, a characteristic pattern of anisotropies in the temperature of the cosmic microwave background. The observed absence of such anisotropies places constraints on theories in which galaxy formation is seeded by strings, but it is anticipated that the next generation of experiments will detect them.

Did BICEP2 see vector modes? First B-mode constraints on cosmic defects.

PubMed

Moss, Adam; Pogosian, Levon

2014-05-02

Scaling networks of cosmic defects, such as strings and textures, actively generate scalar, vector, and tensor metric perturbations throughout the history of the Universe. In particular, vector modes sourced by defects are an efficient source of the cosmic microwave background B-mode polarization. We use the recently released BICEP2 and POLARBEAR B-mode polarization spectra to constrain properties of a wide range of different types of cosmic strings networks. We find that in order for strings to provide a satisfactory fit on their own, the effective interstring distance needs to be extremely large--spectra that fit the data best are more representative of global strings and textures. When a local string contribution is considered together with the inflationary B-mode spectrum, the fit is improved. We discuss implications of these results for theories that predict cosmic defects.

Cosmic string lensing and closed timelike curves

NASA Astrophysics Data System (ADS)

Shlaer, Benjamin; Tye, S.-H. Henry

2005-08-01

In an analysis of the gravitational lensing by two relativistic cosmic strings, we argue that the formation of closed timelike curves proposed by Gott is unstable in the presence of particles (e.g. the cosmic microwave background radiation). Because of the attractorlike behavior of the closed timelike curve, we argue that this instability is very generic. A single graviton or photon in the vicinity, no matter how soft, is sufficient to bend the strings and prevent the formation of closed timelike curves. We also show that the gravitational lensing due to a moving cosmic string is enhanced by its motion, not suppressed.

Exact solutions of the Schrödinger equation with a coulomb ring-shaped potential in the cosmic string spacetime

NASA Astrophysics Data System (ADS)

Wang, Zhi; Long, Zheng-wen; Long, Chao-yun; Teng, Jing

2015-05-01

We study the Schrödinger equation with a Coulomb ring-shaped potential in the spacetime of a cosmic string, and the solutions of the system are obtained by using the generalized parametric Nikiforov-Uvarov (NU) method. They show that the quantum dynamics of a physical system depend on the non-trivial topological features of the cosmic string spacetime and the energy levels of the considered quantum system depend explicitly on the angular deficit α which characterizes the global structure of the metric in the cosmic string spacetime.

Formation of large-scale structure from cosmic strings and massive neutrinos

NASA Technical Reports Server (NTRS)

Scherrer, Robert J.; Melott, Adrian L.; Bertschinger, Edmund

1989-01-01

Numerical simulations of large-scale structure formation from cosmic strings and massive neutrinos are described. The linear power spectrum in this model resembles the cold-dark-matter power spectrum. Galaxy formation begins early, and the final distribution consists of isolated density peaks embedded in a smooth background, leading to a natural bias in the distribution of luminous matter. The distribution of clustered matter has a filamentary appearance with large voids.

Topological defects in extended inflation

NASA Technical Reports Server (NTRS)

Copeland, Edmund J.; Kolb, Edward W.; Liddle, Andrew R.

1990-01-01

The production of topological defects, especially cosmic strings, in extended inflation models was considered. In extended inflation, the Universe passes through a first-order phase transition via bubble percolation, which naturally allows defects to form at the end of inflation. The correlation length, which determines the number density of the defects, is related to the mean size of bubbles when they collide. This mechanism allows a natural combination of inflation and large scale structure via cosmic strings.

Excited cosmic strings with superconducting currents

NASA Astrophysics Data System (ADS)

Hartmann, Betti; Michel, Florent; Peter, Patrick

2017-12-01

We present a detailed analysis of excited cosmic string solutions that possess superconducting currents. These currents can be excited inside the string core, and—if the condensate is large enough—can lead to the excitations of the Higgs field. Next to the case with global unbroken symmetry, we discuss also the effects of the gauging of this symmetry and show that excited condensates persist when coupled to an electromagnetic field. The space-time of such strings is also constructed by solving the Einstein equations numerically and we show how the local scalar curvature is modified by the excitation. We consider the relevance of our results on the cosmic string network evolution as well as observations of primordial gravitational waves and cosmic rays.

Klein-Gordon oscillator with position-dependent mass in the rotating cosmic string spacetime

NASA Astrophysics Data System (ADS)

Wang, Bing-Qian; Long, Zheng-Wen; Long, Chao-Yun; Wu, Shu-Rui

2018-02-01

A spinless particle coupled covariantly to a uniform magnetic field parallel to the string in the background of the rotating cosmic string is studied. The energy levels of the electrically charged particle subject to the Klein-Gordon oscillator are analyzed. Afterwards, we consider the case of the position-dependent mass and show how these energy levels depend on the parameters in the problem. Remarkably, it shows that for the special case, the Klein-Gordon oscillator coupled covariantly to a homogeneous magnetic field with the position-dependent mass in the rotating cosmic string background has the similar behaviors to the Klein-Gordon equation with a Coulomb-type configuration in a rotating cosmic string background in the presence of an external magnetic field.

Bianchi type-VIh string cloud cosmological models with bulk viscosity

NASA Astrophysics Data System (ADS)

Tripathy, Sunil K.; Behera, Dipanjali

2010-11-01

String cloud cosmological models are studied using spatially homogeneous and anisotropic Bianchi type VIh metric in the frame work of general relativity. The field equations are solved for massive string cloud in presence of bulk viscosity. A general linear equation of state of the cosmic string tension density with the proper energy density of the universe is considered. The physical and kinematical properties of the models have been discussed in detail and the limits of the anisotropic parameter responsible for different phases of the universe are explored.

Evidence for a scaling solution in cosmic-string evolution

NASA Technical Reports Server (NTRS)

Bennett, David P.; Bouchet, Francois R.

1988-01-01

Numerical simulations are used to study the most fundamental issue of cosmic-string evolution: the existence of a scaling solution. Strong evidence is found that a scaling solution does indeed exist. This justifies the main assumption on which the cosmic-string theories of galaxy formation is based. The main conclusion coincides with that of Albrecht and Turok (1985) but the results are not consistent with theirs. In fact, the results indicate that the details of string evolution are very different from the standard dogma.

Brane inflation and cosmic string tension in superstring theory

NASA Astrophysics Data System (ADS)

Firouzjahi, Hassan; Tye, S.-H. Henry

2005-03-01

In a simple reanalysis of the KKLMMT scenario, we argue that the slow roll condition in the D3-overline {D}3 -brane inflationary scenario in superstring theory requires no more than a moderate tuning. The cosmic string tension is very sensitive to the conformal coupling: with less fine-tuning, the cosmic string tension (as well as the ratio of tensor to scalar perturbation mode) increases rapidly and can easily saturate the present observational bound. In a multi-throat brane inflationary scenario, this feature substantially improves the chance of detecting and measuring the properties of the cosmic strings as a window to the superstring theory and our pre-inflationary universe.

Analytical Solutions to Backreaction on Cosmic Strings

NASA Astrophysics Data System (ADS)

Wachter, Jeremy M.

2017-08-01

We present analytical studies of gravitational and electromagnetic backreaction on cosmic strings. For oscillating loops of cosmic string, we present a general argument for how kinks must change; additionally, we apply this general argument to the geometrically simple case of the Garfinkle-Vachaspati loop. Our results suggest that the formation of cusps on loops is delayed, and so we should expect fewer cuspy signatures to be seen in gravitational wave observations. Electromagnetic backreaction we show to reduce currents on a string at least as rapidly as necessary to avoid a paradox, and currents induced on a superconducting straight string will be asymptotically reduced to zero.

Is the 'great attractor' a loop of cosmic string?

NASA Astrophysics Data System (ADS)

Hoffman, Y.; Zurek, W. H.

1988-05-01

Recent measurements of galaxy velocities suggest that the observed large-scale streaming may be attributed to a massive "attractor". The authors explore the idea that the streaming was induced by a large, moving loop of cosmic string. A stationary loop induces a velocity field that falls off as r-1, where r is the distance from the loop. This is somewhat modified by the motion of the loop, but the r-1 profile still persists in much of the wake of the string. The standard inflationary models of cold or hot dark matter predict, on the other hand, a velocity that should fall off as r-3 away from the density peak. Extension of this model to the Local Supercluster allows one to understand its Virgocentric velocity field of r-1.

Quantum vacuum interaction between two cosmic strings revisited

NASA Astrophysics Data System (ADS)

Muñoz-Castañeda, J. M.; Bordag, M.

2014-03-01

We reconsider the quantum vacuum interaction energy between two straight parallel cosmic strings. This problem was discussed several times in an approach treating both strings perturbatively and treating only one perturbatively. Here we point out that a simplifying assumption made by Bordag [Ann. Phys. (Berlin) 47, 93 (1990).] can be justified and show that, despite the global character of the background, the perturbative approach delivers a correct result. We consider the applicability of the scattering methods, developed in the past decade for the Casimir effect, for the cosmic string and find it not applicable. We calculate the scattering T-operator on one string. Finally, we consider the vacuum interaction of two strings when each carries a two-dimensional delta function potential.

LETTER TO THE EDITOR: A disintegrating cosmic string

NASA Astrophysics Data System (ADS)

Griffiths, J. B.; Docherty, P.

2002-06-01

We present a simple sandwich gravitational wave of the Robinson-Trautman family. This is interpreted as representing a shock wave with a spherical wavefront which propagates into a Minkowski background minus a wedge (i.e. the background contains a cosmic string). The deficit angle (the tension) of the string decreases through the gravitational wave, which then ceases. This leaves an expanding spherical region of Minkowski space behind it. The decay of the cosmic string over a finite interval of retarded time may be considered to generate the gravitational wave.

THE FLOW AROUND A COSMIC STRING. I. HYDRODYNAMIC SOLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beresnyak, Andrey; Nordita, KTH Royal Institute of Technology and Stockholm University, SE-10691

2015-05-10

Cosmic strings are linear topological defects which are hypothesized to be produced during inflation. Most searches for strings have relied on the string’s lensing of background galaxies or the cosmic microwave background. In this paper, I obtained a solution for the supersonic flow of collisional gas past the cosmic string which has two planar shocks with a shock compression ratio that depends on the angle defect of the string and its speed. The shocks result in the compression and heating of the gas and, given favorable conditions, particle acceleration. Gas heating and over-density in an unusual wedge shape can bemore » detected by observing the Hi line at high redshifts. Particle acceleration can occur in the present-day universe when the string crosses the hot gas contained in galaxy clusters and, since the consequences of such a collision persist for cosmological timescales, could be located by looking at unusual large-scale radio sources situated on a single spatial plane.« less

Searching for cosmic strings in CMB anisotropy maps using wavelets and curvelets

NASA Astrophysics Data System (ADS)

Hergt, Lukas; Amara, Adam; Brandenberger, Robert; Kacprzak, Tomasz; Réfrégier, Alexandre

2017-06-01

We use wavelet and curvelet transforms to extract signals of cosmic strings from simulated cosmic microwave background (CMB) temperature anisotropy maps, and to study the limits on the cosmic string tension which various ongoing CMB temperature anisotropy experiments will be able to achieve. We construct sky maps with size and angular resolution corresponding to various experiments. These maps contain the signals of a scaling solution of long string segments with a given string tension G μ, the contribution of the dominant Gaussian primordial cosmological fluctuations, and pixel by pixel white noise with an amplitude corresponding to the instrumental noise of the various experiments. In the case that we include white noise, we find that using curvelets we obtain lower bounds on the string tension than with wavelets. For maps with Planck specification, we obtain bounds comparable to what was obtained by the Planck collaboration [1]. Experiments with better angular resolution such as the South Pole Telescope third generation (SPT-3G) survey will be able to yield stronger limits. For maps with a specification of SPT-3G we find that string signals will be visible down to a string tension of G μ = 1.4 × 10-7.

Models for small-scale structure on cosmic strings. II. Scaling and its stability

NASA Astrophysics Data System (ADS)

Vieira, J. P. P.; Martins, C. J. A. P.; Shellard, E. P. S.

2016-11-01

We make use of the formalism described in a previous paper [Martins et al., Phys. Rev. D 90, 043518 (2014)] to address general features of wiggly cosmic string evolution. In particular, we highlight the important role played by poorly understood energy loss mechanisms and propose a simple Ansatz which tackles this problem in the context of an extended velocity-dependent one-scale model. We find a general procedure to determine all the scaling solutions admitted by a specific string model and study their stability, enabling a detailed comparison with future numerical simulations. A simpler comparison with previous Goto-Nambu simulations supports earlier evidence that scaling is easier to achieve in the matter era than in the radiation era. In addition, we also find that the requirement that a scaling regime be stable seems to notably constrain the allowed range of energy loss parameters.

On the motion of a quantum particle in the spinning cosmic string space–time

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hassanabadi, H., E-mail: h.hasanabadi@shahroodut.ac.ir; Afshardoost, A.; Zarrinkamar, S.

2015-05-15

We analyze the energy spectrum and the wave function of a particle subjected to magnetic field in the spinning cosmic string space–time and investigate the influence of the spinning reference frame and topological defect on the system. To do this we solve Schrödinger equation in the spinning cosmic string background. In our work, instead of using an approximation in the calculations, we use the quasi-exact ansatz approach which gives the exact solutions for some primary levels. - Highlights: • Solving the Schrödinger equation in the spinning cosmic string space time. • Proposing a quasi-exact analytical solution to the general formmore » of the corresponding equation. • Generalizing the previous works.« less

Cosmic string detection with tree-based machine learning

NASA Astrophysics Data System (ADS)

Vafaei Sadr, A.; Farhang, M.; Movahed, S. M. S.; Bassett, B.; Kunz, M.

2018-07-01

We explore the use of random forest and gradient boosting, two powerful tree-based machine learning algorithms, for the detection of cosmic strings in maps of the cosmic microwave background (CMB), through their unique Gott-Kaiser-Stebbins effect on the temperature anisotropies. The information in the maps is compressed into feature vectors before being passed to the learning units. The feature vectors contain various statistical measures of the processed CMB maps that boost cosmic string detectability. Our proposed classifiers, after training, give results similar to or better than claimed detectability levels from other methods for string tension, Gμ. They can make 3σ detection of strings with Gμ ≳ 2.1 × 10-10 for noise-free, 0.9'-resolution CMB observations. The minimum detectable tension increases to Gμ ≳ 3.0 × 10-8 for a more realistic, CMB S4-like (II) strategy, improving over previous results.

Cosmic String Detection with Tree-Based Machine Learning

NASA Astrophysics Data System (ADS)

Vafaei Sadr, A.; Farhang, M.; Movahed, S. M. S.; Bassett, B.; Kunz, M.

2018-05-01

We explore the use of random forest and gradient boosting, two powerful tree-based machine learning algorithms, for the detection of cosmic strings in maps of the cosmic microwave background (CMB), through their unique Gott-Kaiser-Stebbins effect on the temperature anisotropies. The information in the maps is compressed into feature vectors before being passed to the learning units. The feature vectors contain various statistical measures of the processed CMB maps that boost cosmic string detectability. Our proposed classifiers, after training, give results similar to or better than claimed detectability levels from other methods for string tension, Gμ. They can make 3σ detection of strings with Gμ ≳ 2.1 × 10-10 for noise-free, 0.9΄-resolution CMB observations. The minimum detectable tension increases to Gμ ≳ 3.0 × 10-8 for a more realistic, CMB S4-like (II) strategy, improving over previous results.

Topics in Cosmic String Physics and Vacuum Stability of Field Theories

NASA Astrophysics Data System (ADS)

Dasgupta, Indranil

1998-01-01

In this thesis I examine aspects of the vacuum state of quantum field theories. Namely, I study topological defects in the vacuum which appear as localized regions of non-zero energy density if the model system is unable to relax to a homogeneous and isotropic ground state because of topological constraints. I also examine the stability of the so called false vacua in theories that have multiple vacuum states with different energy densities. I first consider topological defects in the form of strings and independently the decay of false vacua in models of particle physics where the presence of either defects or of false vacua leads to interesting phenomenology. Then I describe a situation in which the defects arising from topological properties of the vacuum in turn affect the stability of the vacuum itself. In the first part of this work (chapters 2 and 3), I explore the phenomenology of cosmic strings. I introduce new string-like topological defects that resemble pairs of strings bound together. I give an existence proof of these 'binary strings' and then develop their cosmological properties in detail. I then propose a simple extension of the Standard Model in which cosmic strings may form and then decay through baryon number violating interactions leading to baryogenesis. I show that the model has distinct and testable signatures. In the second part of this work (chapters 4 and 5), I examine the vacua of several proposed models of gauge mediated dynamical supersymmetry breaking and show that the viable vacua are often unstable. I develop a rigorous theory for approximating vacuum tunneling rates in multi-scalar field theories and by computing bounds on the decay rate of the vacua in these models obtain useful constraints on the parameter space. In the final part of this work (chapter 6), I develop a theory of vacuum tunneling induced by topological defects. I show that defects can speed up vacuum tunneling rates by seeding new kinds of bubbles during a first order phase transition. I then indicate possible phenomenological applications of this effect and develop simple approximation techniques for computing the rate of seeded tunneling.

Perturbations from cosmic strings in cold dark matter

NASA Technical Reports Server (NTRS)

Albrecht, Andreas; Stebbins, Albert

1992-01-01

A systematic linear analysis of the perturbations induced by cosmic strings in cold dark matter is presented. The power spectrum is calculated and it is found that the strings produce a great deal of power on small scales. It is shown that the perturbations on interesting scales are the result of many uncorrelated string motions, which indicates a much more Gaussian distribution than was previously supposed.

Perturbations from cosmic strings in cold dark matter

NASA Technical Reports Server (NTRS)

Albrecht, Andreas; Stebbins, Albert

1991-01-01

A systematic linear analysis of the perturbations induced by cosmic strings in cold dark matter is presented. The power spectrum is calculated and it is found that the strings produce a great deal of power on small scales. It is shown that the perturbations on interesting scales are the result of many uncorrelated string motions, which indicates a much more Gaussian distribution than was previously supposed.

Abelian Higgs cosmic strings: Small-scale structure and loops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hindmarsh, Mark; Stuckey, Stephanie; Bevis, Neil

2009-06-15

Classical lattice simulations of the Abelian Higgs model are used to investigate small-scale structure and loop distributions in cosmic string networks. Use of the field theory ensures that the small-scale physics is captured correctly. The results confirm analytic predictions of Polchinski and Rocha 29 for the two-point correlation function of the string tangent vector, with a power law from length scales of order the string core width up to horizon scale. An analysis of the size distribution of string loops gives a very low number density, of order 1 per horizon volume, in contrast with Nambu-Goto simulations. Further, our loopmore » distribution function does not support the detailed analytic predictions for loop production derived by Dubath et al. 30. Better agreement to our data is found with a model based on loop fragmentation 32, coupled with a constant rate of energy loss into massive radiation. Our results show a strong energy-loss mechanism, which allows the string network to scale without gravitational radiation, but which is not due to the production of string width loops. From evidence of small-scale structure we argue a partial explanation for the scale separation problem of how energy in the very low frequency modes of the string network is transformed into the very high frequency modes of gauge and Higgs radiation. We propose a picture of string network evolution, which reconciles the apparent differences between Nambu-Goto and field theory simulations.« less

Formation of large-scale structure from cosmic-string loops and cold dark matter

NASA Technical Reports Server (NTRS)

Melott, Adrian L.; Scherrer, Robert J.

1987-01-01

Some results from a numerical simulation of the formation of large-scale structure from cosmic-string loops are presented. It is found that even though G x mu is required to be lower than 2 x 10 to the -6th (where mu is the mass per unit length of the string) to give a low enough autocorrelation amplitude, there is excessive power on smaller scales, so that galaxies would be more dense than observed. The large-scale structure does not include a filamentary or connected appearance and shares with more conventional models based on Gaussian perturbations the lack of cluster-cluster correlation at the mean cluster separation scale as well as excessively small bulk velocities at these scales.

Cosmic strings - A problem or a solution?

NASA Technical Reports Server (NTRS)

Bennett, David P.; Bouchet, Francois R.

1988-01-01

The most fundamental issue in the theory of cosmic strings is addressed by means of Numerical Simulations: the existence of a scaling solution. The resolution of this question will determine whether cosmic strings can form the basis of an attractive theory of galaxy formation or prove to be a cosmological disaster like magnetic monopoles or domain walls. After a brief discussion of our numerical technique, results are presented which, though still preliminary, offer the best support to date of this scaling hypothesis.

Straight spinning cosmic strings in Brans-Dicke gravity

NASA Astrophysics Data System (ADS)

Dos Santos, S. Mittmann; da Silva, J. M. Hoff; Cindra, J. L.

2018-03-01

An exact solution of straight spinning cosmic strings in Brans-Dicke theory of gravitation is presented. The possibility of the existence of closed time-like curves around these cosmic strings is analyzed. Furthermore, the stability about the formation of the topological defect discussed here is checked. It is shown that the existence of a suitable choice for the integration constants in which closed time-like curves are not allowed. We also study the (im)possibility of using the obtained spacetime in the rotational curves problem.

High redshift signatures in the 21 cm forest due to cosmic string wakes

NASA Astrophysics Data System (ADS)

Tashiro, Hiroyuki; Sekiguchi, Toyokazu; Silk, Joseph

2014-01-01

Cosmic strings induce minihalo formation in the early universe. The resultant minihalos cluster in string wakes and create a ``21 cm forest'' against the cosmic microwave background (CMB) spectrum. Such a 21 cm forest can contribute to angular fluctuations of redshifted 21 cm signals integrated along the line of sight. We calculate the root-mean-square amplitude of the 21 cm fluctuations due to strings and show that these fluctuations can dominate signals from minihalos due to primordial density fluctuations at high redshift (zgtrsim10), even if the string tension is below the current upper bound, Gμ < 1.5 × 10-7. Our results also predict that the Square Kilometre Array (SKA) can potentially detect the 21 cm fluctuations due to strings with Gμ ≈ 7.5 × 10-8 for the single frequency band case and 4.0 × 10-8 for the multi-frequency band case.

Self-similar motion of a Nambu-Goto string

NASA Astrophysics Data System (ADS)

Igata, Takahisa; Houri, Tsuyoshi; Harada, Tomohiro

2016-09-01

We study the self-similar motion of a string in a self-similar spacetime by introducing the concept of a self-similar string, which is defined as the world sheet to which a homothetic vector field is tangent. It is shown that in Nambu-Goto theory, the equations of motion for a self-similar string reduce to those for a particle. Moreover, under certain conditions such as the hypersurface orthogonality of the homothetic vector field, the equations of motion for a self-similar string simplify to the geodesic equations on a (pseudo)Riemannian space. As a concrete example, we investigate a self-similar Nambu-Goto string in a spatially flat Friedmann-Lemaître-Robertson-Walker expanding universe with self-similarity and obtain solutions of open and closed strings, which have various nontrivial configurations depending on the rate of the cosmic expansion. For instance, we obtain a circular solution that evolves linearly in the cosmic time while keeping its configuration by the balance between the effects of the cosmic expansion and string tension. We also show the instability for linear radial perturbation of the circular solutions.

Local constraints on cosmic string loops from photometry and pulsar timing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pshirkov, M. S.; Tuntsov, A. V.; Sternberg Astronomical Institute, M.V. Lomonosov Moscow State University, 119992

2010-04-15

We constrain the cosmological density of cosmic string loops using two observational signatures--gravitational microlensing and the Kaiser-Stebbins effect. Photometry from RXTE and CoRoT space missions and pulsar timing from Parkes Pulsar Timing Array, Arecibo and Green Bank radio telescopes allow us to probe cosmic strings in a wide range of tensions G{mu}/c{sup 2}=10{sup -16} divide 10{sup -10}. We find that pulsar timing data provide the most stringent constraints on the abundance of light strings at the level {Omega}{sub s{approx}}10{sup -3}. Future observational facilities such as the Square Kilometer Array will allow one to improve these constraints by orders of magnitude.

Perturbations from strings don't look like strings!

NASA Technical Reports Server (NTRS)

Albrecht, Andreas; Stebbins, Albert

1991-01-01

A systematic analysis is challenging popular ideas about perturbation from cosmic strings. One way in which the picture has changed is reviewed. It is concluded that, while the scaling properties of cosmic strings figure significantly in the analysis, care must be taken when thinking in terms of single time snapshots. The process of seeding density perturbations is not fundamentally localized in time, and this fact can wash out many of the details which appear in a single snapshot.

Superclustering in the explosion scenario. II - Prolate spheroidal shells from superconducting cosmic strings

NASA Technical Reports Server (NTRS)

Borden, David; Ostriker, Jeremiah P.; Weinberg, David H.

1989-01-01

If galaxies form on shells, then clusters of galaxies should form at the vertices where three shells intersect. Weinberg, Ostriker, and Dekel (WOD, 1989) studied this picture quantitatively and found that an intersecting spherical shell model reproduces many of the properties of the observed distribution of galaxy clusters, but that too much superclustering is produced. In this paper, the WOD analysis is repeated with prolate spheroids that could be created by superconducting cosmic strings. It is found that most of the attractive features of the WOD model are maintained in the more general case and there is slight improvement in some aspects, but that the overall problem of excessive superclustering is not really alleviated.

Analytic study of small scale structure on cosmic strings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polchinski, Joseph; Rocha, Jorge V.; Department of Physics, University of California, Santa Barbara, California 93106

2006-10-15

The properties of string networks at scales well below the horizon are poorly understood, but they enter critically into many observables. We argue that in some regimes, stretching will be the only relevant process governing the evolution. In this case, the string two-point function is determined up to normalization: the fractal dimension approaches one at short distance, but the rate of approach is characterized by an exponent that plays an essential role in network properties. The smoothness at short distance implies, for example, that cosmic string lensing images are almost undistorted. We then add in loop production as a perturbationmore » and find that it diverges at small scales. This need not invalidate the stretching model, since the loop production occurs in localized regions, but it implies a complicated fragmentation process. Our ability to model this process is limited, but we argue that loop production peaks a few orders of magnitude below the horizon scale, without the inclusion of gravitational radiation. We find agreement with some features of simulations, and interesting discrepancies that must be resolved by future work.« less

Gamma-ray bursts from cusps on superconducting cosmic strings at large redshifts

NASA Technical Reports Server (NTRS)

Paczynski, Bohdan

1988-01-01

Babul et al. (1987) proposed that some gamma-ray bursts may be caused by energy released at the cusps of oscillating loops made of superconducting cosmic strings. It is claimed that there were some errors and omissions in that work, which are claimed to be corrected in the present paper. Arguments are presented, that given certain assumptions, the cusps on oscillating superconducting cosmic strings produce highly collimated and energetic electromagnetic bursts and that a fair fraction of electromagnetic energy is likely to come out as gamma rays.

The COBE cosmic 3 K anisotropy experiment: A gravity wave and cosmic string probe

NASA Technical Reports Server (NTRS)

Bennett, Charles L.; Smoot, George F.

1989-01-01

Among the experiments to be carried into orbit next year, by the COBE satellite, are differential microwave radiometers. They will make sensitive all-sky maps of the temperature of the cosmic microwave background radiation at three frequencies, giving dipole, quadrupole, and higher order multipole measurements of the background radiation. The experiment will either detect, or place significant constraints on, the existence of cosmic strings and long wavelength gravity waves.

Cosmic-string-induced hot dark matter perturbations

NASA Technical Reports Server (NTRS)

Van Dalen, Anthony

1990-01-01

This paper investigates the evolution of initially relativistic matter, radiation, and baryons around cosmic string seed perturbations. A detailed analysis of the linear evolution of spherical perturbations in a universe is carried out, and this formalism is used to study the evolution of perturbations around a sphere of uniform density and fixed radius, approximating a loop of cosmic string. It was found that, on scales less than a few megaparsec, the results agree with the nonrelativistic calculation of previous authors. On greater scales, there is a deviation approaching a factor of 2-3 in the perturbation mass. It is shown that a scenario with cosmic strings, hot dark matter, and a Hubble constant greater than 75 km/sec per Mpc can generally produce structure on the observed mass scales and at the appropriate time: 1 + z = about 4 for galaxies and 1 + z = about 1.5 for Abell clusters.

Imprints of cosmic strings on the cosmological gravitational wave background

NASA Astrophysics Data System (ADS)

Kleidis, K.; Papadopoulos, D. B.; Verdaguer, E.; Vlahos, L.

2008-07-01

The equation which governs the temporal evolution of a gravitational wave (GW) in curved space-time can be treated as the Schrödinger equation for a particle moving in the presence of an effective potential. When GWs propagate in an expanding universe with constant effective potential, there is a critical value (kc) of the comoving wave number which discriminates the metric perturbations into oscillating (k>kc) and nonoscillating (k

Self-energy and self-force in the space-time of a thick cosmic string

NASA Astrophysics Data System (ADS)

Khusnutdinov, N. R.; Bezerra, V. B.

2001-10-01

We calculate the self-energy and self-force for an electrically charged particle at rest in the background of Gott-Hiscock cosmic string space-time. We find the general expression for the self-energy which is expressed in terms of the S matrix of the scattering problem. The self-energy continuously falls down outward from the string's center with the maximum at the origin of the string. The self-force is repulsive for an arbitrary position of the particle. It tends to zero in the string's center and also far from the string and it has a maximum value at the string's surface. The plots of the numerical calculations of the self-energy and self-force are shown.

Thermal stabilization of superconducting sigma strings and their drum vortons

NASA Astrophysics Data System (ADS)

Carter, Brandon; Brandenberger, Robert H.; Davis, Anne-Christine

2002-05-01

We discuss various issues related to stabilized embedded strings in a thermal background. In particular, we demonstrate that such strings will generically become superconducting at moderately low temperatures, thus enhancing their stability. We then present a new class of defects-drum vortons-which arise when a small symmetry breaking term is added to the potential. We display these points within the context of the O(4) sigma model, relevant for hadrodynamics below the QCD scale. This model admits ``embedded defects'' (topological defect configurations of a simpler-in this case O(2) symmetric-model obtained by imposing an embedding constraint) that are unstable in the full model at zero temperature, but that can be stabilized (by electromagnetic coupling to photons) in a thermal gas at moderately high termperatures. It is shown here that below the embedded defect stabilization threshold, there will still be stabilized cosmic string defects. However, they will not be of the symmetric embedded vortex type, but of an ``asymmetric'' vortex type, and are automatically superconducting. In the presence of weak symmetry breaking terms, such as arise naturally when using the O(4) model for hadrodynamics, the strings become the boundary of a new kind of cosmic sigma membrane, with tension given by the pion mass. The string current would then make it possible for a loop to attain a (classically) stable equilibrium state that differs from an ``ordinary'' vorton state by the presence of a sigma membrane stretched across it in a drum-like configuration. Such defects will however be entirely destabilized if the symmetry breaking is too strong, as is found to be the case-due to the rather large value of the pion mass-in the hadronic application of the O(4) sigma model.

Is QSO 1146 + 111B,C due to lensing by a cosmic string?

NASA Technical Reports Server (NTRS)

Gott, J. R., III

1986-01-01

A newly discovered lens candidate, QSO 1146 + 111B,C, is discussed which appears to consist of two images of equal brightness of a quasar at redshift 1.01 separated by 2.6 arcmin. If this is produced by a cosmic string, its mass per unit length is about 4.0 x 10 to the 23rd g/cm or more. This value is large enough to be interesting for string-assisted galaxy formation and near the upper limits implied by the isotropy of the cosmic microwave background and constraints on gravitational radiation.

Cosmic strings: Gravitation without local curvature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helliwell, T.M.; Konkowski, D.A.

1987-05-01

Cosmic strings are very long, thin structures which might stretch over vast reaches of the universe. If they exist, they would have been formed during phase transitions in the very early universe. The space-time surrounding a straight cosmic string is flat but nontrivial: A two-dimensional spatial section is a cone rather than a plane. This feature leads to unique gravitational effects. The flatness of the cone means that many of the gravitational effects can be understood with no mathematics beyond trigonometry. This includes the observational predictions of the double imaging of quasars and the truncation of the images of galaxies.

Cosmic strings and the microwave sky. I - Anisotropy from moving strings

NASA Technical Reports Server (NTRS)

Stebbins, Albert

1988-01-01

A method is developed for calculating the component of the microwave anisotropy around cosmic string loops due to their rapidly changing gravitational fields. The method is only valid for impact parameters from the string much smaller than the horizon size at the time the photon passes the string. The method makes it possible to calculate the temperature pattern around arbitrary string configurations numerically in terms of one-dimensional integrals. This method is applied to temperature jump across a string, confirming and extending previous work. It is also applied to cusps and kinks on strings, and to determining the temperature pattern far from a strong loop. The temperature pattern around a few loop configurations is explicitly calculated. Comparisons with the work of Brandenberger et al. (1986) indicates that they have overestimated the MBR anisotropy from gravitational radiation emitted from loops.

Cosmological cosmic strings

NASA Technical Reports Server (NTRS)

Gregory, Ruth

1988-01-01

The effect of an infinite cosmic string on a cosmological background is investigated. It is found that the metric is approximately a scaled version of the empty space string metric, i.e., conical in nature. Results are used to place bounds on the amount of cylindrical gravitational radiation currently emitted by such a string. The gravitational radiation equations are then analyzed explicitly and it is shown that even initially large disturbances are rapidly damped as the expansion proceeds. The implications of the gravitational radiation background and the limitations of the quadrupole formula are discussed.

Small scale structure on cosmic strings

NASA Technical Reports Server (NTRS)

Albrecht, Andreas

1989-01-01

The current understanding of cosmic string evolution is discussed, and the focus placed on the question of small scale structure on strings, where most of the disagreements lie. A physical picture designed to put the role of the small scale structure into more intuitive terms is presented. In this picture it can be seen how the small scale structure can feed back in a major way on the overall scaling solution. It is also argued that it is easy for small scale numerical errors to feed back in just such a way. The intuitive discussion presented here may form the basis for an analytic treatment of the small scale structure, which argued in any case would be extremely valuable in filling the gaps in the present understanding of cosmic string evolution.

Landau quantization in the spinning cosmic string spacetime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muniz, C.R., E-mail: celiomuniz@yahoo.com; Bezerra, V.B.; Cunha, M.S.

2014-11-15

We analyze the quantum phenomenon arising from the interaction of a spinless charged particle with a rotating cosmic string, under the action of a static and uniform magnetic field parallel to the string. We calculate the energy levels of the particle in the non-relativistic approach, showing how these energies depend on the parameters involved in the problem. In order to do this, we solve the time independent Schrödinger equation in the geometry of the spinning cosmic string, taking into account that the coupling between the rotation of the spacetime and the angular momentum of the particle is very weak, suchmore » that makes sense to apply the Schrödinger equation in a curved background whose metric has an off diagonal term which involves time and space. It is also assumed that the particle orbits sufficiently far from the boundary of the region of closed timelike curves which exist around this topological defect. Finally, we find the Landau levels of the particle in the presence of a spinning cosmic string endowed with internal structure, i.e., having a finite width and uniformly filled with both material and vacuum energies. - Highlights: • Solution of the wave equation characterizing the problem. • Energy levels of the particle in spacetime of the structureless string. • Expression for an analogous of the quadratic Zeeman effect. • Energy levels of the particle in spacetime of the string with internal structure. • Evidence of the string structure by the internal existence of the vacuum energy.« less

Relativistic Anandan quantum phase and the Aharonov–Casher effect under Lorentz symmetry breaking effects in the cosmic string spacetime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bakke, K., E-mail: kbakke@fisica.ufpb.br; Furtado, C., E-mail: furtado@fisica.ufpb.br; Belich, H., E-mail: belichjr@gmail.com

2016-09-15

From the modified Maxwell theory coupled to gravity, we establish a possible scenario of the violation of the Lorentz symmetry and write an effective metric for the cosmic string spacetime. Then, we investigate the arising of an analogue of the Anandan quantum phase for a relativistic Dirac neutral particle with a permanent magnetic dipole moment in the cosmic string spacetime under Lorentz symmetry breaking effects. Besides, we analyse the influence of the effects of the Lorentz symmetry violation and the topology of the defect on the Aharonov–Casher geometric quantum phase in the nonrelativistic limit.

Distortion of the cosmic background radiation by superconducting strings

NASA Technical Reports Server (NTRS)

Ostriker, J. P.; Thompson, C.

1987-01-01

Superconducting cosmic strings can be significant energy sources, keeping the universe ionized past the commonly assumed epoch of recombination. As a result, the spectrum of the cosmic background radiation is distorted in the presence of heated primordial gas via the Suniaev-Zel'dovich effect. Thiis distortion can be relatively large: the Compton y parameter attains a maximum in the range 0.001-0.005, with these values depending on the mass scale of the string. A significant contribution to y comes from loops decaying at high redshift when the universe is optically thick to Thomson scattering. Moreover, the isotropic spectral distortion is large compared to fluctuations at all angular scales.

Cosmic string with a light massive neutrino

NASA Technical Reports Server (NTRS)

Albrecht, Andreas; Stebbins, Albert

1992-01-01

We have estimated the power spectra of density fluctuations produced by cosmic strings with neutrino hot dark matter (HDM). Normalizing at 8/h Mpc, we find that the spectrum has more power on small scales than HDM + inflation, less than cold dark matter (CDM) + inflation, and significantly less the CDM + strings. With HDM, large wakes give significant contribution to the power on the galaxy scale and may give rise to large sheets of galaxies.

Rapidly moving cosmic strings and chronology protection

NASA Astrophysics Data System (ADS)

Ori, Amos

1991-10-01

Recently, Gott has provided a family of solutions of the Einstein equations describing pairs of parallel cosmic strings in motion. He has shown that if the strings' relative velocity is sufficiently high, there exist closed timelike curves (CTC's) in the spacetime. Here we show that if there are CTC's in such a solution, then every t=const hypersurface in the spacetime intersects CTC's. Therefore, these solutions do not contradict the chronology protection conjecture of Hawking.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hergt, Lukas; Amara, Adam; Kacprzak, Tomasz

We use wavelet and curvelet transforms to extract signals of cosmic strings from simulated cosmic microwave background (CMB) temperature anisotropy maps, and to study the limits on the cosmic string tension which various ongoing CMB temperature anisotropy experiments will be able to achieve. We construct sky maps with size and angular resolution corresponding to various experiments. These maps contain the signals of a scaling solution of long string segments with a given string tension G μ, the contribution of the dominant Gaussian primordial cosmological fluctuations, and pixel by pixel white noise with an amplitude corresponding to the instrumental noise ofmore » the various experiments. In the case that we include white noise, we find that using curvelets we obtain lower bounds on the string tension than with wavelets. For maps with Planck specification, we obtain bounds comparable to what was obtained by the Planck collaboration [1]. Experiments with better angular resolution such as the South Pole Telescope third generation (SPT-3G) survey will be able to yield stronger limits. For maps with a specification of SPT-3G we find that string signals will be visible down to a string tension of G μ = 1.4 × 10{sup −7}.« less

Wormhole at the core of an infinite cosmic string

NASA Astrophysics Data System (ADS)

Aros, Rodrigo O.; Zamorano, Nelson

1997-11-01

We study a solution of Einstein's equations that describes a straight cosmic string with a variable angular deficit, starting with a 2π deficit at the core. We show that the coordinate singularity associated with this defect can be interpreted as a traversable wormhole lodging at the core of the string. A negative energy density gradually decreases the angular deficit as the distance from the core increases, ending, at radial infinity, in a Minkowski spacetime. The negative energy density can be confined to a small transversal section of the string by gluing to it an exterior Gott-like solution that freezes the angular deficit existing at the matching border. The equation of state of the string is such that any massive particle may stay at rest anywhere in this spacetime. In this sense this is a 2+1 spacetime solution. A generalization that includes the existence of two interacting parallel wormholes is displayed. These wormholes are not traversable. Finally, we point out that a similar result, flat at infinity and with a 2π defect (or excess) at the core, has been recently published by Dyer and Marleau. Even though theirs is a local string fully coupled to gravity, our toy model captures important aspects of this solution.

String mediated phase transitions

NASA Technical Reports Server (NTRS)

Copeland, ED; Haws, D.; Rivers, R.; Holbraad, S.

1988-01-01

It is demonstrated from first principles how the existence of string-like structures can cause a system to undergo a phase transition. In particular, the role of topologically stable cosmic string in the restoration of spontaneously broken symmetries is emphasized. How the thermodynamic properties of strings alter when stiffness and nearest neighbor string-string interactions are included is discussed.

Improved calculation of the gravitational wave spectrum from kinks on infinite cosmic strings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsui, Yuka; Horiguchi, Koichiro; Nitta, Daisuke

2016-11-01

Gravitational wave observations provide unique opportunities to search for cosmic strings. One of the strongest sources of gravitational waves is discontinuities of cosmic strings, called kinks, which are generated at points of intersection. Kinks on infinite strings are known to generate a gravitational wave background over a wide range of frequencies. In this paper, we calculate the spectrum of the gravitational wave background by numerically solving the evolution equation for the distribution function of the kink sharpness. We find that the number of kinks for small sharpness is larger than the analytical estimate used in a previous work, which makesmore » a difference in the spectral shape. Our numerical approach enables us to make a more precise prediction on the spectral amplitude for future gravitational wave experiments.« less

Stochastic background from cosmic (super)strings: Popcorn-like and (Gaussian) continuous regimes

NASA Astrophysics Data System (ADS)

Regimbau, Tania; Giampanis, Stefanos; Siemens, Xavier; Mandic, Vuk

2012-03-01

In the era of the next generation of gravitational wave experiments a stochastic background from cusps of cosmic (super)strings is expected to be probed and, if not detected, to be significantly constrained. A popcornlike background can be, for part of the parameter space, as pronounced as the (Gaussian) continuous contribution from unresolved sources that overlap in frequency and time. We study both contributions from unresolved cosmic string cusps over a range of frequencies relevant to ground based interferometers, such as the LIGO/Virgo second generation and Einstein Telescope third generation detectors, the space antenna LISA, and pulsar timing arrays. We compute the sensitivity (at the 2σ level) in the parameter space for the LIGO/Virgo second generation detector, the Einstein Telescope detector, LISA, and pulsar timing arrays. We conclude that the popcorn regime is complementary to the continuous background. Its detection could therefore enhance confidence in a stochastic background detection and possibly help determine fundamental string parameters such as the string tension and the reconnection probability.

Constraints on cosmic superstrings from Kaluza-Klein emission.

PubMed

Dufaux, Jean-François

2012-07-06

Cosmic superstrings interact generically with a tower of light and/or strongly coupled Kaluza-Klein (KK) modes associated with the geometry of the internal space. We study the production of KK particles by cosmic superstring loops, and show that it is constrained by big bang nucleosynthesis. We study the resulting constraints in the parameter space of the underlying string theory model and highlight their complementarity with the regions that can be probed by current and upcoming gravitational wave experiments.

Cosmic strings and ultra-high energy cosmic rays

NASA Technical Reports Server (NTRS)

Bhattacharjee, Pijushpani

1989-01-01

The flux is calculated of ultrahigh energy protons due to the process of cusp evaporation from cosmic string loops. For the standard value of the dimensionless cosmic string parameter epsilon is identical to G(sub mu) approx. = 10(exp -6), the flux is several orders of magnitude below the observed cosmic ray flux of ultrahigh energy protons. However, the flux at any energy initially increases as the value of epsilon is decreased. This at first suggests that there may be a lower limit on the value of epsilon, which would imply a lower limit on the temperature of a cosmic string forming phase transition in the early universe. However, the calculation shows that this is not the case -- the particle flux at any energy reaches its highest value at epsilon approx. = 10(exp -15) and it then decreases for further decrease of the value of epsilon. This is due to the fact that for too small values of epsilon (less than 10(exp -15)), the energy loss of the loops through the cusp evaporation process itself (rather than gravitational energy loss of the loops) becomes the dominant factor that controls the behavior of the number density of the loops at the relevant times of emission of the particles. The highest flux at any energy remains at least four orders of magnitude below the observed flux. There is thus no lower limit on epsilon.

Cosmological applications of singular hypersurfaces in general relativity

NASA Astrophysics Data System (ADS)

Laguna-Castillo, Pablo

Three applications to cosmology of surface layers, based on Israel's formalism of singular hypersurfaces and thin shells in general relativity, are presented. Einstein's field equations are analyzed in the presence of a bubble nucleated in vacuum phase transitions within the context of the old inflationary universe scenario. The evolution of a bubble with vanishing surface energy density is studied. It is found that such bubbles lead to a worm-hole matching. Next, the observable four-dimensional universe is considered as a singular hypersurface of discontinuity embedded in a five-dimensional Kaluza-Klein cosmology. It is possible to rewrite the projected five-dimensional Einstein equations on the surface layer in a similar way to the four-dimensional Robertson-Walker cosmology equations. Next, a model is described for an infinite-length, straight U(1) cosmic string as a cylindrical, singular shell enclosing a region of false vacuum. A set of equations is introduced which are required to develop a three-dimensional computer code whose purpose is to study the process of intercommuting cosmic strings with the inclusion of gravitational effects. The outcome is evolution and constraint equations for the gravitational, scalar and gauge field of two initially separated, perpendicular, cosmic strings.

Cosmic string loops as the seeds of super-massive black holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bramberger, Sebastian F.; Brandenberger, Robert H.; Jreidini, Paul

2015-06-01

Recent discoveries of super-massive black holes at high redshifts indicate a possible tension with the standard ΛCDM paradigm of early universe cosmology which has difficulties in explaining the origin of the required nonlinear compact seeds which trigger the formation of these super-massive black holes. Here we show that cosmic string loops which result from a scaling solution of strings formed during a phase transition in the very early universe lead to an additional source of compact seeds. The number density of string-induced seeds dominates at high redshifts and can help trigger the formation of the observed super-massive black holes.

Effects of ordinary and superconducting cosmic strings on primordial nucleosynthesis

NASA Technical Reports Server (NTRS)

Hodges, Hardy M.; Turner, Michael S.

1988-01-01

A precise calculation is done of the primordial nucleosynthesis constraint on the energy per length of ordinary and superconducting cosmic strings. A general formula is provided for the constraint on the string tension for ordinary strings. Using the current values for the various parameters that describe the evolution of loops, the constraint for ordinary strings is G mu less than 2.2 x 10 to the minus 5 power. Our constraint is weaker than previously quoted limits by a factor of approximately 5. For superconducting loops, with currents generated by primordial magnetic fields, the constraint can be less or more stringent than this limit, depending on the strength of the magnetic field. It is also found in this case that there is a negligible amount of entropy production if the electromagnetic radiation from strings thermalizes with the radiation background.

Black strings, low viscosity fluids, and violation of cosmic censorship.

PubMed

Lehner, Luis; Pretorius, Frans

2010-09-03

We describe the behavior of 5-dimensional black strings, subject to the Gregory-Laflamme instability. Beyond the linear level, the evolving strings exhibit a rich dynamics, where at intermediate stages the horizon can be described as a sequence of 3-dimensional spherical black holes joined by black string segments. These segments are themselves subject to a Gregory-Laflamme instability, resulting in a self-similar cascade, where ever-smaller satellite black holes form connected by ever-thinner string segments. This behavior is akin to satellite formation in low-viscosity fluid streams subject to the Rayleigh-Plateau instability. The simulation results imply that the string segments will reach zero radius in finite asymptotic time, whence the classical space-time terminates in a naked singularity. Since no fine-tuning is required to excite the instability, this constitutes a generic violation of cosmic censorship.

Psyche=singularity: A comparison of Carl Jung's transpersonal psychology and Leonard Susskind's holographic string theory

NASA Astrophysics Data System (ADS)

Desmond, Timothy

In this dissertation I discern what Carl Jung calls the mandala image of the ultimate archetype of unity underlying and structuring cosmos and psyche by pointing out parallels between his transpersonal psychology and Stanford physicist Leonard Susskind's string theory. Despite his atheistic, materialistically reductionist interpretation of it, I demonstrate how Susskind's string theory of holographic information conservation at the event horizons of black holes, and the cosmic horizon of the universe, corroborates the following four topics about which Jung wrote: (1) his near-death experience of the cosmic horizon after a heart attack in 1944; ( 2) his equation relating psychic energy to mass, "Psyche=highest intensity in the smallest space" (1997, 162), which I translate into the equation, Psyche=Singularity; (3) his theory that the mandala, a circle or sphere with a central point, is the symbolic image of the ultimate archetype of unity through the union of opposites, which structures both cosmos and psyche, and which rises spontaneously from the collective unconscious to compensate a conscious mind torn by irreconcilable demands (1989, 334-335, 396-397); and (4) his theory of synchronicity. I argue that Susskind's inside-out black hole model of our Big Bang universe forms a geometrically perfect mandala: a central Singularity encompassed by a two-dimensional sphere which serves as a universal memory bank. Moreover, in precise fulfillment of Jung's theory, Susskind used that mandala to reconcile the notoriously incommensurable paradigms of general relativity and quantum mechanics, providing in the process a mathematically plausible explanation for Jung's near-death experience of his past, present, and future life simultaneously at the cosmic horizon. Finally, Susskind's theory also provides a plausible cosmological model to explain Jung's theory of synchronicity--meaningful coincidences may be tied together by strings at the cosmic horizon, from which they radiate inward as the holographic "movie" of our three-dimensional world.

Void statistics, scaling, and the origins of large-scale structure

NASA Technical Reports Server (NTRS)

Fry, J. N.; Giovanelli, Riccardo; Haynes, Martha P.; Melott, Adrian L.; Scherrer, Robert J.

1989-01-01

The probability that a volume of the universe of given size and shape spaced at random will be void of galaxies is used here to study various models of the origin of cosmological structures. Numerical simulations are conducted on hot-particle and cold-particle-modulated inflationary models with and without biasing, on isothermal or initially Poisson models, and on models where structure is seeded by loops of cosmic string. For the Pisces-Perseus redshift compilation of Giovanelli and Haynes (1985), it is found that hierarchical scaling is obeyed for subsamples constructed with different limiting magnitudes and subsamples taken at random. This result confirms that the hierarchical ansatz holds valid to high order and supports the idea that structure in the observed universe evolves by a regular process from an almost Gaussian primordial state. Neutrino models without biasing show the effect of a strong feature in the initial power spectrum. Cosmic string models do not agree well with the galaxy data.

A survey of solutions in a gravitational Born-Infeld theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chern, Jann-Long, E-mail: chern@math.ncu.edu.tw; Yang, Sze-Guang, E-mail: sgyang@math.ncu.edu.tw

2014-03-15

An elliptic equation that arises from a cosmic string model with the action of the Born-Infeld nonlinear electromagnetism, is considered. We classify and establish the uniqueness of radially symmetric solutions.

An upper limit on the stochastic gravitational-wave background of cosmological origin.

PubMed

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Di Virgilio, A; Díaz, M; Dietz, A; Donovan, F; Dooley, K L; Doomes, E E; Drago, M; Drever, R W P; Dueck, J; Duke, I; Dumas, J-C; Dwyer, J G; Echols, C; Edgar, M; Effler, A; Ehrens, P; Ely, G; Espinoza, E; Etzel, T; Evans, M; Evans, T; Fafone, V; Fairhurst, S; Faltas, Y; Fan, Y; Fazi, D; Fehrmann, H; Ferrante, I; Fidecaro, F; Finn, L S; Fiori, I; Flaminio, R; Flasch, K; Foley, S; Forrest, C; Fotopoulos, N; Fournier, J-D; Franc, J; Franzen, A; Frasca, S; Frasconi, F; Frede, M; Frei, M; Frei, Z; Freise, A; Frey, R; Fricke, T; Fritschel, P; Frolov, V V; Fyffe, M; Galdi, V; Gammaitoni, L; Garofoli, J A; Garufi, F; Genin, E; Gennai, A; Gholami, I; Giaime, J A; Giampanis, S; Giardina, K D; Giazotto, A; Goda, K; Goetz, E; Goggin, L M; González, G; Gorodetsky, M L; Gobler, S; Gouaty, R; Granata, M; Granata, V; Grant, A; Gras, S; Gray, C; Gray, M; Greenhalgh, R J S; Gretarsson, A M; Greverie, C; Grimaldi, F; Grosso, R; Grote, H; Grunewald, S; Guenther, M; Guidi, G; Gustafson, E K; Gustafson, R; Hage, B; Hallam, J M; Hammer, D; Hammond, G D; Hanna, C; Hanson, J; Harms, J; Harry, G M; Harry, I W; Harstad, E D; Haughian, K; Hayama, K; Heefner, J; Heitmann, H; Hello, P; Heng, I S; Heptonstall, A; Hewitson, M; Hild, S; Hirose, E; Hoak, D; Hodge, K A; Holt, K; Hosken, D J; Hough, J; Hoyland, D; Huet, D; Hughey, B; Huttner, S H; Ingram, D R; Isogai, T; Ito, M; Ivanov, A; Johnson, B; Johnson, W W; Jones, D I; Jones, G; Jones, R; Sancho de la Jordana, L; Ju, L; Kalmus, P; Kalogera, V; Kandhasamy, S; Kanner, J; Kasprzyk, D; Katsavounidis, E; Kawabe, K; Kawamura, S; Kawazoe, F; Kells, W; Keppel, D G; Khalaidovski, A; Khalili, F Y; Khan, R; Khazanov, E; King, P; Kissel, J S; Klimenko, S; Kokeyama, K; Kondrashov, V; Kopparapu, R; Koranda, S; Kozak, D; Krishnan, B; Kumar, R; Kwee, P; La Penna, P; Lam, P K; Landry, M; Lantz, B; Laval, M; Lazzarini, A; Lei, H; Lei, M; Leindecker, N; Leonor, I; Leroy, N; Letendre, N; Li, C; Lin, H; Lindquist, P E; Littenberg, T B; Lockerbie, N A; Lodhia, D; Longo, M; Lorenzini, M; Loriette, V; Lormand, M; Losurdo, G; Lu, P; Lubinski, M; Lucianetti, A; Lück, H; Machenschalk, B; Macinnis, M; Mackowski, J-M; Mageswaran, M; Mailand, K; Majorana, E; Man, N; Mandel, I; Mandic, V; Mantovani, M; Marchesoni, F; Marion, F; Márka, S; Márka, Z; Markosyan, A; Markowitz, J; Maros, E; Marque, J; Martelli, F; Martin, I W; Martin, R M; Marx, J N; Mason, K; Masserot, A; Matichard, F; Matone, L; Matzner, R A; Mavalvala, N; McCarthy, R; McClelland, D E; McGuire, S C; McHugh, M; McIntyre, G; McKechan, D J A; McKenzie, K; Mehmet, M; Melatos, A; Melissinos, A C; Mendell, G; Menéndez, D F; Menzinger, F; Mercer, R A; Meshkov, S; Messenger, C; Meyer, M S; Michel, C; Milano, L; Miller, J; Minelli, J; Minenkov, Y; Mino, Y; Mitrofanov, V P; Mitselmakher, G; Mittleman, R; Miyakawa, O; Moe, B; Mohan, M; Mohanty, S D; Mohapatra, S R P; Moreau, J; Moreno, G; Morgado, N; Morgia, A; Morioka, T; Mors, K; Mosca, S; Mossavi, K; Mours, B; Mowlowry, C; Mueller, G; Muhammad, D; Mühlen, H Zur; Mukherjee, S; Mukhopadhyay, H; Mullavey, A; Müller-Ebhardt, H; Munch, J; Murray, P G; Myers, E; Myers, J; Nash, T; Nelson, J; Neri, I; Newton, G; Nishizawa, A; Nocera, F; Numata, K; Ochsner, E; O'Dell, J; Ogin, G H; O'Reilly, B; O'Shaughnessy, R; Ottaway, D J; Ottens, R S; Overmier, H; Owen, B J; Pagliaroli, G; Palomba, C; Pan, Y; Pankow, C; Paoletti, F; Papa, M A; Parameshwaraiah, V; Pardi, S; Pasqualetti, A; Passaquieti, R; Passuello, D; Patel, P; Pedraza, M; Penn, S; Perreca, A; Persichetti, G; Pichot, M; Piergiovanni, F; Pierro, V; Pinard, L; Pinto, I M; Pitkin, M; Pletsch, H J; Plissi, M V; Poggiani, R; Postiglione, F; Principe, M; Prix, R; Prodi, G A; Prokhorov, L; Punken, O; Punturo, M; Puppo, P; Putten, S van der; Quetschke, V; Raab, F J; Rabaste, O; Rabeling, D S; Radkins, H; Raffai, P; Raics, Z; Rainer, N; Rakhmanov, M; Rapagnani, P; Raymond, V; Re, V; Reed, C M; Reed, T; Regimbau, T; Rehbein, H; Reid, S; Reitze, D H; Ricci, F; Riesen, R; Riles, K; Rivera, B; Roberts, P; Robertson, N A; 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Tarabrin, S P; Taylor, J R; Taylor, R; Terenzi, R; Thacker, J; Thorne, K A; Thorne, K S; Thüring, A; Tokmakov, K V; Toncelli, A; Tonelli, M; Torres, C; Torrie, C; Tournefier, E; Travasso, F; Traylor, G; Trias, M; Trummer, J; Ugolini, D; Ulmen, J; Urbanek, K; Vahlbruch, H; Vajente, G; Vallisneri, M; Vass, S; Vaulin, R; Vavoulidis, M; Vecchio, A; Vedovato, G; van Veggel, A A; Veitch, J; Veitch, P; Veltkamp, C; Verkindt, D; Vetrano, F; Viceré, A; Villar, A; Vinet, J-Y; Vocca, H; Vorvick, C; Vyachanin, S P; Waldman, S J; Wallace, L; Ward, H; Ward, R L; Was, M; Weidner, A; Weinert, M; Weinstein, A J; Weiss, R; Wen, L; Wen, S; Wette, K; Whelan, J T; Whitcomb, S E; Whiting, B F; Wilkinson, C; Willems, P A; Williams, H R; Williams, L; Willke, B; Wilmut, I; Winkelmann, L; Winkler, W; Wipf, C C; Wiseman, A G; Woan, G; Wooley, R; Worden, J; Wu, W; Yakushin, I; Yamamoto, H; Yan, Z; Yoshida, S; Yvert, M; Zanolin, M; Zhang, J; Zhang, L; Zhao, C; Zotov, N; Zucker, M E; Zweizig, J

2009-08-20

A stochastic background of gravitational waves is expected to arise from a superposition of a large number of unresolved gravitational-wave sources of astrophysical and cosmological origin. It should carry unique signatures from the earliest epochs in the evolution of the Universe, inaccessible to standard astrophysical observations. Direct measurements of the amplitude of this background are therefore of fundamental importance for understanding the evolution of the Universe when it was younger than one minute. Here we report limits on the amplitude of the stochastic gravitational-wave background using the data from a two-year science run of the Laser Interferometer Gravitational-wave Observatory (LIGO). Our result constrains the energy density of the stochastic gravitational-wave background normalized by the critical energy density of the Universe, in the frequency band around 100 Hz, to be <6.9 x 10(-6) at 95% confidence. The data rule out models of early Universe evolution with relatively large equation-of-state parameter, as well as cosmic (super)string models with relatively small string tension that are favoured in some string theory models. This search for the stochastic background improves on the indirect limits from Big Bang nucleosynthesis and cosmic microwave background at 100 Hz.

Superconducting cosmic string: Equation of state for spacelike and timelike current in the neutral limit

NASA Astrophysics Data System (ADS)

Peter, Patrick

1992-02-01

The equation of state relating the tension T and the energy per unit length U of a cosmic string is investigated in the simplest nontrivial case, namely, that of a field theory with U(1)local×U(1)global invariance, in four dimensions, which is interpretable as the zero-charge-coupling-constant limit of the more general superconducting string models that have been previously investigated. This limit has the advantage of giving vacuum vortex defects that are strictly local so that the quantities such as U and T that are relevant for the macroscopic description can be computed without ambiguity. In the case of ``electric'' states (with timelike current) for which no comparable previous calculations exist, it is shown there is a critical frequency wc beyond which the vortex becomes unstable due to ``charge'' carrier emission. In the case of ``magnetic'' states (with spacelike current), the present analysis provides more precise results than those of previous investigations, whose predictions are broadly confirmed for typical moderate models in which the tension T remains comparable to the energy density U though not for extreme models, in which serious discrepancies are revealed.

Cosmic string wakes and large-scale structure

NASA Technical Reports Server (NTRS)

Charlton, Jane C.

1988-01-01

The formation of structure from infinite cosmic string wakes is modeled for a universe dominated by cold dark matter (CDM). Cross-sectional slices through the wake distribution tend to outline empty regions with diameters which are not inconsistent with the range of sizes of the voids in the CfA slice of the universe. The topology of the wake distribution is found to be spongy rather than cell-like. Correlations between CDM wakes do not extend much beyond a horizon length, so it is unlikely that CDM wakes are responsible for the correlations between clusters of galaxies. An estimate of the fraction of matter to accrete onto CDM wakes indicates that wakes could be more important in galaxy formation than previously anticipated.

Semiclassical gravitational effects on the gravitational lensing in the spacetime of topological defects

NASA Astrophysics Data System (ADS)

Jusufi, Kimet; Rahaman, Farook; Banerjee, Ayan

2018-02-01

The theory of gravitational lensing has revealed many generic and fundamental properties of compact objects like black holes and wormholes. In this article, we utilize a recent formulation to compute the quantum effects on the deflection angle of a light ray, namely, the Gauss-Bonnet theorem (GBT) to explore the semiclassical gravitational effects in the spacetime of a point-like global monopole and a cosmic string. Previously, the Gauss-Bonnet theorem (Gibbons and Werner, 2008) was proposed as an alternative way to compute the deflection angle of light in a static, spherically symmetric and asymptotically flat spacetime. In the present article we have used the celebrated GBT that applied to the optical metric as well as the geodesic method in computing the deflection angle. Interestingly one can observe that we have found an exact result between GBT and the standard approach up to the third-order contributions terms by modifying the domain of integration for cosmic string and global monopole deflection angles. Finally we have considered the time delay in the cosmic string/global monopole spacetime and found that the delay in time is proportional to the linear mass density of the cosmic string and global monopole parameter, respectively.

Priming the search for cosmic superstrings using GADGET2 simulations

NASA Astrophysics Data System (ADS)

Cousins, Bryce; Jia, Hewei; Braverman, William; Chernoff, David

2018-01-01

String theory is an extensive mathematical theory which, despite its broad explanatory power, is still lacking empirical support. However, this may change when considering the scope of cosmology, where “cosmic superstrings” may serve as observational evidence. According to string theory, these superstrings were stretched to cosmic scales in the early Universe and may now be detectable, via microlensing or gravitational radiation. Negative results from prior surveys have put some limits on superstring properties, so to investigate the parameter space more effectively, we ask: “where should we expect to find cosmic superstrings, and how many should we predict?” This research investigates these questions by simulating cosmic string behavior during structure formation in the universe using GADGET2. The sizes and locations of superstring clusters are assessed using kernel density estimation and radial correlation functions. Currently, only preliminary small-scale simulations have been performed, producing superstring clustering with low sensitivity. However, future simulations of greater magnitude will offer far higher resolution, allowing us to more precisely track superstring behavior within structures. Such results will guide future searches, most imminently those made possible by LSST and WFIRST.

Phenomenology of soft hadron interactions and the relevant EAS data

NASA Technical Reports Server (NTRS)

Kalmykov, N. N.; Khristiansen, G. B.; Motova, M. V.

1984-01-01

The interpretation of the experimental data in superhigh energy cosmic rays requires the calculations using various models of elementary hadron interaction. One should prefer the models justified by accelerator data and giving definite predictions for superhigh energies. The model of quark-gluon pomeron strings (the QGPS models) satisfies this requirement.

Isocurvature fluctuations through axion trapping by cosmic string wakes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Layek, Biswanath

2005-03-15

We consider wakelike density fluctuations produced by cosmic strings at the quark-hadron transition in the early universe. We show that low momentum axions which are produced through the radiation from the axionic string at an earlier stage, may get trapped inside these wakes due to delayed hadronization in these overdense regions. As the interfaces, bordering the wakes, collapse, the axions pick-up momentum from the walls and finally leave the wake regions. These axions thus can produce large scale isocurvature fluctuations. We have calculated the detailed profile of these axionic density fluctuations and discuss its astrophysical consequences.

Cosmic microwave background constraints for global strings and global monopoles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lopez-Eiguren, Asier; Lizarraga, Joanes; Urrestilla, Jon

We present the first cosmic microwave background (CMB) power spectra from numerical simulations of the global O( N ) linear σ-model, with N =2,3, which have global strings and monopoles as topological defects. In order to compute the CMB power spectra we compute the unequal time correlators (UETCs) of the energy-momentum tensor, showing that they fall off at high wave number faster than naive estimates based on the geometry of the defects, indicating non-trivial (anti-)correlations between the defects and the surrounding Goldstone boson field. We obtain source functions for Einstein-Boltzmann solvers from the UETCs, using a recently developed method thatmore » improves the modelling at the radiation-matter transition. We show that the interpolation function that mimics the transition is similar to other defect models, but not identical, confirming the non-universality of the interpolation function. The CMB power spectra for global strings and global monopoles have the same overall shape as those obtained using the non-linear σ-model approximation, which is well captured by a large- N calculation. However, the amplitudes are larger than the large- N calculation would naively predict, and in the case of global strings much larger: a factor of 20 at the peak. Finally we compare the CMB power spectra with the latest CMB data in other to put limits on the allowed contribution to the temperature power spectrum at multipole l = 10 of 1.7% for global strings and 2.4% for global monopoles. These limits correspond to symmetry-breaking scales of 2.9× 10{sup 15} GeV (6.3× 10{sup 14} GeV with the expected logarithmic scaling of the effective string tension between the simulation time and decoupling) and 6.4× 10{sup 15} GeV respectively. The bound on global strings is a significant one for the ultra-light axion scenario with axion masses m {sub a} ∼< 10{sup −28} eV . These upper limits indicate that gravitational waves from global topological defects will not be observable at the gravitational wave observatory LISA.« less

Cosmic strings and baryon decay catalysis

NASA Technical Reports Server (NTRS)

Gregory, Ruth; Perkins, W. B.; Davis, A.-C.; Brandenberger, R. H.

1989-01-01

Cosmic strings, like monopoles, can catalyze proton decay. For integer charged fermions, the cross section for catalysis is not amplified, unlike in the case of monopoles. The catalysis processes are reviewed both in the free quark and skyrmion pictures and the implications for baryogenesis are discussed. A computation of the cross section for monopole catalyzed skyrmion decay is presented using classical physics. Also discussed are some effects which can screen catalysis processes.

Supersymmetric k-defects

DOE PAGES

Koehn, Michael; Trodden, Mark

2016-03-03

In supersymmetric theories, topological defects can have nontrivial behaviors determined purely by whether or not supersymmetry is restored in the defect core. A well-known example of this is that some supersymmetric cosmic strings are automatically superconducting, leading to important cosmological effects and constraints. We investigate the impact of nontrivial kinetic interactions, present in a number of particle physics models of interest in cosmology, on the relationship between supersymmetry and supercurrents on strings. Furthermore, we find that in some cases it is possible for superconductivity to be disrupted by the extra interactions.

Scalar Casimir densities and forces for parallel plates in cosmic string spacetime

NASA Astrophysics Data System (ADS)

Bezerra de Mello, E. R.; Saharian, A. A.; Abajyan, S. V.

2018-04-01

We analyze the Green function, the Casimir densities and forces associated with a massive scalar quantum field confined between two parallel plates in a higher dimensional cosmic string spacetime. The plates are placed orthogonal to the string, and the field obeys the Robin boundary conditions on them. The boundary-induced contributions are explicitly extracted in the vacuum expectation values (VEVs) of the field squared and of the energy-momentum tensor for both the single plate and two plates geometries. The VEV of the energy-momentum tensor, in additional to the diagonal components, contains an off diagonal component corresponding to the shear stress. The latter vanishes on the plates in special cases of Dirichlet and Neumann boundary conditions. For points outside the string core the topological contributions in the VEVs are finite on the plates. Near the string the VEVs are dominated by the boundary-free part, whereas at large distances the boundary-induced contributions dominate. Due to the nonzero off diagonal component of the vacuum energy-momentum tensor, in addition to the normal component, the Casimir forces have nonzero component parallel to the boundary (shear force). Unlike the problem on the Minkowski bulk, the normal forces acting on the separate plates, in general, do not coincide if the corresponding Robin coefficients are different. Another difference is that in the presence of the cosmic string the Casimir forces for Dirichlet and Neumann boundary conditions differ. For Dirichlet boundary condition the normal Casimir force does not depend on the curvature coupling parameter. This is not the case for other boundary conditions. A new qualitative feature induced by the cosmic string is the appearance of the shear stress acting on the plates. The corresponding force is directed along the radial coordinate and vanishes for Dirichlet and Neumann boundary conditions. Depending on the parameters of the problem, the radial component of the shear force can be either positive or negative.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vieira, H.S., E-mail: horacio.santana.vieira@hotmail.com; Centro de Ciências, Tecnologia e Saúde, Universidade Estadual da Paraíba, CEP 58233-000, Araruna, PB; Bezerra, V.B., E-mail: valdir@fisica.ufpb.br

Charged massive scalar fields are considered in the gravitational and electromagnetic field produced by a dyonic black hole with a cosmic string along its axis of symmetry. Exact solutions of both angular and radial parts of the covariant Klein–Gordon equation in this background are obtained, and are given in terms of the confluent Heun functions. The role of the presence of the cosmic string in these solutions is showed up. From the radial solution, we obtain the exact wave solutions near the exterior horizon of the black hole, and discuss the Hawking radiation spectrum and the energy flux. -- Highlights:more » •A cosmic string is introduced along the axis of symmetry of the dyonic black hole. •The covariant Klein–Gordon equation for a charged massive scalar field in this background is analyzed. •Both angular and radial parts are transformed to a confluent Heun equation. •The resulting Hawking radiation spectrum and the energy flux are obtained.« less

Cosmic strings in the real sky

NASA Technical Reports Server (NTRS)

Hogan, Craig J.

1987-01-01

Observational strategies for finding effects associated with the gravitational lensing of distant objects by strings are discussed. In particular, a proposed search program at Steward Observatory to find chains of Galaxy image pairs is described.

Fragmentation of cosmic-string loops

NASA Technical Reports Server (NTRS)

York, Thomas

1989-01-01

The fragmentation of cosmic string loops is discussed, and the results of a simulation of this process are presented. The simulation can evolve any of a large class of loops essentially exactly, including allowing fragments that collide to join together. Such reconnection enhances the production of small fragments, but not drastically. With or without reconnections, the fragmentation process produces a collection of nonself-intersecting loops whose typical length is on the order of the persistence length of the initial loop.

Topology of microwave background fluctuations - Theory

NASA Technical Reports Server (NTRS)

Gott, J. Richard, III; Park, Changbom; Bies, William E.; Bennett, David P.; Juszkiewicz, Roman

1990-01-01

Topological measures are used to characterize the microwave background temperature fluctuations produced by 'standard' scenarios (Gaussian) and by cosmic strings (non-Gaussian). Three topological quantities: total area of the excursion regions, total length, and total curvature (genus) of the isotemperature contours, are studied for simulated Gaussian microwave background anisotropy maps and then compared with those of the non-Gaussian anisotropy pattern produced by cosmic strings. In general, the temperature gradient field shows the non-Gaussian behavior of the string map more distinctively than the temperature field for all topology measures. The total contour length and the genus are found to be more sensitive to the existence of a stringy pattern than the usual temperature histogram. Situations when instrumental noise is superposed on the map, are considered to find the critical signal-to-noise ratio for which strings can be detected.

Stochastic gravitational waves from cosmic string loops in scaling

NASA Astrophysics Data System (ADS)

Ringeval, Christophe; Suyama, Teruaki

2017-12-01

If cosmic strings are formed in the early universe, their associated loops emit gravitational waves during the whole cosmic history and contribute to the stochastic gravitational wave background at all frequencies. We provide a new estimate of the stochastic gravitational wave spectrum by considering a realistic cosmological loop distribution, in scaling, as it can be inferred from Nambu-Goto numerical simulations. Our result takes into account various effects neglected so far. We include both gravitational wave emission and backreaction effects on the loop distribution and show that they produce two distinct features in the spectrum. Concerning the string microstructure, in addition to the presence of cusps and kinks, we show that gravitational wave bursts created by the collision of kinks could dominate the signal for wiggly strings, a situation which may be favoured in the light of recent numerical simulations. In view of these new results, we propose four prototypical scenarios, within the margin of the remaining theoretical uncertainties, for which we derive the corresponding signal and estimate the constraints on the string tension put by both the LIGO and European Pulsar Timing Array (EPTA) observations. The less constrained of these scenarios is shown to have a string tension GU <= 7.2 × 10‑11, at 95% of confidence. Smooth loops carrying two cusps per oscillation verify the two-sigma bound GU <= 1.0 × 10‑11 while the most constrained of all scenarios describes very kinky loops and satisfies GU <= 6.7× 10‑14 at 95% of confidence.

On Closed Timelike Curves and Warped Brane World Models

NASA Astrophysics Data System (ADS)

Slagter, Reinoud Jan

2013-09-01

At first glance, it seems possible to construct in general relativity theory causality violating solutions. The most striking one is the Gott spacetime. Two cosmic strings, approaching each other with high velocity, could produce closed timelike curves. It was quickly recognized that this solution violates physical boundary conditions. The effective one particle generator becomes hyperbolic, so the center of mass is tachyonic. On a 5-dimensional warped spacetime, it seems possible to get an elliptic generator, so no obstruction is encountered and the velocity of the center of mass of the effective particle has an overlap with the Gott region. So a CTC could, in principle, be constructed. However, from the effective 4D field equations on the brane, which are influenced by the projection of the bulk Weyl tensor on the brane, it follows that no asymptotic conical space time is found, so no angle deficit as in the 4D counterpart model. This could also explain why we do not observe cosmic strings.

Cosmic ray composition and energy spectrum from 1-30 PeV using the 40-string configuration of IceTop and IceCube

NASA Astrophysics Data System (ADS)

IceCube Collaboration; Abbasi, R.; Abdou, Y.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Altmann, D.; Andeen, K.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Baum, V.; Bay, R.; Beattie, K.; Beatty, J. J.; Bechet, S.; Becker, J. K.; Becker, K.-H.; Bell, M.; Benabderrahmane, M. L.; BenZvi, S.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bertrand, D.; Besson, D. Z.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Bose, D.; Böser, S.; Botner, O.; Brayeur, L.; Brown, A. M.; Bruijn, R.; Brunner, J.; Buitink, S.; Caballero-Mora, K. S.; Carson, M.; Casey, J.; Casier, M.; Chirkin, D.; Christy, B.; Clevermann, F.; Cohen, S.; Cowen, D. F.; Silva, A. H. Cruz; Danninger, M.; Daughhetee, J.; Davis, J. C.; De Clercq, C.; Descamps, F.; Desiati, P.; de Vries-Uiterweerd, G.; DeYoung, T.; Díaz-Vélez, J. C.; Dreyer, J.; Dumm, J. P.; Dunkman, M.; Eagan, R.; Eisch, J.; Ellsworth, R. W.; Engdegård, O.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Fedynitch, A.; Feintzeig, J.; Feusels, T.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Flis, S.; Franckowiak, A.; Franke, R.; Frantzen, K.; Fuchs, T.; Gaisser, T. K.; Gallagher, J.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Goodman, J. A.; Góra, D.; Grant, D.; Groß, A.; Grullon, S.; Gurtner, M.; Ha, C.; Ismail, A. Haj; Hallgren, A.; Halzen, F.; Hanson, K.; Heereman, D.; Heimann, P.; Heinen, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Homeier, A.; Hoshina, K.; Huelsnitz, W.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobi, E.; Jacobsen, J.; Japaridze, G. S.; Jlelati, O.; Johansson, H.; Kappes, A.; Karg, T.; Karle, A.; Kiryluk, J.; Kislat, F.; Kläs, J.; Klein, S. R.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Kopper, C.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Krasberg, M.; Kroll, G.; Kunnen, J.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Laihem, K.; Landsman, H.; Larson, M. J.; Lauer, R.; Lesiak-Bzdak, M.; Lünemann, J.; Madsen, J.; Maruyama, R.; Mase, K.; Matis, H. S.; McNally, F.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Miarecki, S.; Middell, E.; Milke, N.; Miller, J.; Mohrmann, L.; Montaruli, T.; Morse, R.; Movit, S. M.; Nahnhauer, R.; Naumann, U.; Nowicki, S. C.; Nygren, D. R.; Obertacke, A.; Odrowski, S.; Olivas, A.; Olivo, M.; O'Murchadha, A.; Panknin, S.; Paul, L.; Pepper, J. A.; de los Heros, C. Pérez; Pieloth, D.; Pirk, N.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Rädel, L.; Rawlins, K.; Redl, P.; Resconi, E.; Rhode, W.; Ribordy, M.; Richman, M.; Riedel, B.; Rodrigues, J. P.; Rothmaier, F.; Rott, C.; Ruhe, T.; Rutledge, D.; Ruzybayev, B.; Ryckbosch, D.; Salameh, T.; Sander, H.-G.; Santander, M.; Sarkar, S.; Saba, S. M.; Schatto, K.; Scheel, M.; Scheriau, F.; Schmidt, T.; Schmitz, M.; Schoenen, S.; Schöneberg, S.; Schönherr, L.; Schönwald, A.; Schukraft, A.; Schulte, L.; Schulz, O.; Seckel, D.; Seo, S. H.; Sestayo, Y.; Seunarine, S.; Smith, M. W. E.; Soiron, M.; Soldin, D.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stasik, A.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Strahler, E. A.; Ström, R.; Sullivan, G. W.; Taavola, H.; Taboada, I.; Tamburro, A.; Ter-Antonyan, S.; Tilav, S.; Toale, P. A.; Toscano, S.; Usner, M.; van Eijndhoven, N.; van der Drift, D.; Van Overloop, A.; van Santen, J.; Vehring, M.; Voge, M.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Walter, M.; Wasserman, R.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Williams, D. R.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, C.; Xu, D. L.; Xu, X. W.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; Ziemann, J.; Zilles, A.; Zoll, M.

2013-02-01

The mass composition of high energy cosmic rays depends on their production, acceleration, and propagation. The study of cosmic ray composition can therefore reveal hints of the origin of these particles. At the South Pole, the IceCube Neutrino Observatory is capable of measuring two components of cosmic ray air showers in coincidence: the electromagnetic component at high altitude (2835 m) using the IceTop surface array, and the muonic component above ˜1 TeV using the IceCube array. This unique detector arrangement provides an opportunity for precision measurements of the cosmic ray energy spectrum and composition in the region of the knee and beyond. We present the results of a neural network analysis technique to study the cosmic ray composition and the energy spectrum from 1 PeV to 30 PeV using data recorded using the 40-string/40-station configuration of the IceCube Neutrino Observatory.

How to simulate global cosmic strings with large string tension

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klaer, Vincent B.; Moore, Guy D., E-mail: vklaer@theorie.ikp.physik.tu-darmstadt.de, E-mail: guy.moore@physik.tu-darmstadt.de

Global string networks may be relevant in axion production in the early Universe, as well as other cosmological scenarios. Such networks contain a large hierarchy of scales between the string core scale and the Hubble scale, ln( f {sub a} / H ) ∼ 70, which influences the network dynamics by giving the strings large tensions T ≅ π f {sub a} {sup 2} ln( f {sub a} / H ). We present a new numerical approach to simulate such global string networks, capturing the tension without an exponentially large lattice.

Power suppression at large scales in string inflation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cicoli, Michele; Downes, Sean; Dutta, Bhaskar, E-mail: mcicoli@ictp.it, E-mail: sddownes@physics.tamu.edu, E-mail: dutta@physics.tamu.edu

2013-12-01

We study a possible origin of the anomalous suppression of the power spectrum at large angular scales in the cosmic microwave background within the framework of explicit string inflationary models where inflation is driven by a closed string modulus parameterizing the size of the extra dimensions. In this class of models the apparent power loss at large scales is caused by the background dynamics which involves a sharp transition from a fast-roll power law phase to a period of Starobinsky-like slow-roll inflation. An interesting feature of this class of string inflationary models is that the number of e-foldings of inflationmore » is inversely proportional to the string coupling to a positive power. Therefore once the string coupling is tuned to small values in order to trust string perturbation theory, enough e-foldings of inflation are automatically obtained without the need of extra tuning. Moreover, in the less tuned cases the sharp transition responsible for the power loss takes place just before the last 50-60 e-foldings of inflation. We illustrate these general claims in the case of Fibre Inflation where we study the strength of this transition in terms of the attractor dynamics, finding that it induces a pivot from a blue to a redshifted power spectrum which can explain the apparent large scale power loss. We compute the effects of this pivot for example cases and demonstrate how magnitude and duration of this effect depend on model parameters.« less

Power suppression at large scales in string inflation

NASA Astrophysics Data System (ADS)

Cicoli, Michele; Downes, Sean; Dutta, Bhaskar

2013-12-01

We study a possible origin of the anomalous suppression of the power spectrum at large angular scales in the cosmic microwave background within the framework of explicit string inflationary models where inflation is driven by a closed string modulus parameterizing the size of the extra dimensions. In this class of models the apparent power loss at large scales is caused by the background dynamics which involves a sharp transition from a fast-roll power law phase to a period of Starobinsky-like slow-roll inflation. An interesting feature of this class of string inflationary models is that the number of e-foldings of inflation is inversely proportional to the string coupling to a positive power. Therefore once the string coupling is tuned to small values in order to trust string perturbation theory, enough e-foldings of inflation are automatically obtained without the need of extra tuning. Moreover, in the less tuned cases the sharp transition responsible for the power loss takes place just before the last 50-60 e-foldings of inflation. We illustrate these general claims in the case of Fibre Inflation where we study the strength of this transition in terms of the attractor dynamics, finding that it induces a pivot from a blue to a redshifted power spectrum which can explain the apparent large scale power loss. We compute the effects of this pivot for example cases and demonstrate how magnitude and duration of this effect depend on model parameters.

Self-Energy in the Gott-Hiscock Space-Time

NASA Astrophysics Data System (ADS)

Khusnutdinov, Nail R.; Bezerra, Valdir B.

We calculate the self-energy for an electrically charged particle at rest in the background of Gott-Hiscock cosmic string space-time. The self-energy continuously falls down out-ward from string's with maximum at the origin of the string. The plots of the numerical of the self-energy and the height of barrier are shown.

Is it really naked? On cosmic censorship in string theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frolov, Andrei V.

We investigate the possibility of cosmic censorship violation in string theory using a characteristic double-null code, which penetrates horizons and is capable of resolving the spacetime all the way to the singularity. We perform high-resolution numerical simulations of the evolution of negative mass initial scalar field profiles, which were argued to provide a counterexample to cosmic censorship conjecture for AdS-asymptotic spacetimes in five-dimensional supergravity. In no instances formation of naked singularity is seen. Instead, numerical evidence indicates that black holes form in the collapse. Our results are consistent with earlier numerical studies, and explicitly show where the 'no black hole'more » argument breaks.« less

Smoot Cosmology Group

Science.gov Websites

the Cosmic Background Radiation as a tool to understand the structure and history of the Universe and its relation to the structure of space-time. Likewise, gravitational lensing, the search for evidence of cosmic strings, and the cosmic infrared background tell us about the structure of space-time and

Vacuum Polarization by a Magnetic Flux Tube at Finite Temperature in the Cosmic String Space-Time

NASA Astrophysics Data System (ADS)

Spinelly, J.; Bezerra de Mello, E. R.

In this paper, we analyze the effect produced by the temperature in the vacuum polarization associated with a charged massless scalar field in the presence of a magnetic flux tube in the cosmic string space-time. Three different configurations of magnetic fields are taken into account: (i) a homogeneous field inside the tube, (ii) a field proportional to 1/r, and (iii) a cylindrical shell with δ-function. In these three cases, the axis of the infinitely long tube of radius R coincides with the cosmic string. Because of the complexity of this analysis in the region inside the tube, we consider the thermal effect in the region outside. In order to develop this analysis, we construct the thermal Green function associated with this system for the three above-mentioned situations considering points in the region outside the tube. We explicitly calculate, in the high-temperature limit, the thermal average of the field square and the energy-momentum tensor.

Gravity Waves and Linear Inflation From Axion Monodromy

DOE Office of Scientific and Technical Information (OSTI.GOV)

McAllister, Liam; /Cornell U., LEPP /Cornell U., Phys. Dept.; Silverstein, Eva

2010-08-26

Wrapped branes in string compactifications introduce a monodromy that extends the field range of individual closed-string axions to beyond the Planck scale. Furthermore, approximate shift symmetries of the system naturally control corrections to the axion potential. This suggests a general mechanism for chaotic inflation driven by monodromy-extended closed-string axions. We systematically analyze this possibility and show that the mechanism is compatible with moduli stabilization and can be realized in many types of compactifications, including warped Calabi-Yau manifolds and more general Ricci-curved spaces. In this broad class of models, the potential is linear in the canonical inflaton field, predicting a tensormore » to scalar ratio r {approx} 0.07 accessible to upcoming cosmic microwave background (CMB) observations.« less

Non-topological cycloops

NASA Astrophysics Data System (ADS)

Lake, Matthew; Thomas, Steven; Ward, John

2010-01-01

We propose a mechanism for the creation of cosmic string loops with dynamically stabilised windings in the internal space. Assuming a velocity correlations regime in the post-inflationary epoch, such windings are seen to arise naturally in string networks prior to loop formation. The angular momentum of the string in the compact space may then be sufficient to ensure that the windings remain stable after the loop chops off from the network, even if the internal manifold is simply connected. For concreteness we embed our model in the Klebanov-Strassler geometry, which provides a natural mechanism for brane inflation, as well a being one of the best understood compactification schemes in type IIB string theory. We see that the interaction of angular momentum with the string tension causes the loop to oscillate between phases of expansion and contraction. This, in principle, should give rise to a distinct gravitational wave signature, the future detection of which could provide indirect evidence for the existence of extra dimensions.

Dark matter cosmic string in the gravitational field of a black hole

NASA Astrophysics Data System (ADS)

Nakonieczny, Łukasz; Nakonieczna, Anna; Rogatko, Marek

2018-03-01

We examined analytically and proposed a numerical model of an Abelian Higgs dark matter vortex in the spacetime of a stationary axisymmetric Kerr black hole. In analytical calculations the dark matter sector was modeled by an addition of a U(1)-gauge field coupled to the visible sector. The backreaction analysis revealed that the impact of the dark vortex presence is far more complicated than causing only a deficit angle. The vortex causes an ergosphere shift and the event horizon velocity is also influenced by its presence. These phenomena are more significant than in the case of a visible vortex sector. The area of the event horizon of a black hole is diminished and this decline is larger in comparison to the Kerr black hole with an Abelian Higgs vortex case. After analyzing the gravitational properties for the general setup, we focused on the subset of models that are motivated by particle physics. We retained the Abelian Higgs model as a description of the dark matter sector (this sector contained a heavy dark photon and an additional complex scalar) and added a real scalar representing the real component of the Higgs doublet in the unitary gauge, as well as an additional U(1)-gauge field representing an ordinary electromagnetic field. Moreover, we considered two coupling channels between the visible and dark sectors, which were the kinetic mixing between the gauge fields and a quartic coupling between the scalar fields. After solving the equations of motion for the matter fields numerically we analyzed properties of the cosmic string in the dark matter sector and its influence on the visible sector fields that are directly coupled to it. We found out that the presence of the cosmic string induced spatial variation in the vacuum expectation value of the Higgs field and a nonzero electromagnetic field around the black hole.

Cosmological backgrounds of gravitational waves and eLISA/NGO: phase transitions, cosmic strings and other sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Binétruy, Pierre; Dufaux, Jean-François; Bohé, Alejandro

We review several cosmological backgrounds of gravitational waves accessible to direct-detection experiments, with a special emphasis on those backgrounds due to first-order phase transitions and networks of cosmic (super-)strings. For these two particular sources, we revisit in detail the computation of the gravitational wave background and improve the results of previous works in the literature. We apply our results to identify the scientific potential of the NGO/eLISA mission of ESA regarding the detectability of cosmological backgrounds.

Finite temperature corrections and embedded strings in noncommutative geometry and the standard model with neutrino mixing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martins, R. A.

The recent extension of the standard model to include massive neutrinos in the framework of noncommutative geometry and the spectral action principle involves new scalar fields and their interactions with the usual complex scalar doublet. After ensuring that they bring no unphysical consequences, we address the question of how these fields affect the physics predicted in the Weinberg-Salam theory, particularly in the context of the electroweak phase transition. Applying the Dolan-Jackiw procedure, we calculate the finite temperature corrections, and find that the phase transition is first order. The new scalar interactions significantly improve the stability of the electroweak Z string,more » through the 'bag' phenomenon described by Vachaspati and Watkins ['Bound states can stabilize electroweak strings', Phys. Lett. B 318, 163-168 (1993)]. (Recently, cosmic strings have climbed back into interest due to a new evidence.) Sourced by static embedded strings, an internal space analogy of Cartan's torsion is drawn, and a possible Higgs-force-like 'gravitational' effect of this nonpropagating torsion on the fermion masses is described. We also check that the field generating the Majorana mass for the {nu}{sub R} is nonzero in the physical vacuum.« less

Dynamical behavior and Jacobi stability analysis of wound strings

NASA Astrophysics Data System (ADS)

Lake, Matthew J.; Harko, Tiberiu

2016-06-01

We numerically solve the equations of motion (EOM) for two models of circular cosmic string loops with windings in a simply connected internal space. Since the windings cannot be topologically stabilized, stability must be achieved (if at all) dynamically. As toy models for realistic compactifications, we consider windings on a small section of mathbb {R}^2, which is valid as an approximation to any simply connected internal manifold if the winding radius is sufficiently small, and windings on an S^2 of constant radius mathcal {R}. We then use Kosambi-Cartan-Chern (KCC) theory to analyze the Jacobi stability of the string equations and determine bounds on the physical parameters that ensure dynamical stability of the windings. We find that, for the same initial conditions, the curvature and topology of the internal space have nontrivial effects on the microscopic behavior of the string in the higher dimensions, but that the macroscopic behavior is remarkably insensitive to the details of the motion in the compact space. This suggests that higher-dimensional signatures may be extremely difficult to detect in the effective (3+1)-dimensional dynamics of strings compactified on an internal space, even if configurations with nontrivial windings persist over long time periods.

Quantum fluctuations of the superconducting cosmic string

NASA Technical Reports Server (NTRS)

Zhang, Shoucheng

1987-01-01

Quantum fluctuations of the proposed superconducting string with Bose charge carriers are studied in terms of the vortices on the string world sheet. In the thermodynamical limit, it is found that they appear in the form of free vortices rather than as bound pairs. This fluctuation mode violates the topological conservation law on which superconductivity is based. However, this limit may not be reached. The critical size of the superconducting string is estimated as a function of the coupling constants involved.

Accelerating dark energy cosmological model in two fluids with hybrid scale factor

NASA Astrophysics Data System (ADS)

Mishra, B.; Sahoo, P. K.; Ray, Pratik P.

In this paper, we have investigated the anisotropic behavior of the accelerating universe in Bianchi V spacetime in the framework of General Relativity (GR). The matter field we have considered is of two non-interacting fluids, i.e. the usual string fluid and dark energy (DE) fluid. In order to represent the pressure anisotropy, the skewness parameters are introduced along three different spatial directions. To achieve a physically realistic solutions to the field equations, we have considered a scale factor, known as hybrid scale factor, which is generated by a time-varying deceleration parameter. This simulates a cosmic transition from early deceleration to late time acceleration. It is observed that the string fluid dominates the universe at early deceleration phase but does not affect nature of cosmic dynamics substantially at late phase, whereas the DE fluid dominates the universe in present time, which is in accordance with the observations results. Hence, we analyzed here the role of two fluids in the transitional phases of universe with respect to time which depicts the reason behind the cosmic expansion and DE. The role of DE with variable equation of state parameter (EoS) and skewness parameters, is also discussed along with physical and geometrical properties.

String solutions in spherically-symmetric f(R) gravity vacuum

NASA Astrophysics Data System (ADS)

Dil, Emre

Dynamical evolution of the cosmic string in a spherically symmetric f(R) gravity vacuum is studied for a closed and straight string. We first set the background spacetime metric for a constant curvature scalar R = R0, and obtain the Killing fields for it. Using the standard gauge coordinates and constraints for both closed and straight strings, we present the equation of motions and find the solutions of them. We then analyze the dynamics of the string by studying the behavior of the string radius and periastron radius, with respect to both proper time and azimuthal angle, for various values of f(R) functions. Consequently, we conclude that the value of f(R) dramatically affects the closed string collapse time and the straight string angular deviation.

f(T) gravity and energy distribution in Landau-Lifshitz prescription

NASA Astrophysics Data System (ADS)

Ganiou, M. G.; Houndjo, M. J. S.; Tossa, J.

We investigate in this paper the Landau-Lifshitz energy distribution in the framework of f(T) theory view as a modified version of Teleparallel theory. From some important Teleparallel theory results on the localization of energy, our investigations generalize the Landau-Lifshitz prescription from the computation of the energy-momentum complex to the framework of f(T) gravity as it is done in the modified versions of General Relativity. We compute the energy density in the first step for three plane-symmetric metrics in vacuum. We find for the second metric that the energy density vanishes independently of f(T) models. We find that the Teleparallel Landau-Lifshitz energy-momentum complex formulations for these metrics are different from those obtained in General Relativity for the same metrics. Second, the calculations are performed for the cosmic string spacetime metric. It results that the energy distribution depends on the mass M and the radius r of cosmic string and it is strongly affected by the parameter of the considered quadratic and cubic f(T) models. Our investigation with this metric induces interesting results susceptible to be tested with some astrophysics hypothesis.

Dynamics of cosmic strings with higher-dimensional windings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamauchi, Daisuke; Lake, Matthew J.; Thailand Center of Excellence in Physics, Ministry of Education,Bangkok 10400

2015-06-11

We consider F-strings with arbitrary configurations in the Minkowski directions of a higher-dimensional spacetime, which also wrap and spin around S{sup 1} subcycles of constant radius in an arbitrary internal manifold, and determine the relation between the higher-dimensional and the effective four-dimensional quantities that govern the string dynamics. We show that, for any such configuration, the motion of the windings in the compact space may render the string effectively tensionless from a four-dimensional perspective, so that it remains static with respect to the large dimensions. Such a critical configuration occurs when (locally) exactly half the square of the string lengthmore » lies in the large dimensions and half lies in the compact space. The critical solution is then seen to arise as a special case, in which the wavelength of the windings is equal to their circumference. As examples, long straight strings and circular loops are considered in detail, and the solutions to the equations of motion that satisfy the tensionless condition are presented. These solutions are then generalized to planar loops and arbitrary three-dimensional configurations. Under the process of dimensional reduction, in which higher-dimensional motion is equivalent to an effective worldsheet current (giving rise to a conserved charge), this phenomenon may be seen as the analogue of the tensionless condition which arises for superconducting and chiral-current carrying cosmic strings.« less

Dynamics of cosmic strings with higher-dimensional windings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamauchi, Daisuke; Lake, Matthew J., E-mail: yamauchi@resceu.s.u-tokyo.ac.jp, E-mail: matthewj@nu.ac.th

2015-06-01

We consider F-strings with arbitrary configurations in the Minkowski directions of a higher-dimensional spacetime, which also wrap and spin around S{sup 1} subcycles of constant radius in an arbitrary internal manifold, and determine the relation between the higher-dimensional and the effective four-dimensional quantities that govern the string dynamics. We show that, for any such configuration, the motion of the windings in the compact space may render the string effectively tensionless from a four-dimensional perspective, so that it remains static with respect to the large dimensions. Such a critical configuration occurs when (locally) exactly half the square of the string lengthmore » lies in the large dimensions and half lies in the compact space. The critical solution is then seen to arise as a special case, in which the wavelength of the windings is equal to their circumference. As examples, long straight strings and circular loops are considered in detail, and the solutions to the equations of motion that satisfy the tensionless condition are presented. These solutions are then generalized to planar loops and arbitrary three-dimensional configurations. Under the process of dimensional reduction, in which higher-dimensional motion is equivalent to an effective worldsheet current (giving rise to a conserved charge), this phenomenon may be seen as the analogue of the tensionless condition which arises for superconducting and chiral-current carrying cosmic strings.« less

Topological interactions in spacetimes with thick line defects

NASA Astrophysics Data System (ADS)

Moraes, Fernando; Carvalho, A. M.; Costa, Ismael V.; Oliveira, F. A.; Furtado, Claudio

2003-08-01

In this work we study the topologically induced electric self-energy and self-force on a long, straight, wire in two distinct, but similar, spacetimes: (i) the Gott-Hiscock thick cosmic string spacetime, and (ii) the spacetime of a continuous distribution of infinitely thin cosmic strings over a disk of finite radius. In each case we obtain the electric self-energy and self-force both in the internal and external regions of the defect distribution. The self-force is always repulsive, independently of the sign of the charge, and is maximum on the string’s surface, in both cases.

Gamma-ray bursts from superconducting cosmic strings at large redshifts

NASA Technical Reports Server (NTRS)

Babul, Arif; Paczynski, Bohdan; Spergel, David

1987-01-01

The relation between cusp events and gamma-rays bursts is investigated. The optical depth of the universe to X-rays and gamma-rays of various energies is calculated and discussed. The cosmological evolution of cosmic strings is examined, and the energetics and time-scales related to the cusp phenomena are estimated. It is noted that it is possible to have energy bursts with a duration of a few seconds or less from cusps at z = 1000; the maximum amount of energy associated with such an event is limited to 10 to the 7th ergs/sq cm.

Cosmic String Searches

NASA Astrophysics Data System (ADS)

Hoffman, Y.; Hogan, C.

The author discusses observational strategies for finding effects associated with the gravitational lensing of distant objects by strings. In particular, the requirements of a survey to find chains of galaxy image pairs or single galaxies with sharp edges are studied in some detail, and a proposed search program at Steward Observatory is described.

No-scale inflation

NASA Astrophysics Data System (ADS)

Ellis, John; Garcia, Marcos A. G.; Nanopoulos, Dimitri V.; Olive, Keith A.

2016-05-01

Supersymmetry is the most natural framework for physics above the TeV scale, and the corresponding framework for early-Universe cosmology, including inflation, is supergravity. No-scale supergravity emerges from generic string compactifications and yields a non-negative potential, and is therefore a plausible framework for constructing models of inflation. No-scale inflation yields naturally predictions similar to those of the Starobinsky model based on R+{R}2 gravity, with a tilted spectrum of scalar perturbations: {n}s∼ 0.96, and small values of the tensor-to-scalar perturbation ratio r\\lt 0.1, as favoured by Planck and other data on the cosmic microwave background (CMB). Detailed measurements of the CMB may provide insights into the embedding of inflation within string theory as well as its links to collider physics.

Cosmic string wakes

NASA Technical Reports Server (NTRS)

Stebbins, Albert; Veeraraghavan, Shoba; Silk, Joseph; Brandenberger, Robert; Turok, Neil

1987-01-01

Accretion of matter onto wakes left behind by horizon-sized pieces of cosmic string is investigated, and the effects of wakes on the large-scale structure of the universe are determined. Accretion of cold matter onto wakes, the effects of a long string on fluids with finite velocity dispersion or sound speeds, the interactions between loops and wakes, and the conditions for wakes to survive disruption by loops are discussed. It is concluded that the most important wakes are those which were formed at the time of equal matter and radiation density. This leads to sheetlike overdense regions of galaxies with a mean separation in agreement with the scale of the bubbles of de Lapparent, Geller, and Huchra (1986). However, for the value of G(mu) favored from galaxy formation considerations in a universe with cold dark matter, a wake accretes matter from a distance of only about 1.5 Mpc, which is much less than the distance between the wakes.

Pair production in the gravitational field of a cosmic string

NASA Astrophysics Data System (ADS)

Harari, Diego D.; Skarzhinsky, Vladimir D.

1990-04-01

We show that many elementary particle physics processes, such as pair production by a high energy photon, that take place in Minkowski space only if a non-uniform external field provides for momentum non-conservation, do occur in the space-time around a straight cosmic string, even though the space is locally flat and there is no local gravitational potential. We exemplify this mechanism through the evaluation of the cross section per unit length of string for the decay of a massless scalar particle into a pair of massive particles. The cross sections for this kind of processes are typically small. Nevertheless, it is interesting to realize how these reactions occur due to topological properties of space, rather than to the action of a local field. V.S. is grateful to Mario Castagnino for hospitality at the Instituto de Astronomía y Física del Espacio during a visit while this work was done.

Superconducting cosmic strings as sources of cosmological fast radio bursts

NASA Astrophysics Data System (ADS)

Ye, Jiani; Wang, Kai; Cai, Yi-Fu

2017-11-01

In this paper we calculate the radio burst signals from three kinds of structures of superconducting cosmic strings. By taking into account the observational factors including scattering and relativistic effects, we derive the event rate of radio bursts as a function of redshift with the theoretical parameters Gμ and I of superconducting strings. Our analyses show that cusps and kinks may have noticeable contributions to the event rate and in most cases cusps would dominate the contribution, while the kink-kink collisions tend to have secondary effects. By fitting theoretical predictions with the normalized data of fast radio bursts, we for the first time constrain the parameter space of superconducting strings and report that the parameter space of Gμ ˜ [10^{-14}, 10^{-12}] and I ˜ [10^{-1}, 102] GeV fit the observation well although the statistic significance is low due to the lack of observational data. Moreover, we derive two types of best fittings, with one being dominated by cusps with a redshift z = 1.3, and the other dominated by kinks at the range of the maximal event rate.

Comment on high resolution simulations of cosmic strings. 1: Network evoloution

NASA Technical Reports Server (NTRS)

Turok, Neil; Albrecht, Andreas

1990-01-01

Comments are made on recent claims (Albrecht and Turok, 1989) regarding simulations of cosmic string evolution. Specially, it was claimed that results were dominated by a numerical artifact which rounds out kinks on a scale of the order of the correlation length on the network. This claim was based on an approximate analysis of an interpolation equation which is solved herein. The typical rounding scale is actually less than one fifth of the correlation length, and comparable with other numerical cutoffs. Results confirm previous estimates of numerical uncertainties, and show that the approximations poorly represent the real solutions to the interpolation equation.

Cosmic string induced peculiar velocities

NASA Technical Reports Server (NTRS)

Van Dalen, Anthony; Schramm, David N.

1988-01-01

This paper considers the scenario of a flat universe with a network of heavy cosmic strings as the primordial fluctuation spectrum. The joint probability of finding streaming velocities of at least 600 km/s on large scales and local peculiar velocities of less than 800 km/s is calculated. It is shown how the effects of loops breaking up and being born with a spectrum of sizes can be estimated. It is found that to obtain large-scale streaming velocities of at least 600 km/s, it is necessary that either a large value for beta G mu exist or the effect of loop fissioning and production details be considerable.

Lensing effects in a nematic liquid crystal with topological defects.

PubMed

Sátiro, C; Moraes, F

2006-06-01

Light traveling through a liquid crystal with disclinations perceives a geometrical background which causes lensing effects similar to the ones predicted for cosmic objects like global monopoles and cosmic strings. In this paper we explore the effective geometry as perceived by light in such media. The comparison between both systems suggests that experiments can be done in the laboratory to simulate optical properties, like gravitational lensing, of cosmic objects.

Gravitational lensing effects of vacuum strings - Exact solutions

NASA Technical Reports Server (NTRS)

Gott, J. R., III

1985-01-01

Exact interior and exterior solutions to Einstein's field equations are derived for vacuum strings. The exterior solution for a uniform density vacuum string corresponds to a conical space while the interior solution is that of a spherical cap. For Mu equals 0-1/4 the external metric is ds-squared = -dt-squared + dr-squared + (1-4 Mu)-squared r-squared dphi-squared + dz-squared, where Mu is the mass per unit length in the string in Planck masses per Planck length. A maximum mass per unit length for a string is 6.73 x 10 to the 27th g/cm. It is shown that strings cause temperature fluctuations in the cosmic microwave background and produce equal brightness double QSO images separated by up to several minutes of arc. Formulae for lensing probabilities, image splittings, and time delays are derived for strings in a realistic cosmological setting. String searches using ST, the VLA, and the COBE satellite are discussed.

Probing cosmic strings with satellite CMB measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeong, E.; Baccigalupi, Carlo; Smoot, G.F., E-mail: ehjeong@sissa.it, E-mail: bacci@sissa.it, E-mail: gfsmoot@lbl.gov

2010-09-01

We study the problem of searching for cosmic string signal patterns in the present high resolution and high sensitivity observations of the Cosmic Microwave Background (CMB). This article discusses a technique capable of recognizing Kaiser-Stebbins effect signatures in total intensity anisotropy maps from isolated strings. We derive the statistical distributions of null detections from purely Gaussian fluctuations and instrumental performances of the operating satellites, and show that the biggest factor that produces confusion is represented by the acoustic oscillation features of the scale comparable to the size of horizon at recombination. Simulations show that the distribution of null detections convergesmore » to a χ{sup 2} distribution, with detectability threshold at 99% confidence level corresponding to a string induced step signal with an amplitude of about 100 μK which corresponds to a limit of roughly Gμ ∼ 1.5 × 10{sup −6}. We implement simulations for deriving the statistics of spurious detections caused by extra-Galactic and Galactic foregrounds. For diffuse Galactic foregrounds, which represents the dominant source of contamination, we construct sky masks outlining the available region of the sky where the Galactic confusion is sub-dominant, specializing our analysis to the case represented by the frequency coverage and nominal sensitivity and resolution of the Planck experiment. As for other CMB measurements, the maximum available area, corresponding to 7%, is reached where the foreground emission is expected to be minimum, in the 70–100 GHz interval.« less

Quantum no-scale regimes in string theory

NASA Astrophysics Data System (ADS)

Coudarchet, Thibaut; Fleming, Claude; Partouche, Hervé

2018-05-01

We show that in generic no-scale models in string theory, the flat, expanding cosmological evolutions found at the quantum level can be attracted to a "quantum no-scale regime", where the no-scale structure is restored asymptotically. In this regime, the quantum effective potential is dominated by the classical kinetic energies of the no-scale modulus and dilaton. We find that this natural preservation of the classical no-scale structure at the quantum level occurs when the initial conditions of the evolutions sit in a subcritical region of their space. On the contrary, supercritical initial conditions yield solutions that have no analogue at the classical level. The associated intrinsically quantum universes are sentenced to collapse and their histories last finite cosmic times. Our analysis is done at 1-loop, in perturbative heterotic string compactified on tori, with spontaneous supersymmetry breaking implemented by a stringy version of the Scherk-Schwarz mechanism.

The NANOGrav Nine-Year Data Set: Limits on the Isotropic Stochastic Gravitational Wave Background

NASA Technical Reports Server (NTRS)

Arzoumanian, Z.; Brazier, A.; Burke-Spolaor, S.; Chamberlin, S. J.; Chatterjee, S.; Christy, B.; Cordes, J. M.; Cornish, N. J.; Crowter, K.; Demorest, P. B.;

DOE Office of Scientific and Technical Information (OSTI.GOV)

Namikawa, Toshiya

We study the reconstruction of the cosmic rotation power spectrum produced by parity-violating physics, with an eye to ongoing and near future cosmic microwave background (CMB) experiments such as BICEP Array, CMBS4, LiteBIRD and Simons Observatory. In addition to the inflationary gravitational waves and gravitational lensing, measurements of other various effects on CMB polarization open new window into the early Universe. One of these is anisotropies of the cosmic polarization rotation which probes the Chern-Simons term generally predicted by string theory. The anisotropies of the cosmic rotation are also generated by the primordial magnetism and in the Standard Model extentionmore » framework. The cosmic rotation anisotropies can be reconstructed as quadratic in CMB anisotropies. However, the power of the reconstructed cosmic rotation is a CMB four-point correlation and is not directly related to the cosmic-rotation power spectrum. Understanding all contributions in the four-point correlation is required to extract the cosmic rotation signal. Here, assuming inflationary motivated cosmic-rotation models, we employ simulation to quantify each contribution to the four-point correlation and find that (1) a secondary contraction of the trispectrum increases the total signal-to-noise, (2) a bias from the lensing-induced trispectrum is significant compared to the statistical errors in, e.g., LiteBIRD and CMBS4-like experiments, (3) the use of a realization-dependent estimator decreases the statistical errors by 10%–20%, depending on experimental specifications, and (4) other higher-order contributions are negligible at least for near future experiments.« less

Cosmic Ray Flux Measurement with AMANDA-II

NASA Astrophysics Data System (ADS)

Chirkin, Dmitry A.; AMANDA Collaboration

2003-07-01

AMANDA-I I is a neutrino telescope composed of 677 optical sensors organized along 19 strings buried deep in the Antarctic ice cap. It is designed to detect Cherenkov light produced by cosmic-rayand neutrino-induced muons. The ma jority of events recorded by AMANDA-I I are caused by muons which are produced in the atmosphere by high-energy cosmic rays. The leading uncertainties in simulating such events come from the choice of the high-energy model used to describe the first interaction of the cosmic rays, uncertainties in our knowledge and implementation of the ice properties at the depth of the detector, and individual optical module sensitivities. A method is developed that results in a flux measurement of cosmic rays with energies 1.5-200 TeV per nucleon (95% of primaries causing low-multiplicity events in AMANDA-I I have energies in this range) indep endent of ice model and optical module sensitivities. Predictions of six commonly-used high-energy interaction models QGSJET, VENUS, NEXUS, DPMJET, HDPM, and SYBILL are compared to data. Best agreement with direct measurements is achieved with QGSJET, VENUS, and NEXUS (preliminary: Φ0,H = 0.106 ± 0.007 m-2 s-1 sr-1 TeV-1 , γH = 2.70 ± 0.02).

Modulus D-term inflation

NASA Astrophysics Data System (ADS)

Kadota, Kenji; Kobayashi, Tatsuo; Saga, Ikumi; Sumita, Keigo

2018-04-01

We propose a new model of single-field D-term inflation in supergravity, where the inflation is driven by a single modulus field which transforms non-linearly under the U(1) gauge symmetry. One of the notable features of our modulus D-term inflation scenario is that the global U(1) remains unbroken in the vacuum and hence our model is not plagued by the cosmic string problem which can exclude most of the conventional D-term inflation models proposed so far due to the CMB observations.

Induced vacuum energy-momentum tensor in the background of a cosmic string

NASA Astrophysics Data System (ADS)

Sitenko, Yu A.; Vlasii, N. D.

2012-05-01

A massive scalar field is quantized in the background of a cosmic string which is generalized to a static flux-carrying codimension-2 brane in the locally flat multidimensional spacetime. We find that the finite energy-momentum tensor is induced in the vacuum. The dependence of the tensor components on the brane flux and tension, as well as on the coupling to the spacetime curvature scalar, is comprehensively analyzed. The tensor components are holomorphic functions of space dimension, decreasing exponentially with the distance from the brane. The case of the massless quantized scalar field is also considered, and the relevance of Bernoulli’s polynomials of even order for this case is discussed.

Global structure of Gott's two-string spacetime

NASA Astrophysics Data System (ADS)

Cutler, Curt

1992-01-01

Gott has recently obtained exact solutions to Einstein's equation representing two infinitely long, straight cosmic strings that gravitationally scatter off each other. A remarkable feature of these solutions is that they contain closed timelike curves when the relative velocity of the strings is sufficiently high. In this paper we elucidate the global structure of Gott's two-string spacetime. In particular, we prove that the closed timelike curves are confined to a certain region of the spacetime, and that the spacetime contains complete spacelike, edgeless, achronal hypersurfaces, from which the causality-violating regions may be said to evolve. We then explicitly determine the boundary of the region containing closed timelike curves.

Testing parity-violating physics from cosmic rotation power reconstruction

DOE PAGES

Namikawa, Toshiya

2017-02-22

We study the reconstruction of the cosmic rotation power spectrum produced by parity-violating physics, with an eye to ongoing and near future cosmic microwave background (CMB) experiments such as BICEP Array, CMBS4, LiteBIRD and Simons Observatory. In addition to the inflationary gravitational waves and gravitational lensing, measurements of other various effects on CMB polarization open new window into the early Universe. One of these is anisotropies of the cosmic polarization rotation which probes the Chern-Simons term generally predicted by string theory. The anisotropies of the cosmic rotation are also generated by the primordial magnetism and in the Standard Model extentionmore » framework. The cosmic rotation anisotropies can be reconstructed as quadratic in CMB anisotropies. However, the power of the reconstructed cosmic rotation is a CMB four-point correlation and is not directly related to the cosmic-rotation power spectrum. Understanding all contributions in the four-point correlation is required to extract the cosmic rotation signal. Here, assuming inflationary motivated cosmic-rotation models, we employ simulation to quantify each contribution to the four-point correlation and find that (1) a secondary contraction of the trispectrum increases the total signal-to-noise, (2) a bias from the lensing-induced trispectrum is significant compared to the statistical errors in, e.g., LiteBIRD and CMBS4-like experiments, (3) the use of a realization-dependent estimator decreases the statistical errors by 10%–20%, depending on experimental specifications, and (4) other higher-order contributions are negligible at least for near future experiments.« less

Computational algorithms dealing with the classical and statistical mechanics of celestial scale polymers in space elevator technology

NASA Astrophysics Data System (ADS)

Knudsen, Steven; Golubovic, Leonardo

Prospects to build Space Elevator (SE) systems have become realistic with ultra-strong materials such as carbon nano-tubes and diamond nano-threads. At cosmic length-scales, space elevators can be modeled as polymer like floppy strings of tethered mass beads. A new venue in SE science has emerged with the introduction of the Rotating Space Elevator (RSE) concept supported by novel algorithms discussed in this presentation. An RSE is a loopy string reaching into outer space. Unlike the classical geostationary SE concepts of Tsiolkovsky, Artsutanov, and Pearson, our RSE exhibits an internal rotation. Thanks to this, objects sliding along the RSE loop spontaneously oscillate between two turning points, one of which is close to the Earth whereas the other one is in outer space. The RSE concept thus solves a major problem in SE technology which is how to supply energy to the climbers moving along space elevator strings. The investigation of the classical and statistical mechanics of a floppy string interacting with objects sliding along it required development of subtle computational algorithms described in this presentation

The dynamics of domain walls and strings

NASA Technical Reports Server (NTRS)

Gregory, Ruth; Haws, David; Garfinkle, David

1989-01-01

The leading order finite-width corrections to the equation of motion describing the motion of a domain wall are derived. The regime in which this equation of motion is invalid is discussed. Spherically and cylindrically symmetric solutions to this equation of motion are found. A misconception that has arisen in recent years regarding the rigidity (or otherwise) of cosmic strings is also clarified.

A Multiscale pipeline for the search of string-induced CMB anisotropies

NASA Astrophysics Data System (ADS)

Vafaei Sadr, A.; Movahed, S. M. S.; Farhang, M.; Ringeval, C.; Bouchet, F. R.

2018-03-01

We propose a multiscale edge-detection algorithm to search for the Gott-Kaiser-Stebbins imprints of a cosmic string (CS) network on the cosmic microwave background (CMB) anisotropies. Curvelet decomposition and extended Canny algorithm are used to enhance the string detectability. Various statistical tools are then applied to quantify the deviation of CMB maps having a CS contribution with respect to pure Gaussian anisotropies of inflationary origin. These statistical measures include the one-point probability density function, the weighted two-point correlation function (TPCF) of the anisotropies, the unweighted TPCF of the peaks and of the up-crossing map, as well as their cross-correlation. We use this algorithm on a hundred of simulated Nambu-Goto CMB flat sky maps, covering approximately 10 per cent of the sky, and for different string tensions Gμ. On noiseless sky maps with an angular resolution of 0.9 arcmin, we show that our pipeline detects CSs with Gμ as low as Gμ ≳ 4.3 × 10-10. At the same resolution, but with a noise level typical to a CMB-S4 phase II experiment, the detection threshold would be to Gμ ≳ 1.2 × 10-7.

Cosmic strings and chronology protection

NASA Astrophysics Data System (ADS)

Grant, James D. E.

1993-03-01

A space consisting of two rapidly moving cosmic strings has recently been constructed by Gott that contains closed timelike curves. The global structure of this space is analyzed and it is found that, away from the strings, the space is identical to a generalized Misner space. The vacuum expectation value of the energy-momentum tensor for a conformally coupled scalar field is calculated on this generalized Misner space. It is found to diverge very weakly on the chronology horizon, but more strongly on the polarized hypersurfaces. The divergence on the polarized hypersurfaces is strong enough that when the proper geodesic interval around any polarized hypersurface is of the order of the Planck length squared, the perturbation to the metric caused by the back reaction will be of the order one. Thus we expect the structure of the space will be radically altered by the back reaction before quantum gravitational effects become important. This suggests that Hawking's ``chronology protection conjecture'' holds for spaces with a noncompactly generated chronology horizon.

Clumpy cold dark matter

NASA Technical Reports Server (NTRS)

Silk, Joseph; Stebbins, Albert

1993-01-01

A study is conducted of cold dark matter (CDM) models in which clumpiness will inhere, using cosmic strings and textures suited to galaxy formation. CDM clumps of 10 million solar mass/cu pc density are generated at about z(eq) redshift, with a sizable fraction surviving. Observable implications encompass dark matter cores in globular clusters and in galactic nuclei. Results from terrestrial dark matter detection experiments may be affected by clumpiness in the Galactic halo.

Calculation of intensity of high energy muon groups observed deep underground

NASA Technical Reports Server (NTRS)

Vavilov, Y. N.; Dedenko, L. G.

1985-01-01

The intensity of narrow muon groups observed in Kolar Gold Field (KGF) at the depth of 3375 m.w.e. was calculated in terms of quark-gluon strings model for high energy hadron - air nuclei interactions by the method of direct modeling of nuclear cascade in the air and muon propagation in the ground for normal primary cosmic ray composition. The calculated intensity has been found to be approx. 10 to the 4 times less than one observed experimentally.

Cosmic microwave background anomalies in an open universe.

PubMed

Liddle, Andrew R; Cortês, Marina

2013-09-13

We argue that the observed large-scale cosmic microwave anomalies, discovered by WMAP and confirmed by the Planck satellite, are most naturally explained in the context of a marginally open universe. Particular focus is placed on the dipole power asymmetry, via an open universe implementation of the large-scale gradient mechanism of Erickcek et al. Open inflation models, which are motivated by the string landscape and which can excite "supercurvature" perturbation modes, can explain the presence of a very-large-scale perturbation that leads to a dipole modulation of the power spectrum measured by a typical observer. We provide a specific implementation of the scenario which appears compatible with all existing constraints.

Eventful horizons: String theory in de Sitter and anti-de Sitter

NASA Astrophysics Data System (ADS)

Kleban, Matthew Benjamin

String theory purports to be a theory of quantum gravity. As such, it should have much to say about the deep mysteries surrounding the very early stages of our universe. For this reason, although the theory is notoriously difficult to directly test, data from experimental cosmology may provide a way to probe the high energy physics of string theory. In the first part of this thesis, I will address the important issue of the testability of string theory using observations of the cosmic microwave background radiation. In the second part, I will study some formal difficulties that arise in attempting to understand string theory in de Sitter spacetime. In the third part, I will study the singularity of an eternal anti de Sitter Schwarzschild black hole, using the AdS/CFT correspondence.

Rotating elastic string loops in flat and black hole spacetimes: stability, cosmic censorship and the Penrose process

NASA Astrophysics Data System (ADS)

Natário, José; Queimada, Leonel; Vicente, Rodrigo

2018-04-01

We rederive the equations of motion for relativistic strings, that is, one-dimensional elastic bodies whose internal energy depends only on their stretching, and use them to study circular string loops rotating in the equatorial plane of flat and black hole spacetimes. We start by obtaining the conditions for equilibrium, and find that: (i) if the string’s longitudinal speed of sound does not exceed the speed of light then its radius when rotating in Minkowski’s spacetime is always larger than its radius when at rest; (ii) in Minkowski’s spacetime, equilibria are linearly stable for rotation speeds below a certain threshold, higher than the string’s longitudinal speed of sound, and linearly unstable for some rotation speeds above it; (iii) equilibria are always linearly unstable in Schwarzschild’s spacetime. Moreover, we study interactions of a rotating string loop with a Kerr black hole, namely in the context of the weak cosmic censorship conjecture and the Penrose process. We find that: (i) elastic string loops that satisfy the null energy condition cannot overspin extremal black holes; (ii) elastic string loops that satisfy the dominant energy condition cannot increase the maximum efficiency of the usual particle Penrose process; (iii) if the dominant energy condition (but not the weak energy condition) is violated then the efficiency can be increased. This last result hints at the interesting possibility that the dominant energy condition may underlie the well known upper bounds for the efficiencies of energy extraction processes (including, for example, superradiance).

The area of isodensity contours in cosmological models and galaxy surveys

NASA Technical Reports Server (NTRS)

Ryden, Barbara S.; Melott, Adrian L.; Craig, David A.; Gott, J. Richard, III; Weinberg, David H.

1989-01-01

The contour crossing statistic, defined as the mean number of times per unit length that a straight line drawn through the field crosses a given contour, is applied to model density fields and to smoothed samples of galaxies. Models in which the matter is in a bubble structure, in a filamentary net, or in clusters can be distinguished from Gaussian density distributions. The shape of the contour crossing curve in the initially Gaussian fields considered remains Gaussian after gravitational evolution and biasing, as long as the smoothing length is longer than the mass correlation length. With a smoothing length of 5/h Mpc, models containing cosmic strings are indistinguishable from Gaussian distributions. Cosmic explosion models are significantly non-Gaussian, having a bubbly structure. Samples from the CfA survey and the Haynes and Giovanelli (1986) survey are more strongly non-Gaussian at a smoothing length of 6/h Mpc than any of the models examined. At a smoothing length of 12/h Mpc, the Haynes and Giovanelli sample appears Gaussian.

Wave propagation in metamaterials mimicking the topology of a cosmic string

NASA Astrophysics Data System (ADS)

Fernández-Núñez, Isabel; Bulashenko, Oleg

2018-04-01

We study the interference and diffraction of light when it propagates through a metamaterial medium mimicking the spacetime of a cosmic string—a topological defect with curvature singularity. The phenomenon may look like a gravitational analogue of the Aharonov-Bohm effect, since the light propagates in a region where the Riemann tensor vanishes, being nonetheless affected by the non-zero curvature confined to the string core. We carry out the full-wave numerical simulation of the metamaterial medium and give the analytical interpretation of the results by use of the asymptotic theory of diffraction, which turns out to be in excellent agreement. In particular, we show that the main features of wave propagation in a medium with conical singularity can be explained by four-wave interference involving two geometrical optics and two diffracted waves.

Topological defects in the Georgi-Machacek model

NASA Astrophysics Data System (ADS)

Chatterjee, Chandrasekar; Kurachi, Masafumi; Nitta, Muneto

2018-06-01

We study topological defects in the Georgi-Machacek model in a hierarchical symmetry breaking in which extra triplets acquire vacuum expectation values before the doublet. We find a possibility of topologically stable non-Abelian domain walls and non-Abelian flux tubes (vortices or cosmic strings) in this model. In the limit of the vanishing U (1 )Y gauge coupling in which the custodial symmetry becomes exact, the presence of a vortex spontaneously breaks the custodial symmetry, giving rise to S2 Nambu-Goldstone (NG) modes localized around the vortex corresponding to non-Abelian fluxes. Vortices are continuously degenerated by these degrees of freedom, thereby called non-Abelian. By taking into account the U (1 )Y gauge coupling, the custodial symmetry is explicitly broken, the NG modes are lifted to become pseudo-NG modes, and all non-Abelian vortices fall into a topologically stable Z string. This is in contrast to the standard model in which Z strings are nontopological and are unstable in the realistic parameter region. Non-Abelian domain walls also break the custodial symmetry and are accompanied by localized S2 NG modes. Finally, we discuss the existence of domain wall solutions bounded by flux tubes, where their S2 NG modes match. The domain walls may quantum mechanically decay by creating a hole bounded by a flux tube loop, and would be cosmologically safe. Gravitational waves produced from unstable domain walls could be detected by future experiments.

Topological defects in alternative theories to cosmic inflation and string cosmology

NASA Astrophysics Data System (ADS)

Alexander, Stephon H. S.

The physics of the Early Universe is described in terms of the inflationary paradigm, which is based on a marriage between Einstein's general theory of relativity minimally coupled to quantum field theory. Inflation was posed to solve some of the outstanding problems of the Standard Big Bang Cosmology (SBB) such as the horizon, formation of structure and monopole problems. Despite its observational and theoretical successes, inflation is plagued with fine tuning and initial singularity problems. On the other hand, superstring/M theory, a theory of quantum gravity, possesses symmetries which naturally avoid space-time singularities. This thesis investigates alternative theories to cosmic inflation for solving the initial singularity, horizon and monopole problems, making use of topological defects. It was proposed by Dvali, Liu and Vaschaspati that the monopole problem can be solved without inflation if domain walls "sweep" up the monopoles in the early universe, thus reducing their number density significantly. Necessary for this mechanism to work is the presence of an attractive force between the monopole and the domain wall as well as a channel for the monopole's unwinding. We show numerically and analytically in two field theory models that for global defects the attraction is a universal result but the unwinding is model specific. The second part of this thesis investigates a string/M theory inspired model for solving the horizon problem. It was proposed by Moffat, Albrecht and Magueijo that the horizon problem is solved with a "phase transition" associated with a varying speed of light before the surface of last scattering. We provide a string/M theory mechanism based on assuming that our space-time is a D-3 brane probing a bulk supergravity black hole bulk background. This mechanism provides the necessary time variation of the velocity of light to solve the horizon problem. We suggest a mechanism which stablilizes the speed of light on the D-3 brane. We finally address the cosmological initial singularity problem using the target space duality inherent in string/M theory. It was suggested by Brandenberger and Vafa that superstring theory can solve the singularity problem and in addition explain why only three spatial dimensions can become large. We show that under specific conditions this mechanism still persists when including the effects of D-branes.

Observation of the cosmic-ray shadow of the Moon with IceCube

NASA Astrophysics Data System (ADS)

Aartsen, M. G.; Abbasi, R.; Abdou, Y.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Altmann, D.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Baum, V.; Bay, R.; Beatty, J. J.; Bechet, S.; Becker Tjus, J.; Becker, K.-H.; Bell, M.; Benabderrahmane, M. L.; BenZvi, S.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bernhard, A.; Bertrand, D.; Besson, D. Z.; Binder, G.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohaichuk, S.; Bohm, C.; Bose, D.; Böser, S.; Botner, O.; Brayeur, L.; Bretz, H.-P.; Brown, A. M.; Bruijn, R.; Brunner, J.; Carson, M.; Casey, J.; Casier, M.; Chirkin, D.; Christov, A.; Christy, B.; Clark, K.; Clevermann, F.; Coenders, S.; Cohen, S.; Cowen, D. F.; Cruz Silva, A. H.; Danninger, M.; Daughhetee, J.; Davis, J. C.; De Clercq, C.; De Ridder, S.; Desiati, P.; de With, M.; DeYoung, T.; Díaz-Vélez, J. C.; Dunkman, M.; Eagan, R.; Eberhardt, B.; Eisch, J.; Ellsworth, R. W.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Fedynitch, A.; Feintzeig, J.; Feusels, T.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Flis, S.; Franckowiak, A.; Franke, R.; Frantzen, K.; Fuchs, T.; Gaisser, T. K.; Gallagher, J.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Golup, G.; Gonzalez, J. G.; Goodman, J. A.; Góra, D.; Grandmont, D. T.; Grant, D.; Groß, A.; Ha, C.; Haj Ismail, A.; Hallen, P.; Hallgren, A.; Halzen, F.; Hanson, K.; Heereman, D.; Heinen, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Homeier, A.; Hoshina, K.; Huelsnitz, W.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobi, E.; Jacobsen, J.; Jagielski, K.; Japaridze, G. S.; Jero, K.; Jlelati, O.; Kaminsky, B.; Kappes, A.; Karg, T.; Karle, A.; Kelley, J. L.; Kiryluk, J.; Kislat, F.; Kläs, J.; Klein, S. R.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Kopper, C.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Krasberg, M.; Krings, K.; Kroll, G.; Kunnen, J.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Landsman, H.; Larson, M. J.; Lesiak-Bzdak, M.; Leuermann, M.; Leute, J.; Lünemann, J.; Madsen, J.; Maruyama, R.; Mase, K.; Matis, H. S.; McNally, F.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Miarecki, S.; Middell, E.; Milke, N.; Miller, J.; Mohrmann, L.; Montaruli, T.; Morse, R.; Nahnhauer, R.; Naumann, U.; Niederhausen, H.; Nowicki, S. C.; Nygren, D. R.; Obertacke, A.; Odrowski, S.; Olivas, A.; Olivo, M.; O'Murchadha, A.; Paul, L.; Pepper, J. A.; Pérez de los Heros, C.; Pfendner, C.; Pieloth, D.; Pinat, E.; Pirk, N.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Rädel, L.; Rameez, M.; Rawlins, K.; Redl, P.; Reimann, R.; Resconi, E.; Rhode, W.; Ribordy, M.; Richman, M.; Riedel, B.; Rodrigues, J. P.; Rott, C.; Ruhe, T.; Ruzybayev, B.; Ryckbosch, D.; Saba, S. M.; Salameh, T.; Sander, H.-G.; Santander, M.; Sarkar, S.; Schatto, K.; Scheel, M.; Scheriau, F.; Schmidt, T.; Schmitz, M.; Schoenen, S.; Schöneberg, S.; Schönwald, A.; Schukraft, A.; Schulte, L.; Schulz, O.; Seckel, D.; Sestayo, Y.; Seunarine, S.; Sheremata, C.; Smith, M. W. E.; Soldin, D.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stasik, A.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Strahler, E. A.; Ström, R.; Sullivan, G. W.; Taavola, H.; Taboada, I.; Tamburro, A.; Tepe, A.; Ter-Antonyan, S.; Tešić, G.; Tilav, S.; Toale, P. A.; Toscano, S.; Usner, M.; van der Drift, D.; van Eijndhoven, N.; Van Overloop, A.; van Santen, J.; Vehring, M.; Voge, M.; Vraeghe, M.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Wasserman, R.; Weaver, Ch.; Wellons, M.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Williams, D. R.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, C.; Xu, D. L.; Xu, X. W.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; Ziemann, J.; Zierke, S.; Zoll, M.; IceCube Collaboration

2014-05-01

We report on the observation of a significant deficit of cosmic rays from the direction of the Moon with the IceCube detector. The study of this "Moon shadow" is used to characterize the angular resolution and absolute pointing capabilities of the detector. The detection is based on data taken in two periods before the completion of the detector: between April 2008 and May 2009, when IceCube operated in a partial configuration with 40 detector strings deployed in the South Pole ice, and between May 2009 and May 2010 when the detector operated with 59 strings. Using two independent analysis methods, the Moon shadow has been observed to high significance (>6σ) in both detector configurations. The observed location of the shadow center is within 0.2° of its expected position when geomagnetic deflection effects are taken into account. This measurement validates the directional reconstruction capabilities of IceCube.

Second order perturbations of a macroscopic string: Covariant approach

NASA Astrophysics Data System (ADS)

Larsen, A. L.; Nicolaidis, A.

2001-06-01

Using a world-sheet covariant formalism, we derive the equations of motion for second order perturbations of a generic macroscopic string, thus generalizing previous results for first order perturbations. We give the explicit results for the first and second order perturbations of a contracting near-circular string; these results are relevant for the understanding of the possible outcome when a cosmic string contracts under its own tension, as discussed in a series of papers by Vilenkin and Garriga. In particular, second order perturbations are necessary for a consistent computation of the energy. We also quantize the perturbations and derive the mass formula up to second order in perturbations for an observer using world-sheet time τ. The high frequency modes give the standard Minkowski result while, interestingly enough, the Hamiltonian turns out to be nondiagonal in oscillators for low-frequency modes. Using an alternative definition of the vacuum, it is possible to diagonalize the Hamiltonian, and the standard string mass spectrum appears for all frequencies. We finally discuss how our results are also relevant for the problems concerning string-spreading near a black hole horizon, as originally discussed by Susskind.

Dark energy from the string axiverse.

PubMed

Kamionkowski, Marc; Pradler, Josef; Walker, Devin G E

2014-12-19

String theories suggest the existence of a plethora of axionlike fields with masses spread over a huge number of decades. Here, we show that these ideas lend themselves to a model of quintessence with no super-Planckian field excursions and in which all dimensionless numbers are order unity. The scenario addresses the "Why now?" problem-i.e., Why has accelerated expansion begun only recently?-by suggesting that the onset of dark-energy domination occurs randomly with a slowly decreasing probability per unit logarithmic interval in cosmic time. The standard axion potential requires us to postulate a rapid decay of most of the axion fields that do not become dark energy. The need for these decays is averted, though, with the introduction of a slightly modified axion potential. In either case, a universe like ours arises in roughly 1 in 100 universes. The scenario may have a host of observable consequences.

Earth Versus Neutrinos: Measuring the Total Muon-Neutrino-to-Nucleon Cross Section at Ultra-High Energies through Differential Earth Absorption of Muon Neutrinos from Cosmic Rays Using the IceCube Detector

NASA Astrophysics Data System (ADS)

Miarecki, Sandra Christine

The IceCube Neutrino Detector at the South Pole was constructed to measure the flux of high-energy neutrinos and to try to identify their cosmic sources. In addition to these astrophysical neutrinos, IceCube also detects the neutrinos that result from cosmic ray interactions with the atmosphere. These atmospheric neutrinos can be used to measure the total muon neutrino-to-nucleon cross section by measuring neutrino absorption in the Earth. The measurement involves isolating a sample of 10,784 Earth-transiting muons detected by IceCube in its 79-string configuration. The cross-section is determined using a two-dimensional fit in measured muon energy and zenith angle and is presented as a multiple of the Standard Model expectation as calculated by Cooper-Sarkar, Mertsch, and Sarkar in 2011. A multiple of 1.0 would indicate agreement with the Standard Model. The results of this analysis find the multiple to be 1.30 (+0.21 -0.19 statistical) (+0.40 -0.44 systematic) for the neutrino energy range of 6.3 to 980 TeV, which is in agreement with the Standard Model expectation.

Fermionic vacuum polarization by an Abelian magnetic tube in the cosmic string spacetime

NASA Astrophysics Data System (ADS)

Maior de Sousa, M. S.; Ribeiro, R. F.; Bezerra de Mello, E. R.

2017-02-01

In this paper, we consider a charged massive fermionic quantum field in the idealized cosmic string spacetime and in the presence of a magnetic field confined in a cylindrical tube of finite radius. Three distinct configurations for the magnetic fields are taken into account: (i) a cylindrical shell of radius a , (ii) a magnetic field proportional to 1 /r , and (iii) a constant magnetic field. In these three cases, the axis of the infinitely long tube of radius a coincides with the cosmic string. Our main objectives in this paper are to analyze the fermionic condensate (FC) and the vacuum expectation value (VEV) of the fermionic energy-momentum tensor. In order to do that, we explicitly construct the complete set of normalized wave functions for each configuration of the magnetic field. We show that in the region outside the tube, the FC and the VEV of the energy-momentum tensor are decomposed into two parts: The first ones correspond to the zero-thickness magnetic flux contributions, and the second ones are induced by the nontrivial structure of the magnetic field, named core-induced contributions. The latter present specific forms depending on the magnetic field configuration considered. We also show that the VEV of the energy-momentum tensor is diagonal and obeys the conservation condition, and its trace is expressed in terms of the fermionic condensate. The zero-thickness contributions to the FC and VEV of the energy-momentum tensor depend only on the fractional part of the ration of the magnetic flux inside the tube by the quantum one. As to the core-induced contributions, they depend on the total magnetic flux inside the tube and, consequently, in general, are not a periodic function of the magnetic flux.

European Pulsar Timing Array limits on an isotropic stochastic gravitational-wave background

NASA Astrophysics Data System (ADS)

Lentati, L.; Taylor, S. R.; Mingarelli, C. M. F.; Sesana, A.; Sanidas, S. A.; Vecchio, A.; Caballero, R. N.; Lee, K. J.; van Haasteren, R.; Babak, S.; Bassa, C. G.; Brem, P.; Burgay, M.; Champion, D. J.; Cognard, I.; Desvignes, G.; Gair, J. R.; Guillemot, L.; Hessels, J. W. T.; Janssen, G. H.; Karuppusamy, R.; Kramer, M.; Lassus, A.; Lazarus, P.; Liu, K.; Osłowski, S.; Perrodin, D.; Petiteau, A.; Possenti, A.; Purver, M. B.; Rosado, P. A.; Smits, R.; Stappers, B.; Theureau, G.; Tiburzi, C.; Verbiest, J. P. W.

2015-11-01

We present new limits on an isotropic stochastic gravitational-wave background (GWB) using a six pulsar data set spanning 18 yr of observations from the 2015 European Pulsar Timing Array data release. Performing a Bayesian analysis, we fit simultaneously for the intrinsic noise parameters for each pulsar, along with common correlated signals including clock, and Solar system ephemeris errors, obtaining a robust 95 per cent upper limit on the dimensionless strain amplitude A of the background of A < 3.0 × 10-15 at a reference frequency of 1 yr-1 and a spectral index of 13/3, corresponding to a background from inspiralling supermassive black hole binaries, constraining the GW energy density to Ωgw(f)h2 < 1.1 × 10-9 at 2.8 nHz. We also present limits on the correlated power spectrum at a series of discrete frequencies, and show that our sensitivity to a fiducial isotropic GWB is highest at a frequency of ˜5 × 10-9 Hz. Finally, we discuss the implications of our analysis for the astrophysics of supermassive black hole binaries, and present 95 per cent upper limits on the string tension, Gμ/c2, characterizing a background produced by a cosmic string network for a set of possible scenarios, and for a stochastic relic GWB. For a Nambu-Goto field theory cosmic string network, we set a limit Gμ/c2 < 1.3 × 10-7, identical to that set by the Planck Collaboration, when combining Planck and high-ℓ cosmic microwave background data from other experiments. For a stochastic relic background, we set a limit of Ω ^relic_gw(f)h^2<1.2 × 10^{-9}, a factor of 9 improvement over the most stringent limits previously set by a pulsar timing array.

The IceCube Collaboration:contributions to the 30 th International Cosmic Ray Conference (ICRC 2007),

DOE Office of Scientific and Technical Information (OSTI.GOV)

IceCube Collaboration; Ackermann, M.

2007-11-02

This paper bundles 40 contributions by the IceCube collaboration that were submitted to the 30th International Cosmic Ray Conference ICRC 2007. The articles cover studies on cosmic rays and atmospheric neutrinos, searches for non-localized, extraterrestrial {nu}{sub e}, {nu}{sub {mu}} and {nu}{sub {tau}} signals, scans for steady and intermittent neutrino point sources, searches for dark matter candidates, magnetic monopoles and other exotic particles, improvements in analysis techniques, as well as future detector extensions. The IceCube observatory will be finalized in 2011 to form a cubic-kilometer ice-Cherenkov detector at the location of the geographic South Pole. At the present state of construction,more » IceCube consists of 52 paired IceTop surface tanks and 22 IceCube strings with a total of 1426 Digital Optical Modules deployed at depths up to 2350 m. The observatory also integrates the 19 string AMANDA subdetector, that was completed in 2000 and extends IceCube's reach to lower energies. Before the deployment of IceTop, cosmic air showers were registered with the 30 station SPASE-2 surface array. IceCube's low noise Digital Optical Modules are very reliable, show a uniform response and record waveforms of arriving photons that are resolvable with nanosecond precision over a large dynamic range. Data acquisition, reconstruction and simulation software are running in production mode and the analyses, profiting from the improved data quality and increased overall sensitivity, are well under way.« less

Stationary black holes with stringy hair

NASA Astrophysics Data System (ADS)

Boos, Jens; Frolov, Valeri P.

2018-01-01

We discuss properties of black holes which are pierced by special configurations of cosmic strings. For static black holes, we consider radial strings in the limit when the number of strings grows to infinity while the tension of each single string tends to zero. In a properly taken limit, the stress-energy tensor of the string distribution is finite. We call such matter stringy matter. We present a solution of the Einstein equations for an electrically charged static black hole with the stringy matter, with and without a cosmological constant. This solution is a warped product of two metrics. One of them is a deformed 2-sphere, whose Gaussian curvature is determined by the energy density of the stringy matter. We discuss the embedding of a corresponding distorted sphere into a three-dimensional Euclidean space and formulate consistency conditions. We also found a relation between the square of the Weyl tensor invariant of the four-dimensional spacetime of the stringy black holes and the energy density of the stringy matter. In the second part of the paper, we discuss test stationary strings in the Kerr geometry and in its Kerr-NUT-(anti-)de Sitter generalizations. Explicit solutions for strings that are regular at the event horizon are obtained. Using these solutions, the stress-energy tensor of the stringy matter in these geometries is calculated. Extraction of the angular momentum from rotating black holes by such strings is also discussed.

End Point of Black Ring Instabilities and the Weak Cosmic Censorship Conjecture.

PubMed

Figueras, Pau; Kunesch, Markus; Tunyasuvunakool, Saran

2016-02-19

We produce the first concrete evidence that violation of the weak cosmic censorship conjecture can occur in asymptotically flat spaces of five dimensions by numerically evolving perturbed black rings. For certain thin rings, we identify a new, elastic-type instability dominating the evolution, causing the system to settle to a spherical black hole. However, for sufficiently thin rings the Gregory-Laflamme mode is dominant, and the instability unfolds similarly to that of black strings, where the horizon develops a structure of bulges connected by necks which become ever thinner over time.

Quantum gravity and taoist cosmology: Exploring the ancient origins of phenomenological string theory.

PubMed

Rosen, Steven M

2017-12-01

This paper carries forward the author's contribution to PBMP's previous special issue on Integral Biomathics (Rosen 2015). In the earlier paper, the crisis in contemporary theoretical physics was described and it was demonstrated that the problem can be addressed effectively only by shifting the foundations of physics from objectivist Cartesian philosophy to phenomenological philosophy. To that end, a phenomenological string theory was proposed based on qualitative topology and hypercomplex numbers. The current presentation takes this further by delving into the ancient Chinese origin of phenomenological string theory. First, we discover a deep connection between the Klein bottle, which is crucial to the theory, and the Ho-t'u, an old Chinese number archetype central to Taoist cosmology. The two structures are seen to mirror each other in expressing the curious psychophysical (phenomenological) action pattern at the heart of microphysics. But tackling the question of quantum gravity requires that a whole family of topological dimensions be brought into play. What we find in engaging with these structures is a closely related family of Taoist forebears that, in concert with their successors, provide a blueprint for cosmic evolution. Whereas conventional string theory accounts for the generation of nature's fundamental forces via a notion of symmetry breaking that is essentially static and thus unable to explain cosmogony successfully, phenomenological/Taoist string theory is guided by the dialectical interplay between symmetry and asymmetry inherent in the principle of synsymmetry. This dynamic concept of cosmic change is elaborated on in the three concluding sections of the paper. Here, a detailed analysis of cosmogony is offered, first in terms of the theory of dimensional development and its Taoist (yin-yang) counterpart, then in terms of the evolution of the elemental force particles through cycles of expansion and contraction in a spiraling universe. The paper closes by considering the role of the analyst per se in the further evolution of the cosmos. Copyright © 2017 Elsevier Ltd. All rights reserved.

CEM2k and LAQGSM Codes as Event-Generators for Space Radiation Shield and Cosmic Rays Propagation Applications

NASA Technical Reports Server (NTRS)

Mashnik, S. G.; Gudima, K. K.; Sierk, A. J.; Moskalenko, I. V.

2002-01-01

Space radiation shield applications and studies of cosmic ray propagation in the Galaxy require reliable cross sections to calculate spectra of secondary particles and yields of the isotopes produced in nuclear reactions induced both by particles and nuclei at energies from threshold to hundreds of GeV per nucleon. Since the data often exist in a very limited energy range or sometimes not at all, the only way to obtain an estimate of the production cross sections is to use theoretical models and codes. Recently, we have developed improved versions of the Cascade-Exciton Model (CEM) of nuclear reactions: the codes CEM97 and CEM2k for description of particle-nucleus reactions at energies up to about 5 GeV. In addition, we have developed a LANL version of the Quark-Gluon String Model (LAQGSM) to describe reactions induced both by particles and nuclei at energies up to hundreds of GeVhucleon. We have tested and benchmarked the CEM and LAQGSM codes against a large variety of experimental data and have compared their results with predictions by other currently available models and codes. Our benchmarks show that CEM and LAQGSM codes have predictive powers no worse than other currently used codes and describe many reactions better than other codes; therefore both our codes can be used as reliable event-generators for space radiation shield and cosmic ray propagation applications. The CEM2k code is being incorporated into the transport code MCNPX (and several other transport codes), and we plan to incorporate LAQGSM into MCNPX in the near future. Here, we present the current status of the CEM2k and LAQGSM codes, and show results and applications to studies of cosmic ray propagation in the Galaxy.

Systematic Uncertainties in High-Energy Hadronic Interaction Models

NASA Astrophysics Data System (ADS)

Zha, M.; Knapp, J.; Ostapchenko, S.

2003-07-01

Hadronic interaction models for cosmic ray energies are uncertain since our knowledge of hadronic interactions is extrap olated from accelerator experiments at much lower energies. At present most high-energy models are based on Grib ov-Regge theory of multi-Pomeron exchange, which provides a theoretical framework to evaluate cross-sections and particle production. While experimental data constrain some of the model parameters, others are not well determined and are therefore a source of systematic uncertainties. In this paper we evaluate the variation of results obtained with the QGSJET model, when modifying parameters relating to three ma jor sources of uncertainty: the form of the parton structure function, the role of diffractive interactions, and the string hadronisation. Results on inelastic cross sections, on secondary particle production and on the air shower development are discussed.

Antiproton Production by CR on Air Nuclei

NASA Technical Reports Server (NTRS)

Maskalenko, I. V.; Mashnik, S. G.

2003-01-01

Recent measurements of the cosmic ray (CR) antiproton flux have been shown to challenge existing CR propagation models. In particular, the conventional reacceleration model designed to match secondary/primary nuclei ratios produces too few antiprotons. Recently there appear some indications that the atmospheric contribution to antiproton production is considerably underestimated, which implies that antiproton CR flux might be lower. This may be the primary reason of the discrepancy discovered in CR propagation. We use the Los Alamos version of the Quark-Gluon String Model code LAQGSM together with available data on antiproton production on nuclei to analyse the accuracy of existing parameterizations of antiproton production cross section. The LAQGSM model has been shown to reproduce well nuclear reactions and hadronic data in the range 0.01-800 GeV/nucleon.

Dirac oscillator interacting with a topological defect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carvalho, J.; Furtado, C.; Moraes, F.

In this work we study the interaction problem of a Dirac oscillator with gravitational fields produced by topological defects. The energy levels of the relativistic oscillator in the cosmic string and in the cosmic dislocation space-times are sensible to curvature and torsion associated to these defects and are important evidence of the influence of the topology on this system. In the presence of a localized magnetic field the energy levels acquire a term associated with the Aharonov-Bohm effect. We obtain the eigenfunctions and eigenvalues and see that in the nonrelativistic limit some results known in standard quantum mechanics are reached.

Constraining the break of spatial diffeomorphism invariance with Planck data

NASA Astrophysics Data System (ADS)

Graef, L. L.; Benetti, M.; Alcaniz, J. S.

2017-07-01

The current most accepted paradigm for the early universe cosmology, the inflationary scenario, shows a good agreement with the recent Cosmic Microwave Background (CMB) and polarization data. However, when the inflation consistency relation is relaxed, these observational data exclude a larger range of red tensor tilt values, prevailing the blue ones which are not predicted by the minimal inflationary models. Recently, it has been shown that the assumption of spatial diffeomorphism invariance breaking (SDB) in the context of an effective field theory of inflation leads to interesting observational consequences. Among them, the possibility of generating a blue tensor spectrum, which can recover the specific consistency relation of the String Gas Cosmology, for a certain choice of parameters. We use the most recent CMB data to constrain the SDB model and test its observational viability through a Bayesian analysis assuming as reference an extended ΛCDM+tensor perturbation model, which considers a power-law tensor spectrum parametrized in terms of the tensor-to-scalar ratio, r, and the tensor spectral index, nt. If the inflation consistency relation is imposed, r=-8 nt, we obtain a strong evidence in favor of the reference model whereas if such relation is relaxed, a weak evidence in favor of the model with diffeomorphism breaking is found. We also use the same CMB data set to make an observational comparison between the SDB model, standard inflation and String Gas Cosmology.

Limits on Neutrino Emission from Gamma-Ray Bursts with the 40 String IceCube Detector

NASA Astrophysics Data System (ADS)

Abbasi, R.; Abdou, Y.; Abu-Zayyad, T.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Andeen, K.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Bay, R.; Bazo Alba, J. L.; Beattie, K.; Beatty, J. J.; Bechet, S.; Becker, J. K.; Becker, K.-H.; Benabderrahmane, M. L.; Benzvi, S.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bertrand, D.; Besson, D. Z.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Bose, D.; Böser, S.; Botner, O.; Braun, J.; Brown, A. M.; Buitink, S.; Carson, M.; Chirkin, D.; Christy, B.; Clem, J.; Clevermann, F.; Cohen, S.; Colnard, C.; Cowen, D. F.; D'Agostino, M. V.; Danninger, M.; Daughhetee, J.; Davis, J. C.; de Clercq, C.; Demirörs, L.; Depaepe, O.; Descamps, F.; Desiati, P.; de Vries-Uiterweerd, G.; Deyoung, T.; Díaz-Vélez, J. C.; Dierckxsens, M.; Dreyer, J.; Dumm, J. P.; Ehrlich, R.; Eisch, J.; Ellsworth, R. W.; Engdegård, O.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Fedynitch, A.; Feusels, T.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Foerster, M. M.; Fox, B. D.; Franckowiak, A.; Franke, R.; Gaisser, T. K.; Gallagher, J.; Geisler, M.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Goodman, J. A.; Grant, D.; Griesel, T.; Groß, A.; Grullon, S.; Gurtner, M.; Ha, C.; Hallgren, A.; Halzen, F.; Han, K.; Hanson, K.; Heinen, D.; Helbing, K.; Herquet, P.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Homeier, A.; Hoshina, K.; Hubert, D.; Huelsnitz, W.; Hülß, J.-P.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobsen, J.; Japaridze, G. S.; Johansson, H.; Joseph, J. M.; Kampert, K.-H.; Kappes, A.; Karg, T.; Karle, A.; Kelley, J. L.; Kemming, N.; Kenny, P.; Kiryluk, J.; Kislat, F.; Klein, S. R.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Kowarik, T.; Krasberg, M.; Krings, T.; Kroll, G.; Kuehn, K.; Kuwabara, T.; Labare, M.; Lafebre, S.; Laihem, K.; Landsman, H.; Larson, M. J.; Lauer, R.; Lehmann, R.; Lünemann, J.; Madsen, J.; Majumdar, P.; Marotta, A.; Maruyama, R.; Mase, K.; Matis, H. S.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Middell, E.; Milke, N.; Miller, J.; Montaruli, T.; Morse, R.; Movit, S. M.; Nahnhauer, R.; Nam, J. W.; Naumann, U.; Nießen, P.; Nygren, D. R.; Odrowski, S.; Olivas, A.; Olivo, M.; O'Murchadha, A.; Ono, M.; Panknin, S.; Paul, L.; Pérez de Los Heros, C.; Petrovic, J.; Piegsa, A.; Pieloth, D.; Porrata, R.; Posselt, J.; Price, P. B.; Prikockis, M.; Przybylski, G. T.; Rawlins, K.; Redl, P.; Resconi, E.; Rhode, W.; Ribordy, M.; Rizzo, A.; Rodrigues, J. P.; Roth, P.; Rothmaier, F.; Rott, C.; Ruhe, T.; Rutledge, D.; Ruzybayev, B.; Ryckbosch, D.; Sander, H.-G.; Santander, M.; Sarkar, S.; Schatto, K.; Schmidt, T.; Schoenwald, A.; Schukraft, A.; Schultes, A.; Schulz, O.; Schunck, M.; Seckel, D.; Semburg, B.; Seo, S. H.; Sestayo, Y.; Seunarine, S.; Silvestri, A.; Slipak, A.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stephens, G.; Stezelberger, T.; Stokstad, R. G.; Stoyanov, S.; Strahler, E. A.; Straszheim, T.; Sullivan, G. W.; Swillens, Q.; Taavola, H.; Taboada, I.; Tamburro, A.; Tarasova, O.; Tepe, A.; Ter-Antonyan, S.; Tilav, S.; Toale, P. A.; Toscano, S.; Tosi, D.; Turčan, D.; van Eijndhoven, N.; Vandenbroucke, J.; van Overloop, A.; van Santen, J.; Vehring, M.; Voge, M.; Voigt, B.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Walter, M.; Weaver, C.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Williams, D. R.; Wischnewski, R.; Wissing, H.; Wolf, M.; Woschnagg, K.; Xu, C.; Xu, X. W.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.

2011-04-01

IceCube has become the first neutrino telescope with a sensitivity below the TeV neutrino flux predicted from gamma-ray bursts if gamma-ray bursts are responsible for the observed cosmic-ray flux above 1018eV. Two separate analyses using the half-complete IceCube detector, one a dedicated search for neutrinos from pγ interactions in the prompt phase of the gamma-ray burst fireball and the other a generic search for any neutrino emission from these sources over a wide range of energies and emission times, produced no evidence for neutrino emission, excluding prevailing models at 90% confidence.

Constraints on the production of primordial magnetic seeds in pre-big bang cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gasperini, M., E-mail: gasperini@ba.infn.it

We study the amplification of the electromagnetic fluctuations, and the production of 'seeds' for the cosmic magnetic fields, in a class of string cosmology models whose scalar and tensor perturbations reproduce current observations and satisfy known phenomenological constraints. We find that the condition of efficient seeds production can be satisfied and compatible with all constraints only in a restricted region of parameter space, but we show that such a region has significant intersections with the portions of parameter space where the produced background of relic gravitational waves is strong enough to be detectable by aLIGO/Virgo and/or by eLISA.

Constraints on the production of primordial magnetic seeds in pre-big bang cosmology

NASA Astrophysics Data System (ADS)

Gasperini, M.

2017-06-01

We study the amplification of the electromagnetic fluctuations, and the production of "seeds" for the cosmic magnetic fields, in a class of string cosmology models whose scalar and tensor perturbations reproduce current observations and satisfy known phenomenological constraints. We find that the condition of efficient seeds production can be satisfied and compatible with all constraints only in a restricted region of parameter space, but we show that such a region has significant intersections with the portions of parameter space where the produced background of relic gravitational waves is strong enough to be detectable by aLIGO/Virgo and/or by eLISA.

The Mock LISA Data Challenge Round 3: New and Improved Sources

NASA Technical Reports Server (NTRS)

Baker, John

2008-01-01

The Mock LISA Data Challenges are a program to demonstrate and encourage the development of data-analysis capabilities for LISA. Each round of challenges consists of several data sets containing simulated instrument noise and gravitational waves from sources of undisclosed parameters. Participants are asked to analyze the data sets and report the maximum information they can infer about the source parameters. The challenges are being released in rounds of increasing complexity and realism. Challenge 3. currently in progress, brings new source classes, now including cosmic-string cusps and primordial stochastic backgrounds, and more realistic signal models for supermassive black-hole inspirals and galactic double white dwarf binaries.

Measurement of the Anisotropy of Cosmic-ray Arrival Directions with IceCube

NASA Astrophysics Data System (ADS)

Abbasi, R.; Abdou, Y.; Abu-Zayyad, T.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Andeen, K.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Bay, R.; Bazo Alba, J. L.; Beattie, K.; Beatty, J. J.; Bechet, S.; Becker, J. K.; Becker, K.-H.; Benabderrahmane, M. L.; BenZvi, S.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bertrand, D.; Besson, D. Z.; Bissok, M.; Blaufuss, E.; Boersma, D. J.; Bohm, C.; Böser, S.; Botner, O.; Bradley, L.; Braun, J.; Buitink, S.; Carson, M.; Chirkin, D.; Christy, B.; Clem, J.; Clevermann, F.; Cohen, S.; Colnard, C.; Cowen, D. F.; D'Agostino, M. V.; Danninger, M.; Davis, J. C.; De Clercq, C.; Demirörs, L.; Depaepe, O.; Descamps, F.; Desiati, P.; de Vries-Uiterweerd, G.; DeYoung, T.; Díaz-Vélez, J. C.; Dierckxsens, M.; Dreyer, J.; Dumm, J. P.; Duvoort, M. R.; Ehrlich, R.; Eisch, J.; Ellsworth, R. W.; Engdegård, O.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Feusels, T.; Filimonov, K.; Finley, C.; Foerster, M. M.; Fox, B. D.; Franckowiak, A.; Franke, R.; Gaisser, T. K.; Gallagher, J.; Geisler, M.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Goodman, J. A.; Grant, D.; Griesel, T.; Groß, A.; Grullon, S.; Gurtner, M.; Ha, C.; Hallgren, A.; Halzen, F.; Han, K.; Hanson, K.; Helbing, K.; Herquet, P.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Homeier, A.; Hoshina, K.; Hubert, D.; Huelsnitz, W.; Hülß, J.-P.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobsen, J.; Japaridze, G. S.; Johansson, H.; Joseph, J. M.; Kampert, K.-H.; Karg, T.; Karle, A.; Kelley, J. L.; Kemming, N.; Kenny, P.; Kiryluk, J.; Kislat, F.; Klein, S. R.; Knops, S.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Koskinen, D. J.; Kowalski, M.; Kowarik, T.; Krasberg, M.; Krings, T.; Kroll, G.; Kuehn, K.; Kuwabara, T.; Labare, M.; Lafebre, S.; Laihem, K.; Landsman, H.; Lauer, R.; Lehmann, R.; Lennarz, D.; Lünemann, J.; Madsen, J.; Majumdar, P.; Marotta, A.; Maruyama, R.; Mase, K.; Matis, H. S.; Matusik, M.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Middell, E.; Milke, N.; Miller, J.; Montaruli, T.; Morse, R.; Movit, S. M.; Nahnhauer, R.; Nam, J. W.; Naumann, U.; Nießen, P.; Nygren, D. R.; Odrowski, S.; Olivas, A.; Olivo, M.; O'Murchadha, A.; Ono, M.; Panknin, S.; Paul, L.; Pérez de los Heros, C.; Petrovic, J.; Piegsa, A.; Pieloth, D.; Porrata, R.; Posselt, J.; Price, P. B.; Prikockis, M.; Przybylski, G. T.; Rawlins, K.; Redl, P.; Resconi, E.; Rhode, W.; Ribordy, M.; Rizzo, A.; Rodrigues, J. P.; Roth, P.; Rothmaier, F.; Rott, C.; Roucelle, C.; Ruhe, T.; Rutledge, D.; Ruzybayev, B.; Ryckbosch, D.; Sander, H.-G.; Santander, M.; Sarkar, S.; Schatto, K.; Schlenstedt, S.; Schmidt, T.; Schukraft, A.; Schultes, A.; Schulz, O.; Schunck, M.; Seckel, D.; Semburg, B.; Seo, S. H.; Sestayo, Y.; Seunarine, S.; Silvestri, A.; Slipak, A.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stephens, G.; Stezelberger, T.; Stokstad, R. G.; Stoyanov, S.; Strahler, E. A.; Straszheim, T.; Sullivan, G. W.; Swillens, Q.; Taavola, H.; Taboada, I.; Tamburro, A.; Tarasova, O.; Tepe, A.; Ter-Antonyan, S.; Tilav, S.; Toale, P. A.; Toscano, S.; Tosi, D.; Turčan, D.; van Eijndhoven, N.; Vandenbroucke, J.; Van Overloop, A.; van Santen, J.; Voge, M.; Voigt, B.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Walter, M.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Wikström, G.; Williams, D. R.; Wischnewski, R.; Wissing, H.; Wolf, M.; Woschnagg, K.; Xu, C.; Xu, X. W.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; IceCube Collaboration

2010-08-01

We report the first observation of an anisotropy in the arrival direction of cosmic rays with energies in the multi-TeV region in the Southern sky using data from the IceCube detector. Between 2007 June and 2008 March, the partially deployed IceCube detector was operated in a configuration with 1320 digital optical sensors distributed over 22 strings at depths between 1450 and 2450 m inside the Antarctic ice. IceCube is a neutrino detector, but the data are dominated by a large background of cosmic-ray muons. Therefore, the background data are suitable for high-statistics studies of cosmic rays in the southern sky. The data include 4.3 billion muons produced by downward-going cosmic-ray interactions in the atmosphere; these events were reconstructed with a median angular resolution of 3° and a median energy of ~20 TeV. Their arrival direction distribution exhibits an anisotropy in right ascension with a first-harmonic amplitude of (6.4 ± 0.2 stat. ± 0.8 syst.) × 10-4.

On the initial regime of pre-big bang cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gasperini, M., E-mail: gasperini@ba.infn.it

The production of a background of super-horizon curvature perturbations with the appropriate (red) spectrum needed to trigger the cosmic anisotropies observed on large scales is associated, in the context of pre-big bang inflation, with a phase of growing string coupling. The extension towards the past of such a phase is not limited in time by the dynamical backreaction of the quantum perturbations of the cosmological geometry and of its sources. A viable, slightly red spectrum of scalar perturbations can thus be the output of an asymptotic, perturbative regime which is well compatible with an initial string-vacuum state satisfying the postulatemore » of 'Asymptotic Past Triviality'.« less

The 6D superswirl

NASA Astrophysics Data System (ADS)

Parameswaran, S. L.; Tasinato, G.; Zavala, I.

2006-03-01

We present a novel supersymmetric solution to a nonlinear sigma model coupled to supergravity. The solution represents a static, supersymmetric, codimension-two object, which is different to the familiar cosmic strings. In particular, we consider 6D chiral gauged supergravity, whose spectrum contains a number of hypermultiplets. The scalar components of the hypermultiplet are charged under a gauge field, and supersymmetry implies that they experience a simple paraboloid-like (or 2D infinite well) potential, which is minimised when they vanish. Unlike conventional vortices, the energy density of our configuration is not localized to a string-like core. The solutions have two timelike singularities in the internal manifold, which provide the necessary boundary conditions to ensure that the scalars do not lie at the minimum of their potential. The 4D spacetime is flat, and the solution is a continuous deformation of the so-called "rugby ball" solution, which has been studied in the context of the cosmological constant problem. It represents an unexpected class of supersymmetric solutions to the 6D theory, which have gravity, gauge fluxes and hyperscalars all active in the background.

A new class of non-topological solitons

NASA Technical Reports Server (NTRS)

Frieman, Joshua A.; Lynn, Bryan W.

1989-01-01

A class of non-topological solitons was constructed in renormalizable scalar field theories with nonlinear self-interactions. For large charge Q, the soliton mass increases linearly with Q, i.e., the soliton mass density is approximately independent of charge. Such objects could be naturally produced in a phase transition in the early universe or in the decay of superconducting cosmic strings.

Lattice black branes: sphere packing in general relativity

NASA Astrophysics Data System (ADS)

Dias, Óscar J. C.; Santos, Jorge E.; Way, Benson

2018-05-01

We perturbatively construct asymptotically R^{1,3}× T^2 black branes with multiple inhomogeneous directions and show that some of them are thermodynamically preferred over uniform branes in both the microcanonical and canonical ensembles. This demonstrates that, unlike five-dimensional black strings, the instability of some unstable black branes has a plausible endpoint that does not require a violation of cosmic censorship.

Exploring cosmic origins with CORE: Inflation

NASA Astrophysics Data System (ADS)

Finelli, F.; Bucher, M.; Achúcarro, A.; Ballardini, M.; Bartolo, N.; Baumann, D.; Clesse, S.; Errard, J.; Handley, W.; Hindmarsh, M.; Kiiveri, K.; Kunz, M.; Lasenby, A.; Liguori, M.; Paoletti, D.; Ringeval, C.; Väliviita, J.; van Tent, B.; Vennin, V.; Ade, P.; Allison, R.; Arroja, F.; Ashdown, M.; Banday, A. J.; Banerji, R.; Bartlett, J. G.; Basak, S.; de Bernardis, P.; Bersanelli, M.; Bonaldi, A.; Borril, J.; Bouchet, F. R.; Boulanger, F.; Brinckmann, T.; Burigana, C.; Buzzelli, A.; Cai, Z.-Y.; Calvo, M.; Carvalho, C. S.; Castellano, G.; Challinor, A.; Chluba, J.; Colantoni, I.; Coppolecchia, A.; Crook, M.; D'Alessandro, G.; D'Amico, G.; Delabrouille, J.; Desjacques, V.; De Zotti, G.; Diego, J. M.; Di Valentino, E.; Feeney, S.; Fergusson, J. R.; Fernandez-Cobos, R.; Ferraro, S.; Forastieri, F.; Galli, S.; García-Bellido, J.; de Gasperis, G.; Génova-Santos, R. T.; Gerbino, M.; González-Nuevo, J.; Grandis, S.; Greenslade, J.; Hagstotz, S.; Hanany, S.; Hazra, D. K.; Hernández-Monteagudo, C.; Hervias-Caimapo, C.; Hills, M.; Hivon, E.; Hu, B.; Kisner, T.; Kitching, T.; Kovetz, E. D.; Kurki-Suonio, H.; Lamagna, L.; Lattanzi, M.; Lesgourgues, J.; Lewis, A.; Lindholm, V.; Lizarraga, J.; López-Caniego, M.; Luzzi, G.; Maffei, B.; Mandolesi, N.; Martínez-González, E.; Martins, C. J. A. P.; Masi, S.; McCarthy, D.; Matarrese, S.; Melchiorri, A.; Melin, J.-B.; Molinari, D.; Monfardini, A.; Natoli, P.; Negrello, M.; Notari, A.; Oppizzi, F.; Paiella, A.; Pajer, E.; Patanchon, G.; Patil, S. P.; Piat, M.; Pisano, G.; Polastri, L.; Polenta, G.; Pollo, A.; Poulin, V.; Quartin, M.; Ravenni, A.; Remazeilles, M.; Renzi, A.; Roest, D.; Roman, M.; Rubiño-Martin, J. A.; Salvati, L.; Starobinsky, A. A.; Tartari, A.; Tasinato, G.; Tomasi, M.; Torrado, J.; Trappe, N.; Trombetti, T.; Tucci, M.; Tucker, C.; Urrestilla, J.; van de Weygaert, R.; Vielva, P.; Vittorio, N.; Young, K.; Zannoni, M.

2018-04-01

We forecast the scientific capabilities to improve our understanding of cosmic inflation of CORE, a proposed CMB space satellite submitted in response to the ESA fifth call for a medium-size mission opportunity. The CORE satellite will map the CMB anisotropies in temperature and polarization in 19 frequency channels spanning the range 60–600 GHz. CORE will have an aggregate noise sensitivity of 1.7 μKṡ arcmin and an angular resolution of 5' at 200 GHz. We explore the impact of telescope size and noise sensitivity on the inflation science return by making forecasts for several instrumental configurations. This study assumes that the lower and higher frequency channels suffice to remove foreground contaminations and complements other related studies of component separation and systematic effects, which will be reported in other papers of the series "Exploring Cosmic Origins with CORE." We forecast the capability to determine key inflationary parameters, to lower the detection limit for the tensor-to-scalar ratio down to the 10‑3 level, to chart the landscape of single field slow-roll inflationary models, to constrain the epoch of reheating, thus connecting inflation to the standard radiation-matter dominated Big Bang era, to reconstruct the primordial power spectrum, to constrain the contribution from isocurvature perturbations to the 10‑3 level, to improve constraints on the cosmic string tension to a level below the presumptive GUT scale, and to improve the current measurements of primordial non-Gaussianities down to the fNLlocal < 1 level. For all the models explored, CORE alone will improve significantly on the present constraints on the physics of inflation. Its capabilities will be further enhanced by combining with complementary future cosmological observations.

Inflation from periodic extra dimensions

NASA Astrophysics Data System (ADS)

Higaki, Tetsutaro; Tatsuta, Yoshiyuki

2017-07-01

We discuss a realization of a small field inflation based on string inspired supergravities. In theories accompanying extra dimensions, compactification of them with small radii is required for realistic situations. Since the extra dimension can have a periodicity, there will appear (quasi-)periodic functions under transformations of moduli of the extra dimensions in low energy scales. Such a periodic property can lead to a UV completion of so-called multi-natural inflation model where inflaton potential consists of a sum of multiple sinusoidal functions with a decay constant smaller than the Planck scale. As an illustration, we construct a SUSY breaking model, and then show that such an inflaton potential can be generated by a sum of world sheet instantons in intersecting brane models on extra dimensions containing orbifold. We show also predictions of cosmic observables by numerical analyzes.

Dynamical dark energy: Scalar fields and running vacuum

NASA Astrophysics Data System (ADS)

Solà, Joan; Gómez-Valent, Adrià; de Cruz Pérez, Javier

2017-03-01

Recent analyses in the literature suggest that the concordance ΛCDM model with rigid cosmological term, Λ = const. may not be the best description of the cosmic acceleration. The class of “running vacuum models”, in which Λ = Λ(H) evolves with the Hubble rate, has been shown to fit the string of SNIa + BAO + H(z) + LSS + CMB data significantly better than the ΛCDM. Here, we provide further evidence on the time-evolving nature of the dark energy (DE) by fitting the same cosmological data in terms of scalar fields. As a representative model, we use the original Peebles and Ratra potential, V ∝ ϕ-α. We find clear signs of dynamical DE at ˜ 4σ c.l., thus reconfirming through a nontrivial scalar field approach the strong hints formerly found with other models and parametrizations.

Inflation from periodic extra dimensions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Higaki, Tetsutaro; Tatsuta, Yoshiyuki, E-mail: thigaki@rk.phys.keio.ac.jp, E-mail: y_tatsuta@akane.waseda.jp

We discuss a realization of a small field inflation based on string inspired supergravities. In theories accompanying extra dimensions, compactification of them with small radii is required for realistic situations. Since the extra dimension can have a periodicity, there will appear (quasi-)periodic functions under transformations of moduli of the extra dimensions in low energy scales. Such a periodic property can lead to a UV completion of so-called multi-natural inflation model where inflaton potential consists of a sum of multiple sinusoidal functions with a decay constant smaller than the Planck scale. As an illustration, we construct a SUSY breaking model, andmore » then show that such an inflaton potential can be generated by a sum of world sheet instantons in intersecting brane models on extra dimensions containing orbifold. We show also predictions of cosmic observables by numerical analyzes.« less

Limits on neutrino emission from gamma-ray bursts with the 40 string IceCube detector.

PubMed

Abbasi, R; Abdou, Y; Abu-Zayyad, T; Adams, J; Aguilar, J A; Ahlers, M; Andeen, K; Auffenberg, J; Bai, X; Baker, M; Barwick, S W; Bay, R; Bazo Alba, J L; Beattie, K; Beatty, J J; Bechet, S; Becker, J K; Becker, K-H; Benabderrahmane, M L; BenZvi, S; Berdermann, J; Berghaus, P; Berley, D; Bernardini, E; Bertrand, D; Besson, D Z; Bindig, D; Bissok, M; Blaufuss, E; Blumenthal, J; Boersma, D J; Bohm, C; Bose, D; Böser, S; Botner, O; Braun, J; Brown, A M; Buitink, S; Carson, M; Chirkin, D; Christy, B; Clem, J; Clevermann, F; Cohen, S; Colnard, C; Cowen, D F; D'Agostino, M V; Danninger, M; Daughhetee, J; Davis, J C; De Clercq, C; Demirörs, L; Depaepe, O; Descamps, F; Desiati, P; de Vries-Uiterweerd, G; DeYoung, T; Díaz-Vélez, J C; Dierckxsens, M; Dreyer, J; Dumm, J P; Ehrlich, R; Eisch, J; Ellsworth, R W; Engdegård, O; Euler, S; Evenson, P A; Fadiran, O; Fazely, A R; Fedynitch, A; Feusels, T; Filimonov, K; Finley, C; Fischer-Wasels, T; Foerster, M M; Fox, B D; Franckowiak, A; Franke, R; Gaisser, T K; Gallagher, J; Geisler, M; Gerhardt, L; Gladstone, L; Glüsenkamp, T; Goldschmidt, A; Goodman, J A; Grant, D; Griesel, T; Gross, A; Grullon, S; Gurtner, M; Ha, C; Hallgren, A; Halzen, F; Han, K; Hanson, K; Heinen, D; Helbing, K; Herquet, P; Hickford, S; Hill, G C; Hoffman, K D; Homeier, A; Hoshina, K; Hubert, D; Huelsnitz, W; Hülss, J-P; Hulth, P O; Hultqvist, K; Hussain, S; Ishihara, A; Jacobsen, J; Japaridze, G S; Johansson, H; Joseph, J M; Kampert, K-H; Kappes, A; Karg, T; Karle, A; Kelley, J L; Kemming, N; Kenny, P; Kiryluk, J; Kislat, F; Klein, S R; Köhne, J-H; Kohnen, G; Kolanoski, H; Köpke, L; Kopper, S; Koskinen, D J; Kowalski, M; Kowarik, T; Krasberg, M; Krings, T; Kroll, G; Kuehn, K; Kuwabara, T; Labare, M; Lafebre, S; Laihem, K; Landsman, H; Larson, M J; Lauer, R; Lehmann, R; Lünemann, J; Madsen, J; Majumdar, P; Marotta, A; Maruyama, R; Mase, K; Matis, H S; Meagher, K; Merck, M; Mészáros, P; Meures, T; Middell, E; Milke, N; Miller, J; Montaruli, T; Morse, R; Movit, S M; Nahnhauer, R; Nam, J W; Naumann, U; Niessen, P; Nygren, D R; Odrowski, S; Olivas, A; Olivo, M; O'Murchadha, A; Ono, M; Panknin, S; Paul, L; Pérez de los Heros, C; Petrovic, J; Piegsa, A; Pieloth, D; Porrata, R; Posselt, J; Price, P B; Prikockis, M; Przybylski, G T; Rawlins, K; Redl, P; Resconi, E; Rhode, W; Ribordy, M; Rizzo, A; Rodrigues, J P; Roth, P; Rothmaier, F; Rott, C; Ruhe, T; Rutledge, D; Ruzybayev, B; Ryckbosch, D; Sander, H-G; Santander, M; Sarkar, S; Schatto, K; Schmidt, T; Schoenwald, A; Schukraft, A; Schultes, A; Schulz, O; Schunck, M; Seckel, D; Semburg, B; Seo, S H; Sestayo, Y; Seunarine, S; Silvestri, A; Slipak, A; Spiczak, G M; Spiering, C; Stamatikos, M; Stanev, T; Stephens, G; Stezelberger, T; Stokstad, R G; Stoyanov, S; Strahler, E A; Straszheim, T; Sullivan, G W; Swillens, Q; Taavola, H; Taboada, I; Tamburro, A; Tarasova, O; Tepe, A; Ter-Antonyan, S; Tilav, S; Toale, P A; Toscano, S; Tosi, D; Turčan, D; van Eijndhoven, N; Vandenbroucke, J; Van Overloop, A; van Santen, J; Vehring, M; Voge, M; Voigt, B; Walck, C; Waldenmaier, T; Wallraff, M; Walter, M; Weaver, C; Wendt, C; Westerhoff, S; Whitehorn, N; Wiebe, K; Wiebusch, C H; Williams, D R; Wischnewski, R; Wissing, H; Wolf, M; Woschnagg, K; Xu, C; Xu, X W; Yodh, G; Yoshida, S; Zarzhitsky, P

2011-04-08

IceCube has become the first neutrino telescope with a sensitivity below the TeV neutrino flux predicted from gamma-ray bursts if gamma-ray bursts are responsible for the observed cosmic-ray flux above 10(18)  eV. Two separate analyses using the half-complete IceCube detector, one a dedicated search for neutrinos from pγ interactions in the prompt phase of the gamma-ray burst fireball and the other a generic search for any neutrino emission from these sources over a wide range of energies and emission times, produced no evidence for neutrino emission, excluding prevailing models at 90% confidence.

Constraining the break of spatial diffeomorphism invariance with Planck data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graef, L.L.; Benetti, M.; Alcaniz, J.S., E-mail: leilagraef@on.br, E-mail: micolbenetti@on.br, E-mail: alcaniz@on.br

The current most accepted paradigm for the early universe cosmology, the inflationary scenario, shows a good agreement with the recent Cosmic Microwave Background (CMB) and polarization data. However, when the inflation consistency relation is relaxed, these observational data exclude a larger range of red tensor tilt values, prevailing the blue ones which are not predicted by the minimal inflationary models. Recently, it has been shown that the assumption of spatial diffeomorphism invariance breaking (SDB) in the context of an effective field theory of inflation leads to interesting observational consequences. Among them, the possibility of generating a blue tensor spectrum, whichmore » can recover the specific consistency relation of the String Gas Cosmology, for a certain choice of parameters. We use the most recent CMB data to constrain the SDB model and test its observational viability through a Bayesian analysis assuming as reference an extended ΛCDM+tensor perturbation model, which considers a power-law tensor spectrum parametrized in terms of the tensor-to-scalar ratio, r , and the tensor spectral index, n {sub t} . If the inflation consistency relation is imposed, r =−8 n {sub t} , we obtain a strong evidence in favor of the reference model whereas if such relation is relaxed, a weak evidence in favor of the model with diffeomorphism breaking is found. We also use the same CMB data set to make an observational comparison between the SDB model, standard inflation and String Gas Cosmology.« less

Beyond Inflation:. A Cyclic Universe Scenario

NASA Astrophysics Data System (ADS)

Turok, Neil; Steinhardt, Paul J.

2005-08-01

Inflation has been the leading early universe scenario for two decades, and has become an accepted element of the successful 'cosmic concordance' model. However, there are many puzzling features of the resulting theory. It requires both high energy and low energy inflation, with energy densities differing by a hundred orders of magnitude. The questions of why the universe started out undergoing high energy inflation, and why it will end up in low energy inflation, are unanswered. Rather than resort to anthropic arguments, we have developed an alternative cosmology, the cyclic universe [1], in which the universe exists in a very long-lived attractor state determined by the laws of physics. The model shares inflation's phenomenological successes without requiring an epoch of high energy inflation. Instead, the universe is made homogeneous and flat, and scale-invariant adiabatic perturbations are generated during an epoch of low energy acceleration like that seen today, but preceding the last big bang. Unlike inflation, the model requires low energy acceleration in order for a periodic attractor state to exist. The key challenge facing the scenario is that of passing through the cosmic singularity at t = 0. Substantial progress has been made at the level of linearised gravity, which is reviewed here. The challenge of extending this to nonlinear gravity and string theory remains.

Beyond Inflation: A Cyclic Universe Scenario

NASA Astrophysics Data System (ADS)

Turok, Neil; Steinhardt, Paul J.

2005-01-01

Inflation has been the leading early universe scenario for two decades, and has become an accepted element of the successful `cosmic concordance' model. However, there are many puzzling features of the resulting theory. It requires both high energy and low energy inflation, with energy densities differing by a hundred orders of magnitude. The questions of why the universe started out undergoing high energy inflation, and why it will end up in low energy inflation, are unanswered. Rather than resort to anthropic arguments, we have developed an alternative cosmology, the cyclic universe, in which the universe exists in a very long-lived attractor state determined by the laws of physics. The model shares inflation's phenomenological successes without requiring an epoch of high energy inflation. Instead, the universe is made homogeneous and flat, and scale-invariant adiabatic perturbations are generated during an epoch of low energy acceleration like that seen today, but preceding the last big bang. Unlike inflation, the model requires low energy acceleration in order for a periodic attractor state to exist. The key challenge facing the scenario is that of passing through the cosmic singularity at t = 0. Substantial progress has been made at the level of linearised gravity, which is reviewed here. The challenge of extending this to nonlinear gravity and string theory remains.

Evaluation of Production Cross Sections of Li, Be, B in CR

NASA Technical Reports Server (NTRS)

Moskalenko, I. V.; Mashnik, S. G.

2003-01-01

Accurate evaluation of the production cross section of light elements is important for models of cosmic ray (CR) propagation, galactic chemical evolution, and cosmological studies. However, the experimental spallation cross section data are scarce and often unavailable to CR community while semi-empirical systematics are frequently wrong by a significant factor. Running sophisticated nuclear codes is not an option of choice for everyone either. We use the Los Alamos versions of the Quark-Gluon String Model code LAQGSM and the improved Cascade-Exciton Model code CEM2k together with all available data from Los Alamos Nuclear Laboratory (LANL) nuclear database to produce evaluated production cross sections of isotopes of Li, Be, and B suitable for astrophysical applications. The LAQGSM and CEM2k models have been shown to reproduce well nuclear reactions and hadronic data in the range 0.01-800 GeV/nucleon.

Phase transitions triggered by quantum fluctuations in the inflationary universe

NASA Technical Reports Server (NTRS)

Nagasawa, Michiyasu; Yokoyama, Junichi

1991-01-01

The dynamics of a second-order phase transition during inflation, which is induced by time-variation of spacetime curvature, is studied as a natural mechanism to produce topological defects of typical grand unification scales such as cosmic strings or global textures. It is shown that their distribution is almost scale-invariant with small- and large-scale cutoffs. Also discussed is how these cutoffs are given.

Vacuum polarization and classical self-action near higher-dimensional defects

NASA Astrophysics Data System (ADS)

Grats, Yuri V.; Spirin, Pavel

2017-02-01

We analyze the gravity-induced effects associated with a massless scalar field in a higher-dimensional spacetime being the tensor product of (d-n)-dimensional Minkowski space and n-dimensional spherically/cylindrically symmetric space with a solid/planar angle deficit. These spacetimes are considered as simple models for a multidimensional global monopole (if n≥slant 3) or cosmic string (if n=2) with (d-n-1) flat extra dimensions. Thus, we refer to them as conical backgrounds. In terms of the angular-deficit value, we derive the perturbative expression for the scalar Green function, valid for any d≥slant 3 and 2≤slant n≤slant d-1, and compute it to the leading order. With the use of this Green function we compute the renormalized vacuum expectation value of the field square {< φ {2}(x)rangle }_{ren} and the renormalized vacuum averaged of the scalar-field energy-momentum tensor {< T_{M N}(x)rangle }_{ren} for arbitrary d and n from the interval mentioned above and arbitrary coupling constant to the curvature ξ . In particular, we revisit the computation of the vacuum polarization effects for a non-minimally coupled massless scalar field in the spacetime of a straight cosmic string. The same Green function enables to consider the old purely classical problem of the gravity-induced self-action of a classical point-like scalar or electric charge, placed at rest at some fixed point of the space under consideration. To deal with divergences, which appear in consideration of the two problems, we apply the dimensional-regularization technique, widely used in quantum field theory. The explicit dependence of the results upon the dimensionalities of both the bulk and conical submanifold is discussed.

The NANOGrav 11 Year Data Set: Pulsar-timing Constraints on the Stochastic Gravitational-wave Background

NASA Astrophysics Data System (ADS)

Arzoumanian, Z.; Baker, P. T.; Brazier, A.; Burke-Spolaor, S.; Chamberlin, S. J.; Chatterjee, S.; Christy, B.; Cordes, J. M.; Cornish, N. J.; Crawford, F.; Thankful Cromartie, H.; Crowter, K.; DeCesar, M.; Demorest, P. B.; Dolch, T.; Ellis, J. A.; Ferdman, R. D.; Ferrara, E.; Folkner, W. M.; Fonseca, E.; Garver-Daniels, N.; Gentile, P. A.; Haas, R.; Hazboun, J. S.; Huerta, E. A.; Islo, K.; Jones, G.; Jones, M. L.; Kaplan, D. L.; Kaspi, V. M.; Lam, M. T.; Lazio, T. J. W.; Levin, L.; Lommen, A. N.; Lorimer, D. R.; Luo, J.; Lynch, R. S.; Madison, D. R.; McLaughlin, M. A.; McWilliams, S. T.; Mingarelli, C. M. F.; Ng, C.; Nice, D. J.; Park, R. S.; Pennucci, T. T.; Pol, N. S.; Ransom, S. M.; Ray, P. S.; Rasskazov, A.; Siemens, X.; Simon, J.; Spiewak, R.; Stairs, I. H.; Stinebring, D. R.; Stovall, K.; Swiggum, J.; Taylor, S. R.; Vallisneri, M.; van Haasteren, R.; Vigeland, S.; Zhu, W. W.; The NANOGrav Collaboration

2018-05-01

We search for an isotropic stochastic gravitational-wave background (GWB) in the newly released 11 year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). While we find no evidence for a GWB, we place constraints on a population of inspiraling supermassive black hole (SMBH) binaries, a network of decaying cosmic strings, and a primordial GWB. For the first time, we find that the GWB constraints are sensitive to the solar system ephemeris (SSE) model used and that SSE errors can mimic a GWB signal. We developed an approach that bridges systematic SSE differences, producing the first pulsar-timing array (PTA) constraints that are robust against SSE errors. We thus place a 95% upper limit on the GW-strain amplitude of A GWB < 1.45 × 10‑15 at a frequency of f = 1 yr‑1 for a fiducial f ‑2/3 power-law spectrum and with interpulsar correlations modeled. This is a factor of ∼2 improvement over the NANOGrav nine-year limit calculated using the same procedure. Previous PTA upper limits on the GWB (as well as their astrophysical and cosmological interpretations) will need revision in light of SSE systematic errors. We use our constraints to characterize the combined influence on the GWB of the stellar mass density in galactic cores, the eccentricity of SMBH binaries, and SMBH–galactic-bulge scaling relationships. We constrain the cosmic-string tension using recent simulations, yielding an SSE-marginalized 95% upper limit of Gμ < 5.3 × 10‑11—a factor of ∼2 better than the published NANOGrav nine-year constraints. Our SSE-marginalized 95% upper limit on the energy density of a primordial GWB (for a radiation-dominated post-inflation universe) is ΩGWB(f) h 2 < 3.4 × 10‑10.

The Birth of String Theory

NASA Astrophysics Data System (ADS)

Cappelli, Andrea; Castellani, Elena; Colomo, Filippo; Di Vecchia, Paolo

2012-04-01

Part I. Overview: 1. Introduction and synopsis; 2. Rise and fall of the hadronic string G. Veneziano; 3. Gravity, unification, and the superstring J. H. Schwarz; 4. Early string theory as a challenging case study for philosophers E. Castellani; Part II. The Prehistory: The Analytic S-Matrix: 5. Introduction to Part II; 6. Particle theory in the sixties: from current algebra to the Veneziano amplitude M. Ademollo; 7. The path to the Veneziano model H. R. Rubinstein; 8. Two-component duality and strings P. G. O. Freund; 9. Note on the prehistory of string theory M. Gell-Mann; Part III. The Dual Resonance Model: 10. Introduction to Part III; 11. From the S-matrix to string theory P. Di Vecchia; 12. Reminiscence on the birth of string theory J. A. Shapiro; 13. Personal recollections D. Amati; 14. Early string theory at Fermilab and Rutgers L. Clavelli; 15. Dual amplitudes in higher dimensions: a personal view C. Lovelace; 16. Personal recollections on dual models R. Musto; 17. Remembering the 'supergroup' collaboration F. Nicodemi; 18. The '3-Reggeon vertex' S. Sciuto; Part IV. The String: 19. Introduction to Part IV; 20. From dual models to relativistic strings P. Goddard; 21. The first string theory: personal recollections L. Susskind; 22. The string picture of the Veneziano model H. B. Nielsen; 23. From the S-matrix to string theory Y. Nambu; 24. The analogue model for string amplitudes D. B. Fairlie; 25. Factorization in dual models and functional integration in string theory S. Mandelstam; 26. The hadronic origins of string theory R. C. Brower; Part V. Beyond the Bosonic String: 27. Introduction to Part V; 28. From dual fermion to superstring D. I. Olive; 29. Dual models with fermions: memoirs of an early string theorist P. Ramond; 30. Personal recollections A. Neveu; 31. Aspects of fermionic dual models E. Corrigan; 32. The dual quark models K. Bardakci and M. B. Halpern; 33. Remembering the dawn of relativistic strings J.-L. Gervais; 34. Early string theory in Cambridge: personal recollections C. Montonen; Part VI. The Superstring: 35. Introduction to Part VI; 36. Supersymmetry in string theory F. Gliozzi; 37. Gravity from strings: personal reminiscences of early developments T. Yoneya; 38. From the Nambu-Goto to the σ-model action L. Brink; 39. Locally supersymmetric action for superstring P. Di Vecchia; 40. Personal recollections E. Cremmer; 41. The scientific contributions of Joël Scherk J. H. Schwarz; Part VII. Preparing the String Renaissance: 42. Introduction to Part VII; 43. From strings to superstrings: a personal perspective M. B. Green; 44. Quarks, strings and beyond A. M. Polyakov; 45. The rise of the superstring theory A. Cappelli and F. Colomo; Appendices; Index.

The D-material universe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elghozi, Thomas; Mavromatos, Nick E.; Sakellariadou, Mairi

In a previous publication by some of the authors (N.E.M., M.S. and M.F.Y.), we have argued that the ''D-material universe'', that is a model of a brane world propagating in a higher-dimensional bulk populated by collections of D-particle stringy defects, provides a model for the growth of large-scale structure in the universe via the vector field in its spectrum. The latter corresponds to D-particle recoil velocity excitations as a result of the interactions of the defects with stringy matter and radiation on the brane world. In this article, we first elaborate further on the results of the previous study onmore » the galactic growth era and analyse the circumstances under which the D-particle recoil velocity fluid may ''mimic'' dark matter in galaxies. A lensing phenomenology is also presented for some samples of galaxies, which previously were known to provide tension for modified gravity (TeVeS) models. The current model is found in agreement with these lensing data. Then we discuss a cosmic evolution for the D-material universe by analysing the conditions under which the late eras of this universe associated with large-scale structure are connected to early epochs, where inflation takes place. It is shown that inflation is induced by dense populations of D-particles in the early universe, with the rôle of the inflaton field played by the condensate of the D-particle recoil-velocity fields under their interaction with relativistic stringy matter, only for sufficiently large brane tensions and low string mass scales compared to the Hubble scale. On the other hand, for large string scales, where the recoil-velocity condensate fields are weak, inflation cannot be driven by the D-particle defects alone. In such cases inflation may be driven by dilaton (or other moduli) fields in the underlying string theory.« less

A bridge between unified cosmic history by f( R)-gravity and BIonic system

NASA Astrophysics Data System (ADS)

Sepehri, Alireza; Capozziello, Salvatore; Setare, Mohammad Reza

2016-04-01

Recently, the cosmological deceleration-acceleration transition redshift in f( R) gravity has been considered in order to address consistently the problem of cosmic evolution. It is possible to show that the deceleration parameter changes sign at a given redshift according to observational data. Furthermore, a f( R) gravity cosmological model can be constructed in brane-antibrane system starting from the very early universe and accounting for the cosmological redshift at all phases of cosmic history, from inflation to late time acceleration. Here we propose a f( R) model where transition redshifts correspond to inflation-deceleration and deceleration-late time acceleration transitions starting froma BIon system. At the point where the universe was born, due to the transition of k black fundamental strings to the BIon configuration, the redshift is approximately infinity and decreases with reducing temperature (z˜ T2). The BIon is a configuration in flat space of a universe-brane and a parallel anti-universe-brane connected by a wormhole. This wormhole is a channel for flowing energy from extra dimensions into our universe, occurring at inflation and decreasing with redshift as z˜ T^{4+1/7}. Dynamics consists with the fact that the wormhole misses its energy and vanishes as soon as inflation ends and deceleration begins. Approaching two universe branes together, a tachyon is originated, it grows up and causes the formation of a wormhole. We show that, in the framework of f( R) gravity, the cosmological redshift depends on the tachyonic potential and has a significant decrease at deceleration-late time acceleration transition point (z˜ T^{2/3}). As soon as today acceleration approaches, the redshift tends to zero and the cosmological model reduces to the standard Λ CDM cosmology.

Multiflavor string-net models

NASA Astrophysics Data System (ADS)

Lin, Chien-Hung

2017-05-01

We generalize the string-net construction to multiple flavors of strings, each of which is labeled by the elements of an Abelian group Gi. The same flavor of strings can branch, while different flavors of strings can cross one another and thus they form intersecting string nets. We systematically construct the exactly soluble lattice Hamiltonians and the ground-state wave functions for the intersecting string-net condensed phases. We analyze the braiding statistics of the low-energy quasiparticle excitations and find that our model can realize all the topological phases as the string-net model with group G =∏iGi . In this respect, our construction provides various ways of building lattice models which realize topological order G , corresponding to different partitions of G and thus different flavors of string nets. In fact, our construction concretely demonstrates the Künneth formula by constructing various lattice models with the same topological order. As an example, we construct the G =Z2×Z2×Z2 string-net model which realizes a non-Abelian topological phase by properly intersecting three copies of toric codes.

Cosmic ray spectrum and composition from three years of IceTop and IceCube

NASA Astrophysics Data System (ADS)

Rawlins, K.; IceCube Collaboration

2016-05-01

IceTop is the surface component of the IceCube Observatory, composed of frozen water tanks at the top of IceCube’s strings. Data from this detector can be analyzed in different ways with the goal of measuring cosmic ray spectrum and composition. The shower size S125 from IceTop alone can be used as a proxy for primary energy, and unfolded into an all-particle spectrum. In addition, S125 from the surface can be combined with high-energy muon energy loss information from the deep IceCube detector for those air showers which pass through both. Using these coincident events in a complementary analysis, both the spectrum and mass composition of primary cosmic rays can be extracted in parallel using a neural network. Both of these analyses have been performed on three years of IceTop and IceCube data. Both all-particle spectra as well as individual spectra for elemental groups are presented.

Cosmic ray energy spectrum measurement with the Antarctic Muon and Neutrino Detector Array (AMANDA)

NASA Astrophysics Data System (ADS)

Chirkin, Dmitry Aleksandrovich

AMANDA-II is a neutrino telescope composed of 677 optical sensors organized along 19 strings buried deep in the Antarctic ice cap. It is designed to detect Cherenkov light produced by cosmic-ray- and neutrino-induced charged leptons. The majority of events recorded by AMANDA-II are caused by muons which are produced in the atmosphere by high-energy cosmic rays. The leading uncertainties in simulating such events come from the choice of the high-energy model used to describe the first interaction of the cosmic rays, uncertainties in our knowledge and implementation of the ice properties at the depth of the detector, and individual optical module sensitivities. Contributions from uncertainties in the atmospheric conditions and muon cross sections in ice are smaller. The downgoing muon simulation was substantially improved by using the extensive air shower generator CORSIKA to describe the shower development in the atmosphere, and by writing a new software package for the muon propagation (MMC), which reduced computational and algorithm errors below the level of uncertainties of the muon cross sections in ice. A method was developed that resulted in a flux measurement of cosmic rays with energies 1.5--200 TeV per nucleon (95% of primaries causing low-multiplicity events in AMANDA-II have energies in this range) independent of ice model and optical module sensitivities. Predictions of six commonly used high-energy interaction models (QGSJET, VENUS, NEXUS, DPMJET, HDPM, and SIBYLL) are compared to data. The best agreement with direct measurements is achieved with QGSJET, VENUS, and NEXUS. Assuming a power-law energy spectrum (phi0,i · E -gammai) for cosmic-ray components from hydrogen to iron (i = H,..., Fe) and their mass distribution according to Wiebel-South (Wiebel-South & Biermann, 1999), phi 0,i and gammai were corrected to achieve the best description of the data. For the hydrogen component, values of phi0,H = 0.106 +/- 0.007 m-2 sr-1s-1TeV-1 , gammaH = 2.70 +/- 0.02 are obtained. For the South Pole, a vertical muon flux at 1 TeV of (1.05 +/- 0.07) · 10 -10 cm-2 sr-1s -1GeV-1 is obtained (for all interaction models), and the fitted spectral index is 2.66 +/- 0.02 (for QGSJET, VENUS, and NEXUS). The difference in the predicted value of the spectral index gamma between high-energy interaction models is as much as 0.1, which is explained by the difference in the observed muon multiplicity at the depth of the detector in data simulated with different interaction models.

Light Z' in heterotic string standardlike models

NASA Astrophysics Data System (ADS)

Athanasopoulos, P.; Faraggi, A. E.; Mehta, V. M.

2014-05-01

The discovery of the Higgs boson at the LHC supports the hypothesis that the Standard Model provides an effective parametrization of all subatomic experimental data up to the Planck scale. String theory, which provides a viable perturbative approach to quantum gravity, requires for its consistency the existence of additional gauge symmetries beyond the Standard Model. The construction of heterotic string models with a viable light Z' is, however, highly constrained. We outline the construction of standardlike heterotic string models that allow for an additional Abelian gauge symmetry that may remain unbroken down to low scales. We present a string inspired model, consistent with the string constraints.

Cosmological structure formation from soft topological defects

NASA Technical Reports Server (NTRS)

Hill, Christopher T.; Schramm, David N.; Fry, J. N.

1988-01-01

Some models have extremely low-mass pseudo-Goldstone bosons that can lead to vacuum phase transitions at late times, after the decoupling of the microwave background.. This can generate structure formation at redshifts z greater than or approx 10 on mass scales as large as M approx 10 to the 18th solar masses. Such low energy transitions can lead to large but phenomenologically acceptable density inhomogeneities in soft topological defects (e.g., domain walls) with minimal variations in the microwave anisotropy, as small as delta Y/T less than or approx 10 to the minus 6 power. This mechanism is independent of the existence of hot, cold, or baryonic dark matter. It is a novel alternative to both cosmic string and to inflationary quantum fluctuations as the origin of structure in the Universe.

Identification of market trends with string and D2-brane maps

NASA Astrophysics Data System (ADS)

Bartoš, Erik; Pinčák, Richard

2017-08-01

The multidimensional string objects are introduced as a new alternative for an application of string models for time series forecasting in trading on financial markets. The objects are represented by open string with 2-endpoints and D2-brane, which are continuous enhancement of 1-endpoint open string model. We show how new object properties can change the statistics of the predictors, which makes them the candidates for modeling a wide range of time series systems. String angular momentum is proposed as another tool to analyze the stability of currency rates except the historical volatility. To show the reliability of our approach with application of string models for time series forecasting we present the results of real demo simulations for four currency exchange pairs.

p-adic string theories provide lattice Discretization to the ordinary string worldsheet.

PubMed

Ghoshal, Debashis

2006-10-13

A class of models called p-adic strings is useful in understanding the tachyonic instability of string theory. These are found to be empirically related to the ordinary strings in the p-->1 limit. We propose that these models provide discretization for the string worldsheet and argue that the limit is naturally thought of as a continuum limit in the sense of the renormalization group.

p-adic String Theories Provide Lattice Discretization to the Ordinary String Worldsheet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghoshal, Debashis

2006-10-13

A class of models called p-adic strings is useful in understanding the tachyonic instability of string theory. These are found to be empirically related to the ordinary strings in the p{yields}1 limit. We propose that these models provide discretization for the string worldsheet and argue that the limit is naturally thought of as a continuum limit in the sense of the renormalization group.

Deviation from Standard Inflationary Cosmology and the Problems in Ekpyrosis

NASA Astrophysics Data System (ADS)

Tseng, Chien-Yao

There are two competing models of our universe right now. One is Big Bang with inflation cosmology. The other is the cyclic model with ekpyrotic phase in each cycle. This paper is divided into two main parts according to these two models. In the first part, we quantify the potentially observable effects of a small violation of translational invariance during inflation, as characterized by the presence of a preferred point, line, or plane. We explore the imprint such a violation would leave on the cosmic microwave background anisotropy, and provide explicit formulas for the expected amplitudes ( alma*l'm') of the spherical-harmonic coefficients. We then provide a model and study the two-point correlation of a massless scalar (the inflaton) when the stress tensor contains the energy density from an infinitely long straight cosmic string in addition to a cosmological constant. Finally, we discuss if inflation can reconcile with the Liouville's theorem as far as the fine-tuning problem is concerned. In the second part, we find several problems in the cyclic/ekpyrotic cosmology. First of all, quantum to classical transition would not happen during an ekpyrotic phase even for superhorizon modes, and therefore the fluctuations cannot be interpreted as classical. This implies the prediction of scale-free power spectrum in ekpyrotic/cyclic universe model requires more inspection. Secondly, we find that the usual mechanism to solve fine-tuning problems is not compatible with eternal universe which contains infinitely many cycles in both direction of time. Therefore, all fine-tuning problems including the flatness problem still asks for an explanation in any generic cyclic models.

Frontiers in Numerical Relativity

NASA Astrophysics Data System (ADS)

Evans, Charles R.; Finn, Lee S.; Hobill, David W.

2011-06-01

Preface; Participants; Introduction; 1. Supercomputing and numerical relativity: a look at the past, present and future David W. Hobill and Larry L. Smarr; 2. Computational relativity in two and three dimensions Stuart L. Shapiro and Saul A. Teukolsky; 3. Slowly moving maximally charged black holes Robert C. Ferrell and Douglas M. Eardley; 4. Kepler's third law in general relativity Steven Detweiler; 5. Black hole spacetimes: testing numerical relativity David H. Bernstein, David W. Hobill and Larry L. Smarr; 6. Three dimensional initial data of numerical relativity Ken-ichi Oohara and Takashi Nakamura; 7. Initial data for collisions of black holes and other gravitational miscellany James W. York, Jr.; 8. Analytic-numerical matching for gravitational waveform extraction Andrew M. Abrahams; 9. Supernovae, gravitational radiation and the quadrupole formula L. S. Finn; 10. Gravitational radiation from perturbations of stellar core collapse models Edward Seidel and Thomas Moore; 11. General relativistic implicit radiation hydrodynamics in polar sliced space-time Paul J. Schinder; 12. General relativistic radiation hydrodynamics in spherically symmetric spacetimes A. Mezzacappa and R. A. Matzner; 13. Constraint preserving transport for magnetohydrodynamics John F. Hawley and Charles R. Evans; 14. Enforcing the momentum constraints during axisymmetric spacelike simulations Charles R. Evans; 15. Experiences with an adaptive mesh refinement algorithm in numerical relativity Matthew W. Choptuik; 16. The multigrid technique Gregory B. Cook; 17. Finite element methods in numerical relativity P. J. Mann; 18. Pseudo-spectral methods applied to gravitational collapse Silvano Bonazzola and Jean-Alain Marck; 19. Methods in 3D numerical relativity Takashi Nakamura and Ken-ichi Oohara; 20. Nonaxisymmetric rotating gravitational collapse and gravitational radiation Richard F. Stark; 21. Nonaxisymmetric neutron star collisions: initial results using smooth particle hydrodynamics Christopher S. Kochanek and Charles R. Evans; 22. Relativistic hydrodynamics James R. Wilson and Grant J. Mathews; 23. Computational dynamics of U(1) gauge strings: probability of reconnection of cosmic strings Richard A. Matzner; 24. Dynamically inhomogenous cosmic nucleosynthesis Hannu Kurki-Suonio; 25. Initial value solutions in planar cosmologies Peter Anninos, Joan Centrella and Richard Matzner; 26. An algorithmic overview of an Einstein solver Roger Ove; 27. A PDE compiler for full-metric numerical relativity Jonathan Thornburg; 28. Numerical evolution on null cones R. Gomez and J. Winicour; 29. Normal modes coupled to gravitational waves in a relativistic star Yasufumi Kojima; 30. Cosmic censorship and numerical relativity Dalia S. Goldwirth, Amos Ori and Tsvi Piran.

Dynamical black holes in low-energy string theory

NASA Astrophysics Data System (ADS)

Aniceto, Pedro; Rocha, Jorge V.

2017-05-01

We investigate time-dependent spherically symmetric solutions of the four-dimensional Einstein-Maxwell-axion-dilaton system, with the dilaton coupling that occurs in low-energy effective heterotic string theory. A class of dilaton-electrovacuum radiating solutions with a trivial axion, previously found by Güven and Yörük, is re-derived in a simpler manner and its causal structure is clarified. It is shown that such dynamical spacetimes featuring apparent horizons do not possess a regular light-like past null infinity or future null infinity, depending on whether they are radiating or accreting. These solutions are then extended in two ways. First we consider a Vaidya-like generalisation, which introduces a null dust source. Such spacetimes are used to test the status of cosmic censorship in the context of low-energy string theory. We prove that — within this family of solutions — regular black holes cannot evolve into naked singularities by accreting null dust, unless standard energy conditions are violated. Secondly, we employ S-duality to derive new time-dependent dyon solutions with a nontrivial axion turned on. Although they share the same causal structure as their Einstein-Maxwell-dilaton counterparts, these solutions possess both electric and magnetic charges.

Quantum gravity in the Southern Cone Conference. Proceedings. Conference, Bariloche (Argentina), 7 - 10 Jan 1998.

NASA Astrophysics Data System (ADS)

1999-04-01

The following topics are discussed: Black hole formation by canonical dynamics of gravitating shells; canonical quantum gravity; Vassiliev invariants; midisuperspace models; quantum spacetime; large-N limit of superconformal field theories and supergravity; world-volume fields and background coupling of branes; gauge enhancement and chirality changes in nonperturbative orbifold models; chiral p-forms; formally renormalizable gravitationally self-interacting string models; gauge supergravities for all odd dimensions; black hole radiation and S-matrix; primordial black holes; fluctuations in a thermal field and dissipation of a black hole spacetime in far-field limit; adiabatic interpretation of particle creation in a de Sitter universe; nonequilibrium dynamics of quantum fields in inflationary cosmology; magnetic fields in the early Universe; classical regime of a quantum universe obtained through a functional method; decoherence and correlations in semiclassical cosmology; fluid of primordial fluctuations; causal statistical mechanics calculation of initial cosmic entropy and quantum gravity prospects and black hole-D-brane correspondence.

Unified cosmic history in modified gravity: From F(R) theory to Lorentz non-invariant models

NASA Astrophysics Data System (ADS)

Nojiri, Shin'Ichi; Odintsov, Sergei D.

2011-08-01

The classical generalization of general relativity is considered as the gravitational alternative for a unified description of the early-time inflation with late-time cosmic acceleration. The structure and cosmological properties of a number of modified theories, including traditional F(R) and Hořava-Lifshitz F(R) gravity, scalar-tensor theory, string-inspired and Gauss-Bonnet theory, non-local gravity, non-minimally coupled models, and power-counting renormalizable covariant gravity are discussed. Different representations of and relations between such theories are investigated. It is shown that some versions of the above theories may be consistent with local tests and may provide a qualitatively reasonable unified description of inflation with the dark energy epoch. The cosmological reconstruction of different modified gravities is provided in great detail. It is demonstrated that eventually any given universe evolution may be reconstructed for the theories under consideration, and the explicit reconstruction is applied to an accelerating spatially flat Friedmann-Robertson-Walker (FRW) universe. Special attention is paid to Lagrange multiplier constrained and conventional F(R) gravities, for latter F(R) theory, the effective ΛCDM era and phantom divide crossing acceleration are obtained. The occurrences of the Big Rip and other finite-time future singularities in modified gravity are reviewed along with their solutions via the addition of higher-derivative gravitational invariants.

Supersymmetric B – L inflation near the conformal coupling

DOE PAGES

Arai, Masato; Kawai, Shinsuke; Okada, Nobuchika

2014-06-01

We investigate a novel scenario of cosmological inflation in a gauged B-L extended minimal supersymmetric Standard Model with R-symmetry. We use a noncanonical Kähler potential and a superpotential, both preserving the R-symmetry to construct a model of slow-roll inflation. The model is controlled by two real parameters: the nonminimal coupling ξ that originates from the Kähler potential, and the breaking scale v of the U (1)B-L symmetry. We compute the spectrum of the cosmological microwave background radiation and show that the prediction of the model fits well the recent Planck satellite observation for a wide range of the parameter space.more » We also find that the typical reheating temperature of the model is low enough to avoid the gravitino problem but nevertheless allows sufficient production of the baryon asymmetry if we take into account the effect of resonance enhancement. The model is free from cosmic strings that impose stringent constraints on generic U (1)B-L based scenarios, as in our scenario the U (1)B-L symmetry is broken from the onset.« less

String Fragmentation Model in Space Radiation Problems

NASA Technical Reports Server (NTRS)

Tang, Alfred; Johnson, Eloise (Editor); Norbury, John W.; Tripathi, R. K.

2002-01-01

String fragmentation models such as the Lund Model fit experimental particle production cross sections very well in the high-energy limit. This paper gives an introduction of the massless relativistic string in the Lund Model and shows how it can be modified with a simple assumption to produce formulas for meson production cross sections for space radiation research. The results of the string model are compared with inclusive pion production data from proton-proton collision experiments.

Astronomical constraints on the cosmic evolution of the fine structure constant and possible quantum dimensions.

PubMed

Carilli, C L; Menten, K M; Stocke, J T; Perlman, E; Vermeulen, R; Briggs, F; de Bruyn , A G; Conway, J; Moore, C P

2000-12-25

We present measurements of absorption by the 21 cm hyperfine transition of neutral hydrogen toward radio sources at substantial look-back times. These data are used in combination with observations of rotational transitions of common interstellar molecules to set limits on the evolution of the fine structure constant: alpha/ alpha<3.5x10(-15) yr(-1), to a look-back time of 4.8 Gyr. In the context of string theory, the limit on the secular evolution of the scale factor of the compact dimensions, R, is &Rdot/ R<10(-15) yr(-1). Including terrestrial and other astronomical measurements places 2sigma limits on slow oscillations of R from the present to the epoch of cosmic nucleosynthesis, just seconds after the big bang, of DeltaR /R<10(-5).

Computer Center: BASIC String Models of Genetic Information Transfer.

ERIC Educational Resources Information Center

Spain, James D., Ed.

1984-01-01

Discusses some of the major genetic information processes which may be modeled by computer program string manipulation, focusing on replication and transcription. Also discusses instructional applications of using string models. (JN)

Cosmic censorship conjecture in Kerr-Sen black hole

NASA Astrophysics Data System (ADS)

Gwak, Bogeun

2017-06-01

The validity of the cosmic censorship conjecture for the Kerr-Sen black hole, which is a solution to the low-energy effective field theory for four-dimensional heterotic string theory, is investigated using charged particle absorption. When the black hole absorbs the particle, the charge on it changes owing to the conserved quantities of the particle. Changes in the black hole are constrained to the equation for the motion of the particle and are consistent with the laws of thermodynamics. Particle absorption increases the mass of the Kerr-Sen black hole to more than that of the absorbed charges such as angular momentum and electric charge; hence, the black hole cannot be overcharged. In the near-extremal black hole, we observe a violation of the cosmic censorship conjecture for the angular momentum in the first order of expansion and the electric charge in the second order. However, considering an adiabatic process carrying the conserved quantities as those of the black hole, we prove the stability of the black hole horizon. Thus, we resolve the violation. This is consistent with the third law of thermodynamics.

Estimating the weak-lensing rotation signal in radio cosmic shear surveys

NASA Astrophysics Data System (ADS)

Thomas, Daniel B.; Whittaker, Lee; Camera, Stefano; Brown, Michael L.

2017-09-01

Weak lensing has become an increasingly important tool in cosmology and the use of galaxy shapes to measure cosmic shear has become routine. The weak-lensing distortion tensor contains two other effects in addition to the two components of shear: the convergence and rotation. The rotation mode is not measurable using the standard cosmic shear estimators based on galaxy shapes, as there is no information on the original shapes of the images before they were lensed. Due to this, no estimator has been proposed for the rotation mode in cosmological weak-lensing surveys, and the rotation mode has never been constrained. Here, we derive an estimator for this quantity, which is based on the use of radio polarization measurements of the intrinsic position angles of galaxies. The rotation mode can be sourced by physics beyond Λ cold dark matter (ΛCDM), and also offers the chance to perform consistency checks of ΛCDM and of weak-lensing surveys themselves. We present simulations of this estimator and show that, for the pedagogical example of cosmic string spectra, this estimator could detect a signal that is consistent with the constraints from Planck. We examine the connection between the rotation mode and the shear B modes and thus how this estimator could help control systematics in future radio weak-lensing surveys.

Compression of strings with approximate repeats.

PubMed

Allison, L; Edgoose, T; Dix, T I

1998-01-01

We describe a model for strings of characters that is loosely based on the Lempel Ziv model with the addition that a repeated substring can be an approximate match to the original substring; this is close to the situation of DNA, for example. Typically there are many explanations for a given string under the model, some optimal and many suboptimal. Rather than commit to one optimal explanation, we sum the probabilities over all explanations under the model because this gives the probability of the data under the model. The model has a small number of parameters and these can be estimated from the given string by an expectation-maximization (EM) algorithm. Each iteration of the EM algorithm takes O(n2) time and a few iterations are typically sufficient. O(n2) complexity is impractical for strings of more than a few tens of thousands of characters and a faster approximation algorithm is also given. The model is further extended to include approximate reverse complementary repeats when analyzing DNA strings. Tests include the recovery of parameter estimates from known sources and applications to real DNA strings.

Constraining the String Gauge Field by Galaxy Rotation Curves and Perihelion Precession of Planets

NASA Astrophysics Data System (ADS)

Cheung, Yeuk-Kwan E.; Xu, Feng

2013-09-01

We discuss a cosmological model in which the string gauge field coupled universally to matter gives rise to an extra centripetal force and will have observable signatures on cosmological and astronomical observations. Several tests are performed using data including galaxy rotation curves of 22 spiral galaxies of varied luminosities and sizes and perihelion precessions of planets in the solar system. The rotation curves of the same group of galaxies are independently fit using a dark matter model with the generalized Navarro-Frenk-White (NFW) profile and the string model. A remarkable fit of galaxy rotation curves is achieved using the one-parameter string model as compared to the three-parameter dark matter model with the NFW profile. The average χ2 value of the NFW fit is 9% better than that of the string model at a price of two more free parameters. Furthermore, from the string model, we can give a dynamical explanation for the phenomenological Tully-Fisher relation. We are able to derive a relation between field strength, galaxy size, and luminosity, which can be verified with data from the 22 galaxies. To further test the hypothesis of the universal existence of the string gauge field, we apply our string model to the solar system. Constraint on the magnitude of the string field in the solar system is deduced from the current ranges for any anomalous perihelion precession of planets allowed by the latest observations. The field distribution resembles a dipole field originating from the Sun. The string field strength deduced from the solar system observations is of a similar magnitude as the field strength needed to sustain the rotational speed of the Sun inside the Milky Way. This hypothesis can be tested further by future observations with higher precision.

Minimal string theories and integrable hierarchies

NASA Astrophysics Data System (ADS)

Iyer, Ramakrishnan

Well-defined, non-perturbative formulations of the physics of string theories in specific minimal or superminimal model backgrounds can be obtained by solving matrix models in the double scaling limit. They provide us with the first examples of completely solvable string theories. Despite being relatively simple compared to higher dimensional critical string theories, they furnish non-perturbative descriptions of interesting physical phenomena such as geometrical transitions between D-branes and fluxes, tachyon condensation and holography. The physics of these theories in the minimal model backgrounds is succinctly encoded in a non-linear differential equation known as the string equation, along with an associated hierarchy of integrable partial differential equations (PDEs). The bosonic string in (2,2m-1) conformal minimal model backgrounds and the type 0A string in (2,4 m) superconformal minimal model backgrounds have the Korteweg-de Vries system, while type 0B in (2,4m) backgrounds has the Zakharov-Shabat system. The integrable PDE hierarchy governs flows between backgrounds with different m. In this thesis, we explore this interesting connection between minimal string theories and integrable hierarchies further. We uncover the remarkable role that an infinite hierarchy of non-linear differential equations plays in organizing and connecting certain minimal string theories non-perturbatively. We are able to embed the type 0A and 0B (A,A) minimal string theories into this single framework. The string theories arise as special limits of a rich system of equations underpinned by an integrable system known as the dispersive water wave hierarchy. We find that there are several other string-like limits of the system, and conjecture that some of them are type IIA and IIB (A,D) minimal string backgrounds. We explain how these and several other string-like special points arise and are connected. In some cases, the framework endows the theories with a non-perturbative definition for the first time. Notably, we discover that the Painleve IV equation plays a key role in organizing the string theory physics, joining its siblings, Painleve I and II, whose roles have previously been identified in this minimal string context. We then present evidence that the conjectured type II theories have smooth non-perturbative solutions, connecting two perturbative asymptotic regimes, in a 't Hooft limit. Our technique also demonstrates evidence for new minimal string theories that are not apparent in a perturbative analysis.

Modeling and simulation performance of sucker rod beam pump

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aditsania, Annisa, E-mail: annisaaditsania@gmail.com; Rahmawati, Silvy Dewi, E-mail: silvyarahmawati@gmail.com; Sukarno, Pudjo, E-mail: psukarno@gmail.com

2015-09-30

Artificial lift is a mechanism to lift hydrocarbon, generally petroleum, from a well to surface. This is used in the case that the natural pressure from the reservoir has significantly decreased. Sucker rod beam pumping is a method of artificial lift. Sucker rod beam pump is modeled in this research as a function of geometry of the surface part, the size of sucker rod string, and fluid properties. Besides its length, sucker rod string also classified into tapered and un-tapered. At the beginning of this research, for easy modeling, the sucker rod string was assumed as un-tapered. The assumption provedmore » non-realistic to use. Therefore, the tapered sucker rod string modeling needs building. The numerical solution of this sucker rod beam pump model is computed using finite difference method. The numerical result shows that the peak of polished rod load for sucker rod beam pump unit C-456-D-256-120, for non-tapered sucker rod string is 38504.2 lb, while for tapered rod string is 25723.3 lb. For that reason, to avoid the sucker rod string breaks due to the overload, the use of tapered sucker rod beam string is suggested in this research.« less

Effects of overlapping strings in pp collisions

DOE PAGES

Bierlich, Christian; Gustafson, Gösta; Lönnblad, Leif; ...

2015-03-26

In models for hadron collisions based on string hadronization, the strings are usually treated as independent, allowing no interaction between the confined colour fields. In studies of nucleus collisions it has been suggested that strings close in space can fuse to form "colour ropes." Such ropes are expected to give more strange particles and baryons, which also has been suggested as a signal for plasma formation. Overlapping strings can also be expected in pp collisions, where usually no phase transition is expected. In particular at the high LHC energies the expected density of strings is quite high. To investigate possiblemore » effects of rope formation, we present a model in which strings are allowed to combine into higher multiplets, giving rise to increased production of baryons and strangeness, or recombine into singlet structures and vanish. Also a crude model for strings recombining into junction structures is considered, again giving rise to increased baryon production. The models are implemented in the DIPSY MC event generator, using PYTHIA8 for hadronization, and comparison to pp minimum bias data, reveals improvement in the description of identified particle spectra.« less

A numerical study of the string function using a primitive equation ocean model

NASA Astrophysics Data System (ADS)

Tyler, R. H.; Käse, R.

We use results from a primitive-equation ocean numerical model (SCRUM) to test a theoretical 'string function' formulation put forward by Tyler and Käse in another article in this issue. The string function acts as a stream function for the large-scale potential energy flow under the combined beta and topographic effects. The model results verify that large-scale anomalies propagate along the string function contours with a speed correctly given by the cross-string gradient. For anomalies having a scale similar to the Rossby radius, material rates of change in the layer mass following the string velocity are balanced by material rates of change in relative vorticity following the flow velocity. It is shown that large-amplitude anomalies can be generated when wind stress is resonant with the string function configuration.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Namikawa, Toshiya

We present here a new method for delensing B modes of the cosmic microwave background (CMB) using a lensing potential reconstructed from the same realization of the CMB polarization (CMB internal delensing). The B -mode delensing is required to improve sensitivity to primary B modes generated by, e.g., the inflationary gravitational waves, axionlike particles, modified gravity, primordial magnetic fields, and topological defects such as cosmic strings. However, the CMB internal delensing suffers from substantial biases due to correlations between observed CMB maps to be delensed and that used for reconstructing a lensing potential. Since the bias depends on realizations, wemore » construct a realization-dependent (RD) estimator for correcting these biases by deriving a general optimal estimator for higher-order correlations. The RD method is less sensitive to simulation uncertainties. Compared to the previous ℓ -splitting method, we find that the RD method corrects the biases without substantial degradation of the delensing efficiency.« less

Investigating dark matter substructure with pulsar timing - II. Improved limits on small-scale cosmology

NASA Astrophysics Data System (ADS)

Clark, Hamish A.; Lewis, Geraint F.; Scott, Pat

2016-02-01

Ultracompact minihaloes (UCMHs) have been proposed as a type of dark matter substructure seeded by large-amplitude primordial perturbations and topological defects. UCMHs are expected to survive to the present era, allowing constraints to be placed on their cosmic abundance using observations within our own Galaxy. Constraints on their number density can be linked to conditions in the early Universe that impact structure formation, such as increased primordial power on small scales, generic weak non-Gaussianity, and the presence of cosmic strings. We use new constraints on the abundance of UCMHs from pulsar timing to place generalized limits on the parameters of each of these cosmological scenarios. At some scales, the limits are the strongest to date, exceeding those from dark matter annihilation. Our new limits have the added advantage of being independent of the particle nature of dark matter, as they are based only on gravitational effects.

Tilted string cosmologies

NASA Astrophysics Data System (ADS)

Clancy, Dominic; Feinstein, Alexander; Lidsey, James E.; Tavakol, Reza

1999-04-01

Global symmetries of the string effective action are employed to generate tilted, homogeneous Bianchi type VIh string cosmologies from a previously known stiff perfect fluid solution to Einstein gravity. The dilaton field is not constant on the surfaces of homogeneity. The future asymptotic state of the models is interpreted as a plane wave and is itself an exact solution to the string equations of motion to all orders in the inverse string tension. An inhomogeneous generalization of the Bianchi type III model is also found.

Tensionless Strings and Supersymmetric Sigma Models: Aspects of the Target Space Geometry

NASA Astrophysics Data System (ADS)

Bredthauer, Andreas

2007-01-01

In this thesis, two aspects of string theory are discussed, tensionless strings and supersymmetric sigma models. The equivalent to a massless particle in string theory is a tensionless string. Even almost 30 years after it was first mentioned, it is still quite poorly understood. We discuss how tensionless strings give rise to exact solutions to supergravity and solve closed tensionless string theory in the ten dimensional maximally supersymmetric plane wave background, a contraction of AdS(5)xS(5) where tensionless strings are of great interest due to their proposed relation to higher spin gauge theory via the AdS/CFT correspondence. For a sigma model, the amount of supersymmetry on its worldsheet restricts the geometry of the target space. For N=(2,2) supersymmetry, for example, the target space has to be bi-hermitian. Recently, with generalized complex geometry, a new mathematical framework was developed that is especially suited to discuss the target space geometry of sigma models in a Hamiltonian formulation. Bi-hermitian geometry is so-called generalized Kaehler geometry but the relation is involved. We discuss various amounts of supersymmetry in phase space and show that this relation can be established by considering the equivalence between the Hamilton and Lagrange formulation of the sigma model. In the study of generalized supersymmetric sigma models, we find objects that favor a geometrical interpretation beyond generalized complex geometry.

No time machine construction in open 2+1 gravity with timelike total energy-momentum

NASA Astrophysics Data System (ADS)

Tiglio, Manuel H.

1998-09-01

It is shown that in (2+1)-dimensional gravity an open spacetime with timelike sources and total energy momentum cannot have a stable compactly generated Cauchy horizon. This constitutes a proof of a version of Kabat's conjecture and shows, in particular, that not only a Gott time machine cannot be formed from processes such as the decay of a single cosmic string as has been shown by Carroll et al., but that, in a precise sense, a time machine cannot be constructed at all.

Structures in general relativity

NASA Astrophysics Data System (ADS)

Tieu, Steven

Structures within general relativity are examined. The differences between man-made structures and those predicted by the Einstein differential equations are very subtle. Exotic structures such as the Godel Universe and the Gott cosmic string are examined with emphasis on closed time-like curves. Newtonian models are seen to also have an exotic aspect in that a vast halo consisting of unknown matter dominates the galaxy. We introduce a model for galaxies based on a general relativity framework with the goal of excluding such artifacts from the system while describing the flat-rotation curves. Structures within this model were speculated to be exotic but after close scrutiny, their nature is shown to be benign. Numerical approaches are applied to model four galaxies: The Milky Way, NGC 3031, NGC 3198 and NGC 7331. Density and mass are deduced from these models and compared to the Newtonian models. Within the visible/HI region, there is 30% reduction in total mass. Extending the model to 10 times beyond the HI region using various fall-off scenerios, it is shown that there is only modest increase of the accumulated mass. In comparison to the Newtonian approach to galactic dynamics, the massive halos are not required to account for the flat velocity profiles.

Mean transverse momenta correlations in hadron-hadron collisions in MC toy model with repulsing strings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Altsybeev, Igor

2016-01-22

In the present work, Monte-Carlo toy model with repulsing quark-gluon strings in hadron-hadron collisions is described. String repulsion creates transverse boosts for the string decay products, giving modifications of observables. As an example, long-range correlations between mean transverse momenta of particles in two observation windows are studied in MC toy simulation of the heavy-ion collisions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bierlich, Christian; Gustafson, Gösta; Lönnblad, Leif

In models for hadron collisions based on string hadronization, the strings are usually treated as independent, allowing no interaction between the confined colour fields. In studies of nucleus collisions it has been suggested that strings close in space can fuse to form "colour ropes." Such ropes are expected to give more strange particles and baryons, which also has been suggested as a signal for plasma formation. Overlapping strings can also be expected in pp collisions, where usually no phase transition is expected. In particular at the high LHC energies the expected density of strings is quite high. To investigate possiblemore » effects of rope formation, we present a model in which strings are allowed to combine into higher multiplets, giving rise to increased production of baryons and strangeness, or recombine into singlet structures and vanish. Also a crude model for strings recombining into junction structures is considered, again giving rise to increased baryon production. The models are implemented in the DIPSY MC event generator, using PYTHIA8 for hadronization, and comparison to pp minimum bias data, reveals improvement in the description of identified particle spectra.« less

String theory--the physics of string-bending and other electric guitar techniques.

PubMed

Grimes, David Robert

2014-01-01

Electric guitar playing is ubiquitous in practically all modern music genres. In the hands of an experienced player, electric guitars can sound as expressive and distinct as a human voice. Unlike other more quantised instruments where pitch is a discrete function, guitarists can incorporate micro-tonality and, as a result, vibrato and sting-bending are idiosyncratic hallmarks of a player. Similarly, a wide variety of techniques unique to the electric guitar have emerged. While the mechano-acoustics of stringed instruments and vibrating strings are well studied, there has been comparatively little work dedicated to the underlying physics of unique electric guitar techniques and strings, nor the mechanical factors influencing vibrato, string-bending, fretting force and whammy-bar dynamics. In this work, models for these processes are derived and the implications for guitar and string design discussed. The string-bending model is experimentally validated using a variety of strings and vibrato dynamics are simulated. The implications of these findings on the configuration and design of guitars is also discussed.

String Theory - The Physics of String-Bending and Other Electric Guitar Techniques

PubMed Central

Grimes, David Robert

2014-01-01

Electric guitar playing is ubiquitous in practically all modern music genres. In the hands of an experienced player, electric guitars can sound as expressive and distinct as a human voice. Unlike other more quantised instruments where pitch is a discrete function, guitarists can incorporate micro-tonality and, as a result, vibrato and sting-bending are idiosyncratic hallmarks of a player. Similarly, a wide variety of techniques unique to the electric guitar have emerged. While the mechano-acoustics of stringed instruments and vibrating strings are well studied, there has been comparatively little work dedicated to the underlying physics of unique electric guitar techniques and strings, nor the mechanical factors influencing vibrato, string-bending, fretting force and whammy-bar dynamics. In this work, models for these processes are derived and the implications for guitar and string design discussed. The string-bending model is experimentally validated using a variety of strings and vibrato dynamics are simulated. The implications of these findings on the configuration and design of guitars is also discussed. PMID:25054880

Cosmological moduli and the post-inflationary universe: A critical review

NASA Astrophysics Data System (ADS)

Kane, Gordon; Sinha, Kuver; Watson, Scott

2015-06-01

We critically review the role of cosmological moduli in determining the post-inflationary history of the universe. Moduli are ubiquitous in string and M-theory constructions of beyond the Standard Model physics, where they parametrize the geometry of the compactification manifold. For those with masses determined by supersymmetry (SUSY) breaking this leads to their eventual decay slightly before Big Bang nucleosynthesis (BBN) (without spoiling its predictions). This results in a matter dominated phase shortly after inflation ends, which can influence baryon and dark matter genesis, as well as observations of the cosmic microwave background (CMB) and the growth of large-scale structure. Given progress within fundamental theory, and guidance from dark matter and collider experiments, nonthermal histories have emerged as a robust and theoretically well-motivated alternative to a strictly thermal one. We review this approach to the early universe and discuss both the theoretical challenges and the observational implications.

Liquid Crystal Colloids

NASA Astrophysics Data System (ADS)

Smalyukh, Ivan I.

2018-03-01

Colloids are abundant in nature, science, and technology, with examples ranging from milk to quantum dots and the colloidal atom paradigm. Similarly, liquid crystal ordering is important in contexts ranging from biological membranes to laboratory models of cosmic strings and liquid crystal displays in consumer devices. Some of the most exciting recent developments in both of these soft matter fields emerge at their interface, in the fast-growing research arena of liquid crystal colloids. Mesoscale self-assembly in such systems may lead to artificial materials and to structures with emergent physical behavior arising from patterning of molecular order and nano- or microparticles into precisely controlled configurations. Liquid crystal colloids show exceptional promise for new discovery that may impinge on composite material fabrication, low-dimensional topology, photonics, and so on. Starting from physical underpinnings, I review the state of the art in this fast-growing field, with a focus on its scientific and technological potential.

Temperature characterisation of the CLOUD chamber at CERN

NASA Astrophysics Data System (ADS)

Dias, A. M.; Almeida, J.; Kirkby, J.; Mathot, S.; Onnela, A.; Vogel, A.; Ehrhart, S.

2014-12-01

Temperature stability, uniformity and absolute scale inside the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN are important for experiments on aerosol particle nucleation and ice/liquid cloud formation. In order to measure the air temperature, a comprehensive set of arrays ("strings") of platinum resistance thermometers, thermocouples and optical sensors have been installed inside the 26 m3 chamber. The thermal sensors must meet several challenging design requirements: ultra-clean materials, 0.01 K measurement sensitivity, high absolute precision (<0.1 K), 200 K - 373 K range, ability to operate in high electric fields (20 kV/m), and fast response in air (~1 s) in order to measure rapid changes of temperature during ice/liquid cloud formation in the chamber by adiabatic pressure reductions. This presentation will focus on the design of the thermometer strings and the thermal performance of the chamber during the CLOUD8 and CLOUD9 campaigns, 2013-2014, together with the planned upgrades of the CLOUD thermal system.

Cosmic Catastrophes

NASA Astrophysics Data System (ADS)

Wheeler, J. Craig

2000-07-01

In this tour de force of the ultimate and extreme in astrophysics, renowned astrophysicist and author J. Craig Wheeler takes us on a breathtaking journey to supernovae, black holes, gamma-ray bursts and adventures in hyperspace. This is no far-fetched science fiction tale, but an enthusiastic exploration of ideas at the cutting edge of current astrophysics. Wheeler follows the tortuous life of a star from birth to evolution and death, and goes on to consider the complete collapse of a star into a black hole, worm-hole time machines, the possible birth of baby bubble universes, and the prospect of a revolutionary view of space and time in a ten-dimensional string theory. Along the way he offers evidence that suggests the Universe is accelerating and describes recent developments in understanding gamma-ray bursts--perhaps the most catastrophic cosmic events of all. With the use of lucid analogies, simple language and crystal-clear cartoons, Cosmic Catastrophes makes accessible some of the most exciting and mind-bending objects and ideas in the Universe. J. Craig Wheeler is currently Samuel T. and Fern Yanagisawa Regents Professor of Astronomy at the University of Texas at Austin and Vice President of the American Astronomical Society as of 1999.

Characterization of binary string statistics for syntactic landmine detection

NASA Astrophysics Data System (ADS)

Nasif, Ahmed O.; Mark, Brian L.; Hintz, Kenneth J.

2011-06-01

Syntactic landmine detection has been proposed to detect and classify non-metallic landmines using ground penetrating radar (GPR). In this approach, the GPR return is processed to extract characteristic binary strings for landmine and clutter discrimination. In our previous work, we discussed the preprocessing methodology by which the amplitude information of the GPR A-scan signal can be effectively converted into binary strings, which identify the impedance discontinuities in the signal. In this work, we study the statistical properties of the binary string space. In particular, we develop a Markov chain model to characterize the observed bit sequence of the binary strings. The state is defined as the number of consecutive zeros between two ones in the binarized A-scans. Since the strings are highly sparse (the number of zeros is much greater than the number of ones), defining the state this way leads to fewer number of states compared to the case where each bit is defined as a state. The number of total states is further reduced by quantizing the number of consecutive zeros. In order to identify the correct order of the Markov model, the mean square difference (MSD) between the transition matrices of mine strings and non-mine strings is calculated up to order four using training data. The results show that order one or two maximizes this MSD. The specification of the transition probabilities of the chain can be used to compute the likelihood of any given string. Such a model can be used to identify characteristic landmine strings during the training phase. These developments on modeling and characterizing the string statistics can potentially be part of a real-time landmine detection algorithm that identifies landmine and clutter in an adaptive fashion.

From decay to complete breaking: pulling the strings in SU(2) Yang-Mills theory.

PubMed

Pepe, M; Wiese, U-J

2009-05-15

We study {2Q+1} strings connecting two static charges Q in (2+1)D SU(2) Yang-Mills theory. While the fundamental {2} string between two charges Q=1/2 is unbreakable, the adjoint {3} string connecting two charges Q=1 can break. When a {4} string is stretched beyond a critical length, it decays into a {2} string by gluon pair creation. When a {5} string is stretched, it first decays into a {3} string, which eventually breaks completely. The energy of the screened charges at the ends of a string is well described by a phenomenological constituent gluon model.

Pitch glide effect induced by a nonlinear string-barrier interaction

NASA Astrophysics Data System (ADS)

Kartofelev, Dmitri; Stulov, Anatoli; Välimäki, Vesa

2015-10-01

Interactions of a vibrating string with its supports and other spatially distributed barriers play a significant role in the physics of many stringed musical instruments. It is well known that the tone of the string vibrations is determined by the string supports, and that the boundary conditions of the string termination may cause a short-lasting initial fundamental frequency shifting. Generally, this phenomenon is associated with the nonlinear modulation of the stiff string tension. The aim of this paper is to study the initial frequency glide phenomenon that is induced only by the string-barrier interaction, apart from other possible physical causes, and without the interfering effects of dissipation and dispersion. From a numerical simulation perspective, this highly nonlinear problem may present various difficulties, not the least of which is the risk of numerical instability. We propose a numerically stable and a purely kinematic model of the string-barrier interaction, which is based on the travelling wave solution of the ideal string vibration. The model is capable of reproducing the motion of the vibrating string exhibiting the initial fundamental frequency glide, which is caused solely by the complex nonlinear interaction of the string with its termination. The results presented in this paper can expand our knowledge and understanding of the timbre evolution and the physical principles of sound generation of numerous stringed instruments, such as lutes called the tambura, sitar and biwa.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kinney, William H., E-mail: whkinney@buffalo.edu

We consider observational limits on a proposed model of the string landscape in inflation. In this scenario, effects from the decoherence of entangled quantum states in long-wavelength modes in the universe result in modifications to the Friedmann Equation and a corresponding modification to inflationary dynamics. Previous work [1, 2] suggested that such effects could provide an explanation for well-known anomalies in the Cosmic Microwave Background (CMB), such as the lack of power on large scales and the ''cold spot'' seen by both the WMAP and Planck satellites. In this paper, we compute limits on these entanglement effects from the Planckmore » CMB data combined with the BICEP/Keck polarization measurement, and find no evidence for observable modulations to the power spectrum from landscape entanglement, and no sourcing of observable CMB anomalies. The originally proposed model with an exponential potential is ruled out to high significance. Assuming a Starobinsky-type R {sup 2} inflation model, which is consistent with CMB constraints, data place a 2σ lower bound of b > 6.46 × 10{sup 7} GeV on the Supersymmetry breaking scale associated with entanglement corrections.« less

Novel string field theory with also negative energy constituents/objects gives Veneziano amplitude

NASA Astrophysics Data System (ADS)

Nielsen, H. B.; Ninomiya, M.

2018-02-01

We have proposed a new type of string field theory. The main point of the present article is to cure some technical troubles: missing two out three terms in Veneziano amplitude. Our novel string field theory, describes a theory with many strings in terms of "objects", which are not exactly, but close to Charles Thorn's string bits. The new point is that the objects in terms of which the universe states are constructed, and which have an essentially 26-momentum variable called J μ , can have the energy J 0 be also negative as well as positive. We get a long way in deriving in this model the Veneziano model and obtain all the three terms needed for a four point amplitude. This result strongly indicates that our novel string field theory is indeed string theory.

Astrophysics and astronomy (Scientific session of the Physical Sciences Division of the Russian Academy of Sciences, 26 January 2011)

NASA Astrophysics Data System (ADS)

2011-10-01

An Astrophysics and Astronomy scientific session of the Physical Sciences Division of the Russian Academy of Sciences (RAS) was held in the Conference Hall of the P N Lebedev Physical Institute, RAS, on 26 January 2011. The following reports were put on the session's agenda posted on the web site www.gpad.ac.ru of the Physical Sciences Division, RAS: (1) Cherepashchuk A M (Sternberg Astronomical Institute, Moscow State University, Moscow) "Investigation of X-ray sources"; (2) Shustov B M (Institute of Astronomy, Russian Academy of Sciences, Moscow) "Asteroid and comet hazards: physical and other aspects"; (3) Sazhin M V (Sternberg Astronomical Institute, Moscow State University, Moscow) "Search for cosmic strings"; (4) Zakharov A F (Russian Federation State Scientific Center 'A I Alikhanov Institute for Theoretical and Experimental Physics', Moscow) "Exoplanet search using gravitational microlensing". Papers written on the basis of the reports are published below. • Optical investigations of X-ray binary systems, A M Cherepashchuk Physics-Uspekhi, 2011, Volume 54, Number 10, Pages 1061-1067 • Asteroid and comet hazards: the role of physical sciences in solving the problem, B M Shustov Physics-Uspekhi, 2011, Volume 54, Number 10, Pages 1068-1071 • Search for cosmic strings using optical and radio astronomy methods, O S Sazhina, M V Sazhin, M Capaccioli, G Longo Physics-Uspekhi, 2011, Volume 54, Number 10, Pages 1072-1077 • Search for exoplanets using gravitational microlensing, A F Zakharov Physics-Uspekhi, 2011, Volume 54, Number 10, Pages 1077-1084

CONSTRAINING THE STRING GAUGE FIELD BY GALAXY ROTATION CURVES AND PERIHELION PRECESSION OF PLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheung, Yeuk-Kwan E.; Xu Feng, E-mail: cheung@nju.edu.cn

2013-09-01

We discuss a cosmological model in which the string gauge field coupled universally to matter gives rise to an extra centripetal force and will have observable signatures on cosmological and astronomical observations. Several tests are performed using data including galaxy rotation curves of 22 spiral galaxies of varied luminosities and sizes and perihelion precessions of planets in the solar system. The rotation curves of the same group of galaxies are independently fit using a dark matter model with the generalized Navarro-Frenk-White (NFW) profile and the string model. A remarkable fit of galaxy rotation curves is achieved using the one-parameter stringmore » model as compared to the three-parameter dark matter model with the NFW profile. The average {chi}{sup 2} value of the NFW fit is 9% better than that of the string model at a price of two more free parameters. Furthermore, from the string model, we can give a dynamical explanation for the phenomenological Tully-Fisher relation. We are able to derive a relation between field strength, galaxy size, and luminosity, which can be verified with data from the 22 galaxies. To further test the hypothesis of the universal existence of the string gauge field, we apply our string model to the solar system. Constraint on the magnitude of the string field in the solar system is deduced from the current ranges for any anomalous perihelion precession of planets allowed by the latest observations. The field distribution resembles a dipole field originating from the Sun. The string field strength deduced from the solar system observations is of a similar magnitude as the field strength needed to sustain the rotational speed of the Sun inside the Milky Way. This hypothesis can be tested further by future observations with higher precision.« less

Windings of twisted strings

NASA Astrophysics Data System (ADS)

Casali, Eduardo; Tourkine, Piotr

2018-03-01

Twistor string models have been known for more than a decade now but have come back under the spotlight recently with the advent of the scattering equation formalism which has greatly generalized the scope of these models. A striking ubiquitous feature of these models has always been that, contrary to usual string theory, they do not admit vibrational modes and thus describe only conventional field theory. In this paper we report on the surprising discovery of a whole new sector of one of these theories which we call "twisted strings," when spacetime has compact directions. We find that the spectrum is enhanced from a finite number of states to an infinite number of interacting higher spin massive states. We describe both bosonic and world sheet supersymmetric models, their spectra and scattering amplitudes. These models have distinctive features of both string and field theory, for example they are invariant under stringy T-duality but have the high energy behavior typical of field theory. Therefore they describe a new kind of field theories in target space, sitting on their own halfway between string and field theory.

Quarks, Symmetries and Strings - a Symposium in Honor of Bunji Sakita's 60th Birthday

NASA Astrophysics Data System (ADS)

Kaku, M.; Jevicki, A.; Kikkawa, K.

1991-04-01

The Table of Contents for the full book PDF is as follows: * Preface * Evening Banquet Speech * I. Quarks and Phenomenology * From the SU(6) Model to Uniqueness in the Standard Model * A Model for Higgs Mechanism in the Standard Model * Quark Mass Generation in QCD * Neutrino Masses in the Standard Model * Solar Neutrino Puzzle, Horizontal Symmetry of Electroweak Interactions and Fermion Mass Hierarchies * State of Chiral Symmetry Breaking at High Temperatures * Approximate |ΔI| = 1/2 Rule from a Perspective of Light-Cone Frame Physics * Positronium (and Some Other Systems) in a Strong Magnetic Field * Bosonic Technicolor and the Flavor Problem * II. Strings * Supersymmetry in String Theory * Collective Field Theory and Schwinger-Dyson Equations in Matrix Models * Non-Perturbative String Theory * The Structure of Non-Perturbative Quantum Gravity in One and Two Dimensions * Noncritical Virasoro Algebra of d < 1 Matrix Model and Quantized String Field * Chaos in Matrix Models ? * On the Non-Commutative Symmetry of Quantum Gravity in Two Dimensions * Matrix Model Formulation of String Field Theory in One Dimension * Geometry of the N = 2 String Theory * Modular Invariance form Gauge Invariance in the Non-Polynomial String Field Theory * Stringy Symmetry and Off-Shell Ward Identities * q-Virasoro Algebra and q-Strings * Self-Tuning Fields and Resonant Correlations in 2d-Gravity * III. Field Theory Methods * Linear Momentum and Angular Momentum in Quaternionic Quantum Mechanics * Some Comments on Real Clifford Algebras * On the Quantum Group p-adics Connection * Gravitational Instantons Revisited * A Generalized BBGKY Hierarchy from the Classical Path-Integral * A Quantum Generated Symmetry: Group-Level Duality in Conformal and Topological Field Theory * Gauge Symmetries in Extended Objects * Hidden BRST Symmetry and Collective Coordinates * Towards Stochastically Quantizing Topological Actions * IV. Statistical Methods * A Brief Summary of the s-Channel Theory of Superconductivity * Neural Networks and Models for the Brain * Relativistic One-Body Equations for Planar Particles with Arbitrary Spin * Chiral Property of Quarks and Hadron Spectrum in Lattice QCD * Scalar Lattice QCD * Semi-Superconductivity of a Charged Anyon Gas * Two-Fermion Theory of Strongly Correlated Electrons and Charge-Spin Separation * Statistical Mechanics and Error-Correcting Codes * Quantum Statistics

Modeling the influence of string collective phenomena on the long range rapidity correlations between the transverse momentum and the multiplicities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andronov, E.; Vechernin, V.

2016-01-22

The long-range rapidity correlations between the multiplicities (n-n) and the transverse momentum and the multiplicity (pT-n) of charge particles are analyzed in the framework of the simple string inspired model with two types of sources. The sources of the first type correspond to the initial strings formed in a hadronic collision. The sources of the second type imitate the appearance of the emitters of a new kind resulting from interaction (fusion) of the initial strings. The model enabled to describe effectively the influence of the string fusion effects on the strength both the n-n and the pT-n correlations. It wasmore » found that in the region, where the process of string fusion comes into play, the calculation results predict the non-monotonic behaviour of the n-n and pT-n correlation coefficients with the growth of the mean number of initial strings, i.e. with the increase of the collision centrality. It was shown also that the increase of the event-by-event fluctuation in the number of primary strings leads to the change of the pT-n correlation sign from negative to positive. One can try to search these signatures of string collective phenomena in interactions of various nuclei at different energies varying the class of collision centrality and its width.« less

The string prediction models as invariants of time series in the forex market

NASA Astrophysics Data System (ADS)

Pincak, R.

2013-12-01

In this paper we apply a new approach of string theory to the real financial market. The models are constructed with an idea of prediction models based on the string invariants (PMBSI). The performance of PMBSI is compared to support vector machines (SVM) and artificial neural networks (ANN) on an artificial and a financial time series. A brief overview of the results and analysis is given. The first model is based on the correlation function as invariant and the second one is an application based on the deviations from the closed string/pattern form (PMBCS). We found the difference between these two approaches. The first model cannot predict the behavior of the forex market with good efficiency in comparison with the second one which is, in addition, able to make relevant profit per year. The presented string models could be useful for portfolio creation and financial risk management in the banking sector as well as for a nonlinear statistical approach to data optimization.

String model for the dynamics of glass-forming liquids

PubMed Central

Pazmiño Betancourt, Beatriz A.; Douglas, Jack F.; Starr, Francis W.

2014-01-01

We test the applicability of a living polymerization theory to describe cooperative string-like particle rearrangement clusters (strings) observed in simulations of a coarse-grained polymer melt. The theory quantitatively describes the interrelation between the average string length L, configurational entropy Sconf, and the order parameter for string assembly Φ without free parameters. Combining this theory with the Adam-Gibbs model allows us to predict the relaxation time τ in a lower temperature T range than accessible by current simulations. In particular, the combined theories suggest a return to Arrhenius behavior near Tg and a low T residual entropy, thus avoiding a Kauzmann “entropy crisis.” PMID:24880303

String model for the dynamics of glass-forming liquids.

PubMed

Pazmiño Betancourt, Beatriz A; Douglas, Jack F; Starr, Francis W

2014-05-28

We test the applicability of a living polymerization theory to describe cooperative string-like particle rearrangement clusters (strings) observed in simulations of a coarse-grained polymer melt. The theory quantitatively describes the interrelation between the average string length L, configurational entropy Sconf, and the order parameter for string assembly Φ without free parameters. Combining this theory with the Adam-Gibbs model allows us to predict the relaxation time τ in a lower temperature T range than accessible by current simulations. In particular, the combined theories suggest a return to Arrhenius behavior near Tg and a low T residual entropy, thus avoiding a Kauzmann "entropy crisis."

Interaction with a field: a simple integrable model with backreaction

NASA Astrophysics Data System (ADS)

Mouchet, Amaury

2008-09-01

The classical model of an oscillator linearly coupled to a string captures, for a low price in technique, many general features of more realistic models for describing a particle interacting with a field or an atom in an electromagnetic cavity. The scattering matrix and the asymptotic in and out-waves on the string can be computed exactly and the phenomenon of resonant scattering can be introduced in the simplest way. The dissipation induced by the coupling of the oscillator to the string can be studied completely. In the case of a d'Alembert string, the backreaction leads to an Abraham-Lorentz-Dirac-like equation. In the case of a Klein-Gordon string, one can see explicitly how radiation governs the (meta)stability of the (quasi)bounded mode.

Confusing the heterotic string

NASA Astrophysics Data System (ADS)

Benett, D.; Brene, N.; Mizrachi, Leah; Nielsen, H. B.

1986-10-01

A confusion mechanism is proposed as a global modification of the heterotic string model. It envolves a confusion hypersurface across which the two E 8's of the heterotic string are permuted. A remarkable numerical coincidence is found which prevents an inconsistency in the model. The low energy limit of this theory (after compactification) is typically invariant under one E 8 only, thereby removing the shadow world from the original model.

An obstacle to building a time machine

NASA Astrophysics Data System (ADS)

Carroll, Sean M.; Farhi, Edward; Guth, Alan H.

1992-01-01

Gott (1991) has shown that a spacetime with two infinite parallel cosmic strings passing each other with sufficient velocity contains closed timelike curves. An attempt to build such a time machine is discussed. Using the energy-momentum conservation laws in the equivalent (2 + 1)-dimensional theory, the spacetime representing the decay of one gravitating particle into two is explicitly constructed; there is never enough mass in an open universe to build the time machine from the products of decays of stationary particles. More generally, the Gott time machine cannot exist in any open (2 + 1)-dimensional universe for which the total momentum is timelike.

Almost Classical Creation of a Universe

NASA Astrophysics Data System (ADS)

Guendelman, E. I.; Portnoy, J.

We study the problem of a 1+1 cord with a dynamical massless scalar field living in it, which separates a false vacuum and a conical region in a 2+1 space. A stable ``particle-like'' configuration can be found. Also, oscillating solutions exist which can tunnel to an expanding type solution. The most outstanding feature for these oscillating solution is that we do not need a singularity to create an infinite universe from them, and that an arbitrarily small tunneling is needed to achieve this. Possible consequences for similar processes, involving cosmic strings in 3+1 dimensions are discussed.

Fast spinning strings on η deformed AdS 5 × S 5

NASA Astrophysics Data System (ADS)

Banerjee, Aritra; Bhattacharyya, Arpan; Roychowdhury, Dibakar

2018-02-01

In this paper, considering the correspondence between spin chains and string sigma models, we explore the rotating string solutions over η deformed AdS 5 × S 5 in the so-called fast spinning limit. In our analysis, we focus only on the bosonic part of the full superstring action and compute the relevant limits on both ( R × S 3) η and ( R × S 5) η models. The resulting system reveals that in the fast spinning limit, the sigma model on η deformed S 5 could be approximately thought of as the continuum limit of anisotropic SU(3) Heisenberg spin chain model. We compute the energy for a certain class of spinning strings in deformed S 5 and we show that this energy can be mapped to that of a similar spinning string in the purely imaginary β deformed background.

Simulation of swimming strings immersed in a viscous fluid flow

NASA Astrophysics Data System (ADS)

Huang, Wei-Xi; Sung, Hyung Jin

2006-11-01

In nature, many phenomena involve interactions between flexible bodies and their surrounding viscous fluid, such as a swimming fish or a flapping flag. The intrinsic dynamics is complicate and not well understood. A flexible string can be regarded as a one-dimensional flag model. Many similarities can be found between the flapping string and swimming fish, although different wake speed results in a drag force for the flapping string and a propulsion force for the swimming fish. In the present study, we propose a mathematical formulation for swimming strings immersed in a viscous fluid flow. Fluid motion is governed by the Navier-Stokes equations and a momentum forcing is added in order to bring the fluid to move at the same velocity with the immersed surface. A flexible inextensible string model is described by another set of equations with an additional momentum forcing which is a result of the fluid viscosity and the pressure difference across the string. The momentum forcing is calculated by a feedback loop. Simulations of several numerical examples are carried out, including a hanging string which starts moving under gravity without ambient fluid, a swinging string immersed in a quiescent viscous fluid, a string swimming within a uniform surrounding flow, and flow over two side-by-side strings. The numerical results agree well with the theoretical analysis and previous experimental observations. Further simulation of a swimming fish is under consideration.

Cosmic dust synthesis by accretion and coagulation

NASA Technical Reports Server (NTRS)

Praburam, G.; Goree, J.

1995-01-01

The morphology of grains grown by accretion and coagulation is revaled by a new laboratory method of synthesizing cosmic dust analogs. Submicron carbon particles, grown by accretion of carbon atoms from a gas, have a spherical shape with a cauliflower-like surface and an internal micro-structure of radial columns. This shape is probably common for grains grown by accretion at a temperature well below the melting point. Coagulated grains, consisting of spheres that collided to form irregular strings, were also synthesized. Another shape we produced had a bumpy non- spherical morphology, like an interplanetary particle collected in the terrestrial stratosphere. Besides these isolated grains, large spongy aggregates of nanometer-size particles were also found for various experimental conditions. Grains were synthesized using ions to sputter a solid target, producing an atomic vapor at a low temperature. The ions were provided by a plasma, which also provided electrostatic levitation of the grains during their growth. The temporal development of grain growth was studied by extinguishing the plasma after various intervals.

CMB internal delensing with general optimal estimator for higher-order correlations

DOE PAGES

Namikawa, Toshiya

2017-05-24

We present here a new method for delensing B modes of the cosmic microwave background (CMB) using a lensing potential reconstructed from the same realization of the CMB polarization (CMB internal delensing). The B -mode delensing is required to improve sensitivity to primary B modes generated by, e.g., the inflationary gravitational waves, axionlike particles, modified gravity, primordial magnetic fields, and topological defects such as cosmic strings. However, the CMB internal delensing suffers from substantial biases due to correlations between observed CMB maps to be delensed and that used for reconstructing a lensing potential. Since the bias depends on realizations, wemore » construct a realization-dependent (RD) estimator for correcting these biases by deriving a general optimal estimator for higher-order correlations. The RD method is less sensitive to simulation uncertainties. Compared to the previous ℓ -splitting method, we find that the RD method corrects the biases without substantial degradation of the delensing efficiency.« less

Soft X-ray excess in the Coma cluster from a Cosmic Axion Background

DOE Office of Scientific and Technical Information (OSTI.GOV)

Angus, Stephen; Conlon, Joseph P.; Marsh, M.C. David

2014-09-01

We show that the soft X-ray excess in the Coma cluster can be explained by a cosmic background of relativistic axion-like particles (ALPs) converting into photons in the cluster magnetic field. We provide a detailed self-contained review of the cluster soft X-ray excess, the proposed astrophysical explanations and the problems they face, and explain how a 0.1- 1 keV axion background naturally arises at reheating in many string theory models of the early universe. We study the morphology of the soft excess by numerically propagating axions through stochastic, multi-scale magnetic field models that are consistent with observations of Faraday rotation measuresmore » from Coma. By comparing to ROSAT observations of the 0.2- 0.4 keV soft excess, we find that the overall excess luminosity is easily reproduced for g{sub aγγ} ∼ 2 × 10{sup -13} Ge {sup -1}. The resulting morphology is highly sensitive to the magnetic field power spectrum. For Gaussian magnetic field models, the observed soft excess morphology prefers magnetic field spectra with most power in coherence lengths on O(3 kpc) scales over those with most power on O(12 kpc) scales. Within this scenario, we bound the mean energy of the axion background to 50 eV∼< ( E{sub a} ) ∼< 250 eV, the axion mass to m{sub a} ∼< 10{sup -12} eV, and derive a lower bound on the axion-photon coupling g{sub aγγ} ∼> √(0.5/Δ N{sub eff}) 1.4 × 10{sup -13} Ge {sup -1}.« less

A note on probabilistic models over strings: the linear algebra approach.

PubMed

Bouchard-Côté, Alexandre

2013-12-01

Probabilistic models over strings have played a key role in developing methods that take into consideration indels as phylogenetically informative events. There is an extensive literature on using automata and transducers on phylogenies to do inference on these probabilistic models, in which an important theoretical question is the complexity of computing the normalization of a class of string-valued graphical models. This question has been investigated using tools from combinatorics, dynamic programming, and graph theory, and has practical applications in Bayesian phylogenetics. In this work, we revisit this theoretical question from a different point of view, based on linear algebra. The main contribution is a set of results based on this linear algebra view that facilitate the analysis and design of inference algorithms on string-valued graphical models. As an illustration, we use this method to give a new elementary proof of a known result on the complexity of inference on the "TKF91" model, a well-known probabilistic model over strings. Compared to previous work, our proving method is easier to extend to other models, since it relies on a novel weak condition, triangular transducers, which is easy to establish in practice. The linear algebra view provides a concise way of describing transducer algorithms and their compositions, opens the possibility of transferring fast linear algebra libraries (for example, based on GPUs), as well as low rank matrix approximation methods, to string-valued inference problems.

Book Review

NASA Astrophysics Data System (ADS)

Rickles, Dean

Although ostensibly a festschrift for Gabriele Veneziano, this book also marks an important step in the historical study of string theory, featuring several excellent chapters on the earliest period of string theory, as it emerged from the study of strong interaction physics and dual resonance models. Veneziano is often crowned 'the father of string theory' since it was he who discovered the amplitude that led to the dual resonance models that then led to string theory in something like the form we know it today (though not immediately into a quantum theory of gravity). However, as the historical articles in this book make plain, Veneziano was but a small (albeit vital) component in the creation of string theory.

String unification scale and the hyper-charge Kac-Moody level in the non-supersymmetric standard model

NASA Astrophysics Data System (ADS)

Cho, Gi-Chol; Hagiwara, Kaoru

1998-02-01

The string theory predicts the unification of the gauge couplings and gravity. The minimal supersymmetric Standard Model, however, gives the unification scale ~2x1016 GeV which is significantly smaller than the string scale ~5x1017 GeV of the weak coupling heterotic string theory. We study the unification scale of the non-supersymmetric minimal Standard Model quantitatively at the two-loop level. We find that the unification scale should be at most ~4x1016 GeV and the desired Kac-Moody level of the hyper-charge coupling should be 1.33<~kY<~1.35.

Coupled scalar fields in the late Universe: the mechanical approach and the late cosmic acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burgazli, Alvina; Zhuk, Alexander; Morais, João

In this paper, we consider the Universe at the late stage of its evolution and deep inside the cell of uniformity. At these scales, we consider the Universe to be filled with dust-like matter in the form of discretely distributed galaxies, a minimally coupled scalar field and radiation as matter sources. We investigate such a Universe in the mechanical approach. This means that the peculiar velocities of the inhomogeneities (in the form of galaxies) as well as fluctuations of other perfect fluids are non-relativistic. Such fluids are designated as coupled because they are concentrated around inhomogeneities. In the present papermore » we investigate the conditions under which a scalar field can become coupled, and show that, at the background level, such coupled scalar field behaves as a two component perfect fluid: a network of frustrated cosmic strings with EoS parameter w =-1/3 and a cosmological constant. The potential of this scalar field is very flat at the present time. Hence, the coupled scalar field can provide the late cosmic acceleration. The fluctuations of the energy density and pressure of this field are concentrated around the galaxies screening their gravitational potentials. Therefore, such scalar fields can be regarded as coupled to the inhomogeneities.« less

Matrix theory interpretation of discrete light cone quantization string worldsheets

PubMed

Grignani; Orland; Paniak; Semenoff

2000-10-16

We study the null compactification of type-IIA string perturbation theory at finite temperature. We prove a theorem about Riemann surfaces establishing that the moduli spaces of infinite-momentum-frame superstring worldsheets are identical to those of branched-cover instantons in the matrix-string model conjectured to describe M theory. This means that the identification of string degrees of freedom in the matrix model proposed by Dijkgraaf, Verlinde, and Verlinde is correct and that its natural generalization produces the moduli space of Riemann surfaces at all orders in the genus expansion.

Entanglement branes in a two-dimensional string theory

DOE PAGES

Donnelly, William; Wong, Gabriel

2017-09-20

What is the meaning of entanglement in a theory of extended objects such as strings? To address this question we consider the spatial entanglement between two intervals in the Gross-Taylor model, the string theory dual to two-dimensional Yang-Mills theory at large N. The string diagrams that contribute to the entanglement entropy describe open strings with endpoints anchored to the entangling surface, as first argued by Susskind. We develop a canonical theory of these open strings, and describe how closed strings are divided into open strings at the level of the Hilbert space. Here, we derive the modular Hamiltonian for themore » Hartle-Hawking state and show that the corresponding reduced density matrix describes a thermal ensemble of open strings ending on an object at the entangling surface that we call an entanglement brane, or E-brane.« less

Discrete symmetries in the heterotic-string landscape

NASA Astrophysics Data System (ADS)

Athanasopoulos, P.

2015-07-01

We describe a new type of discrete symmetry that relates heterotic-string models. It is based on the spectral flow operator which normally acts within a general N = (2, 2) model and we use this operator to construct a map between N = (2, 0) models. The landscape of N = (2, 0) models is of particular interest among all heterotic-string models for two important reasons: Firstly, N =1 spacetime SUSY requires (2, 0) superconformal invariance and secondly, models with the well motivated by the Standard Model SO(10) unification structure are of this type. This idea was inspired by a new discrete symmetry in the space of fermionic ℤ2 × ℤ2 heterotic-string models that exchanges the spinors and vectors of the SO(10) GUT group, dubbed spinor-vector duality. We will describe how to generalize this to arbitrary internal rational Conformal Field Theories.

Higher winding strings and confined monopoles in N=2 supersymmetric QCD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Auzzi, R.; Bolognesi, S.; Shifman, M.

2010-04-15

We consider composite string solutions in N=2 SQCD with the gauge group U(N), the Fayet-Iliopoulos term {xi}{ne}0 and N (s)quark flavors. These bulk theories support non-Abelian strings and confined monopoles identified with kinks in the two-dimensional world-sheet theory. Similar and more complicated kinks (corresponding to composite confined monopoles) must exist in the world-sheet theories on composite strings. In a bid to detect them we analyze the Hanany-Tong (HT) model, focusing on a particular example of N=2. Unequal quark mass terms in the bulk theory result in the twisted masses in the N=(2,2) HT model. For spatially coinciding 2-strings, we findmore » three distinct minima of potential energy, corresponding to three different 2-strings. Then we find BPS-saturated kinks interpolating between each pair of vacua. Two kinks can be called elementary. They emanate one unit of the magnetic flux and have the same mass as the conventional 't Hooft-Polyakov monopole on the Coulomb branch of the bulk theory ({xi}=0). The third kink represents a composite bimonopole, with twice the minimal magnetic flux. Its mass is twice the mass of the elementary confined monopole. We find instantons in the HT model, and discuss quantum effects in composite strings at strong coupling. In addition, we study the renormalization group flow in this model.« less

The effect of gas and fluid flows on nonlinear lateral vibrations of rotating drill strings

NASA Astrophysics Data System (ADS)

Khajiyeva, Lelya; Kudaibergenov, Askar; Kudaibergenov, Askat

2018-06-01

In this work we develop nonlinear mathematical models describing coupled lateral vibrations of a rotating drill string under the effect of external supersonic gas and internal fluid flows. An axial compressive load and a torque also affect the drill string. The mathematical models are derived by the use of Novozhilov's nonlinear theory of elasticity with implementation of Hamilton's variation principle. Expressions for the gas flow pressure are determined according to the piston theory. The fluid flow is considered as added mass inside the curved tube of the drill string. Using an algorithm developed in the Mathematica computation program on the basis of the Galerkin approach and the stiffness switching method the numerical solution of the obtained approximate differential equations is found. Influences of the external loads, drill string angular speed of rotation, parameters of the gas and fluid flows on the drill string vibrations are shown.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donnelly, William; Wong, Gabriel

What is the meaning of entanglement in a theory of extended objects such as strings? To address this question we consider the spatial entanglement between two intervals in the Gross-Taylor model, the string theory dual to two-dimensional Yang-Mills theory at large N. The string diagrams that contribute to the entanglement entropy describe open strings with endpoints anchored to the entangling surface, as first argued by Susskind. We develop a canonical theory of these open strings, and describe how closed strings are divided into open strings at the level of the Hilbert space. Here, we derive the modular Hamiltonian for themore » Hartle-Hawking state and show that the corresponding reduced density matrix describes a thermal ensemble of open strings ending on an object at the entangling surface that we call an entanglement brane, or E-brane.« less

String junction as a baryonic constituent

NASA Astrophysics Data System (ADS)

Kalashnikova, Yu. S.; Nefediev, A. V.

1996-02-01

We extend the model for QCD string with quarks to consider the Mercedes Benz string configuration describing the three-quark baryon. Under the assumption of adiabatic separation of quark and string junction motion we formulate and solve the classical equation of motion for the junction. We dare to quantize the motion of the junction, and discuss the impact of these modes on the baryon spectra.

Diffusion of massive particles around an Abelian-Higgs string

NASA Astrophysics Data System (ADS)

Saha, Abhisek; Sanyal, Soma

2018-03-01

We study the diffusion of massive particles in the space time of an Abelian Higgs string. The particles in the early universe plasma execute Brownian motion. This motion of the particles is modeled as a two dimensional random walk in the plane of the Abelian Higgs string. The particles move randomly in the space time of the string according to their geodesic equations. We observe that for certain values of their energy and angular momentum, an overdensity of particles is observed close to the string. We find that the string parameters determine the distribution of the particles. We make an estimate of the density fluctuation generated around the string as a function of the deficit angle. Though the thickness of the string is small, the length is large and the overdensity close to the string may have cosmological consequences in the early universe.

Wilsonian dark matter in string derived Z' model

NASA Astrophysics Data System (ADS)

Delle Rose, L.; Faraggi, A. E.; Marzo, C.; Rizos, J.

2017-09-01

The dark matter issue is among the most perplexing in contemporary physics. The problem is more enigmatic due to the wide range of possible solutions, ranging from the ultralight to the supermassive. String theory gives rise to plausible dark matter candidates due to the breaking of the non-Abelian grand unified theory (GUT) symmetries by Wilson lines. The physical spectrum then contains states that do not satisfy the quantization conditions of the unbroken GUT symmetry. Given that the Standard Model states are identified with broken GUT representations, and provided that any ensuing symmetry breakings are induced by components of GUT states, a remnant discrete symmetry remains that forbids the decay of the Wilsonian states. A class of such states are obtained in a heterotic-string-derived Z' model. The model exploits the spinor-vector duality symmetry, observed in the fermionic Z2×Z2 heterotic-string orbifolds, to generate a Z'∈E6 symmetry that may remain unbroken down to low energies. The E6 symmetry is broken at the string level with discrete Wilson lines. The Wilsonian dark matter candidates in the string-derived model are S O (10 ), and hence Standard Model, singlets and possess non-E6 U(1)Z' charges. Depending on the U(1)Z' breaking scale and the reheating temperature they give rise to different scenarios for the relic abundance, and are in accordance with the cosmological constraints.

Non-perturbative effects and wall-crossing from topological strings

NASA Astrophysics Data System (ADS)

Collinucci, Andrés; Soler, Pablo; Uranga, Angel M.

2009-11-01

We argue that the Gopakumar-Vafa interpretation of the topological string partition function can be used to compute and resum certain non-perturbative brane instanton effects of type II CY compactifications. In particular the topological string A-model encodes the non-perturbative corrections to the hypermultiplet moduli space metric from general D1/D(-1)-brane instantons in 4d Script N = 2 IIB models. We also discuss the reduction to 4d Script N = 1 by fluxes and/or orientifolds and/or D-branes, and the prospects to resum brane instanton contributions to non-perturbative superpotentials. We argue that the connection between non-perturbative effects and the topological string underlies the continuity of non-perturbative effects across lines of BPS stability. We also confirm this statement in mirror B-model matrix model examples, relating matrix model instantons to non-perturbative D-brane instantons. The computation of non-perturbative effects from the topological string requires a 3d circle compactification and T-duality, relating effects from particles and instantons, reminiscent of that involved in the physical derivation of the Kontsevich-Soibelmann wall-crossing formula.

Modeling Harpsichord Plucking: The Plectrum and the String

NASA Astrophysics Data System (ADS)

Perng, Jack; Rossing, Thomas; Smith, Julius

2011-11-01

The harpsichord is a plucked string keyboard instrument that was popular during the Renaissance and Baroque music eras. Although it was later replaced by the more expressive piano, it has mounted a comeback due to the early music movement today. A physical model of the harpsichord's plucking mechanism is presented, detailing the plectrum-string interaction which illustrates many aspects of the harpsichord's characteristic sound.

Note on tachyon moduli and closed strings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carneiro da Cunha, Bruno

2008-07-15

The collective behavior of the SL(2,R) covariant brane states of noncritical c=1 string theory, found in a previous work, is studied in the Fermi liquid approximation. It is found that such states mimic the coset WZW model, whereas only by further restrictions one recovers the double-scaling limit which was purported to be equivalent to closed string models. Another limit is proposed, inspired by the tachyon condensation ideas, where the spectrum is the same of two-dimensional string theory. We close by noting some strange connections between vacuum states of the theory in their different interpretations.

{Γ}-Convergence Analysis of a Generalized XY Model: Fractional Vortices and String Defects

NASA Astrophysics Data System (ADS)

Badal, Rufat; Cicalese, Marco; De Luca, Lucia; Ponsiglione, Marcello

2018-03-01

We propose and analyze a generalized two dimensional XY model, whose interaction potential has n weighted wells, describing corresponding symmetries of the system. As the lattice spacing vanishes, we derive by {Γ}-convergence the discrete-to-continuum limit of this model. In the energy regime we deal with, the asymptotic ground states exhibit fractional vortices, connected by string defects. The {Γ}-limit takes into account both contributions, through a renormalized energy, depending on the configuration of fractional vortices, and a surface energy, proportional to the length of the strings. Our model describes in a simple way several topological singularities arising in Physics and Materials Science. Among them, disclinations and string defects in liquid crystals, fractional vortices and domain walls in micromagnetics, partial dislocations and stacking faults in crystal plasticity.

Spontaneous knotting of an agitated string.

PubMed

Raymer, Dorian M; Smith, Douglas E

2007-10-16

It is well known that a jostled string tends to become knotted; yet the factors governing the "spontaneous" formation of various knots are unclear. We performed experiments in which a string was tumbled inside a box and found that complex knots often form within seconds. We used mathematical knot theory to analyze the knots. Above a critical string length, the probability P of knotting at first increased sharply with length but then saturated below 100%. This behavior differs from that of mathematical self-avoiding random walks, where P has been proven to approach 100%. Finite agitation time and jamming of the string due to its stiffness result in lower probability, but P approaches 100% with long, flexible strings. We analyzed the knots by calculating their Jones polynomials via computer analysis of digital photos of the string. Remarkably, almost all were identified as prime knots: 120 different types, having minimum crossing numbers up to 11, were observed in 3,415 trials. All prime knots with up to seven crossings were observed. The relative probability of forming a knot decreased exponentially with minimum crossing number and Möbius energy, mathematical measures of knot complexity. Based on the observation that long, stiff strings tend to form a coiled structure when confined, we propose a simple model to describe the knot formation based on random "braid moves" of the string end. Our model can qualitatively account for the observed distribution of knots and dependence on agitation time and string length.

Holographic cosmology from BIonic solutions

NASA Astrophysics Data System (ADS)

Sepehri, Alireza; Faizal, Mir; Setare, Mohammad Reza; Ali, Ahmed Farag

2017-02-01

In this paper, we will use a BIonic solution for analyzing the holographic cosmology. A BIonic solution is a configuration of a D3-brane and an anti-D3-brane connected by a wormhole, and holographic cosmology is a recent proposal to explain cosmic expansion by using the holographic principle. In our model, a BIonic configuration will be produced by the transition of fundamental black strings. The formation of a BIonic configuration will cause inflation. As the D3-brane moves away from the anti-D3-brane, the wormhole will get annihilated, and the inflation will end with the annihilation of this wormhole. However, it is possible for a D3-brane to collide with an anti-D3-brane. Such a collision will occur if the distance between the D3-brane and the anti-D3-brane reduces, and this will create tachyonic states. We will demonstrate that these tachyonic states will lead to the formation of a new wormhole, and this will cause acceleration of the universe before such a collision.

Reduced-Size Integer Linear Programming Models for String Selection Problems: Application to the Farthest String Problem.

PubMed

Zörnig, Peter

2015-08-01

We present integer programming models for some variants of the farthest string problem. The number of variables and constraints is substantially less than that of the integer linear programming models known in the literature. Moreover, the solution of the linear programming-relaxation contains only a small proportion of noninteger values, which considerably simplifies the rounding process. Numerical tests have shown excellent results, especially when a small set of long sequences is given.

Charged string loops in Reissner-Nordström black hole background

NASA Astrophysics Data System (ADS)

Oteev, Tursinbay; Kološ, Martin; Stuchlík, Zdeněk

2018-03-01

We study the motion of current carrying charged string loops in the Reissner-Nordström black hole background combining the gravitational and electromagnetic field. Introducing new electromagnetic interaction between central charge and charged string loop makes the string loop equations of motion to be non-integrable even in the flat spacetime limit, but it can be governed by an effective potential even in the black hole background. We classify different types of the string loop trajectories using effective potential approach, and we compare the innermost stable string loop positions with loci of the charged particle innermost stable orbits. We examine string loop small oscillations around minima of the string loop effective potential, and we plot radial profiles of the string loop oscillation frequencies for both the radial and vertical modes. We construct charged string loop quasi-periodic oscillations model and we compare it with observed data from microquasars GRO 1655-40, XTE 1550-564, and GRS 1915+105. We also study the acceleration of current carrying string loops along the vertical axis and the string loop ejection from RN black hole neighbourhood, taking also into account the electromagnetic interaction.

Tachyon and quintessence in brane worlds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chimento, Luis P.; Forte, Monica; Richarte, Martin G.

2009-04-15

Using tachyon or quintessence fields along with a barotropic fluid on the brane we examine the different cosmological stages in a Friedmann-Robertson-Walker universe, from the first radiation scenario to the later era dominated by cosmic string networks. We introduce a new algorithm to generalize previous works on exact solutions and apply it to study tachyon and quintessence fields localized on the brane. We also explore the low and high energy regimes of the solutions. Besides, we show that the tachyon and quintessence fields are driven by an inverse power law potential. Finally, we find several simple exacts solutions for tachyonmore » and/or quintessence fields.« less

A New String Model: NEXUS 3

NASA Astrophysics Data System (ADS)

Werner, K.; Liu, F. M.; Ostapchenko, S.; Pierog, T.

2004-11-01

After discussing conceptual problems with the conventional string model, we present a new approach, based on a theoretically consistent multiple scattering formalism. First results for proton-proton scattering at 158 GeV are discussed.

The structural dynamics of the American five-string banjo

NASA Astrophysics Data System (ADS)

Dickey, Joe

2003-11-01

The American five-string banjo is unique among musical instruments in that many significant parameters that effect tone are easily adjusted. This is probably why so many banjo players fiddle with their banjo. The instrument is a combination of canonical vibrating systems (strings, and a circular membrane) and therefore more amenable to analysis and modeling than most other musical instruments (e.g., the violin). Such an analysis is presented here. The model is a harmonically driven string which excites the other strings and a membrane under tension, causing the membrane to radiate sound. Three figures-of-merit, FOMs, are assumed. They are loudness, brightness, and decay of the sound. The effects of a number of parameters on the proposed FOMs are investigated. Among these are the loss factor and tension of the membrane, the mass of the bridge, and the location on the string of the excitation. It is noted that the calculated effects of the changes agree with generally accepted setup practices.

Retina as Reciprocal Spatial Fourier Transform Space Implies ``Wave-transformation'' Functions, String Theory, the Inappropriate Uncertainty Principle, and Predicts ``Quarked'' Protons.

NASA Astrophysics Data System (ADS)

Mc Leod, Roger David; Mc Leod, David M.

2007-10-01

Vision, via transform space: ``Nature behaves in a reciprocal way;' also, Rect x pressure-input sense-reports as Sinc p, indicating brain interprets reciprocal ``p'' space as object space. Use Mott's and Sneddon's Wave Mechanics and Its Applications. Wave transformation functions are strings of positron, electron, proton, and neutron; uncertainty is a semantic artifact. Neutrino-string de Broglie-Schr"odinger wave-function models for electron, positron, suggest three-quark models for protons, neutrons. Variably vibrating neutrino-quills of this model, with appropriate mass-energy, can be a vertical proton string, quills leftward; thread string circumferentially, forming three interlinked circles with ``overpasses''. Diameters are 2:1:2, center circle has quills radially outward; call it a down quark, charge --1/3, charge 2/3 for outward quills, the up quarks of outer circles. String overlap summations are nodes; nodes also far left and right. Strong nuclear forces may be --px. ``Dislodging" positron with neutrino switches quark-circle configuration to 1:2:1, `downers' outside. Unstable neutron charge is 0. Atoms build. With scale factors, retinal/vision's, and quantum mechanics,' spatial Fourier transforms/inverses are equivalent.

Noncommutative-geometry model for closed bosonic strings

NASA Technical Reports Server (NTRS)

Sen, Siddhartha; Holman, R.

1987-01-01

It is shown how Witten's (1986) noncommutative geometry may be extended to describe the closed bosonic string. For closed strings, an explicit representation is provided of the integral operator needed to construct an action and of an associative product on string fields. The proper choice of the action of the integral operator and the associative product in order to give rise to a reasonable theory is explained, and the consequences of such a choice are discussed. It is shown that the ghost numbers of the operator and associative product can be chosen arbitrarily for both open and closed strings, and that this construct can be used as an action for interacting closed bosonic strings.

Automated Systematic Generation and Exploration of Flat Direction Phenomenology in Free Fermionic Heterotic String Theory

NASA Astrophysics Data System (ADS)

Greenwald, Jared

Any good physical theory must resolve current experimental data as well as offer predictions for potential searches in the future. The Standard Model of particle physics, Grand Unied Theories, Minimal Supersymmetric Models and Supergravity are all attempts to provide such a framework. However, they all lack the ability to predict many of the parameters that each of the theories utilize. String theory may yield a solution to this naturalness (or self-predictiveness) problem as well as offer a unifed theory of gravity. Studies in particle physics phenomenology based on perturbative low energy analysis of various string theories can help determine the candidacy of such models. After a review of principles and problems leading up to our current understanding of the universe, we will discuss some of the best particle physics model building techniques that have been developed using string theory. This will culminate in the introduction of a novel approach to a computational, systematic analysis of the various physical phenomena that arise from these string models. We focus on the necessary assumptions, complexity and open questions that arise while making a fully-automated at direction analysis program.

String tightening as a self-organizing phenomenon.

PubMed

Banerjee, Bonny

2007-09-01

The phenomenon of self-organization has been of special interest to the neural network community throughout the last couple of decades. In this paper, we study a variant of the self-organizing map (SOM) that models the phenomenon of self-organization of the particles forming a string when the string is tightened from one or both of its ends. The proposed variant, called the string tightening self-organizing neural network (STON), can be used to solve certain practical problems, such as computation of shortest homotopic paths, smoothing paths to avoid sharp turns, computation of convex hull, etc. These problems are of considerable interest in computational geometry, robotics path-planning, artificial intelligence (AI) (diagrammatic reasoning), very large scale integration (VLSI) routing, and geographical information systems. Given a set of obstacles and a string with two fixed terminal points in a 2-D space, the STON model continuously tightens the given string until the unique shortest configuration in terms of the Euclidean metric is reached. The STON minimizes the total length of a string on convergence by dynamically creating and selecting feature vectors in a competitive manner. Proof of correctness of this anytime algorithm and experimental results obtained by its deployment have been presented in the paper.

Consistent cosmology with Higgs thermal inflation in a minimal extension of the MSSM

NASA Astrophysics Data System (ADS)

Hindmarsh, Mark; Jones, D. R. Timothy

2013-03-01

We consider a class of supersymmetric inflation models, in which minimal gauged F-term hybrid inflation is coupled renormalisably to the minimal supersymmetric standard model (MSSM), with no extra ingredients; we call this class the ``minimal hybrid inflationary supersymmetric standard model'' (MHISSM). The singlet inflaton couples to the Higgs as well as the waterfall fields, supplying the Higgs μ-term. We show how such models can exit inflation to a vacuum characterised by large Higgs vevs, whose vacuum energy is controlled by supersymmetry-breaking. The true ground state is reached after an intervening period of thermal inflation along the Higgs flat direction, which has important consequences for the cosmology of the F-term inflation scenario. The scalar spectral index is reduced, with a value of approximately 0.976 in the case where the inflaton potential is dominated by the 1-loop radiative corrections. The reheat temperature following thermal inflation is about 109 GeV, which solves the gravitino overclosure problem. A Higgs condensate reduces the cosmic string mass per unit length, rendering it compatible with the Cosmic Microwave Background constraints without tuning the inflaton coupling. With the minimal U(1)' gauge symmetry in the inflation sector, where one of the waterfall fields generates a right-handed neutrino mass, we investigate the Higgs thermal inflation scenario in three popular supersymmetry-breaking schemes: AMSB, GMSB and the CMSSM, focusing on the implications for the gravitino bound. In AMSB enough gravitinos can be produced to account for the observed dark matter abundance through decays into neutralinos. In GMSB we find an upper bound on the gravitino mass of about a TeV, while in the CMSSM the thermally generated gravitinos are sub-dominant. When Big Bang Nucleosynthesis constraints are taken into account, the unstable gravitinos of AMSB and the CMSSM must have a mass O(10) TeV or greater, while in GMSB we find an upper bound on the gravitino mass of O(1) TeV.

Adventures in heterotic string phenomenology

NASA Astrophysics Data System (ADS)

Dundee, George Benjamin

In this Dissertation, we consider three topics in the study of effective field theories derived from orbifold compactifications of the heterotic string. In Chapter 2 we provide a primer for those interested in building models based on orbifold compactifications of the heterotic string. In Chapter 3, we analyze gauge coupling unification in the context of heterotic strings on anisotropic orbifolds. This construction is very much analogous to effective five dimensional orbifold GUT field theories. Our analysis assumes three fundamental scales, the string scale, M S, a compactification scale, MC, and a mass scale for some of the vector-like exotics, MEX; the other exotics are assumed to get mass at MS. In the particular models analyzed, we show that gauge coupling unification is not possible with MEX = M C and in fact we require MEX << MC ˜ 3 x 1016 GeV. We find that about 10% of the parameter space has a proton lifetime (from dimension six gauge exchange) 1033 yr ≲ tau(p → pi0e+) ≲ 1036 yr, which is potentially observable by the next generation of proton decay experiments. 80% of the parameter space gives proton lifetimes below Super-K bounds. In Chapter 4, we examine the relationship between the string coupling constant, gSTRING, and the grand unified gauge coupling constant, alphaGUT, in the models of Chapter 3. We find that the requirement that the theory be perturbative provides a non-trivial constraint on these models. Interestingly, there is a correlation between the proton decay rate (due to dimension six operators) and the string coupling constant in this class of models. Finally, we make some comments concerning the extension of these models to the six (and higher) dimensional case. In Chapter 5, we discuss the issues of supersymmetry breaking and moduli stabilization within the context of E8 ⊗ E8 heterotic orbifold constructions and, in particular, we focus on the class of "mini-landscape" models. These theories contain a non-Abelian hidden gauge sector which generates a non-perturbative superpotential leading to supersymmetry breaking and moduli stabilization. We demonstrate this effect in a simple model which contains many of the features of the more general construction. In addition, we argue that once supersymmetry is broken in a restricted sector of the theory, then all moduli are stabilized by supergravity effects. Finally, we obtain the low energy superparticle spectrum resulting from this simple model.

``SO what Will you do if String Theory is WRONG?''

NASA Astrophysics Data System (ADS)

Emam, Moataz H.

2008-07-01

I briefly discuss the accomplishments of string theory that would survive a complete falsification of the theory as a model of nature and argue the possibility that such a survival may necessarily mean that string theory would become its own discipline, independently of both physics and mathematics.

Accelerating universe with time variation of G and Λ

NASA Astrophysics Data System (ADS)

Darabi, F.

2012-03-01

We study a gravitational model in which scale transformations play the key role in obtaining dynamical G and Λ. We take a non-scale invariant gravitational action with a cosmological constant and a gravitational coupling constant. Then, by a scale transformation, through a dilaton field, we obtain a new action containing cosmological and gravitational coupling terms which are dynamically dependent on the dilaton field with Higgs type potential. The vacuum expectation value of this dilaton field, through spontaneous symmetry breaking on the basis of anthropic principle, determines the time variations of G and Λ. The relevance of these time variations to the current acceleration of the universe, coincidence problem, Mach's cosmological coincidence and those problems of standard cosmology addressed by inflationary models, are discussed. The current acceleration of the universe is shown to be a result of phase transition from radiation toward matter dominated eras. No real coincidence problem between matter and vacuum energy densities exists in this model and this apparent coincidence together with Mach's cosmological coincidence are shown to be simple consequences of a new kind of scale factor dependence of the energy momentum density as ρ˜ a -4. This model also provides the possibility for a super fast expansion of the scale factor at very early universe by introducing exotic type matter like cosmic strings.

Fuzzy Dark Matter from Infrared Confining Dynamics

NASA Astrophysics Data System (ADS)

Davoudiasl, Hooman; Murphy, Christopher W.

2017-04-01

A very light boson of mass O (10-22) eV may potentially be a viable dark matter (DM) candidate, which can avoid phenomenological problems associated with cold DM. Such "fuzzy DM (FDM)" may naturally be an axion with a decay constant fa˜1 016- 1 018 GeV and a mass ma˜μ2/fa with μ ˜1 02 eV . Here, we propose a concrete model, where μ arises as a dynamical scale from infrared confining dynamics, analogous to QCD. Our model is an alternative to the usual approach of generating μ through string theoretic instanton effects. We outline the features of this scenario that result from various cosmological constraints. We find that those constraints are suggestive of a period of mild of inflation, perhaps from a strong first order phase transition, that reheats the standard model (SM) sector only. A typical prediction of our scenario, broadly speaking, is a larger effective number of neutrinos compared to the SM value Neff≈3 , as inferred from precision measurements of the cosmic microwave background. Some of the new degrees of freedom may be identified as "sterile neutrinos," which may be required to explain certain neutrino oscillation anomalies. Hence, aspects of our scenario could be testable in terrestrial experiments, which is a novelty of our FDM model.

Factorization of chiral string amplitudes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Yu-tin; Siegel, Warren; Yuan, Ellis Ye

We re-examine a closed-string model defined by altering the boundary conditions for one handedness of two-dimensional propagators in otherwise-standard string theory. We evaluate the amplitudes using Kawai-Lewellen-Tye factorization into open-string amplitudes. The only modification to standard string theory is effectively that the spacetime Minkowski metric changes overall sign in one open-string factor. This cancels all but a finite number of states: as found in earlier approaches, with enough supersymmetry (e.g., type II) the tree amplitudes reproduce those of the massless truncation of ordinary string theory. However, we now find for the other cases that additional fields, formerly thought to bemore » auxiliary, describe new spin-2 states at the two adjacent mass levels (tachyonic and tardyonic). The tachyon is always a ghost, but can be avoided in the heterotic case.« less

Factorization of chiral string amplitudes

DOE PAGES

Huang, Yu-tin; Siegel, Warren; Yuan, Ellis Ye

2016-09-16

We re-examine a closed-string model defined by altering the boundary conditions for one handedness of two-dimensional propagators in otherwise-standard string theory. We evaluate the amplitudes using Kawai-Lewellen-Tye factorization into open-string amplitudes. The only modification to standard string theory is effectively that the spacetime Minkowski metric changes overall sign in one open-string factor. This cancels all but a finite number of states: as found in earlier approaches, with enough supersymmetry (e.g., type II) the tree amplitudes reproduce those of the massless truncation of ordinary string theory. However, we now find for the other cases that additional fields, formerly thought to bemore » auxiliary, describe new spin-2 states at the two adjacent mass levels (tachyonic and tardyonic). The tachyon is always a ghost, but can be avoided in the heterotic case.« less

Bifurcation analysis and phase diagram of a spin-string model with buckled states.

PubMed

Ruiz-Garcia, M; Bonilla, L L; Prados, A

2017-12-01

We analyze a one-dimensional spin-string model, in which string oscillators are linearly coupled to their two nearest neighbors and to Ising spins representing internal degrees of freedom. String-spin coupling induces a long-range ferromagnetic interaction among spins that competes with a spin-spin antiferromagnetic coupling. As a consequence, the complex phase diagram of the system exhibits different flat rippled and buckled states, with first or second order transition lines between states. This complexity translates to the two-dimensional version of the model, whose numerical solution has been recently used to explain qualitatively the rippled to buckled transition observed in scanning tunneling microscopy experiments with suspended graphene sheets. Here we describe in detail the phase diagram of the simpler one-dimensional model and phase stability using bifurcation theory. This gives additional insight into the physical mechanisms underlying the different phases and the behavior observed in experiments.

Bifurcation analysis and phase diagram of a spin-string model with buckled states

NASA Astrophysics Data System (ADS)

Ruiz-Garcia, M.; Bonilla, L. L.; Prados, A.

2017-12-01

We analyze a one-dimensional spin-string model, in which string oscillators are linearly coupled to their two nearest neighbors and to Ising spins representing internal degrees of freedom. String-spin coupling induces a long-range ferromagnetic interaction among spins that competes with a spin-spin antiferromagnetic coupling. As a consequence, the complex phase diagram of the system exhibits different flat rippled and buckled states, with first or second order transition lines between states. This complexity translates to the two-dimensional version of the model, whose numerical solution has been recently used to explain qualitatively the rippled to buckled transition observed in scanning tunneling microscopy experiments with suspended graphene sheets. Here we describe in detail the phase diagram of the simpler one-dimensional model and phase stability using bifurcation theory. This gives additional insight into the physical mechanisms underlying the different phases and the behavior observed in experiments.

Higher dimensional strange quark matter solutions in self creation cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Şen, R., E-mail: ramazansen-1991@hotmail.com; Aygün, S., E-mail: saygun@comu.edu.tr

In this study, we have generalized the higher dimensional flat Friedmann-Robertson-Walker (FRW) universe solutions for a cloud of string with perfect fluid attached strange quark matter (SQM) in Self Creation Cosmology (SCC). We have obtained that the cloud of string with perfect fluid does not survive and the string tension density vanishes for this model. However, we get dark energy model for strange quark matter with positive density and negative pressure in self creation cosmology.

Modern Quantum Field Theory II - Proceeeings of the International Colloquium

NASA Astrophysics Data System (ADS)

Das, S. R.; Mandal, G.; Mukhi, S.; Wadia, S. R.

1995-08-01

The Table of Contents for the book is as follows: * Foreword * 1. Black Holes and Quantum Gravity * Quantum Black Holes and the Problem of Time * Black Hole Entropy and the Semiclassical Approximation * Entropy and Information Loss in Two Dimensions * Strings on a Cone and Black Hole Entropy (Abstract) * Boundary Dynamics, Black Holes and Spacetime Fluctuations in Dilation Gravity (Abstract) * Pair Creation of Black Holes (Abstract) * A Brief View of 2-Dim. String Theory and Black Holes (Abstract) * 2. String Theory * Non-Abelian Duality in WZW Models * Operators and Correlation Functions in c ≤ 1 String Theory * New Symmetries in String Theory * A Look at the Discretized Superstring Using Random Matrices * The Nested BRST Structure of Wn-Symmetries * Landau-Ginzburg Model for a Critical Topological String (Abstract) * On the Geometry of Wn Gravity (Abstract) * O(d, d) Tranformations, Marginal Deformations and the Coset Construction in WZNW Models (Abstract) * Nonperturbative Effects and Multicritical Behaviour of c = 1 Matrix Model (Abstract) * Singular Limits and String Solutions (Abstract) * BV Algebra on the Moduli Spaces of Riemann Surfaces and String Field Theory (Abstract) * 3. Condensed Matter and Statistical Mechanics * Stochastic Dynamics in a Deposition-Evaporation Model on a Line * Models with Inverse-Square Interactions: Conjectured Dynamical Correlation Functions of the Calogero-Sutherland Model at Rational Couplings * Turbulence and Generic Scale Invariance * Singular Perturbation Approach to Phase Ordering Dynamics * Kinetics of Diffusion-Controlled and Ballistically-Controlled Reactions * Field Theory of a Frustrated Heisenberg Spin Chain * FQHE Physics in Relativistic Field Theories * Importance of Initial Conditions in Determining the Dynamical Class of Cellular Automata (Abstract) * Do Hard-Core Bosons Exhibit Quantum Hall Effect? (Abstract) * Hysteresis in Ferromagnets * 4. Fundamental Aspects of Quantum Mechanics and Quantum Field Theory * Finite Quantum Physics and Noncommutative Geometry * Higgs as Gauge Field and the Standard Model * Canonical Quantisation of an Off-Conformal Theory * Deterministic Quantum Mechanics in One Dimension * Spin-Statistics Relations for Topological Geons in 2+1 Quantum Gravity * Generalized Fock Spaces * Geometrical Expression for Short Distance Singularities in Field Theory * 5. Mathematics and Quantum Field Theory * Knot Invariants from Quantum Field Theories * Infinite Grassmannians and Moduli Spaces of G-Bundles * A Review of an Algebraic Geometry Approach to a Model Quantum Field Theory on a Curve (Abstract) * 6. Integrable Models * Spectral Representation of Correlation Functions in Two-Dimensional Quantum Field Theories * On Various Avatars of the Pasquier Algebra * Supersymmetric Integrable Field Theories and Eight Vertex Free Fermion Models (Abstract) * 7. Lattice Field Theory * From Kondo Model and Strong Coupling Lattice QCD to the Isgur-Wise Function * Effective Confinement from a Logarithmically Running Coupling (Abstract)

Inflation in the standard cosmological model

NASA Astrophysics Data System (ADS)

Uzan, Jean-Philippe

2015-12-01

The inflationary paradigm is now part of the standard cosmological model as a description of its primordial phase. While its original motivation was to solve the standard problems of the hot big bang model, it was soon understood that it offers a natural theory for the origin of the large-scale structure of the universe. Most models rely on a slow-rolling scalar field and enjoy very generic predictions. Besides, all the matter of the universe is produced by the decay of the inflaton field at the end of inflation during a phase of reheating. These predictions can be (and are) tested from their imprint of the large-scale structure and in particular the cosmic microwave background. Inflation stands as a window in physics where both general relativity and quantum field theory are at work and which can be observationally studied. It connects cosmology with high-energy physics. Today most models are constructed within extensions of the standard model, such as supersymmetry or string theory. Inflation also disrupts our vision of the universe, in particular with the ideas of chaotic inflation and eternal inflation that tend to promote the image of a very inhomogeneous universe with fractal structure on a large scale. This idea is also at the heart of further speculations, such as the multiverse. This introduction summarizes the connections between inflation and the hot big bang model and details the basics of its dynamics and predictions. xml:lang="fr"

String limit of the isotropic Heisenberg chain in the four-particle sector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antipov, A. G., E-mail: aga2@csa.ru; Komarov, I. V., E-mail: ivkoma@rambler.r

2008-05-15

The quantum method of variable separation is applied to the spectral problem of the isotropic Heisenberg model. The Baxter difference equation is resolved by means of a special quasiclassical asymptotic expansion. States are identified by multiplicities of limiting values of the Bethe parameters. The string limit of the four-particle sector is investigated. String solutions are singled out and classified. It is shown that only a minor fraction of solutions demonstrate string behavior.

Galileon string measure and other modified measure extended objects

NASA Astrophysics Data System (ADS)

Vulfs, T. O.; Guendelman, E. I.

2017-12-01

We show that it is possible to formulate string theory as a “Galileon string theory”. The Galileon field χ enters in the definition of the integration measure in the action. Following the methods of the modified measure string theory, we find that the final equations are again those of the sigma-model. Moreover, the string tension appears again as an additional dynamical degree of freedom. At the same time, the theory satisfies all requirements of the Galileon higher derivative theory at the action level while the equations of motion are still of the second-order. A Galileon symmetry is displayed explicitly in the conformal string worldsheet frame. Also, we define the Galileon gauge transformations. Generalizations to branes with other modified measures are discussed.

Actomyosin purse strings: renewable resources that make morphogenesis robust and resilient

PubMed Central

Rodriguez-Diaz, Alice; Toyama, Yusuke; Abravanel, Daniel L.; Wiemann, John M.; Wells, Adrienne R.; Tulu, U. Serdar; Edwards, Glenn S.; Kiehart, Daniel P.

2008-01-01

Dorsal closure in Drosophila is a model system for cell sheet morphogenesis and wound healing. During closure two sheets of lateral epidermis move dorsally to close over the amnioserosa and form a continuous epidermis. Forces from the amnioserosa and actomyosin-rich, supracellular purse strings at the leading edges of these lateral epidermal sheets drive closure. Purse strings generate the largest force for closure and occur during development and wound healing throughout phylogeny. We use laser microsurgery to remove some or all of the purse strings from developing embryos. Free edges produced by surgery undergo characteristic responses as follows. Intact cells in the free edges, which previously had no purse string, recoil away from the incision and rapidly assemble new, secondary purse strings. Next, recoil slows, then pauses at a turning point. Following a brief delay, closure resumes and is powered to completion by the secondary purse strings. We confirm that the assembly of the secondary purse strings requires RhoA. We show that α-actinin alternates with nonmuscle myosin II along purse strings and requires nonmuscle myosin II for its localization. Together our data demonstrate that purse strings are renewable resources that contribute to the robust and resilient nature of closure. PMID:19404432

Linear stiff string vibrations in musical acoustics: Assessment and comparison of models.

PubMed

Ducceschi, Michele; Bilbao, Stefan

2016-10-01

Strings are amongst the most common elements found in musical instruments and an appropriate physical description of string dynamics is essential to modelling, analysis, and simulation. For linear vibration in a single polarisation, the most common model is based on the Euler-Bernoulli beam equation under tension. In spite of its simple form, such a model gives unbounded phase and group velocities at large wavenumbers, and such behaviour may be interpreted as unphysical. The Timoshenko model has, therefore, been employed in more recent works to overcome such shortcoming. This paper presents a third model based on the shear beam equations. The three models are here assessed and compared with regard to the perceptual considerations in musical acoustics.

Moduli space potentials for heterotic non-Abelian flux tubes: Weak deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shifman, M.; Yung, A.; Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg 188300

2010-09-15

We consider N=2 supersymmetric QCD with the U(N) gauge group (with no Fayet-Iliopoulos term) and N{sub f} flavors of massive quarks deformed by the mass term {mu} for the adjoint matter, W={mu}A{sup 2}, assuming that N{<=}N{sub f}<2N. This deformation breaks N=2 supersymmetry down to N=1. This theory supports non-Abelian flux tubes (strings) which are stabilized by W. They are referred to as F-term stabilized strings. We focus on the studies of such strings in the vacuum in which N squarks condense, at small {mu}, so that the Z{sub N} strings preserve, in a sense, their Bogomol'nyi-Prasad-Sommerfield nature. The (s)quark massesmore » are assumed to be nondegenerate. We calculate string tensions both in the classical and quantum regimes. Then we translate our results for the tensions in terms of the effective low-energy weighted CP(N{sub f}-1) model on the string world sheet. The bulk {mu} deformation makes this theory N=(0,2) supersymmetric heterotic weighted CP(N{sub f}-1) model in two dimensions. We find the deformation potential on the world sheet. This significantly expands the class of the heterotically deformed CP models emerging on the string world sheet compared to that suggested by Edalati and Tong. Among other things, we show that nonperturbative quantum effects in the bulk theory are exactly reproduced by the quantum effects in the world-sheet theory.« less

Nonlinearity of the forward-backward correlation function in the model with string fusion

NASA Astrophysics Data System (ADS)

Vechernin, Vladimir

2017-12-01

The behavior of the forward-backward correlation functions and the corresponding correlation coefficients between multiplicities and transverse momenta of particles produced in high energy hadronic interactions is analyzed by analytical and MC calculations in the models with and without string fusion. The string fusion is taking into account in simplified form by introducing the lattice in the transverse plane. The results obtained with two alternative definitions of the forward-backward correlation coefficient are compared. It is shown that the nonlinearity of correlation functions increases with the width of observation windows, leading at small string density to a strong dependence of correlation coefficient value on the definition. The results of the modeling enable qualitatively to explain the experimentally observed features in the behavior of the correlation functions between multiplicities and mean transverse momenta at small and large multiplicities.

Dualities in CHL-models

NASA Astrophysics Data System (ADS)

Persson, Daniel; Volpato, Roberto

2018-04-01

We define a very general class of CHL-models associated with any string theory S (bosonic or supersymmetric) compactified on an internal CFT C× Td . We take the orbifold by a pair (g, δ) , where g is a (possibly non-geometric) symmetry of C and δ is a translation along T n . We analyze the T-dualities of these models and show that in general they contain Atkin–Lehner type symmetries. This generalizes our previous work on N=4 CHL-models based on heterotic string theory on T 6 or type II on K3× T2 , as well as the ‘monstrous’ CHL-models based on a compactification of heterotic string theory on the Frenkel–Lepowsky–Meurman CFT V\

Non-perturbative String Theory from Water Waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iyer, Ramakrishnan; Johnson, Clifford V.; /Southern California U.

2012-06-14

We use a combination of a 't Hooft limit and numerical methods to find non-perturbative solutions of exactly solvable string theories, showing that perturbative solutions in different asymptotic regimes are connected by smooth interpolating functions. Our earlier perturbative work showed that a large class of minimal string theories arise as special limits of a Painleve IV hierarchy of string equations that can be derived by a similarity reduction of the dispersive water wave hierarchy of differential equations. The hierarchy of string equations contains new perturbative solutions, some of which were conjectured to be the type IIA and IIB string theoriesmore » coupled to (4, 4k ? 2) superconformal minimal models of type (A, D). Our present paper shows that these new theories have smooth non-perturbative extensions. We also find evidence for putative new string theories that were not apparent in the perturbative analysis.« less

Walking tree heuristics for biological string alignment, gene location, and phylogenies

NASA Astrophysics Data System (ADS)

Cull, P.; Holloway, J. L.; Cavener, J. D.

1999-03-01

Basic biological information is stored in strings of nucleic acids (DNA, RNA) or amino acids (proteins). Teasing out the meaning of these strings is a central problem of modern biology. Matching and aligning strings brings out their shared characteristics. Although string matching is well-understood in the edit-distance model, biological strings with transpositions and inversions violate this model's assumptions. We propose a family of heuristics called walking trees to align biologically reasonable strings. Both edit-distance and walking tree methods can locate specific genes within a large string when the genes' sequences are given. When we attempt to match whole strings, the walking tree matches most genes, while the edit-distance method fails. We also give examples in which the walking tree matches substrings even if they have been moved or inverted. The edit-distance method was not designed to handle these problems. We include an example in which the walking tree "discovered" a gene. Calculating scores for whole genome matches gives a method for approximating evolutionary distance. We show two evolutionary trees for the picornaviruses which were computed by the walking tree heuristic. Both of these trees show great similarity to previously constructed trees. The point of this demonstration is that WHOLE genomes can be matched and distances calculated. The first tree was created on a Sequent parallel computer and demonstrates that the walking tree heuristic can be efficiently parallelized. The second tree was created using a network of work stations and demonstrates that there is suffient parallelism in the phylogenetic tree calculation that the sequential walking tree can be used effectively on a network.

Cosmological perturbations of axion with a dynamical decay constant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kobayashi, Takeshi; INFN, Sezione di Trieste,Via Bonomea 265, 34136 Trieste; Takahashi, Fuminobu

2016-08-25

A QCD axion with a time-dependent decay constant has been known to be able to accommodate high-scale inflation without producing topological defects or too large isocurvature perturbations on CMB scales. We point out that a dynamical decay constant also has the effect of enhancing the small-scale axion isocurvature perturbations. The enhanced axion perturbations can even exceed the periodicity of the axion potential, and thus lead to the formation of axionic domain walls. Unlike the well-studied axionic walls, the walls produced from the enhanced perturbations are not bounded by cosmic strings, and thus would overclose the universe independently of the numbermore » of degenerate vacua along the axion potential.« less

Physical and geometrical aspects of de sitter interior of a gravastar

NASA Astrophysics Data System (ADS)

Morawiec, Pawel Jan

The principal motivation for the investigations reported in this thesis is the gravastar model for physical black holes. According to this model the final state of the gravitational collapse of cold super-dense stars with the mass greater than some critical value is a non-singular object called a gravastar. This thesis presents results related to the various aspects of the de Sitter interior of a gravastar. The main object of the research was a generalized rotating interior of a gravastar. It was shown that the rotation, characterized by the vorticity, is localized on the vortex line. The metric under considerations is the de Sitter metric, however in some variant of the oblate spheroidal coordinates. Additionally a cosmic string on the rotation axis is present. This new result is the de Sitter version of the Mazur string, which was obtained from the four dimensional Levi-Civita metric as the generalization of the three-dimensional cosmic string by Adler and Jackiw. Also, using analogy between rotation in the superfluid and the magnetic field we gave another example of the Cosmic No Hair Theorem, this time "no magnetic fields in de Sitter space". But we also have shown that when the de Sitter event horizon is replaced by a thin shell (with a finite thickness), as it is in the gravastar model, the non-vanishing magnetic field could be present. To our knowledge these are new results. In this thesis we have studied behavior of the massless Dirac field as an example of a matter field in the de Sitter spacetime in the vicinity of an event horizon. We found convenient to work in the frame of the optical geometry of the de Sitter space as it is related to the metric in the static coordinates through a conformal Weyl rescaling and the dynamics of the massless Dirac fields is conformally invariant. The fact that the spatial part of the metric in the optical geometry of de Sitter space is the constant negative curvature Lobachevski space (the Euclidean ant-de Sitter space) suggested the existenc of the emerging de Sitter quantum field theory and conformal field theory correspondence on the de Sitter event horizon. We have studied implications of this conjecture. According to the AdS/CFT correspondence prescription the functional integral over the matter fields described by the action with the properly chosen boundary terms defining the so called partition function as the functional of the boundary values of the matter fields is also the generating functional for the correlation functions in the conformal field theory on the boundary of AdS space. In the case of the optical geometry of the de Sitter space the boundary is the event horizon that is the boundary of its Lobachevski spatial part times time. We have chosen the action for the massless Dirac fields in the optical de Sitter geometry with appropriate surface term and subsequently we have evaluated the real time partition function as the functional of the carefully defined boundary values of the Dirac field. It turns out that this partition functional can be, indeed, interpreted as the generating functional of the real time conformal field theory correlation functions of the fermionic operators, dual to the fermionic fields on the boundary. This means that the conformal field theory correlation functions are evaluated as the vacuum expectation values of the chronologically ordered fermionic operator. This result demonstrates the emergence of the de Sitter/Conformal field theory correspondence on the de Sitter horizon. The presence of the negative curvature Lobachevski geometry in the spatial part of the optical geometry of the de Sitter space, is responsible for the effective one-dimensional behavior of the matter degrees of freedom and of the emergence of the de Sitter/Conformal field theory correspondence on the event horizon. Although we have demonstrated the existence of this correspondence for the fermionic fields only, we anticipate this result to be valid generally.

Love Kills:. Simulations in Penna Ageing Model

NASA Astrophysics Data System (ADS)

Stauffer, Dietrich; Cebrat, Stanisław; Penna, T. J. P.; Sousa, A. O.

The standard Penna ageing model with sexual reproduction is enlarged by adding additional bit-strings for love: Marriage happens only if the male love strings are sufficiently different from the female ones. We simulate at what level of required difference the population dies out.

Evolution of the mean jet shape and dijet asymmetry distribution of an ensemble of holographic jets in strongly coupled plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brewer, Jasmine; Rajagopal, Krishna; Sadofyev, Andrey

Some of the most important experimentally accessible probes of the quark- gluon plasma (QGP) produced in heavy ion collisions come from the analysis of how the shape and energy of sprays of energetic particles produced within a cone with a specified opening angle (jets) in a hard scattering are modified by their passage through the strongly coupled, liquid, QGP. We model an ensemble of back-to-back dijets for the purpose of gaining a qualitative understanding of how the shapes of the individual jets and the asymmetry in the energy of the pairs of jets in the ensemble are modified by theirmore » passage through an expanding cooling droplet of strongly coupled plasma, in the model in a holographic gauge theory that is dual to a 4+1-dimensional black-hole spacetime that is asymptotically anti-de Sitter (AdS). We build our model by constructing an ensemble of strings in the dual gravitational description of the gauge theory. We model QCD jets in vacuum using strings whose endpoints are moving “downward” into the gravitational bulk spacetime with some fixed small angle, an angle that represents the opening angle (ratio of jet mass to jet energy) that the QCD jet would have in vacuum. Such strings must be moving through the gravitational bulk at (close to) the speed of light; they must be (close to) null. This condition does not specify the energy distribution along the string, meaning that it does not specify the shape of the jet being modeled. We study the dynamics of strings that are initially not null and show that strings with a wide range of initial conditions rapidly accelerate and become null and, as they do, develop a similar distribution of their energy density. We use this distribution of the energy density along the string, choose an ensemble of strings whose opening angles and energies are distributed as in perturbative QCD, and show that we can then fix one of the two model parameters such that the mean jet shape for the jets in the ensemble that we have built matches that measured in proton-proton collisions reasonably well. This is a novel way for hybridizing relevant inputs from perturbative QCD and a strongly coupled holographic gauge theory in the service of modeling jets in QGP. We send our ensemble of strings through an expanding cooling droplet of strongly coupled plasma, choosing the second model parameter so as to get a reasonable value for R AA jet , the suppression in the number of jets, and study how the mean jet shape and the dijet asymmetry are modified, comparing both to measurements from heavy ion collisions at the LHC.« less

Evolution of the mean jet shape and dijet asymmetry distribution of an ensemble of holographic jets in strongly coupled plasma

DOE PAGES

Brewer, Jasmine; Rajagopal, Krishna; Sadofyev, Andrey; ...

2018-02-02

Some of the most important experimentally accessible probes of the quark- gluon plasma (QGP) produced in heavy ion collisions come from the analysis of how the shape and energy of sprays of energetic particles produced within a cone with a specified opening angle (jets) in a hard scattering are modified by their passage through the strongly coupled, liquid, QGP. We model an ensemble of back-to-back dijets for the purpose of gaining a qualitative understanding of how the shapes of the individual jets and the asymmetry in the energy of the pairs of jets in the ensemble are modified by theirmore » passage through an expanding cooling droplet of strongly coupled plasma, in the model in a holographic gauge theory that is dual to a 4+1-dimensional black-hole spacetime that is asymptotically anti-de Sitter (AdS). We build our model by constructing an ensemble of strings in the dual gravitational description of the gauge theory. We model QCD jets in vacuum using strings whose endpoints are moving “downward” into the gravitational bulk spacetime with some fixed small angle, an angle that represents the opening angle (ratio of jet mass to jet energy) that the QCD jet would have in vacuum. Such strings must be moving through the gravitational bulk at (close to) the speed of light; they must be (close to) null. This condition does not specify the energy distribution along the string, meaning that it does not specify the shape of the jet being modeled. We study the dynamics of strings that are initially not null and show that strings with a wide range of initial conditions rapidly accelerate and become null and, as they do, develop a similar distribution of their energy density. We use this distribution of the energy density along the string, choose an ensemble of strings whose opening angles and energies are distributed as in perturbative QCD, and show that we can then fix one of the two model parameters such that the mean jet shape for the jets in the ensemble that we have built matches that measured in proton-proton collisions reasonably well. This is a novel way for hybridizing relevant inputs from perturbative QCD and a strongly coupled holographic gauge theory in the service of modeling jets in QGP. We send our ensemble of strings through an expanding cooling droplet of strongly coupled plasma, choosing the second model parameter so as to get a reasonable value for R AA jet , the suppression in the number of jets, and study how the mean jet shape and the dijet asymmetry are modified, comparing both to measurements from heavy ion collisions at the LHC.« less

Evolution of the mean jet shape and dijet asymmetry distribution of an ensemble of holographic jets in strongly coupled plasma

NASA Astrophysics Data System (ADS)

Brewer, Jasmine; Rajagopal, Krishna; Sadofyev, Andrey; van der Schee, Wilke

2018-02-01

Some of the most important experimentally accessible probes of the quark- gluon plasma (QGP) produced in heavy ion collisions come from the analysis of how the shape and energy of sprays of energetic particles produced within a cone with a specified opening angle (jets) in a hard scattering are modified by their passage through the strongly coupled, liquid, QGP. We model an ensemble of back-to-back dijets for the purpose of gaining a qualitative understanding of how the shapes of the individual jets and the asymmetry in the energy of the pairs of jets in the ensemble are modified by their passage through an expanding cooling droplet of strongly coupled plasma, in the model in a holographic gauge theory that is dual to a 4+1-dimensional black-hole spacetime that is asymptotically anti-de Sitter (AdS). We build our model by constructing an ensemble of strings in the dual gravitational description of the gauge theory. We model QCD jets in vacuum using strings whose endpoints are moving "downward" into the gravitational bulk spacetime with some fixed small angle, an angle that represents the opening angle (ratio of jet mass to jet energy) that the QCD jet would have in vacuum. Such strings must be moving through the gravitational bulk at (close to) the speed of light; they must be (close to) null. This condition does not specify the energy distribution along the string, meaning that it does not specify the shape of the jet being modeled. We study the dynamics of strings that are initially not null and show that strings with a wide range of initial conditions rapidly accelerate and become null and, as they do, develop a similar distribution of their energy density. We use this distribution of the energy density along the string, choose an ensemble of strings whose opening angles and energies are distributed as in perturbative QCD, and show that we can then fix one of the two model parameters such that the mean jet shape for the jets in the ensemble that we have built matches that measured in proton-proton collisions reasonably well. This is a novel way for hybridizing relevant inputs from perturbative QCD and a strongly coupled holographic gauge theory in the service of modeling jets in QGP. We send our ensemble of strings through an expanding cooling droplet of strongly coupled plasma, choosing the second model parameter so as to get a reasonable value for R AA jet , the suppression in the number of jets, and study how the mean jet shape and the dijet asymmetry are modified, comparing both to measurements from heavy ion collisions at the LHC.

Axions, Inflation and String Theory

NASA Astrophysics Data System (ADS)

Mack, Katherine J.; Steinhardt, P. J.

2009-01-01

The QCD axion is the leading contender to rid the standard model of the strong-CP problem. If the Peccei-Quinn symmetry breaking occurs before inflation, which is likely in string theory models, axions manifest themselves cosmologically as a form of cold dark matter with a density determined by the axion's initial conditions and by the energy scale of inflation. Constraints on the dark matter density and on the amplitude of CMB isocurvature perturbations currently demand an exponential degree of fine-tuning of both axion and inflationary parameters beyond what is required for particle physics. String theory models generally produce large numbers of axion-like fields; the prospect that any of these fields exist at scales close to that of the QCD axion makes the problem drastically worse. I will discuss the challenge of accommodating string-theoretic axions in standard inflationary cosmology and show that the fine-tuning problems cannot be fully addressed by anthropic principle arguments.

Sv-map between type I and heterotic sigma models

NASA Astrophysics Data System (ADS)

Fan, Wei; Fotopoulos, A.; Stieberger, S.; Taylor, T. R.

2018-05-01

The scattering amplitudes of gauge bosons in heterotic and open superstring theories are related by the single-valued projection which yields heterotic amplitudes by selecting a subset of multiple zeta value coefficients in the α‧ (string tension parameter) expansion of open string amplitudes. In the present work, we argue that this relation holds also at the level of low-energy expansions (or individual Feynman diagrams) of the respective effective actions, by investigating the beta functions of two-dimensional sigma models describing world-sheets of open and heterotic strings. We analyze the sigma model Feynman diagrams generating identical effective action terms in both theories and show that the heterotic coefficients are given by the single-valued projection of the open ones. The single-valued projection appears as a result of summing over all radial orderings of heterotic vertices on the complex plane representing string world-sheet.

Reconstruction of piano hammer force from string velocity.

PubMed

Chaigne, Antoine

2016-11-01

A method is presented for reconstructing piano hammer forces through appropriate filtering of the measured string velocity. The filter design is based on the analysis of the pulses generated by the hammer blow and propagating along the string. In the five lowest octaves, the hammer force is reconstructed by considering two waves only: the incoming wave from the hammer and its first reflection at the front end. For the higher notes, four- or eight-wave schemes must be considered. The theory is validated on simulated string velocities by comparing imposed and reconstructed forces. The simulations are based on a nonlinear damped stiff string model previously developed by Chabassier, Chaigne, and Joly [J. Acoust. Soc. Am. 134(1), 648-665 (2013)]. The influence of absorption, dispersion, and amplitude of the string waves on the quality of the reconstruction is discussed. Finally, the method is applied to real piano strings. The measured string velocity is compared to the simulated velocity excited by the reconstructed force, showing a high degree of accuracy. A number of simulations are compared to simulated strings excited by a force derived from measurements of mass and acceleration of the hammer head. One application to an historic piano is also presented.

Anisotropic string cosmological model in Brans–Dicke theory of gravitation with time-dependent deceleration parameter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maurya, D. Ch., E-mail: dcmaurya563@gmail.com; Zia, R., E-mail: rashidzya@gmail.com; Pradhan, A., E-mail: pradhan.anirudh@gmail.com

We discuss a spatially homogeneous and anisotropic string cosmological models in the Brans–Dicke theory of gravitation. For a spatially homogeneous metric, it is assumed that the expansion scalar θ is proportional to the shear scalar σ. This condition leads to A = kB{sup m}, where k and m are constants. With these assumptions and also assuming a variable scale factor a = a(t), we find solutions of the Brans–Dicke field equations. Various phenomena like the Big Bang, expanding universe, and shift from anisotropy to isotropy are observed in the model. It can also be seen that in early stage ofmore » the evolution of the universe, strings dominate over particles, whereas the universe is dominated by massive strings at the late time. Some physical and geometrical behaviors of the models are also discussed and observed to be in good agreement with the recent observations of SNe la supernovae.« less

Connecting the ambitwistor and the sectorized heterotic strings

NASA Astrophysics Data System (ADS)

Azevedo, Thales; Jusinskas, Renann Lipinski

2017-10-01

The sectorized description of the (chiral) heterotic string using pure spinors has been misleadingly viewed as an infinite tension string. One evidence for this fact comes from the tree level 3-point graviton amplitude, which we show to contain the usual Einstein term plus a higher curvature contribution. After reintroducing a dimensionful parameter ℓ in the theory, we demonstrate that the heterotic model is in fact two-fold, depending on the choice of the supersymmetric sector, and that the spectrum also contains one massive (open string like) multiplet. By taking the limit ℓ → ∞, we finally show that the ambitwistor string is recovered, reproducing the unexpected heterotic state in Mason and Skinner's RNS description.

The Atacama Cosmology Telescope: Cosmological Parameters from the 2008 Power Spectrum

NASA Technical Reports Server (NTRS)

Dunkley, J.; Hlozek, R.; Sievers, J.; Acquaviva, V.; Ade, P. A. R.; Aguirre, P.; Amiri, M.; Appel, J. W.; Barrientos, L. F.; Battistelli, E. S.;

String tensions in deformed Yang-Mills theory

NASA Astrophysics Data System (ADS)

Poppitz, Erich; Shalchian T., M. Erfan

2018-01-01

We study k-strings in deformed Yang-Mills (dYM) with SU(N) gauge group in the semiclassically calculable regime on R^3× S^1 . Their tensions Tk are computed in two ways: numerically, for 2 ≤ N ≤ 10, and via an analytic approach using a re-summed perturbative expansion. The latter serves both as a consistency check on the numerical results and as a tool to analytically study the large-N limit. We find that dYM k-string ratios Tk/T1 do not obey the well-known sine- or Casimir-scaling laws. Instead, we show that the ratios Tk/T1 are bound above by a square root of Casimir scaling, previously found to hold for stringlike solutions of the MIT Bag Model. The reason behind this similarity is that dYM dynamically realizes, in a theoretically controlled setting, the main model assumptions of the Bag Model. We also compare confining strings in dYM and in other four-dimensional theories with abelian confinement, notably Seiberg-Witten theory, and show that the unbroken Z_N center symmetry in dYM leads to different properties of k-strings in the two theories; for example, a "baryon vertex" exists in dYM but not in softly-broken Seiberg-Witten theory. Our results also indicate that, at large values of N, k-strings in dYM do not become free.

Accidental Kähler moduli inflation

NASA Astrophysics Data System (ADS)

Maharana, Anshuman; Rummel, Markus; Sumitomo, Yoske

2015-09-01

We study a model of accidental inflation in type IIB string theory where inflation occurs near the inflection point of a small Kähler modulus. A racetrack structure helps to alleviate the known concern that string-loop corrections may spoil Kähler Moduli Inflation unless having a significant suppression via the string coupling or a special brane setup. Also, the hierarchy of gauge group ranks required for the separation between moduli stabilization and inflationary dynamics is relaxed. The relaxation becomes more significant when we use the recently proposed D-term generated racetrack model.

Segmented strings coupled to a B-field

NASA Astrophysics Data System (ADS)

Vegh, David

2018-04-01

In this paper we study segmented strings in AdS3 coupled to a background two-form whose field strength is proportional to the volume form. By changing the coupling, the theory interpolates between the Nambu-Goto string and the SL(2, ℝ) Wess-Zumino-Witten model. In terms of the kink momentum vectors, the action is independent of the coupling and the classical theory reduces to a single discrete-time Toda-type theory. The WZW model is a singular point in coupling space where the map into Toda variables degenerates.

Bianchi type-II String Cosmological Model with Magnetic Field in Scale-Covariant Theory of Gravitation

NASA Astrophysics Data System (ADS)

Sharma, N. K.; Singh, J. K.

2014-12-01

The spatially homogeneous and totally anisotropic Bianchi type-II cosmological solutions of massive strings have been investigated in the presence of the magnetic field in the framework of scale-covariant theory of gravitation formulated by Canuto et al. (Phys. Rev. Lett. 39, 429, 1977). With the help of special law of variation for Hubble's parameter proposed by Berman (Nuovo Cimento 74, 182, 1983) string cosmological model is obtained in this theory. We use the power law relation between scalar field ϕ and scale factor R to find the solutions. Some physical and kinematical properties of the model are also discussed.

Anisotropic Bianchi Type-I and Type-II Bulk Viscous String Cosmological Models Coupled with Zero Mass Scalar Field

NASA Astrophysics Data System (ADS)

Venkateswarlu, R.; Sreenivas, K.

2014-06-01

The LRS Bianchi type-I and type-II string cosmological models are studied when the source for the energy momentum tensor is a bulk viscous stiff fluid containing one dimensional strings together with zero-mass scalar field. We have obtained the solutions of the field equations assuming a functional relationship between metric coefficients when the metric is Bianchi type-I and constant deceleration parameter in case of Bianchi type-II metric. The physical and kinematical properties of the models are discussed in each case. The effects of Viscosity on the physical and kinematical properties are also studied.

Coupling of transverse and longitudinal waves in piano strings.

PubMed

Etchenique, Nikki; Collin, Samantha R; Moore, Thomas R

2015-04-01

The existence of longitudinal waves in vibrating piano strings has been previously established, as has their importance in producing the characteristic sound of the piano. Modeling of the coupling between the transverse and longitudinal motion of strings indicates that the amplitude of the longitudinal waves are quadratically related to the transverse displacement of the string, however, experimental verification of this relationship is lacking. In the work reported here this relationship is tested by driving the transverse motion of a piano string at only two frequencies, which simplifies the task of unambiguously identifying the constituent signals. The results indicate that the generally accepted relationship between the transverse motion and the longitudinal motion is valid. It is further shown that this dependence on transverse displacement is a good approximation when a string is excited by the impact of the hammer during normal play.

The confining baryonic Y-strings on the lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bakry, Ahmed S.; Chen, Xurong; Zhang, Peng-Ming

2016-01-22

In a string picture, the nucleon is conjectured as consisting of a Y-shaped gluonic string ended by constituent quarks. In this proceeding, we summarize our results on revealing the signature of the confining Y-bosonic string in the gluonic profile due to a system of three static quarks on the lattice at finite temperature. The analysis of the action density unveils a background of a filled-Δ distribution. However, we found that these Δ-shaped profiles are comprised of three Y-shaped Gaussian-like flux tubes. The length of the revealed Y-string-like distribution is maximum near the deconfinement point and approaches the geometrical minimal nearmore » the end of the QCD plateau. The action density width profile returns good fits to a baryonic string model for the junction fluctuations at large quark source separation.« less

Pointless strings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Periwal, V.

1988-01-01

The author proves that bosonic string perturbation theory diverges and is not Borel summable. This is an indication of a non-perturbative instability of the bosonic string vacuum. He formulates two-dimensional sigma models in terms of algebras of functions. He extends this formulation to general C* algebras. He illustrates the utility of these algebraic notions by calculating some determinants of interest in the study of string propagation in orbifold backgrounds. He studies the geometry of spaces of field theories and show that the vanishing of the curvature of the natural Gel'fand-Naimark-Segal metric on such spaces is exactly the strong associativity conditionmore » of the operator product expansion.He shows that string scattering amplitudes arise as invariants of renormalization, when he formulates renormalization in terms of rescalings of the metric on the string world-sheet.« less

Dynamics of a distributed drill string system: Characteristic parameters and stability maps

NASA Astrophysics Data System (ADS)

Aarsnes, Ulf Jakob F.; van de Wouw, Nathan

2018-03-01

This paper involves the dynamic (stability) analysis of distributed drill-string systems. A minimal set of parameters characterizing the linearized, axial-torsional dynamics of a distributed drill string coupled through the bit-rock interaction is derived. This is found to correspond to five parameters for a simple drill string and eight parameters for a two-sectioned drill-string (e.g., corresponding to the pipe and collar sections of a drilling system). These dynamic characterizations are used to plot the inverse gain margin of the system, parametrized in the non-dimensional parameters, effectively creating a stability map covering the full range of realistic physical parameters. This analysis reveals a complex spectrum of dynamics not evident in stability analysis with lumped models, thus indicating the importance of analysis using distributed models. Moreover, it reveals trends concerning stability properties depending on key system parameters useful in the context of system and control design aiming at the mitigation of vibrations.

Adaptation of Laser Microdissection Technique for the Study of a Spontaneous Metastatic Mammary Carcinoma Mouse Model by NanoString Technologies

PubMed Central

Saylor, Karen L.; Anver, Miriam R.; Salomon, David S.; Golubeva, Yelena G.

2016-01-01

Laser capture microdissection (LCM) of tissue is an established tool in medical research for collection of distinguished cell populations under direct microscopic visualization for molecular analysis. LCM samples have been successfully analyzed in a number of genomic and proteomic downstream molecular applications. However, LCM sample collection and preparation procedure has to be adapted to each downstream analysis platform. In this present manuscript we describe in detail the adaptation of LCM methodology for the collection and preparation of fresh frozen samples for NanoString analysis based on a study of a model of mouse mammary gland carcinoma and its lung metastasis. Our adaptation of LCM sample preparation and workflow to the requirements of the NanoString platform allowed acquiring samples with high RNA quality. The NanoString analysis of such samples provided sensitive detection of genes of interest and their associated molecular pathways. NanoString is a reliable gene expression analysis platform that can be effectively coupled with LCM. PMID:27077656

Modeling the Physics of Sliding Objects on Rotating Space Elevators and Other Non-relativistic Strings

NASA Astrophysics Data System (ADS)

Golubovic, Leonardo; Knudsen, Steven

2017-01-01

We consider general problem of modeling the dynamics of objects sliding on moving strings. We introduce a powerful computational algorithm that can be used to investigate the dynamics of objects sliding along non-relativistic strings. We use the algorithm to numerically explore fundamental physics of sliding climbers on a unique class of dynamical systems, Rotating Space Elevators (RSE). Objects sliding along RSE strings do not require internal engines or propulsion to be transported from the Earth's surface into outer space. By extensive numerical simulations, we find that sliding climbers may display interesting non-linear dynamics exhibiting both quasi-periodic and chaotic states of motion. While our main interest in this study is in the climber dynamics on RSEs, our results for the dynamics of sliding object are of more general interest. In particular, we designed tools capable of dealing with strongly nonlinear phenomena involving moving strings of any kind, such as the chaotic dynamics of sliding climbers observed in our simulations.

Holographic hierarchy in the Gaussian matrix model via the fuzzy sphere

NASA Astrophysics Data System (ADS)

Garner, David; Ramgoolam, Sanjaye

2013-10-01

The Gaussian Hermitian matrix model was recently proposed to have a dual string description with worldsheets mapping to a sphere target space. The correlators were written as sums over holomorphic (Belyi) maps from worldsheets to the two-dimensional sphere, branched over three points. We express the matrix model correlators by using the fuzzy sphere construction of matrix algebras, which can be interpreted as a string field theory description of the Belyi strings. This gives the correlators in terms of trivalent ribbon graphs that represent the couplings of irreducible representations of su(2), which can be evaluated in terms of 3j and 6j symbols. The Gaussian model perturbed by a cubic potential is then recognised as a generating function for Ponzano-Regge partition functions for 3-manifolds having the worldsheet as boundary, and equipped with boundary data determined by the ribbon graphs. This can be viewed as a holographic extension of the Belyi string worldsheets to membrane worldvolumes, forming part of a holographic hierarchy linking, via the large N expansion, the zero-dimensional QFT of the Matrix model to 2D strings and 3D membranes. Note that if, after removing the white vertices, the graph contains a blue edge connecting to the same black vertex at both ends, then the triangulation generated from the black edges will contain faces that resemble cut discs. These faces are triangles with two of the edges identified.

Critical string from non-Abelian vortex in four dimensions

DOE PAGES

Shifman, M.; Yung, A.

2015-09-25

In a class of non-Abelian solitonic vortex strings supported in certain N = 2 super-Yang–Mills theories we search for the vortex which can behave as a critical fundamental string. We use the Polchinski–Strominger criterion of the ultraviolet completeness. We identify an appropriate four-dimensional bulk theory: it has the U(2) gauge group, the Fayet–Iliopoulos term and four flavor hypermultiplets. It supports semilocal vortices with the world-sheet theory for orientational (size) moduli described by the weighted CP(2,2) model. The latter is superconformal. Its target space is six-dimensional. The overall Virasoro central charge is critical. Lastly, we show that the world-sheet theory onmore » the vortex supported in this bulk model is the bona fide critical string.« less

Spectral flow as a map between N = (2 , 0)-models

NASA Astrophysics Data System (ADS)

Athanasopoulos, P.; Faraggi, A. E.; Gepner, D.

2014-07-01

The space of (2 , 0) models is of particular interest among all heterotic-string models because it includes the models with the minimal SO (10) unification structure, which is well motivated by the Standard Model of particle physics data. The fermionic Z2 ×Z2 heterotic-string models revealed the existence of a new symmetry in the space of string configurations under the exchange of spinors and vectors of the SO (10) GUT group, dubbed spinor-vector duality. In this paper we generalize this idea to arbitrary internal rational conformal field theories (RCFTs). We explain how the spectral flow operator normally acting within a general (2 , 2) theory can be used as a map between (2 , 0) models. We describe the details, give an example and propose more simple currents that can be used in a similar way.

Mellin transforming the minimal model CFTs: AdS/CFT at strong curvature

DOE PAGES

Lowe, David A.

2016-07-14

Mack has conjectured that all conformal field theories are equivalent to string theories. Here, we explore the example of the two-dimensional minimal model CFTs and confirm that the Mellin transformed amplitudes have the desired properties of string theory in three-dimensional anti-de Sitter spacetime.

A Simplified Model for the Acceleration of Cosmic Ray Particles

ERIC Educational Resources Information Center

Gron, Oyvind

2010-01-01

Two important questions concerning cosmic rays are: Why are electrons in the cosmic rays less efficiently accelerated than nuclei? How are particles accelerated to great energies in ultra-high energy cosmic rays? In order to answer these questions we construct a simple model of the acceleration of a charged particle in the cosmic ray. It is not…

Topics in Covariant Closed String Field Theory and Two-Dimensional Quantum Gravity

NASA Astrophysics Data System (ADS)

Saadi, Maha

1991-01-01

The closed string field theory based on the Witten vertex is found to be nonpolynomial in order to reproduce all tree amplitudes correctly. The interactions have a geometrical pattern of overlaps, which can be thought as the edges of a spherical polyhedron with face-perimeters equal to 2pi. At each vertex of the polyhedron there are three faces, thus all elementary interactions are cubic in the sense that at most three strings can coincide at a point. The quantum action is constructed by substracting counterterms which cancel the overcounting of moduli space, and by adding loop vertices in such a way no possible surfaces are missed. A counterterm that gives the correct one-string one-loop amplitude is formulated. The lowest order loop vertices are analyzed in the cases of genus one and two. Also, a one-loop two -string counterterm that restores BRST invariance to the respective scattering amplitude is constructed. An attempt to understand the formulation of two -dimensional pure gravity from the discrete representation of a two-dimensional surface is made. This is considered as a toy model of string theory. A well-defined mathematical model is used. Its continuum limit cannot be naively interpreted as pure gravity because each term of the sum over surfaces is not positive definite. The model, however, could be considered as an analytic continuation of the standard matrix model formulation of gravity. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).

Connecting science and the musical arts in teaching tone quality: Integrating Helmholtz motion and master violin teachers' pedagogies

NASA Astrophysics Data System (ADS)

Collins, Cheri D.

Is it possible for students to achieve better tone quality from even their factory-made violins? All violins, regardless of cost, have a common capacity for good tone in certain frequencies. These signature modes outline the first position range of a violin (196-600 hertz). To activate this basic capacity of all violins, the string must fully vibrate. To accomplish this the bow must be pulled across the string with enough pressure (relative to its speed and contact point) for the horsehairs to catch. This friction permits the string to vibrate in Helmholtz Motion, which produces a corner that travels along the edge of the string between the bridge and the nut. Creating this corner is the most fundamental technique for achieving good tone. The findings of celebrated scientists Ernest Chladni, Hermann von Helmholtz, and John Schelleng will be discussed and the tone-production pedagogy of master teachers Carl Flesch, Ivan Galamian, Robert Gerle, and Simon Fischer will be investigated. Important connections between the insights of these scientists and master teachers are evident. Integrating science and art can provide teachers with a better understanding of the characteristics of good tone. This can help their students achieve the best possible sound from their instruments. In the private studio the master teacher may not use the words "Helmholtz Motion." Yet through modeling and listening students are able to understand and create a quality tone. Music teachers without experience in string performance may be assigned to teach strings in classroom and ensembles settings. As a result modeling good tone is not always possible. However, all teachers and conductors can understand the fundamental behavior of string vibration and adapt their instruction strategies towards student success. Better tonal quality for any string instrument is ultimately achieved. Mastery and use of the Helmholtz Motion benefits teachers and students alike. Simple practice exercises for teaching and conducting, based on student discovery rather than modeling, are presented in Appendix A: Application. This approach to teaching good tone can be applied successfully in all string settings and levels.

libFLASM: a software library for fixed-length approximate string matching.

PubMed

Ayad, Lorraine A K; Pissis, Solon P P; Retha, Ahmad

2016-11-10

Approximate string matching is the problem of finding all factors of a given text that are at a distance at most k from a given pattern. Fixed-length approximate string matching is the problem of finding all factors of a text of length n that are at a distance at most k from any factor of length ℓ of a pattern of length m. There exist bit-vector techniques to solve the fixed-length approximate string matching problem in time [Formula: see text] and space [Formula: see text] under the edit and Hamming distance models, where w is the size of the computer word; as such these techniques are independent of the distance threshold k or the alphabet size. Fixed-length approximate string matching is a generalisation of approximate string matching and, hence, has numerous direct applications in computational molecular biology and elsewhere. We present and make available libFLASM, a free open-source C++ software library for solving fixed-length approximate string matching under both the edit and the Hamming distance models. Moreover we describe how fixed-length approximate string matching is applied to solve real problems by incorporating libFLASM into established applications for multiple circular sequence alignment as well as single and structured motif extraction. Specifically, we describe how it can be used to improve the accuracy of multiple circular sequence alignment in terms of the inferred likelihood-based phylogenies; and we also describe how it is used to efficiently find motifs in molecular sequences representing regulatory or functional regions. The comparison of the performance of the library to other algorithms show how it is competitive, especially with increasing distance thresholds. Fixed-length approximate string matching is a generalisation of the classic approximate string matching problem. We present libFLASM, a free open-source C++ software library for solving fixed-length approximate string matching. The extensive experimental results presented here suggest that other applications could benefit from using libFLASM, and thus further maintenance and development of libFLASM is desirable.

Prior familiarity with components enhances unconscious learning of relations.

PubMed

Scott, Ryan B; Dienes, Zoltan

2010-03-01

The influence of prior familiarity with components on the implicit learning of relations was examined using artificial grammar learning. Prior to training on grammar strings, participants were familiarized with either the novel symbols used to construct the strings or with irrelevant geometric shapes. Participants familiarized with the relevant symbols showed greater accuracy when judging the correctness of new grammar strings. Familiarity with elemental components did not increase conscious awareness of the basis for discriminations (structural knowledge) but increased accuracy even in its absence. The subjective familiarity of test strings predicted grammaticality judgments. However, prior exposure to relevant symbols did not increase overall test string familiarity or reliance on familiarity when making grammaticality judgments. Familiarity with the symbols increased the learning of relations between them (bigrams and trigrams) thus resulting in greater familiarity for grammatical versus ungrammatical strings. The results have important implications for models of implicit learning.

String duality transformations in f(R) gravity from Noether symmetry approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Capozziello, Salvatore; Gionti, Gabriele S.J.; Vernieri, Daniele, E-mail: capozziello@na.inf.it, E-mail: ggionti@as.arizona.edu, E-mail: vernieri@iap.fr

2016-01-01

We select f(R) gravity models that undergo scale factor duality transformations. As a starting point, we consider the tree-level effective gravitational action of bosonic String Theory coupled with the dilaton field. This theory inherits the Busher's duality of its parent String Theory. Using conformal transformations of the metric tensor, it is possible to map the tree-level dilaton-graviton string effective action into f(R) gravity, relating the dilaton field to the Ricci scalar curvature. Furthermore, the duality can be framed under the standard of Noether symmetries and exact cosmological solutions are derived. Using suitable changes of variables, the string-based f(R) Lagrangians aremore » shown in cases where the duality transformation becomes a parity inversion.« less

Critical non-Abelian vortex in four dimensions and little string theory

NASA Astrophysics Data System (ADS)

Shifman, M.; Yung, A.

2017-08-01

As was shown recently, non-Abelian vortex strings supported in four-dimensional N =2 supersymmetric QCD with the U(2) gauge group and Nf=4 quark multiplets (flavors) become critical superstrings. In addition to the translational moduli, non-Abelian strings under consideration carry six orientational and size moduli. Together, they form a ten-dimensional target space required for a superstring to be critical. The target space of the string sigma model is a product of the flat four-dimensional space and a Calabi-Yau noncompact threefold, namely, the conifold. We study closed string states which emerge in four dimensions and identify them with hadrons of four-dimensional N =2 QCD. One massless state was found previously; it emerges as a massless hypermultiplet associated with the deformation of the complex structure of the conifold. In this paper, we find a number of massive states. To this end, we exploit the approach used in LST little string theory, namely, the equivalence between the critical string on the conifold and noncritical c =1 string with the Liouville field and a compact scalar at the self-dual radius. The states we find carry "baryonic" charge (its definition differs from standard). We interpret them as "monopole necklaces" formed (at strong coupling) by the closed string with confined monopoles attached.

A biomechanical comparison of conventional dynamic compression plates and string-of-pearls™ locking plates using cantilever bending in a canine Ilial fracture model.

PubMed

Kenzig, Allison R; Butler, James R; Priddy, Lauren B; Lacy, Kristen R; Elder, Steven H

2017-07-13

Fracture of the ilium is common orthopedic injury that often requires surgical stabilization in canine patients. Of the various methods of surgical stabilization available, application of a lateral bone plate to the ilium is the most common method of fixation. Many plating options are available, each having its own advantages and disadvantages. The purpose of this study was to evaluate the biomechanical properties of a 3.5 mm String-of-Pearls™ plate and a 3.5 mm dynamic compression plate in a cadaveric canine ilial fracture model. Hemipelves were tested in cantilever bending to failure and construct stiffness, yield load, displacement at yield, ultimate load, and mode of failure were compared. The mean stiffness of dynamic compression plate (116 ± 47 N/mm) and String-of-Pearls™ plate (107 ± 18 N/mm) constructs, mean yield load of dynamic compression plate (793 ± 333 N) and String-of-Pearls™ plate (860 ± 207 N) constructs, mean displacement at yield of dynamic compression plate (8.6 ± 3.0 mm) and String-of-Pearls™ plate (10.2 ± 2.8 mm) constructs, and ultimate load at failure of dynamic compression plate (936 ± 320 N) and String-of-Pearls™ plate (939 ± 191 N) constructs were not significantly different. No differences were found between constructs with respect to mode of failure. No significant biomechanical differences were found between String-of-Pearls™ plate and dynamic compression plate constructs in this simplified cadaveric canine ilial fracture model.

Fuzzy Dark Matter from Infrared Confining Dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davoudiasl, Hooman; Murphy, Christopher W.

A very light boson of mass O ( 10 - 22 ) eV may potentially be a viable dark matter (DM) candidate, which can avoid phenomenological problems associated with cold DM. Such “fuzzy DM (FDM)” may naturally be an axion with a decay constant f a ~ 1 0 16 – 1 0 18 GeV and a mass m a ~ μ 2 / f a with μ ~ 1 0 2 eV . Here, we propose a concrete model, where μ arises as a dynamical scale from infrared confining dynamics, analogous to QCD. This model is an alternative tomore » the usual approach of generating μ through string theoretic instanton effects. We outline the features of this scenario that result from various cosmological constraints. We also found that those constraints are suggestive of a period of mild of inflation, perhaps from a strong first order phase transition, that reheats the standard model (SM) sector only. A typical prediction of our scenario, broadly speaking, is a larger effective number of neutrinos compared to the SM value N eff ≈ 3 , as inferred from precision measurements of the cosmic microwave background. Some of the new degrees of freedom may be identified as “sterile neutrinos,” which may be required to explain certain neutrino oscillation anomalies. Thus, aspects of our scenario could be testable in terrestrial experiments, which is a novelty of our FDM model.« less

Fuzzy Dark Matter from Infrared Confining Dynamics

DOE PAGES

Davoudiasl, Hooman; Murphy, Christopher W.

2017-04-03

A very light boson of mass O ( 10 - 22 ) eV may potentially be a viable dark matter (DM) candidate, which can avoid phenomenological problems associated with cold DM. Such “fuzzy DM (FDM)” may naturally be an axion with a decay constant f a ~ 1 0 16 – 1 0 18 GeV and a mass m a ~ μ 2 / f a with μ ~ 1 0 2 eV . Here, we propose a concrete model, where μ arises as a dynamical scale from infrared confining dynamics, analogous to QCD. This model is an alternative tomore » the usual approach of generating μ through string theoretic instanton effects. We outline the features of this scenario that result from various cosmological constraints. We also found that those constraints are suggestive of a period of mild of inflation, perhaps from a strong first order phase transition, that reheats the standard model (SM) sector only. A typical prediction of our scenario, broadly speaking, is a larger effective number of neutrinos compared to the SM value N eff ≈ 3 , as inferred from precision measurements of the cosmic microwave background. Some of the new degrees of freedom may be identified as “sterile neutrinos,” which may be required to explain certain neutrino oscillation anomalies. Thus, aspects of our scenario could be testable in terrestrial experiments, which is a novelty of our FDM model.« less

Knowledge, Models and Tools in Support of Advanced Distance Learning

DTIC Science & Technology

2006-06-01

including " Dodger Blue", "Indian Red", and "Light Slate Gray" as well as such conventional colors as "Blue" and "Yellow". Which color names are supported...Format String: 1 1 S I 1 1 3 Either one string or an array of 3 numbers Legal Params: (" Dodger Blue") ([0.0235, 0.38, 1.0]) Format String: * *l* Any number...specifying the values of the red, green, and blue components of the color) or a string that names a predefined color. E.g., makeColor (" Dodger Blue

Chern-Simons improved Hamiltonians for strings in three space dimensions

NASA Astrophysics Data System (ADS)

Gordeli, Ivan; Melnikov, Dmitry; Niemi, Antti J.; Sedrakyan, Ara

2016-07-01

In the case of a structureless string the extrinsic curvature and torsion determine uniquely its shape in three-dimensional ambient space, by way of solution of the Frenet equation. In many physical scenarios there are in addition symmetries that constrain the functional form of the ensuing energy function. For example, the energy of a structureless string should be independent of the way the string is framed in the Frenet equation. Thus the energy should only involve the curvature and torsion as dynamical variables, in a manner that resembles the Hamiltonian of the Abelian Higgs model. Here we investigate the effect of symmetry principles in the construction of Hamiltonians for structureless strings. We deduce from the concept of frame independence that in addition to extrinsic curvature and torsion, the string can also engage a three-dimensional Abelian bulk gauge field as a dynamical variable. We find that the presence of a bulk gauge field gives rise to a long-range interaction between different strings. Moreover, when this gauge field is subject to Chern-Simons self-interaction, it becomes plausible that interacting strings are subject to fractional statistics in three space dimensions.

Simulation of Z(3) walls and string production via bubble nucleation in a quark-hadron transition

NASA Astrophysics Data System (ADS)

Gupta, Uma Shankar; Mohapatra, Ranjita K.; Srivastava, Ajit M.; Tiwari, Vivek K.

2010-10-01

We study the dynamics of confinement-deconfinement phase transition in the context of relativistic heavy-ion collisions within the framework of effective models for the Polyakov loop order parameter. We study the formation of Z(3) walls and associated strings in the initial transition from the confining (hadronic) phase to the deconfining [quark-gluon plasma (QGP)] phase via the so-called Kibble mechanism. Essential physics of the Kibble mechanism is contained in a sort of domain structure arising after any phase transition which represents random variation of the order parameter at distances beyond the typical correlation length. We implement this domain structure by using the Polyakov loop effective model with a first order phase transition and confine ourselves with temperature/time ranges so that the first order confinement-deconfinement transition proceeds via bubble nucleation, leading to a well defined domain structure. The formation of Z(3) walls and associated strings results from the coalescence of QGP bubbles expanding in the confining background. We investigate the evolution of the Z(3) wall and string network. We also calculate the energy density fluctuations associated with Z(3) wall network and strings which decay away after the temperature drops below the quark-hadron transition temperature during the expansion of QGP. We discuss evolution of these quantities with changing temperature via Bjorken’s hydrodynamical model and discuss possible experimental signatures resulting from the presence of Z(3) wall network and associate strings.

Simulation of Z(3) walls and string production via bubble nucleation in a quark-hadron transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, Uma Shankar; Tiwari, Vivek K.; Mohapatra, Ranjita K.

2010-10-01

We study the dynamics of confinement-deconfinement phase transition in the context of relativistic heavy-ion collisions within the framework of effective models for the Polyakov loop order parameter. We study the formation of Z(3) walls and associated strings in the initial transition from the confining (hadronic) phase to the deconfining [quark-gluon plasma (QGP)] phase via the so-called Kibble mechanism. Essential physics of the Kibble mechanism is contained in a sort of domain structure arising after any phase transition which represents random variation of the order parameter at distances beyond the typical correlation length. We implement this domain structure by using themore » Polyakov loop effective model with a first order phase transition and confine ourselves with temperature/time ranges so that the first order confinement-deconfinement transition proceeds via bubble nucleation, leading to a well defined domain structure. The formation of Z(3) walls and associated strings results from the coalescence of QGP bubbles expanding in the confining background. We investigate the evolution of the Z(3) wall and string network. We also calculate the energy density fluctuations associated with Z(3) wall network and strings which decay away after the temperature drops below the quark-hadron transition temperature during the expansion of QGP. We discuss evolution of these quantities with changing temperature via Bjorken's hydrodynamical model and discuss possible experimental signatures resulting from the presence of Z(3) wall network and associate strings.« less

Toward a descriptive model of galactic cosmic rays in the heliosphere

NASA Technical Reports Server (NTRS)

Mewaldt, R. A.; Cummings, A. C.; Adams, James H., Jr.; Evenson, Paul; Fillius, W.; Jokipii, J. R.; Mckibben, R. B.; Robinson, Paul A., Jr.

1988-01-01

Researchers review the elements that enter into phenomenological models of the composition, energy spectra, and the spatial and temporal variations of galactic cosmic rays, including the so-called anomalous cosmic ray component. Starting from an existing model, designed to describe the behavior of cosmic rays in the near-Earth environment, researchers suggest possible updates and improvements to this model, and then propose a quantitative approach for extending such a model into other regions of the heliosphere.

Effect of a cosmological constant on propagation of vacuum polarized photons in stationary spacetimes

NASA Astrophysics Data System (ADS)

Bhattacharya, Sourav

2015-06-01

Consideration of vacuum polarization in quantum electrodynamics may affect the momentum dispersion relation for photons for a non-trivial background, due to the appearance of curvature dependent terms in the effective action. We investigate the effect of a positive cosmological constant on this at one-loop order for stationary -vacuum spacetimes. To the best of our knowledge, so far it only has been shown that affects the propagation in a time dependent black hole spacetime. Here we consider the static de Sitter cosmic string and the Kerr-de Sitter spacetime to show that there might occur a non-vanishing effect due to for physical polarizations. The consistency of these results with the polarization sum rule is discussed.

The waiting time problem in a model hominin population.

PubMed

Sanford, John; Brewer, Wesley; Smith, Franzine; Baumgardner, John

2015-09-17

Functional information is normally communicated using specific, context-dependent strings of symbolic characters. This is true within the human realm (texts and computer programs), and also within the biological realm (nucleic acids and proteins). In biology, strings of nucleotides encode much of the information within living cells. How do such information-bearing nucleotide strings arise and become established? This paper uses comprehensive numerical simulation to understand what types of nucleotide strings can realistically be established via the mutation/selection process, given a reasonable timeframe. The program Mendel's Accountant realistically simulates the mutation/selection process, and was modified so that a starting string of nucleotides could be specified, and a corresponding target string of nucleotides could be specified. We simulated a classic pre-human hominin population of at least 10,000 individuals, with a generation time of 20 years, and with very strong selection (50% selective elimination). Random point mutations were generated within the starting string. Whenever an instance of the target string arose, all individuals carrying the target string were assigned a specified reproductive advantage. When natural selection had successfully amplified an instance of the target string to the point of fixation, the experiment was halted, and the waiting time statistics were tabulated. Using this methodology we tested the effect of mutation rate, string length, fitness benefit, and population size on waiting time to fixation. Biologically realistic numerical simulations revealed that a population of this type required inordinately long waiting times to establish even the shortest nucleotide strings. To establish a string of two nucleotides required on average 84 million years. To establish a string of five nucleotides required on average 2 billion years. We found that waiting times were reduced by higher mutation rates, stronger fitness benefits, and larger population sizes. However, even using the most generous feasible parameters settings, the waiting time required to establish any specific nucleotide string within this type of population was consistently prohibitive. We show that the waiting time problem is a significant constraint on the macroevolution of the classic hominin population. Routine establishment of specific beneficial strings of two or more nucleotides becomes very problematic.

Blue spectra of Kalb-Ramond axions and fully anisotropic string cosmologies

NASA Astrophysics Data System (ADS)

Giovannini, Massimo

1999-03-01

The inhomogeneities associated with massless Kalb-Ramond axions can be amplified not only in isotropic (four-dimensional) string cosmological models but also in the fully anisotropic case. If the background geometry is isotropic, the axions (which are not part of the homogeneous background) develop outside the horizon, the growing modes leading, ultimately, to logarithmic energy spectra which are ``red'' in frequency and increase at large distance scales. We show that this conclusion can be avoided not only in the case of higher dimensional backgrounds with contracting internal dimensions but also in the case of string cosmological scenarios which are completely anisotropic in four dimensions. In this case the logarithmic energy spectra turn out to be ``blue'' in frequency and, consequently, decreasing at large distance scales. We elaborate on anisotropic dilaton-driven models and we argue that, incidentally, the background models leading to blue (or flat) logarithmic energy spectra for axionic fluctuations are likely to be isotropized by the effect of string tension corrections.

Search for critical point indications in long-range correlations by energy and system size scanning in string fusion approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovalenko, V. N.; Vechernin, V. V.

2016-01-22

The ultrarelativistic collisions of heavy and light ions in the center-of-mass energy range from a few up to a hundred GeV per nucleon have been considered in string fusion approach. A Monte Carlo model of proton-proton, proton-nucleus, and nucleus-nucleus collisions has been developed, which takes into account both the string fusion and the finite rapidity length of strings, implementing the hadronic scattering through the interaction of color dipoles. It well describes the proton-nucleus and nucleus-nucleus collisions at the partonic level without using Glauber model of nuclear collisions. All parameters are fixed using experimental data on inelastic cross section and multiplicity.more » In the framework of the model, we performed a beam energy and system size scan and studied the behaviour of n-n, pt-n and pt-pt long-range correlation coefficients. The detailed modeling of the event by event charged particles production allowed to provide predictions in the conditions close to the experimental ones allowing a direct comparison to the data.« less

String Scale Gauge Coupling Unification with Vector-Like Exotics and Noncanonical U(1)Y Normalization

NASA Astrophysics Data System (ADS)

Barger, V.; Jiang, Jing; Langacker, Paul; Li, Tianjun

We use a new approach to study string scale gauge coupling unification systematically, allowing both the possibility of noncanonical U(1)Y normalization and the existence of vector-like particles whose quantum numbers are the same as those of the Standard Model (SM) fermions and their Hermitian conjugates and the SM adjoint particles. We first give all the independent sets (Yi) of particles that can be employed to achieve SU(3)C and SU(2)L string scale gauge coupling unification and calculate their masses. Second, for a noncanonical U(1)Y normalization, we obtain string scale SU(3)C ×SU(2)L ×U(1)Y gauge coupling unification by choosing suitable U(1)Y normalizations for each of the Yi sets. Alternatively, for the canonical U(1)Y normalization, we achieve string scale gauge coupling unification by considering suitable combinations of the Yi sets or by introducing additional independent sets (Zi), that do not affect the SU(3)C ×SU(2)L unification at tree level, and then choosing suitable combinations, one from the Yi sets and one from the Zi sets. We also briefly discuss string scale gauge coupling unification in models with higher Kac-Moody levels for SU(2)L or SU(3)C.

From the currency rate quotations onto strings and brane world scenarios

NASA Astrophysics Data System (ADS)

Horváth, D.; Pincak, R.

2012-11-01

In the paper, we study the projections of the real exchange rate dynamics onto the string-like topology. Our approach is inspired by the contemporary movements in the string theory. The string map of data is defined here by the boundary conditions, characteristic length, real valued and the method of redistribution of information. As a practical matter, this map represents the detrending and data standardization procedure. We introduced maps onto 1-end-point and 2-end-point open strings that satisfy the Dirichlet and Neumann boundary conditions. The questions of the choice of extra-dimensions, symmetries, duality and ways to the partial compactification are discussed. Subsequently, we pass to higher dimensional and more complex objects. The 2D-Brane was suggested which incorporated bid-ask spreads. Polarization by the spread was considered which admitted analyzing arbitrage opportunities on the market where transaction costs are taken into account. The model of the rotating string which naturally yields calculation of angular momentum is suitable for tracking of several currency pairs. The systematic way which allows one suggest more structured maps suitable for a simultaneous study of several currency pairs was analyzed by means of the Gâteaux generalized differential calculus. The effect of the string and brane maps on test data was studied by comparing their mean statistical characteristics. The study revealed notable differences between topologies. We review the dependence on the characteristic string length, mean fluctuations and properties of the intra-string statistics. The study explores the coupling of the string amplitude and volatility. The possible utilizations of the string theory approach in financial markets are slight.

Second quantization of a covariant relativistic spacetime string in Steuckelberg-Horwitz-Piron theory

NASA Astrophysics Data System (ADS)

Suleymanov, Michael; Horwitz, Lawrence; Yahalom, Asher

2017-06-01

A relativistic 4D string is described in the framework of the covariant quantum theory first introduced by Stueckelberg [ Helv. Phys. Acta 14, 588 (1941)], and further developed by Horwitz and Piron [ Helv. Phys. Acta 46, 316 (1973)], and discussed at length in the book of Horwitz [Relativistic Quantum Mechanics, Springer (2015)]. We describe the space-time string using the solutions of relativistic harmonic oscillator [ J. Math. Phys. 30, 66 (1989)]. We first study the problem of the discrete string, both classically and quantum mechanically, and then turn to a study of the continuum limit, which contains a basically new formalism for the quantization of an extended system. The mass and energy spectrum are derived. Some comparison is made with known string models.

Tachyon Condensation and Brane Annihilation in Bose-Einstein Condensates: Spontaneous Symmetry Breaking in Restricted Lower-Dimensional Subspace

NASA Astrophysics Data System (ADS)

Takeuchi, Hiromitsu; Kasamatsu, Kenichi; Tsubota, Makoto; Nitta, Muneto

2013-05-01

In brane cosmology, the Big Bang is hypothesized to occur by the annihilation of the brane-anti-brane pair in a collision, where the branes are three-dimensional objects in a higher-dimensional Universe. Spontaneous symmetry breaking accompanied by the formation of lower-dimensional topological defects, e.g. cosmic strings, is triggered by the so-called `tachyon condensation', where the existence of tachyons is attributable to the instability of the brane-anti-brane system. Here, we discuss the closest analogue of the tachyon condensation in atomic Bose-Einstein condensates. We consider annihilation of domain walls, namely branes, in strongly segregated two-component condensates, where one component is sandwiched by two domains of the other component. In this system, the process of the brane annihilation can be projected effectively as ferromagnetic ordering dynamics onto a two-dimensional space. Based on this correspondence, three-dimensional formation of vortices from a domain-wall annihilation is considered to be a kink formation due to spontaneous symmetry breaking in the two-dimensional space. We also discuss a mechanism to create a `vorton' when the sandwiched component has a vortex string bridged between the branes. We hope that this study motivates experimental researches to realize this exotic phenomenon of spontaneous symmetry breaking in superfluid systems.

The COsmic-ray Soil Moisture Interaction Code (COSMIC) for use in data assimilation

NASA Astrophysics Data System (ADS)

Shuttleworth, J.; Rosolem, R.; Zreda, M.; Franz, T.

2013-08-01

Soil moisture status in land surface models (LSMs) can be updated by assimilating cosmic-ray neutron intensity measured in air above the surface. This requires a fast and accurate model to calculate the neutron intensity from the profiles of soil moisture modeled by the LSM. The existing Monte Carlo N-Particle eXtended (MCNPX) model is sufficiently accurate but too slow to be practical in the context of data assimilation. Consequently an alternative and efficient model is needed which can be calibrated accurately to reproduce the calculations made by MCNPX and used to substitute for MCNPX during data assimilation. This paper describes the construction and calibration of such a model, COsmic-ray Soil Moisture Interaction Code (COSMIC), which is simple, physically based and analytic, and which, because it runs at least 50 000 times faster than MCNPX, is appropriate in data assimilation applications. The model includes simple descriptions of (a) degradation of the incoming high-energy neutron flux with soil depth, (b) creation of fast neutrons at each depth in the soil, and (c) scattering of the resulting fast neutrons before they reach the soil surface, all of which processes may have parameterized dependency on the chemistry and moisture content of the soil. The site-to-site variability in the parameters used in COSMIC is explored for 42 sample sites in the COsmic-ray Soil Moisture Observing System (COSMOS), and the comparative performance of COSMIC relative to MCNPX when applied to represent interactions between cosmic-ray neutrons and moist soil is explored. At an example site in Arizona, fast-neutron counts calculated by COSMIC from the average soil moisture profile given by an independent network of point measurements in the COSMOS probe footprint are similar to the fast-neutron intensity measured by the COSMOS probe. It was demonstrated that, when used within a data assimilation framework to assimilate COSMOS probe counts into the Noah land surface model at the Santa Rita Experimental Range field site, the calibrated COSMIC model provided an effective mechanism for translating model-calculated soil moisture profiles into aboveground fast-neutron count when applied with two radically different approaches used to remove the bias between data and model.

Magnetic Bianchi type II string cosmological model in loop quantum cosmology

NASA Astrophysics Data System (ADS)

Rikhvitsky, Victor; Saha, Bijan; Visinescu, Mihai

2014-07-01

The loop quantum cosmology of the Bianchi type II string cosmological model in the presence of a homogeneous magnetic field is studied. We present the effective equations which provide modifications to the classical equations of motion due to quantum effects. The numerical simulations confirm that the big bang singularity is resolved by quantum gravity effects.

Inhomogeneous Einstein-Rosen string cosmology

NASA Astrophysics Data System (ADS)

Clancy, Dominic; Feinstein, Alexander; Lidsey, James E.; Tavakol, Reza

1999-08-01

Families of anisotropic and inhomogeneous string cosmologies containing non-trivial dilaton and axion fields are derived by applying the global symmetries of the string effective action to a generalized Einstein-Rosen metric. The models exhibit a two-dimensional group of Abelian isometries. In particular, two classes of exact solutions are found that represent inhomogeneous generalizations of the Bianchi type VIh cosmology. The asymptotic behavior of the solutions is investigated and further applications are briefly discussed.

Improved limits on dark matter annihilation in the Sun with the 79-string IceCube detector and implications for supersymmetry

NASA Astrophysics Data System (ADS)

Aartsen, M. G.; Abraham, K.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Ahrens, M.; Altmann, D.; Anderson, T.; Ansseau, I.; Anton, G.; Archinger, M.; Arguelles, C.; Arlen, T. C.; Auffenberg, J.; Bai, X.; Barwick, S. W.; Baum, V.; Bay, R.; Beatty, J. J.; Becker Tjus, J.; Becker, K.-H.; Beiser, E.; BenZvi, S.; Berghaus, P.; Berley, D.; Bernardini, E.; Bernhard, A.; Besson, D. Z.; Binder, G.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Börner, M.; Bos, F.; Bose, D.; Böser, S.; Botner, O.; Braun, J.; Brayeur, L.; Bretz, H.-P.; Buzinsky, N.; Casey, J.; Casier, M.; Cheung, E.; Chirkin, D.; Christov, A.; Clark, K.; Classen, L.; Coenders, S.; Collin, G. H.; Conrad, J. M.; Cowen, D. F.; Cruz Silva, A. H.; Danninger, M.; Daughhetee, J.; Davis, J. C.; Day, M.; de André, J. P. A. M.; De Clercq, C.; del Pino Rosendo, E.; Dembinski, H.; De Ridder, S.; Desiati, P.; de Vries, K. D.; de Wasseige, G.; de With, M.; DeYoung, T.; Díaz-Vélez, J. C.; di Lorenzo, V.; Dumm, J. P.; Dunkman, M.; Eberhardt, B.; Edsjö, J.; Ehrhardt, T.; Eichmann, B.; Euler, S.; Evenson, P. A.; Fahey, S.; Fazely, A. R.; Feintzeig, J.; Felde, J.; Filimonov, K.; Finley, C.; Flis, S.; Fösig, C.-C.; Fuchs, T.; Gaisser, T. K.; Gaior, R.; Gallagher, J.; Gerhardt, L.; Ghorbani, K.; Gier, D.; Gladstone, L.; Glagla, M.; Glüsenkamp, T.; Goldschmidt, A.; Golup, G.; Gonzalez, J. G.; Góra, D.; Grant, D.; Griffith, Z.; Groß, A.; Ha, C.; Haack, C.; Haj Ismail, A.; Hallgren, A.; Halzen, F.; Hansen, E.; Hansmann, B.; Hanson, K.; Hebecker, D.; Heereman, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hignight, J.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Holzapfel, K.; Homeier, A.; Hoshina, K.; Huang, F.; Huber, M.; Huelsnitz, W.; Hulth, P. O.; Hultqvist, K.; In, S.; Ishihara, A.; Jacobi, E.; Japaridze, G. S.; Jeong, M.; Jero, K.; Jones, B. J. P.; Jurkovic, M.; Kappes, A.; Karg, T.; Karle, A.; Katz, U.; Kauer, M.; Keivani, A.; Kelley, J. L.; Kemp, J.; Kheirandish, A.; Kiryluk, J.; Klein, S. R.; Kohnen, G.; Koirala, R.; Kolanoski, H.; Konietz, R.; Köpke, L.; Kopper, C.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Krings, K.; Kroll, G.; Kroll, M.; Krückl, G.; Kunnen, J.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Lanfranchi, J. L.; Larson, M. J.; Lesiak-Bzdak, M.; Leuermann, M.; Leuner, J.; Lu, L.; Lünemann, J.; Madsen, J.; Maggi, G.; Mahn, K. B. M.; Mandelartz, M.; Maruyama, R.; Mase, K.; Matis, H. S.; Maunu, R.; McNally, F.; Meagher, K.; Medici, M.; Meier, M.; Meli, A.; Menne, T.; Merino, G.; Meures, T.; Miarecki, S.; Middell, E.; Mohrmann, L.; Montaruli, T.; Morse, R.; Nahnhauer, R.; Naumann, U.; Neer, G.; Niederhausen, H.; Nowicki, S. C.; Nygren, D. R.; Obertacke Pollmann, A.; Olivas, A.; Omairat, A.; O'Murchadha, A.; Palczewski, T.; Pandya, H.; Pankova, D. V.; Paul, L.; Pepper, J. A.; Pérez de los Heros, C.; Pfendner, C.; Pieloth, D.; Pinat, E.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Quinnan, M.; Raab, C.; Rädel, L.; Rameez, M.; Rawlins, K.; Reimann, R.; Relich, M.; Resconi, E.; Rhode, W.; Richman, M.; Richter, S.; Riedel, B.; Robertson, S.; Rongen, M.; Rott, C.; Ruhe, T.; Ryckbosch, D.; Sabbatini, L.; Sander, H.-G.; Sandrock, A.; Sandroos, J.; Sarkar, S.; Savage, C.; Schatto, K.; Schimp, M.; Schlunder, P.; Schmidt, T.; Schoenen, S.; Schöneberg, S.; Schönwald, A.; Schulte, L.; Schumacher, L.; Scott, P.; Seckel, D.; Seunarine, S.; Silverwood, H.; Soldin, D.; Song, M.; Spiczak, G. M.; Spiering, C.; Stahlberg, M.; Stamatikos, M.; Stanev, T.; Stasik, A.; Steuer, A.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Ström, R.; Strotjohann, N. L.; Sullivan, G. W.; Sutherland, M.; Taavola, H.; Taboada, I.; Tatar, J.; Ter-Antonyan, S.; Terliuk, A.; Te{š}ić, G.; Tilav, S.; Toale, P. A.; Tobin, M. N.; Toscano, S.; Tosi, D.; Tselengidou, M.; Turcati, A.; Unger, E.; Usner, M.; Vallecorsa, S.; Vandenbroucke, J.; van Eijndhoven, N.; Vanheule, S.; van Santen, J.; Veenkamp, J.; Vehring, M.; Voge, M.; Vraeghe, M.; Walck, C.; Wallace, A.; Wallraff, M.; Wandkowsky, N.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whelan, B. J.; Wiebe, K.; Wiebusch, C. H.; Wille, L.; Williams, D. R.; Wills, L.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, D. L.; Xu, X. W.; Xu, Y.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zoll, M.

2016-04-01

We present an improved event-level likelihood formalism for including neutrino telescope data in global fits to new physics. We derive limits on spin-dependent dark matter-proton scattering by employing the new formalism in a re-analysis of data from the 79-string IceCube search for dark matter annihilation in the Sun, including explicit energy information for each event. The new analysis excludes a number of models in the weak-scale minimal supersymmetric standard model (MSSM) for the first time. This work is accompanied by the public release of the 79-string IceCube data, as well as an associated computer code for applying the new likelihood to arbitrary dark matter models.

Massless spinning particle and null-string on AdS d : projective-space approach

NASA Astrophysics Data System (ADS)

Uvarov, D. V.

2018-07-01

The massless spinning particle and the tensionless string models on an AdS d background in the projective-space realization are proposed as constrained Hamiltonian systems. Various forms of particle and string Lagrangians are derived and classical mechanics is studied including the Lax-type representation of the equations of motion. After that, the transition to the quantum theory is discussed. The analysis of potential anomalies in the tensionless string model necessitates the introduction of ghosts and BRST charge. It is shown that a quantum BRST charge is nilpotent for any d if coordinate-momentum ordering for the phase-space bosonic variables, Weyl ordering for the fermions and cb () ordering for the ghosts is chosen, while conformal reparametrizations and space-time dilatations turn out to be anomalous for ordering in terms of positive and negative Fourier modes of the phase-space variables and ghosts.

Testing Galactic Cosmic Ray Models

NASA Technical Reports Server (NTRS)

Adams, James H., Jr.

2009-01-01

Models of the Galactic Cosmic Ray Environment are used for designing and planning space missions. The existing models will be reviewed. Spectral representations from these models will be compared with measurements of galactic cosmic ray spectra made on balloon flights and satellite flights over a period of more than 50 years.

Testing Galactic Cosmic Ray Models

NASA Technical Reports Server (NTRS)

Adams, James H., Jr.

2010-01-01

Models of the Galactic Cosmic Ray Environment are used for designing and planning space missions. The exising models will be reviewed. Spectral representations from these models will be compared with measurements of galactic cosmic ray spectra made on balloon flights and satellite flights over a period of more than 50 years.

On the size and velocity distribution of cosmic dust particles entering the atmosphere

PubMed Central

Carrillo‐Sánchez, J. D.; Feng, W.; Nesvorný, D.; Janches, D.

2015-01-01

Abstract The size and velocity distribution of cosmic dust particles entering the Earth's atmosphere is uncertain. Here we show that the relative concentrations of metal atoms in the upper mesosphere, and the surface accretion rate of cosmic spherules, provide sensitive probes of this distribution. Three cosmic dust models are selected as case studies: two are astronomical models, the first constrained by infrared observations of the Zodiacal Dust Cloud and the second by radar observations of meteor head echoes; the third model is based on measurements made with a spaceborne dust detector. For each model, a Monte Carlo sampling method combined with a chemical ablation model is used to predict the ablation rates of Na, K, Fe, Mg, and Ca above 60 km and cosmic spherule production rate. It appears that a significant fraction of the cosmic dust consists of small (<5 µg) and slow (<15 km s−1) particles. PMID:27478282

An evaluation of string theory for the prediction of dynamic tire properties using scale model aircraft tires

NASA Technical Reports Server (NTRS)

Clark, S. K.; Dodge, R. N.; Nybakken, G. H.

1972-01-01

The string theory was evaluated for predicting lateral tire dynamic properties as obtained from scaled model tests. The experimental data and string theory predictions are in generally good agreement using lateral stiffness and relaxation length values obtained from the static or slowly rolling tire. The results indicate that lateral forces and self-aligning torques are linearly proportional to tire lateral stiffness and to the amplitude of either steer or lateral displacement. In addition, the results show that the ratio of input excitation frequency to road speed is the proper independent variable by which frequency should be measured.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, Hugh H.; Balasubramanian, V.; Bernstein, G.

The University of Pennsylvania elementary particle physics/particle cosmology group, funded by the Department of Energy Office of Science, participates in research in high energy physics and particle cosmology that addresses some of the most important unanswered questions in science. The research is divided into five areas. Energy Frontier - We participate in the study of proton-proton collisions at the Large Hadron Collider in Geneva, Switzerland using the ATLAS detector. The University of Pennsylvania group was responsible for the design, installation, and commissioning of the front-end electronics for the Transition Radiation Tracker (TRT) and plays the primary role in its maintenancemore » and operation. We play an important role in the triggering of ATLAS, and we have made large contributions to the TRT performance and to the study and identification of electrons, photons, and taus. We have been actively involved in searches for the Higgs boson and for SUSY and other exotic particles. We have made significant contributions to measurement of Standard Model processes such as inclusive photon production and WW pair production. We also have participated significantly in R&D for upgrades to the ATLAS detector. Cosmic Frontier - The Dark Energy Survey (DES) telescope will be used to elucidate the nature of dark energy and the distribution of dark matter. Penn has played a leading role both in the use of weak gravitational lensing of distant galaxies and the discovery of large numbers of distant supernovae. The techniques and forecasts developed at Penn are also guiding the development of the proposed Large Synoptic Survey Telescope (LSST).We are also developing a new detector, MiniClean, to search for direct detection of dark matter particles. Intensity Frontier - We are participating in the design and R&D of detectors for the Long Baseline Neutrino Experiment (now DUNE), a new experiment to study the properties of neutrinos. Advanced Techology R&D - We have an extensive involvement in electronics required for sophisticated new detectors at the LHC and are developing electronics for the LSST camera. Theoretical Physics - We are carrying out a broad program studying the fundamental forces of nature and early universe cosmology and mathematical physics. Our activities span the range from model building, formal field theory, and string theory to new paradigms for cosmology and the interface of string theory with mathematics. Our effort combines extensive development of the formal aspects of string theory with a focus on real phenomena in particle physics, cosmology and gravity.« less

Evaluation of Galactic Cosmic Ray Models

NASA Technical Reports Server (NTRS)

Adams, James H., Jr.; Heiblim, Samuel; Malott, Christopher

2009-01-01

Models of the galactic cosmic ray spectra have been tested by comparing their predictions to an evaluated database containing more than 380 measured cosmic ray spectra extending from 1960 to the present.

MCNP6 Simulation of Light and Medium Nuclei Fragmentation at Intermediate Energies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mashnik, Stepan Georgievich; Kerby, Leslie Marie

2015-05-22

MCNP6, the latest and most advanced LANL Monte Carlo transport code, representing a merger of MCNP5 and MCNPX, is actually much more than the sum of those two computer codes; MCNP6 is available to the public via RSICC at Oak Ridge, TN, USA. In the present work, MCNP6 was validated and verified (V&V) against different experimental data on intermediate-energy fragmentation reactions, and results by several other codes, using mainly the latest modifications of the Cascade-Exciton Model (CEM) and of the Los Alamos version of the Quark-Gluon String Model (LAQGSM) event generators CEM03.03 and LAQGSM03.03. It was found that MCNP6 usingmore » CEM03.03 and LAQGSM03.03 describes well fragmentation reactions induced on light and medium target nuclei by protons and light nuclei of energies around 1 GeV/nucleon and below, and can serve as a reliable simulation tool for different applications, like cosmic-ray-induced single event upsets (SEU’s), radiation protection, and cancer therapy with proton and ion beams, to name just a few. Future improvements of the predicting capabilities of MCNP6 for such reactions are possible, and are discussed in this work.« less

From the S U (2 ) quantum link model on the honeycomb lattice to the quantum dimer model on the kagome lattice: Phase transition and fractionalized flux strings

NASA Astrophysics Data System (ADS)

Banerjee, D.; Jiang, F.-J.; Olesen, T. Z.; Orland, P.; Wiese, U.-J.

2018-05-01

We consider the (2 +1 ) -dimensional S U (2 ) quantum link model on the honeycomb lattice and show that it is equivalent to a quantum dimer model on the kagome lattice. The model has crystalline confined phases with spontaneously broken translation invariance associated with pinwheel order, which is investigated with either a Metropolis or an efficient cluster algorithm. External half-integer non-Abelian charges [which transform nontrivially under the Z (2 ) center of the S U (2 ) gauge group] are confined to each other by fractionalized strings with a delocalized Z (2 ) flux. The strands of the fractionalized flux strings are domain walls that separate distinct pinwheel phases. A second-order phase transition in the three-dimensional Ising universality class separates two confining phases: one with correlated pinwheel orientations, and the other with uncorrelated pinwheel orientations.

The relationship of dynamical heterogeneity to the Adam-Gibbs and random first-order transition theories of glass formation.

PubMed

Starr, Francis W; Douglas, Jack F; Sastry, Srikanth

2013-03-28

We carefully examine common measures of dynamical heterogeneity for a model polymer melt and test how these scales compare with those hypothesized by the Adam and Gibbs (AG) and random first-order transition (RFOT) theories of relaxation in glass-forming liquids. To this end, we first analyze clusters of highly mobile particles, the string-like collective motion of these mobile particles, and clusters of relative low mobility. We show that the time scale of the high-mobility clusters and strings is associated with a diffusive time scale, while the low-mobility particles' time scale relates to a structural relaxation time. The difference of the characteristic times for the high- and low-mobility particles naturally explains the well-known decoupling of diffusion and structural relaxation time scales. Despite the inherent difference of dynamics between high- and low-mobility particles, we find a high degree of similarity in the geometrical structure of these particle clusters. In particular, we show that the fractal dimensions of these clusters are consistent with those of swollen branched polymers or branched polymers with screened excluded-volume interactions, corresponding to lattice animals and percolation clusters, respectively. In contrast, the fractal dimension of the strings crosses over from that of self-avoiding walks for small strings, to simple random walks for longer, more strongly interacting, strings, corresponding to flexible polymers with screened excluded-volume interactions. We examine the appropriateness of identifying the size scales of either mobile particle clusters or strings with the size of cooperatively rearranging regions (CRR) in the AG and RFOT theories. We find that the string size appears to be the most consistent measure of CRR for both the AG and RFOT models. Identifying strings or clusters with the "mosaic" length of the RFOT model relaxes the conventional assumption that the "entropic droplets" are compact. We also confirm the validity of the entropy formulation of the AG theory, constraining the exponent values of the RFOT theory. This constraint, together with the analysis of size scales, enables us to estimate the characteristic exponents of RFOT.

Semiclassical (qft) and Quantum (string) Rotating Black Holes and Their Evaporation:. New Results

NASA Astrophysics Data System (ADS)

Bouchareb, A.; Ramón Medrano, M.; Sánchez, N. G.

Combination of both quantum field theory (QFT) and string theory in curved backgrounds in a consistent framework, the string analogue model, allows us to provide a full picture of the Kerr-Newman black hole and its evaporation going beyond the current picture. We compute the quantum emission cross-section of strings by a Kerr-Newman black hole (KNbh). It shows the black hole emission at the Hawking temperature Tsem in the early stage of evaporation and the new string emission featuring a Hagedorn transition into a string state of temperature Ts at the last stages. New bounds on J and Q emerge in the quantum string regime (besides the known ones of the classical/semiclassical QFT regime). The last state of evaporation of a semiclassical Kerr-Newman black hole with mass M > mPl, angular momentum J and charge Q is a string state of temperature Ts, string mass Ms, J = 0 and Q = 0, decaying as usual quantum strings do into all kinds of particles. (Naturally, in this framework, there is no loss of information, (there is no paradox at all).) We compute the string entropy Ss(m, j) from the microscopic string density of states of mass m and spin mode j, ρ(m, j). (Besides the Hagedorn transition at Ts) we find for high j (extremal string states j → m2α‧c), a new phase transition at a temperature Tsj = √ {j/hbar }Ts, higher than Ts. By precisely identifying the semiclassical and quantum (string) gravity regimes, we find a new formula for the Kerr black hole entropy Ssem(M, J), as a function of the usual Bekenstein-Hawking entropy S sem(0). For M ≫ mPl and J < GM2/c, S sem(0) is the leading term, but for high angular momentum, (nearly extremal case J = GM2/c), a gravitational phase transition operates and the whole entropy Ssem is drastically different from the Bekenstein-Hawking entropy S sem(0). This new extremal black hole transition occurs at a temperature Tsem J = (J/ℏ)Tsem, higher than the Hawking temperature Tsem.

Dynamically avoiding fine-tuning the cosmological constant: the ``Relaxed Universe''

NASA Astrophysics Data System (ADS)

Bauer, Florian; Solà, Joan; Štefancić, Hrvoje

2010-12-01

We demonstrate that there exists a large class of Script F(R,Script G) action functionals of the scalar curvature and of the Gauß-Bonnet invariant which are able to relax dynamically a large cosmological constant (CC), whatever it be its starting value in the early universe. Hence, it is possible to understand, without fine-tuning, the very small current value Λ0 ~ H02 of the CC as compared to its theoretically expected large value in quantum field theory and string theory. In our framework, this relaxation appears as a pure gravitational effect, where no ad hoc scalar fields are needed. The action involves a positive power of a characteristic mass parameter, Script M, whose value can be, interestingly enough, of the order of a typical particle physics mass of the Standard Model of the strong and electroweak interactions or extensions thereof, including the neutrino mass. The model universe emerging from this scenario (the ``Relaxed Universe'') falls within the class of the so-called ΛXCDM models of the cosmic evolution. Therefore, there is a ``cosmon'' entity X (represented by an effective object, not a field), which in this case is generated by the effective functional Script F(R,Script G) and is responsible for the dynamical adjustment of the cosmological constant. This model universe successfully mimics the essential past epochs of the standard (or ``concordance'') cosmological model (ΛCDM). Furthermore, it provides interesting clues to the coincidence problem and it may even connect naturally with primordial inflation.

Acoustics of the Intonarumori

NASA Astrophysics Data System (ADS)

Serafin, Stefania

2005-04-01

The Intonarumori were a family of musical instruments invented by the Italian futurist composer and painter Luigi Russolo. Each Intonarumori was made of a wooden parallelepiped sound box, inside which a wheel of different sizes and materials was setting into vibration a catgut or metal string. The pitch of the string was varied by using a lever, while the speed of the wheel was controlled by the performer using a crank. At one end of the string there was a drumhead that transmitted vibrations to the speaker. Unfortunately, all the original Intonarumori were destroyed after a fire during World War II. Since then, researchers have tried to understand the sound production mechanism of such instruments, especially by consulting the patents compiled by Russolo or by reading his book ``The art of noise.'' In this paper we describe the acoustics of the Intonarumori. Based on such description, we propose physical models that simulate such instruments. The intonarumori's string is modeled using a one dimensional waveguide, which is excited either by an impact or a friction model. The body of the instrument is modeled using a 3-D rectangular mesh, while the horn is considered as an omnidirectional radiator.

In silico toxicity prediction by support vector machine and SMILES representation-based string kernel.

PubMed

Cao, D-S; Zhao, J-C; Yang, Y-N; Zhao, C-X; Yan, J; Liu, S; Hu, Q-N; Xu, Q-S; Liang, Y-Z

2012-01-01

There is a great need to assess the harmful effects or toxicities of chemicals to which man is exposed. In the present paper, the simplified molecular input line entry specification (SMILES) representation-based string kernel, together with the state-of-the-art support vector machine (SVM) algorithm, were used to classify the toxicity of chemicals from the US Environmental Protection Agency Distributed Structure-Searchable Toxicity (DSSTox) database network. In this method, the molecular structure can be directly encoded by a series of SMILES substrings that represent the presence of some chemical elements and different kinds of chemical bonds (double, triple and stereochemistry) in the molecules. Thus, SMILES string kernel can accurately and directly measure the similarities of molecules by a series of local information hidden in the molecules. Two model validation approaches, five-fold cross-validation and independent validation set, were used for assessing the predictive capability of our developed models. The results obtained indicate that SVM based on the SMILES string kernel can be regarded as a very promising and alternative modelling approach for potential toxicity prediction of chemicals.

Role of string-like collective atomic motion on diffusion and structural relaxation in glass forming Cu-Zr alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Hao; Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4; Zhong, Cheng

2015-04-28

We investigate Cu-Zr liquid alloys using molecular dynamics simulation and well-accepted embedded atom method potentials over a wide range of chemical composition and temperature as model metallic glass-forming (GF) liquids. As with other types of GF materials, the dynamics of these complex liquids are characterized by “dynamic heterogeneity” in the form of transient polymeric clusters of highly mobile atoms that are composed in turn of atomic clusters exhibiting string-like cooperative motion. In accordance with the string model of relaxation, an extension of the Adam-Gibbs (AG) model, changes in the activation free energy ΔG{sub a} with temperature of both the Cumore » and Zr diffusion coefficients D, and the alpha structural relaxation time τ{sub α} can be described to a good approximation by changes in the average string length, L. In particular, we confirm that the strings are a concrete realization of the abstract “cooperatively rearranging regions” of AG. We also find coexisting clusters of relatively “immobile” atoms that exhibit predominantly icosahedral local packing rather than the low symmetry packing of “mobile” atoms. These two distinct types of dynamic heterogeneity are then associated with different fluid structural states. Glass-forming liquids are thus analogous to polycrystalline materials where the icosahedrally packed regions correspond to crystal grains, and the strings reside in the relatively disordered grain boundary-like regions exterior to these locally well-ordered regions. A dynamic equilibrium between localized (“immobile”) and wandering (“mobile”) particles exists in the liquid so that the dynamic heterogeneity can be considered to be type of self-assembly process. We also characterize changes in the local atomic free volume in the course of string-like atomic motion to better understand the initiation and propagation of these fluid excitations.« less

The exceptional sigma model

NASA Astrophysics Data System (ADS)

Arvanitakis, Alex S.; Blair, Chris D. A.

2018-04-01

We detail the construction of the exceptional sigma model, which describes a string propagating in the "extended spacetime" of exceptional field theory. This is to U-duality as the doubled sigma model is to T-duality. Symmetry specifies the Weylinvariant Lagrangian uniquely and we show how it reduces to the correct 10-dimensional string Lagrangians. We also consider the inclusion of a Fradkin-Tseytlin (or generalised dilaton) coupling as well as a reformulation with dynamical tension.

Modeling Regular Replacement for String Constraint Solving

NASA Technical Reports Server (NTRS)

Fu, Xiang; Li, Chung-Chih

2010-01-01

Bugs in user input sanitation of software systems often lead to vulnerabilities. Among them many are caused by improper use of regular replacement. This paper presents a precise modeling of various semantics of regular substitution, such as the declarative, finite, greedy, and reluctant, using finite state transducers (FST). By projecting an FST to its input/output tapes, we are able to solve atomic string constraints, which can be applied to both the forward and backward image computation in model checking and symbolic execution of text processing programs. We report several interesting discoveries, e.g., certain fragments of the general problem can be handled using less expressive deterministic FST. A compact representation of FST is implemented in SUSHI, a string constraint solver. It is applied to detecting vulnerabilities in web applications

Conformal twists, Yang–Baxter σ-models & holographic noncommutativity

NASA Astrophysics Data System (ADS)

Araujo, Thiago; Bakhmatov, Ilya; Colgáin, Eoin Ó.; Sakamoto, Jun-ichi; Sheikh-Jabbari, Mohammad M.; Yoshida, Kentaroh

2018-06-01

Expanding upon earlier results (Araujo et al 2017 Phys. Rev. D 95 105006), we present a compendium of σ-models associated with integrable deformations of AdS5 generated by solutions to homogenous classical Yang–Baxter equation. Each example we study from four viewpoints: conformal (Drinfeld) twists, closed string gravity backgrounds, open string parameters and proposed dual noncommutative (NC) gauge theory. Irrespective of whether the deformed background is a solution to supergravity or generalized supergravity, we show that the open string metric associated with each gravity background is undeformed AdS5 with constant open string coupling and the NC structure Θ is directly related to the conformal twist. One novel feature is that Θ exhibits ‘holographic noncommutativity’: while it may exhibit non-trivial dependence on the holographic direction, its value everywhere in the bulk is uniquely determined by its value at the boundary, thus facilitating introduction of a dual NC gauge theory. We show that the divergence of the NC structure Θ is directly related to the unimodularity of the twist. We discuss the implementation of an outer automorphism of the conformal algebra as a coordinate transformation in the AdS bulk and discuss its implications for Yang–Baxter σ-models and self-T-duality based on fermionic T-duality. Finally, we comment on implications of our results for the integrability of associated open strings and planar integrability of dual NC gauge theories.

A Shifting Shield Provides Protection Against Cosmic Rays

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-12-01

The Sun plays an important role in protecting us from cosmic rays, energetic particles that pelt us from outside our solar system. But can we predict when and how it will provide the most protection, and use this to minimize the damage to both pilotedand roboticspace missions?The Challenge of Cosmic RaysSpacecraft outside of Earths atmosphere and magnetic field are at risk of damage from cosmic rays. [ESA]Galactic cosmic rays are high-energy, charged particles that originate from astrophysical processes like supernovae or even distant active galactic nuclei outside of our solar system.One reason to care about the cosmic rays arriving near Earth is because these particles can provide a significant challenge for space missions traveling above Earths protective atmosphere and magnetic field. Since impacts from cosmic rays can damage human DNA, this risk poses a major barrier to plans for interplanetary travel by crewed spacecraft. And roboticmissions arent safe either: cosmic rays can flip bits, wreaking havoc on spacecraft electronics as well.The magnetic field carried by the solar wind provides a protective shield, deflecting galactic cosmic rays from our solar system. [Walt Feimer/NASA GSFCs Conceptual Image Lab]Shielded by the SunConveniently, we do have some broader protection against galactic cosmic rays: a built-in shield provided by the Sun. The interplanetary magnetic field, which is embedded in the solar wind, deflects low-energy cosmic rays from us at the outer reaches of our solar system, decreasing the flux of these cosmic rays that reach us at Earth.This shield, however, isnt stationary; instead, it moves and changes as the strength and direction of the solar wind moves and changes. This results in a much lower cosmic-ray flux at Earth when solar activity is high i.e., at the peak of the 11-year solar cycle than when solar activity is low. This visible change in local cosmic-ray flux with solar activity is known as solar modulation of the cosmic ray flux at Earth.In a new study, a team of scientists led by Nicola Tomassetti (University of Perugia, Italy) has modeled this solar modulation to better understand the process by which the Suns changing activity influences the cosmic ray flux that reaches us at Earth.Modeling a LagTomassetti and collaborators model uses two solar-activity observables as inputs: the number of sunspots and the tilt angle of the heliospheric current sheet. By modeling basic transport processes in the heliosphere, the authors then track the impact that the changing solar properties have on incoming galactic cosmic rays. In particular, the team explores the time lag between when solar activity changes and when we see the responding change in the cosmic-ray flux.Cosmic-ray flux observations are best fit by the authors model when an 8-month lag is included (red bold line). A comparison model with no lag (black dashed line) is included. [Tomassetti et al. 2017]By comparing their model outputs to the large collection of time-dependent observations of cosmic-ray fluxes, Tomassetti and collaborators show that the best fit to data occurs with an 8-month lag between changing solar activity and local cosmic-ray flux modulation.This is an important outcome for studying the processes that affect the cosmic-ray flux that reaches Earth. But theres an additional intriguing consequence of this result: knowledge of the current solar activity could allow us to predict the modulation that will occur for cosmic rays near Earth an entire 8 months from now! If this model is correct, it brings us one step closer to being able to plan safer space missions for the future.CitationNicola Tomassetti et al 2017 ApJL 849 L32. doi:10.3847/2041-8213/aa9373

[Assessment of an educational technology in the string literature about breastfeeding].

PubMed

de Oliveira, Paula Marciana Pinheiro; Pagliuca, Lorita Marlena Freitag

2013-02-01

The goal of this study was to assess educational technology in the string literature about breastfeeding. The study was conducted between March and September 2009 by breastfeeding experts and experts on string literature. A psychometric model was adopted as the theoretical-methodological framework. For data collection, an instrument was used to assess the content about breastfeeding and the string literature rules. The analysis was based on comparisons of the notes and critical reflections of experts. Ethical guidelines were followed during the study. After the assessments, the educational technology was adjusted until all of the experts agreed. The assessment of educational technology can reduce obstacles to information dissemination and can lead to improvements in quality of life.

Models of Cosmic-Ray Origin

NASA Astrophysics Data System (ADS)

Shapiro, M. M.

2001-08-01

Two models of cosmic-ray genesis are compared: (a) the author s red-dwarf hypothesis requiring the injection of seed particles from coronal mass ejections (CME) prior to shock acceleration, and (b) the direct acceleration of thermal ions and of grains in the ISM, proposed by Meyer, Drury and Ellison. Both models agree that shocks in the expanding envelopes of supernova remnants are principally responsible for acceleration to cosmic-ray energies. Both are designed to overcome the mismatch between the source composition of the Galactic cosmic rays (GCR) and the composition of the thermal ISM gas. Model (a) utilizes the prolific emissions of energetic particles from active dMe and dKe stars via their CME as the agents of seed-particle injection into the ISM. The composition of these seed particles is governed by the FIP (first-ionization potential) selection mechanism that operates for both Galactic cosmic rays and solar energetic particles. Hence it is consistent with the cosmic-ray source composition. Model (b) relies on the sputtering and acceleration of grains in the ISM (along with acceleration of thermal ions) to provide the known source composition. This model considers the FIP ordering of GCR abundances as purely coincidental, and it attributes the relative source abundances to selection according to volatility. Recent cosmic-ray observations in favor of each model are cited.

Asymmetric thin-shell wormholes

NASA Astrophysics Data System (ADS)

Forghani, S. Danial; Mazharimousavi, S. Habib; Halilsoy, Mustafa

2018-06-01

Spacetime wormholes in isotropic spacetimes are represented traditionally by embedding diagrams which were symmetric paraboloids. This mirror symmetry, however, can be broken by considering different sources on different sides of the throat. This gives rise to an asymmetric thin-shell wormhole, whose stability is studied here in the framework of the linear stability analysis. Having constructed a general formulation, using a variable equation of state and related junction conditions, the results are tested for some examples of diverse geometries such as the cosmic string, Schwarzschild, Reissner-Nordström and Minkowski spacetimes. Based on our chosen spacetimes as examples, our finding suggests that symmetry is an important factor to make a wormhole more stable. Furthermore, the parameter γ , which corresponds to the radius dependency of the pressure on the wormholes's throat, can affect the stability in a great extent.

Search for transient gravitational waves in coincidence with short-duration radio transients during 2007-2013

NASA Astrophysics Data System (ADS)

Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; Allocca, A.; Altin, P. A.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Araya, M. C.; Arceneaux, C. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Aufmuth, P.; Aulbert, C.; Babak, S.; Bacon, P.; Bader, M. K. M.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, D.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Baune, C.; Bavigadda, V.; Bazzan, M.; Behnke, B.; Bejger, M.; Bell, A. S.; Bell, C. J.; Berger, B. K.; Bergman, J.; Bergmann, G.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Birney, R.; Biscans, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, S.; Bock, O.; Bodiya, T. P.; Boer, M.; Bogaert, G.; Bogan, C.; Bohe, A.; Bojtos, P.; Bond, C.; Bondu, F.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Braginsky, V. B.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brown, N. M.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Calderón Bustillo, J.; Callister, T.; Calloni, E.; Camp, J. B.; Cannon, K. C.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Casanueva Diaz, J.; Casentini, C.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C. B.; Cerboni Baiardi, L.; Cerretani, G.; Cesarini, E.; Chakraborty, R.; Chalermsongsak, T.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; Chassande-Mottin, E.; Chen, H. Y.; Chen, Y.; Cheng, C.; Chincarini, A.; Chiummo, A.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, S.; Chung, S.; Ciani, G.; Clara, F.; Clark, J. A.; Cleva, F.; Coccia, E.; Cohadon, P.-F.; Colla, A.; Collette, C. G.; Cominsky, L.; Constancio, M.; Conte, A.; Conti, L.; Cook, D.; Corbitt, T. R.; Cornish, N.; Corsi, A.; Cortese, S.; Costa, C. A.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J.-P.; Countryman, S. T.; Couvares, P.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Craig, K.; Creighton, J. D. E.; Cripe, J.; Crowder, S. G.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dal Canton, T.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Darman, N. S.; Dattilo, V.; Dave, I.; Daveloza, H. P.; Davier, M.; Davies, G. S.; Daw, E. J.; Day, R.; DeBra, D.; Debreczeni, G.; Degallaix, J.; De Laurentis, M.; Deléglise, S.; Del Pozzo, W.; Denker, T.; Dent, T.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; DeSalvo, R.; Dhurandhar, S.; Díaz, M. C.; Di Fiore, L.; Di Giovanni, M.; Di Girolamo, T.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Virgilio, A.; Dojcinoski, G.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Douglas, R.; Downes, T. P.; Drago, M.; Drever, R. W. P.; Driggers, J. C.; Du, Z.; Ducrot, M.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H.-B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Engels, W.; Essick, R. C.; Etzel, T.; Evans, M.; Evans, T. M.; Everett, R.; Factourovich, M.; Fafone, V.; Fair, H.; Fairhurst, S.; Fan, X.; Fang, Q.; Farinon, S.; Farr, B.; Farr, W. M.; Favata, M.; Fays, M.; Fehrmann, H.; Fejer, M. M.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Fiori, I.; Fiorucci, D.; Fisher, R. P.; Flaminio, R.; Fletcher, M.; Fournier, J.-D.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fricke, T. T.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H. A. G.; Gair, J. R.; Gammaitoni, L.; Gaonkar, S. G.; Garufi, F.; Gaur, G.; Gehrels, N.; Gemme, G.; Genin, E.; Gennai, A.; George, J.; Gergely, L.; Germain, V.; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.; Glaefke, A.; Goetz, E.; Goetz, R.; Gondan, L.; González, G.; Gonzalez Castro, J. M.; Gopakumar, A.; Gordon, N. A.; Gorodetsky, M. L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Graff, P. B.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Groot, P.; Grote, H.; Grunewald, S.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Hacker, J. J.; Hall, B. R.; Hall, E. D.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Hartman, M. T.; Haster, C.-J.; Haughian, K.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hoak, D.; Hodge, K. A.; Hofman, D.; Hollitt, S. E.; Holt, K.; Holz, D. E.; Hopkins, P.; Hosken, D. J.; Hough, J.; Houston, E. A.; Howell, E. J.; Hu, Y. M.; Huang, S.; Huerta, E. A.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh-Dinh, T.; Idrisy, A.; Indik, N.; Ingram, D. R.; Inta, R.; Isa, H. N.; Isac, J.-M.; Isi, M.; Islas, G.; Isogai, T.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jang, H.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jiménez-Forteza, F.; Johnson, W. W.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; Haris, K.; Kalaghatgi, C. V.; Kalogera, V.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Karki, S.; Kasprzack, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kaur, T.; Kawabe, K.; Kawazoe, F.; Kéfélian, F.; Kehl, M. S.; Keitel, D.; Kelley, D. B.; Kells, W.; Kennedy, R.; Key, J. S.; Khalaidovski, A.; Khalili, F. Y.; Khan, I.; Khan, S.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, Chunglee; Kim, J.; Kim, K.; Kim, Nam-Gyu; Kim, Namjun; Kim, Y.-M.; King, E. J.; King, P. J.; Kinzel, D. L.; Kissel, J. S.; Kleybolte, L.; Klimenko, S.; Koehlenbeck, S. M.; Kokeyama, K.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Kringel, V.; Królak, A.; Krueger, C.; Kuehn, G.; Kumar, P.; Kuo, L.; Kutynia, A.; Lackey, B. D.; Landry, M.; Lange, J.; Lantz, B.; Lasky, P. D.; Lazzarini, A.; Lazzaro, C.; Leaci, P.; Leavey, S.; Lebigot, E. O.; Lee, C. H.; Lee, H. K.; Lee, H. M.; Lee, K.; Lenon, A.; Leonardi, M.; Leong, J. R.; Leroy, N.; Letendre, N.; Levin, Y.; Levine, B. M.; Li, T. G. F.; Libson, A.; Littenberg, T. B.; Lockerbie, N. A.; Logue, J.; Lombardi, A. L.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Lück, H.; Lundgren, A. P.; Luo, J.; Lynch, R.; Ma, Y.; MacDonald, T.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magaña-Sandoval, F.; Magee, R. M.; Mageswaran, M.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, F.; Marion, F.; Márka, S.; Márka, Z.; Markosyan, A. S.; Maros, E.; Martelli, F.; Martellini, L.; Martin, I. W.; Martin, R. M.; Martynov, D. V.; Marx, J. N.; Mason, K.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Mastrogiovanni, S.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; Mazzolo, G.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Meidam, J.; Melatos, A.; Mendell, G.; Mendoza-Gandara, D.; Mercer, R. A.; Merilh, E. L.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Metzdorff, R.; Meyers, P. M.; Mezzani, F.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A. L.; Miller, J.; Millhouse, M.; Minenkov, Y.; Ming, J.; Mirshekari, S.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moggi, A.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, B. C.; Moore, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mossavi, K.; Mours, B.; Mow-Lowry, C. M.; Mueller, C. L.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, D.; Mukherjee, S.; Mukund, K. N.; Mullavey, A.; Munch, J.; Murphy, D. J.; Murray, P. G.; Mytidis, A.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Necula, V.; Nedkova, K.; Nelemans, G.; Neri, M.; Neunzert, A.; Newton, G.; Nguyen, T. T.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Nocera, F.; Nolting, D.; Normandin, M. E. N.; Nuttall, L. K.; Oberling, J.; Ochsner, E.; O'Dell, J.; Oelker, E.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Oliver, M.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; O'Shaughnessy, R.; Ott, C. D.; Ottaway, D. J.; Ottens, R. S.; Overmier, H.; Owen, B. J.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, F.; Paoli, A.; Papa, M. A.; Paris, H. R.; Parker, W.; Pascucci, D.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patricelli, B.; Patrick, Z.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Pereira, R.; Perreca, A.; Phelps, M.; Piccinni, O. J.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pitkin, M.; Pletsch, H. J.; Poggiani, R.; Popolizio, P.; Post, A.; Powell, J.; Prasad, J.; Predoi, V.; Premachandra, S. S.; Prestegard, T.; Price, L. R.; Prijatelj, M.; Principe, M.; Privitera, S.; Prodi, G. A.; Prokhorov, L.; Puncken, O.; Punturo, M.; Puppo, P.; Pürrer, M.; Qi, H.; Qin, J.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rakhmanov, M.; Rapagnani, P.; Raymond, V.; Razzano, M.; Re, V.; Read, J.; Reed, C. M.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Rew, H.; Ricci, F.; Riles, K.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, J. D.; Romano, R.; Romanov, G.; Romie, J. H.; Rosińska, D.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sanchez, E. J.; Sandberg, V.; Sandeen, B.; Sanders, J. R.; Sassolas, B.; Sathyaprakash, B. S.; Saulson, P. R.; Sauter, O. E. S.; Savage, R. L.; Sawadsky, A.; Schale, P.; Schilling, R.; Schmidt, J.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schönbeck, A.; Schreiber, E.; Schuette, D.; Schutz, B. F.; Scott, J.; Scott, S. M.; Sellers, D.; Sentenac, D.; Sequino, V.; Sergeev, A.; Serna, G.; Setyawati, Y.; Sevigny, A.; Shaddock, D. A.; Shahriar, M. S.; Shaltev, M.; Shao, Z.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, A. D.; Simakov, D.; Singer, A.; Singer, L. P.; Singh, A.; Singh, R.; Singhal, A.; Sintes, A. M.; Slagmolen, B. J. J.; Smith, J. R.; Smith, N. D.; Smith, R. J. E.; Son, E. J.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Srivastava, A. K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stephens, B. C.; Stiles, D.; Stone, R.; Strain, K. A.; Straniero, N.; Stratta, G.; Strauss, N. A.; Strigin, S.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sutton, P. J.; Swinkels, B. L.; Szczepańczyk, M. J.; Tacca, M.; Talukder, D.; Tanner, D. B.; Tápai, M.; Tarabrin, S. P.; Taracchini, A.; Taylor, R.; Theeg, T.; Thirugnanasambandam, M. P.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Tomlinson, C.; Tonelli, M.; Torres, C. V.; Torrie, C. I.; Töyrä, D.; Travasso, F.; Traylor, G.; Trifirò, D.; Tringali, M. C.; Trozzo, L.; Tse, M.; Turconi, M.; Tuyenbayev, D.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; Van Den Broeck, C.; Vander-Hyde, D. C.; van der Schaaf, L.; van Heijningen, J. V.; van Veggel, A. A.; Vardaro, M.; Vass, S.; Vasúth, M.; Vaulin, R.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Verkindt, D.; Vetrano, F.; Viceré, A.; Vinciguerra, S.; Vine, D. J.; Vinet, J.-Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Voss, D. V.; Vousden, W. D.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, M.; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, M.; Wang, X.; Wang, Y.; Ward, R. L.; Warner, J.; Was, M.; Weaver, B.; Wei, L.-W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Welborn, T.; Wen, L.; Weßels, P.; Westphal, T.; Wette, K.; Whelan, J. T.; Whitcomb, S. E.; White, D. J.; Whiting, B. F.; Williams, R. D.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Worden, J.; Wright, J. L.; Wu, G.; Yablon, J.; Yam, W.; Yamamoto, H.; Yancey, C. C.; Yap, M. J.; Yu, H.; Yvert, M.; ZadroŻny, A.; Zangrando, L.; Zanolin, M.; Zendri, J.-P.; Zevin, M.; Zhang, F.; Zhang, L.; Zhang, M.; Zhang, Y.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, X. J.; Zucker, M. E.; Zuraw, S. E.; Zweizig, J.; Archibald, A. M.; Banaszak, S.; Berndsen, A.; Boyles, J.; Cardoso, R. F.; Chawla, P.; Cherry, A.; Dartez, L. P.; Day, D.; Epstein, C. R.; Ford, A. J.; Flanigan, J.; Garcia, A.; Hessels, J. W. T.; Hinojosa, J.; Jenet, F. A.; Karako-Argaman, C.; Kaspi, V. M.; Keane, E. F.; Kondratiev, V. I.; Kramer, M.; Leake, S.; Lorimer, D.; Lunsford, G.; Lynch, R. S.; Martinez, J. G.; Mata, A.; McLaughlin, M. A.; McPhee, C. A.; Penucci, T.; Ransom, S.; Roberts, M. S. E.; Rohr, M. D. W.; Stairs, I. H.; Stovall, K.; van Leeuwen, J.; Walker, A. N.; Wells, B. L.; LIGO Scientific Collaboration; Virgo Collaboration

2016-06-01

We present an archival search for transient gravitational-wave bursts in coincidence with 27 single-pulse triggers from Green Bank Telescope pulsar surveys, using the LIGO, Virgo, and GEO interferometer network. We also discuss a check for gravitational-wave signals in coincidence with Parkes fast radio bursts using similar methods. Data analyzed in these searches were collected between 2007 and 2013. Possible sources of emission of both short-duration radio signals and transient gravitational-wave emission include starquakes on neutron stars, binary coalescence of neutron stars, and cosmic string cusps. While no evidence for gravitational-wave emission in coincidence with these radio transients was found, the current analysis serves as a prototype for similar future searches using more sensitive second-generation interferometers.

Instantaneous and scale-versatile gourdron theory: pair momentum equation, quasi-stability concept, and statistical indeterminacy revealing masses of elementary, bio-molecular, and cosmic particles

NASA Astrophysics Data System (ADS)

Naitoh, Ken

2014-04-01

Flexible particles, including hadrons, atoms, hydrated biological molecules, cells, organs containing water, liquid fuel droplets in engines, and stars commonly break up after becoming a gourd shape rather than that of a string; this leads to cyto-fluid dynamics that can explain the proliferation, differentiation, and replication of biomolecules, onto-biology that clarifies the relationship between information, structure, and function, and the gourd theory that clarifies masses, including quark-leptons and Plank energy. The masses are related to the super-magic numbers, including the asymmetric silver ratio and symmetric yamato ratio, and reveal further mechanisms underlying symmetry breaking. This paper gives further theoretical basis and evidence, because the gourd theory reported previously is a little analogical and instinctive.

A review of the generalized uncertainty principle.

PubMed

Tawfik, Abdel Nasser; Diab, Abdel Magied

2015-12-01

Based on string theory, black hole physics, doubly special relativity and some 'thought' experiments, minimal distance and/or maximum momentum are proposed. As alternatives to the generalized uncertainty principle (GUP), the modified dispersion relation, the space noncommutativity, the Lorentz invariance violation, and the quantum-gravity-induced birefringence effects are summarized. The origin of minimal measurable quantities and the different GUP approaches are reviewed and the corresponding observations are analysed. Bounds on the GUP parameter are discussed and implemented in the understanding of recent PLANCK observations of cosmic inflation. The higher-order GUP approaches predict minimal length uncertainty with and without maximum momenta. Possible arguments against the GUP are discussed; for instance, the concern about its compatibility with the equivalence principles, the universality of gravitational redshift and the free fall and law of reciprocal action are addressed.

Chiral phase transition from string theory.

PubMed

Parnachev, Andrei; Sahakyan, David A

2006-09-15

The low energy dynamics of a certain D-brane configuration in string theory is described at weak t'Hooft coupling by a nonlocal version of the Nambu-Jona-Lasinio model. We study this system at finite temperature and strong t'Hooft coupling, using the string theory dual. We show that for sufficiently low temperatures chiral symmetry is broken, while for temperatures larger then the critical value, it gets restored. We compute the latent heat and observe that the phase transition is of the first order.

Ramond and Neveu-Schwarz paraspinning strings in presence of D-branes

NASA Astrophysics Data System (ADS)

Hamam, D.; Belaloui, N.

2018-03-01

We investigate the theory of an open parafermionic string between two parallel Dp-, Dq-branes in Ramond and Neveu-Schwarz sectors. Trilinear commutation relations between the string variables are postulated and the corresponding ones in terms of modes are derived. The analysis of the spectrum shows that one can again have a free tachyon Neveu-Schwarz model for some values of the order of the paraquantization associated to some values of p and q. The consistency of this model requires the calculation of the partition function and its confrontation with the results of the degeneracies. A perfect agreement between the two results is obtained and the closure of the Virasoro superalgebra is confirmed.

Tissue fusion over nonadhering surfaces

PubMed Central

Nier, Vincent; Deforet, Maxime; Duclos, Guillaume; Yevick, Hannah G.; Cochet-Escartin, Olivier; Marcq, Philippe; Silberzan, Pascal

2015-01-01

Tissue fusion eliminates physical voids in a tissue to form a continuous structure and is central to many processes in development and repair. Fusion events in vivo, particularly in embryonic development, often involve the purse-string contraction of a pluricellular actomyosin cable at the free edge. However, in vitro, adhesion of the cells to their substrate favors a closure mechanism mediated by lamellipodial protrusions, which has prevented a systematic study of the purse-string mechanism. Here, we show that monolayers can cover well-controlled mesoscopic nonadherent areas much larger than a cell size by purse-string closure and that active epithelial fluctuations are required for this process. We have formulated a simple stochastic model that includes purse-string contractility, tissue fluctuations, and effective friction to qualitatively and quantitatively account for the dynamics of closure. Our data suggest that, in vivo, tissue fusion adapts to the local environment by coordinating lamellipodial protrusions and purse-string contractions. PMID:26199417

Acoustics of Idakkā: An Indian snare drum with definite pitch.

PubMed

Jose, Kevin; Chatterjee, Anindya; Gupta, Anurag

2018-05-01

The vibration of a homogeneous circular membrane backed by two taut strings is shown to yield several harmonic overtones for a wide range of physical and geometric parameters. Such a membrane is present at each end of the barrel of an idakkā, an Indian snare drum well known for its rich musicality. The audio recordings of the musical drum are analyzed and a case is made for the strong sense of pitch associated with the drum. A computationally inexpensive model of the string-membrane interaction is proposed assuming the strings to be without inertia. The interaction essentially entails wrapping/unwrapping of the string around a curve on the deforming membrane unlike the colliding strings in Western snare drums. The range of parameters for which harmonicity is achieved is examined and is found to be conforming with what is used in actual drum playing and construction.

Propagation of cosmic rays in the galaxy

NASA Technical Reports Server (NTRS)

Daniel, R. R.; Stephens, S. A.

1974-01-01

The characteristics of a model for analyzing the propagation of cosmic rays are discussed. The requirements for analyzing the relevant observational data on cosmic rays are defines as: (1) the chemical and isotopic composition of cosmic rays as a function of energy, (2) the flux and energy spectrum of the individual nucleonic components, (3) the flux and energy spectrum of the electronic component, (4) the cosmic ray prehistory, and (5) the degree of isotropy in their arrival directions as a function of energy. It is stated that the model which has been able to bring to pass the greatest measure of success is the galactic confinement model.

Colored petri net modeling of small interfering RNA-mediated messenger RNA degradation.

PubMed

Nickaeen, Niloofar; Moein, Shiva; Heidary, Zarifeh; Ghaisari, Jafar

2016-01-01

Mathematical modeling of biological systems is an attractive way for studying complex biological systems and their behaviors. Petri Nets, due to their ability to model systems with various levels of qualitative information, have been wildly used in modeling biological systems in which enough qualitative data may not be at disposal. These nets have been used to answer questions regarding the dynamics of different cell behaviors including the translation process. In one stage of the translation process, the RNA sequence may be degraded. In the process of degradation of RNA sequence, small-noncoding RNA molecules known as small interfering RNA (siRNA) match the target RNA sequence. As a result of this matching, the target RNA sequence is destroyed. In this context, the process of matching and destruction is modeled using Colored Petri Nets (CPNs). The model is constructed using CPNs which allow tokens to have a value or type on them. Thus, CPN is a suitable tool to model string structures in which each element of the string has a different type. Using CPNs, long RNA, and siRNA strings are modeled with a finite set of colors. The model is simulated via CPN Tools. A CPN model of the matching between RNA and siRNA strings is constructed in CPN Tools environment. In previous studies, a network of stoichiometric equations was modeled. However, in this particular study, we modeled the mechanism behind the silencing process. Modeling this kind of mechanisms provides us with a tool to examine the effects of different factors such as mutation or drugs on the process.

Document retrieval on repetitive string collections.

PubMed

Gagie, Travis; Hartikainen, Aleksi; Karhu, Kalle; Kärkkäinen, Juha; Navarro, Gonzalo; Puglisi, Simon J; Sirén, Jouni

2017-01-01

Most of the fastest-growing string collections today are repetitive, that is, most of the constituent documents are similar to many others. As these collections keep growing, a key approach to handling them is to exploit their repetitiveness, which can reduce their space usage by orders of magnitude. We study the problem of indexing repetitive string collections in order to perform efficient document retrieval operations on them. Document retrieval problems are routinely solved by search engines on large natural language collections, but the techniques are less developed on generic string collections. The case of repetitive string collections is even less understood, and there are very few existing solutions. We develop two novel ideas, interleaved LCPs and precomputed document lists , that yield highly compressed indexes solving the problem of document listing (find all the documents where a string appears), top- k document retrieval (find the k documents where a string appears most often), and document counting (count the number of documents where a string appears). We also show that a classical data structure supporting the latter query becomes highly compressible on repetitive data. Finally, we show how the tools we developed can be combined to solve ranked conjunctive and disjunctive multi-term queries under the simple [Formula: see text] model of relevance. We thoroughly evaluate the resulting techniques in various real-life repetitiveness scenarios, and recommend the best choices for each case.

Differentiating G-inflation from string gas cosmology using the effective field theory approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Minxi; Liu, Junyu; Lu, Shiyun

A characteristic signature of String Gas Cosmology is primordial power spectra for scalar and tensor modes which are almost scale-invariant but with a red tilt for scalar modes but a blue tilt for tensor modes. This feature, however, can also be realized in the so-called G-inflation model, in which Horndeski operators are introduced which leads to a blue tensor tilt by softly breaking the Null Energy Condition. In this article we search for potential observational differences between these two cosmologies by performing detailed perturbation analyses based on the Effective Field Theory approach. Our results show that, although both two modelsmore » produce blue tilted tensor perturbations, they behave differently in three aspects. Firstly, String Gas Cosmology predicts a specific consistency relation between the index of the scalar modes n {sub s} and that of tensor ones n {sub t} , which is hard to be reproduced by G-inflation. Secondly, String Gas Cosmology typically predicts non-Gaussianities which are highly suppressed on observable scales, while G-inflation gives rise to observationally large non-Gaussianities because the kinetic terms in the action become important during inflation. However, after finely tuning the model parameters of G-inflation it is possible to obtain a blue tensor spectrum and negligible non-Gaussianities with a degeneracy between the two models. This degeneracy can be broken by a third observable, namely the scale dependence of the nonlinearity parameter, which vanishes for G-inflation but has a blue tilt in the case of String Gas Cosmology. Therefore, we conclude that String Gas Cosmology is in principle observationally distinguishable from the single field inflationary cosmology, even allowing for modifications such as G-inflation.« less

Galactic cosmic ray composition and energy spectra

NASA Technical Reports Server (NTRS)

Mewaldt, R. A.

1994-01-01

Galactic cosmic ray nuclei represent a significant risk to long-duration spaceflight outside the magnetosphere. We review briefly existing measurements of the composition and energy spectra of heavy cosmic ray nuclei, pointing out which species and energy ranges are most critical to assessing cosmic ray risks for spaceflight. Key data sets are identified and a table of cosmic ray abundances is presented for elements from H to Ni (Z = 1 to 28). Because of the 22-year nature of the solar modulation cycle, data from the approaching 1998 solar minimum is especially important to reducing uncertainties in the cosmic ray radiation hazard. It is recommended that efforts to model this hazard take advantage of approaches that have been developed to model the astrophysical aspects of cosmic rays.

Initial Systematic Investigations of the Weakly Coupled Free Fermionic Heterotic String Landscape Statistics

NASA Astrophysics Data System (ADS)

Renner, Timothy

2011-12-01

A C++ framework was constructed with the explicit purpose of systematically generating string models using the Weakly Coupled Free Fermionic Heterotic String (WCFFHS) method. The software, optimized for speed, generality, and ease of use, has been used to conduct preliminary systematic investigations of WCFFHS vacua. Documentation for this framework is provided in the Appendix. After an introduction to theoretical and computational aspects of WCFFHS model building, a study of ten-dimensional WCFFHS models is presented. Degeneracies among equivalent expressions of each of the known models are investigated and classified. A study of more phenomenologically realistic four-dimensional models based on the well known "NAHE" set is then presented, with statistics being reported on gauge content, matter representations, and space-time supersymmetries. The final study is a parallel to the NAHE study in which a variation of the NAHE set is systematically extended and examined statistically. Special attention is paid to models with "mirroring"---identical observable and hidden sector gauge groups and matter representations.

Linear Sigma Model Toolshed for D-brane Physics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hellerman, Simeon

Building on earlier work, we construct linear sigma models for strings on curved spaces in the presence of branes. Our models include an extremely general class of brane-worldvolume gauge field configurations. We explain in an accessible manner the mathematical ideas which suggest appropriate worldsheet interactions for generating a given open string background. This construction provides an explanation for the appearance of the derived category in D-brane physic complementary to that of recent work of Douglas.

Characterization of Fluid Flow through a Simplified Heart Valve Model

NASA Astrophysics Data System (ADS)

Katija, Kakani

2005-11-01

Research has shown that the leading vortex of a starting jet makes a larger contribution to mass transport than a straight jet. Physical processes terminate growth of the leading vortex ring at a stroke ratio (L/D) between 3.5 and 4.5. This has enhanced the idea that biological systems optimize vortex formation for fluid transport. Of present interest is how fluid transport through a heart valve induces flutter of the valve leaflets. An attempt to characterize the fluid flow through a heart valve was made using a simplified cylinder-string system. Experiments were conducted in a water tank where a piston pushed fluid out of a cylinder (of diameter D) into surrounding fluid. A latex string was attached to the end of the cylinder to simulate a heart valve leaflet. The FFT of the string motion was computed to quantify the flutter behavior observed in the cylinder-string system. By increasing the stroke ratio, the amplitude of transverse oscillations for all string lengths increases. For the string length D/2, the occurrence of flutter coincides with the formation of the vortex ring trailing jet.

Modeling the plasmasphere based on LEO satellites onboard GPS measurements

NASA Astrophysics Data System (ADS)

Chen, Peng; Yao, Yibin; Li, Qinzheng; Yao, Wanqiang

2017-01-01

The plasmasphere, which is located above the ionosphere, is a significant component of Earth's atmosphere. A global plasmaspheric model was constructed using the total electron content (TEC) along the signal propagation path calculated using onboard Global Positioning System observations from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) and MetOp-A, provided by the COSMIC Data Analysis and Archive Center (CDAAC). First, the global plasmaspheric model was established using only COSMIC TEC, and a set of MetOp-A TEC provided by CDAAC served for external evaluation. Results indicated that the established model using only COSMIC data is highly accurate. Then, COSMIC and MetOp-A TEC were combined to produce a new global plasmaspheric model. Finally, the variational characteristics of global plasmaspheric electron content with latitude, local time, and season were investigated using the global plasmaspheric model established in this paper.

Evolving neural networks with genetic algorithms to study the string landscape

NASA Astrophysics Data System (ADS)

Ruehle, Fabian

2017-08-01

We study possible applications of artificial neural networks to examine the string landscape. Since the field of application is rather versatile, we propose to dynamically evolve these networks via genetic algorithms. This means that we start from basic building blocks and combine them such that the neural network performs best for the application we are interested in. We study three areas in which neural networks can be applied: to classify models according to a fixed set of (physically) appealing features, to find a concrete realization for a computation for which the precise algorithm is known in principle but very tedious to actually implement, and to predict or approximate the outcome of some involved mathematical computation which performs too inefficient to apply it, e.g. in model scans within the string landscape. We present simple examples that arise in string phenomenology for all three types of problems and discuss how they can be addressed by evolving neural networks from genetic algorithms.

Intonation and compensation of fretted string instruments

NASA Astrophysics Data System (ADS)

Varieschi, Gabriele; Gower, Christina

2011-04-01

We discuss theoretical and physical models that are useful for analyzing the intonation of musical instruments such as guitars and mandolins and can be used to improve the tuning on these instruments. The placement of frets on the fingerboard is designed according to mathematical rules and the assumption of an ideal string. The analysis becomes more complicated when we include the effects of deformation of the string and inharmonicity due to other string characteristics. As a consequence, perfect intonation of all the notes on the instrument cannot be achieved, but complex compensation procedures can be introduced to minimize the problem. To test the validity of these procedures, we performed extensive measurements using standard monochord sonometers and other acoustical devices, confirming the correctness of our theoretical models. These experimental activities can be integrated into acoustics courses and laboratories and can become a more advanced version of basic experiments with monochords and sonometers. This work was supported by a grant from the Frank R. Seaver College of Science and Engineering, Loyola Marymount University.

Acceleration and propagation of cosmic rays

NASA Astrophysics Data System (ADS)

Fransson, C.; Epstein, R. I.

1980-11-01

Two general categories of cosmic ray models are discussed, concomitant acceleration and propagation (CAP) models and sequential acceleration and propagation (SAP) models. These normally correspond to the cosmic rays being continuously accelerated in the interstellar medium or being rapidly produced by discrete sources or strong shock waves, respectively. For the CAP models it is found that the ratio of the predominantly secondary nuclei (Li + Be + B + N) to the predominantly primary nuclei (C + O) varies by less than a factor of 1.5 between 1 and 100 GeV per nucleon. This is at variance with current measurements. It thus appears that the evolution of cosmic rays is best described by SAP models.

Local random configuration-tree theory for string repetition and facilitated dynamics of glass

NASA Astrophysics Data System (ADS)

Lam, Chi-Hang

2018-02-01

We derive a microscopic theory of glassy dynamics based on the transport of voids by micro-string motions, each of which involves particles arranged in a line hopping simultaneously displacing one another. Disorder is modeled by a random energy landscape quenched in the configuration space of distinguishable particles, but transient in the physical space as expected for glassy fluids. We study the evolution of local regions with m coupled voids. At a low temperature, energetically accessible local particle configurations can be organized into a random tree with nodes and edges denoting configurations and micro-string propagations respectively. Such trees defined in the configuration space naturally describe systems defined in two- or three-dimensional physical space. A micro-string propagation initiated by a void can facilitate similar motions by other voids via perturbing the random energy landscape, realizing path interactions between voids or equivalently string interactions. We obtain explicit expressions of the particle diffusion coefficient and a particle return probability. Under our approximation, as temperature decreases, random trees of energetically accessible configurations exhibit a sequence of percolation transitions in the configuration space, with local regions containing fewer coupled voids entering the non-percolating immobile phase first. Dynamics is dominated by coupled voids of an optimal group size, which increases as temperature decreases. Comparison with a distinguishable-particle lattice model (DPLM) of glass shows very good quantitative agreements using only two adjustable parameters related to typical energy fluctuations and the interaction range of the micro-strings.

The microphysics and macrophysics of cosmic rays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zweibel, Ellen G.

2013-05-15

This review paper commemorates a century of cosmic ray research, with emphasis on the plasma physics aspects. Cosmic rays comprise only ∼10{sup −9} of interstellar particles by number, but collectively their energy density is about equal to that of the thermal particles. They are confined by the Galactic magnetic field and well scattered by small scale magnetic fluctuations, which couple them to the local rest frame of the thermal fluid. Scattering isotropizes the cosmic rays and allows them to exchange momentum and energy with the background medium. I will review a theory for how the fluctuations which scatter the cosmicmore » rays can be generated by the cosmic rays themselves through a microinstability excited by their streaming. A quasilinear treatment of the cosmic ray–wave interaction then leads to a fluid model of cosmic rays with both advection and diffusion by the background medium and momentum and energy deposition by the cosmic rays. This fluid model admits cosmic ray modified shocks, large scale cosmic ray driven instabilities, cosmic ray heating of the thermal gas, and cosmic ray driven galactic winds. If the fluctuations were extrinsic turbulence driven by some other mechanism, the cosmic ray background coupling would be entirely different. Which picture holds depends largely on the nature of turbulence in the background medium.« less

String Theory Methods for Condensed Matter Physics

NASA Astrophysics Data System (ADS)

Nastase, Horatiu

2017-09-01

Preface; Acknowledgments; Introduction; Part I. Condensed Matter Models and Problems: 1. Lightning review of statistical mechanics, thermodynamics, phases and phase transitions; 2. Magnetism in solids; 3. Electrons in solids: Fermi gas vs. Fermi liquid; 4. Bosonic quasi-particles: phonons and plasmons; 5. Spin-charge separation in 1+1 dimensional solids: spinons and holons; 6. The Ising model and the Heisenberg spin chain; 7. Spin chains and integrable systems; 8. The thermodynamic Bethe ansatz; 9. Conformal field theories and quantum phase transitions; 10. Classical vs. quantum Hall effect; 11. Superconductivity: Landau-Ginzburg, London and BCS; 12. Topology and statistics: Berry and Chern-Simons, anyons and nonabelions; 13. Insulators; 14. The Kondo effect and the Kondo problem; 15. Hydrodynamics and transport properties: from Boltzmann to Navier-Stokes; Part II. Elements of General Relativity and String Theory: 16. The Einstein equation and the Schwarzschild solution; 17. The Reissner-Nordstrom and Kerr-Newman solutions and thermodynamic properties of black holes; 18. Extra dimensions and Kaluza-Klein; 19. Electromagnetism and gravity in various dimensions. Consistent truncations; 20. Gravity plus matter: black holes and p-branes in various dimensions; 21. Weak/strong coupling dualities in 1+1, 2+1, 3+1 and d+1 dimensions; 22. The relativistic point particle and the relativistic string; 23. Lightcone strings and quantization; 24. D-branes and gauge fields; 25. Electromagnetic fields on D-branes. Supersymmetry and N = 4 SYM. T-duality of closed strings; 26. Dualities and M theory; 27. The AdS/CFT correspondence: definition and motivation; Part III. Applying String Theory to Condensed Matter Problems: 28. The pp wave correspondence: string Hamiltonian from N = 4 SYM; 29. Spin chains from N = 4 SYM; 30. The Bethe ansatz: Bethe strings from classical strings in AdS; 31. Integrability and AdS/CFT; 32. AdS/CFT phenomenology: Lifshitz, Galilean and Schrodinger symmetries and their gravity duals; 33. Finite temperature and black holes; 34. Hot plasma equilibrium thermodynamics: entropy, charge density and chemical potential of strongly coupled theories; 35. Spectral functions and transport properties; 36. Dynamic and nonequilibrium properties of plasmas: electric transport, Langevin diffusion and thermalization via black hole quasi-normal modes; 37. The holographic superconductor; 38. The fluid-gravity correspondence: conformal relativistic fluids from black hole horizons; 39. Nonrelativistic fluids: from Einstein to Navier-Stokes and back; Part IV. Advanced Applications: 40. Fermi gas and liquid in AdS/CFT; 41. Quantum Hall effect from string theory; 42. Quantum critical systems and AdS/CFT; 43. Particle-vortex duality and ABJM vs. AdS4 X CP3 duality; 44. Topology and non-standard statistics from AdS/CFT; 45. DBI scalar model for QGP/black hole hydro- and thermo-dynamics; 46. Holographic entanglement entropy in condensed matter; 47. Holographic insulators; 48. Holographic strange metals and the Kondo problem; References; Index.

Exact reconstruction with directional wavelets on the sphere

NASA Astrophysics Data System (ADS)

Wiaux, Y.; McEwen, J. D.; Vandergheynst, P.; Blanc, O.

2008-08-01

A new formalism is derived for the analysis and exact reconstruction of band-limited signals on the sphere with directional wavelets. It represents an evolution of a previously developed wavelet formalism developed by Antoine & Vandergheynst and Wiaux et al. The translations of the wavelets at any point on the sphere and their proper rotations are still defined through the continuous three-dimensional rotations. The dilations of the wavelets are directly defined in harmonic space through a new kernel dilation, which is a modification of an existing harmonic dilation. A family of factorized steerable functions with compact harmonic support which are suitable for this kernel dilation are first identified. A scale-discretized wavelet formalism is then derived, relying on this dilation. The discrete nature of the analysis scales allows the exact reconstruction of band-limited signals. A corresponding exact multi-resolution algorithm is finally described and an implementation is tested. The formalism is of interest notably for the denoising or the deconvolution of signals on the sphere with a sparse expansion in wavelets. In astrophysics, it finds a particular application for the identification of localized directional features in the cosmic microwave background data, such as the imprint of topological defects, in particular, cosmic strings, and for their reconstruction after separation from the other signal components.

Numerical Model for Cosmic Rays Species Production and Propagation in the Galaxy

NASA Technical Reports Server (NTRS)

Farahat, Ashraf; Zhang, Ming; Rassoul, Hamid; Connell, J. J.

2005-01-01

In recent years, considerable progress has been made in studying the propagation and origin of cosmic rays, as new and more accurate data have become available. Many models have been developed to study cosmic ray interactions and propagation showed flexibility in resembling various astrophysical conditions and good agreement with observational data. However, some astrophysical problems cannot be addressed using these models, such as the stochastic nature of the cosmic rays source, small-scale structures and inhomogeneities in the interstellar gas that can affect radioactive secondary abundance in cosmic rays. We have developed a new model and a corresponding computer code that can address some of these limitations. The model depends on the expansion of the backward stochastic solution of the general diffusion transport equation (Zhang 1999) starting from an observer position to solve a group of diffusion transport equations each of which represents a particular element or isotope of cosmic ray nuclei. In this paper we are focusing on key abundance ratios such as B/C, sub-Fe/Fe, (10)Be/(9)Be, (26)Al/(27)Al, (36)Cl/(37)Cl and (54)Mn/(55)Mn, which all have well established cross sections, to evaluate our model. The effect of inhomogeneity in the interstellar medium is investigated. The contribution of certain cosmic ray nuclei to the production of other nuclei is addressed. The contribution of various galactic locations to the production of cosmic ray nuclei observed at solar system is also investigated.

Nuclear Physics Meets the Sources of the Ultra-High Energy Cosmic Rays.

PubMed

Boncioli, Denise; Fedynitch, Anatoli; Winter, Walter

2017-07-07

The determination of the injection composition of cosmic ray nuclei within astrophysical sources requires sufficiently accurate descriptions of the source physics and the propagation - apart from controlling astrophysical uncertainties. We therefore study the implications of nuclear data and models for cosmic ray astrophysics, which involves the photo-disintegration of nuclei up to iron in astrophysical environments. We demonstrate that the impact of nuclear model uncertainties is potentially larger in environments with non-thermal radiation fields than in the cosmic microwave background. We also study the impact of nuclear models on the nuclear cascade in a gamma-ray burst radiation field, simulated at a level of complexity comparable to the most precise cosmic ray propagation code. We conclude with an isotope chart describing which information is in principle necessary to describe nuclear interactions in cosmic ray sources and propagation.

The big bang

NASA Astrophysics Data System (ADS)

Silk, Joseph

Our universe was born billions of years ago in a hot, violent explosion of elementary particles and radiation - the big bang. What do we know about this ultimate moment of creation, and how do we know it? Drawing upon the latest theories and technology, this new edition of The big bang, is a sweeping, lucid account of the event that set the universe in motion. Joseph Silk begins his story with the first microseconds of the big bang, on through the evolution of stars, galaxies, clusters of galaxies, quasars, and into the distant future of our universe. He also explores the fascinating evidence for the big bang model and recounts the history of cosmological speculation. Revised and updated, this new edition features all the most recent astronomical advances, including: Photos and measurements from the Hubble Space Telescope, Cosmic Background Explorer Satellite (COBE), and Infrared Space Observatory; the latest estimates of the age of the universe; new ideas in string and superstring theory; recent experiments on neutrino detection; new theories about the presence of dark matter in galaxies; new developments in the theory of the formation and evolution of galaxies; the latest ideas about black holes, worm holes, quantum foam, and multiple universes.

Exact solutions of bulk viscous with string cloud attached to strange quark matter for higher dimensional FRW universe in Lyra geometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Çağlar, Halife, E-mail: hlfcglr@gmail.com; Aygün, Sezgin, E-mail: saygun@comu.edu.tr

In this study, we have investigated bulk viscous with strange quark matter attached to the string cloud for higher dimensional Friedman-Robertson-Walker (FRW) universe in Lyra geometry. By using varying deceleration parameter and conservation equations we have solved Einstein Field Equations (EFE’s) and obtained generalized exact solutions for our model. Also we have found that string is not survived for bulk viscous with strange quark matter attached to the string cloud in framework higher dimensional FRW universe in Lyra geometry. This result agrees with Kiran and Reddy, Krori et al, Sahoo and Mishra and Mohanty et al. in four and fivemore » dimensions.« less

Aspects of string phenomenology in particle physics and cosmology

NASA Astrophysics Data System (ADS)

Antoniadis, I.

2017-12-01

I discuss possible connections between several scales in particle physics and cosmology, such the the electroweak, inflation, dark energy and Planck scales. In particular, I discuss the physics of extra dimensions and low scale gravity that are motivated from the problem of mass hierarchy, providing an alternative to low energy supersymmetry. I describe their realization in type I string theory with D-branes and I present the main experimental predictions in particle accelerators and their implications in cosmology. I also show that low-mass-scale string compactifications, with a generic D-brane configuration that realizes the Standard Model by open strings, can explain the relatively broad peak in the diphoton invariant mass spectrum at 750 GeV recently reported by the ATLAS and CMS collaborations.

The effective supergravity of little string theory

NASA Astrophysics Data System (ADS)

Antoniadis, Ignatios; Delgado, Antonio; Markou, Chrysoula; Pokorski, Stefan

2018-02-01

In this work we present the minimal supersymmetric extension of the five-dimensional dilaton-gravity theory that captures the main properties of the holographic dual of little string theory. It is described by a particular gauging of N=2 supergravity coupled with one vector multiplet associated with the string dilaton, along the U(1) subgroup of SU(2) R-symmetry. The linear dilaton in the fifth coordinate solution of the equations of motion (with flat string frame metric) breaks half of the supersymmetries to N=1 in four dimensions. Interest in the linear dilaton model has lately been revived in the context of the clockwork mechanism, which has recently been proposed as a new source of exponential scale separation in field theory.

Amplitudes on plane waves from ambitwistor strings

NASA Astrophysics Data System (ADS)

Adamo, Tim; Casali, Eduardo; Mason, Lionel; Nekovar, Stefan

2017-11-01

In marked contrast to conventional string theory, ambitwistor strings remain solvable worldsheet theories when coupled to curved background fields. We use this fact to consider the quantization of ambitwistor strings on plane wave metric and plane wave gauge field backgrounds. In each case, the worldsheet model is anomaly free as a consequence of the background satisfying the field equations. We derive vertex operators (in both fixed and descended picture numbers) for gravitons and gluons on these backgrounds from the worldsheet CFT, and study the 3-point functions of these vertex operators on the Riemann sphere. These worldsheet correlation functions reproduce the known results for 3-point scattering amplitudes of gravitons and gluons in gravitational and gauge theoretic plane wave backgrounds, respectively.

Robust constraint on cosmic textures from the cosmic microwave background.

PubMed

Feeney, Stephen M; Johnson, Matthew C; Mortlock, Daniel J; Peiris, Hiranya V

2012-06-15

Fluctuations in the cosmic microwave background (CMB) contain information which has been pivotal in establishing the current cosmological model. These data can also be used to test well-motivated additions to this model, such as cosmic textures. Textures are a type of topological defect that can be produced during a cosmological phase transition in the early Universe, and which leave characteristic hot and cold spots in the CMB. We apply bayesian methods to carry out a rigorous test of the texture hypothesis, using full-sky data from the Wilkinson Microwave Anisotropy Probe. We conclude that current data do not warrant augmenting the standard cosmological model with textures. We rule out at 95% confidence models that predict more than 6 detectable cosmic textures on the full sky.

Consistency of cosmic-ray source abudances with explosive nucleosynthesis

NASA Technical Reports Server (NTRS)

Kozlovsky, B.; Ramaty, R.

1973-01-01

A model was examined in which the cosmic ray abundances of elements from C to Fe are consistent with explosive nucleosynthesis. The observed abundance of cosmic rays near the earth, cosmic ray source abundance, and solar system abundance are discussed along with the ratios of cosmic ray sources to the solar system abundances.

Existence of topological multi-string solutions in Abelian gauge field theories

NASA Astrophysics Data System (ADS)

Han, Jongmin; Sohn, Juhee

2017-11-01

In this paper, we consider a general form of self-dual equations arising from Abelian gauge field theories coupled with the Einstein equations. By applying the super/subsolution method, we prove that topological multi-string solutions exist for any coupling constant, which improves previously known results. We provide two examples for application: the self-dual Einstein-Maxwell-Higgs model and the gravitational Maxwell gauged O(3) sigma model.

Automorphic Forms and Mock Modular Forms in String Theory

NASA Astrophysics Data System (ADS)

Nazaroglu, Caner

We study a variety of modular invariant objects in relation to string theory. First, we focus on Jacobi forms over generic rank lattices and Siegel forms that appear in N = 2, D = 4 compactifications of heterotic string with Wilson lines. Constraints from low energy spectrum and modularity are employed to deduce the relevant supersymmetric partition functions entirely. This procedure is applied on models that lead to Jacobi forms of index 3, 4, 5 as well as Jacobi forms over root lattices A2 and A3. These computations are then checked against an explicit orbifold model which can be Higgsed to the models under question. Models with a single Wilson line are then studied in detail with their relation to paramodular group Gammam as T-duality group made explicit. These results on the heterotic string side are then turned into predictions for geometric invariants using TypeII - Heterotic duality. Secondly, we study theta functions for indenite signature lattices of generic signature. Building on results in literature for signature (n-1,1) and (n-2,2) lattices, we work out the properties of generalized error functions which we call r-tuple error functions. We then use these functions to build such indenite theta functions and describe their modular completions.

An Interactive Activation Model of the Effect of Context in Perception. Part 2

DTIC Science & Technology

1980-07-15

nonword strings are often seen with letters transposed if the transposition will produce legal strings (Estes, 1975a; c.f. experiment by Stevens reported...Activation Model Rumelhart & McClelland Part II 90 References Anderson, J. A. Neural models with cognitive implications. In D. LaBerge & S. J. Samuels...Washington, DC 20372 Coe391 Dr. Gory PoockNavy Personnel R&D Center Operations Research Department LT Steven D. Harris. MSC, USN San Diego, CA 92152 Code

Quantum phases of a vortex string.

PubMed

Auzzi, Roberto; Prem Kumar, S

2009-12-04

We argue that the world sheet dynamics of magnetic k strings in the Higgs phase of the mass-deformed N = 4 theory is controlled by a bosonic O(3) sigma model with anisotropy and a topological theta term. The theory interpolates between a massless O(2) symmetric regime, a massive O(3) symmetric phase, and another massive phase with a spontaneously broken Z(2) symmetry. The first two phases are separated by a Kosterlitz-Thouless transition. When theta = pi, the O(3) symmetric phase flows to an interacting fixed point; sigma model kinks and their dyonic partners become degenerate, mirroring the behavior of monopoles in the parent gauge theory. This leads to the identification of the kinks with monopoles confined on the string.

Transient and sustained elementary flux mode networks on a catalytic string-based chemical evolution model.

PubMed

Pereira, José A

2014-08-01

Theoretical models designed to test the metabolism-first hypothesis for prebiotic evolution have yield strong indications about the hypothesis validity but could sometimes use a more extensive identification between model objects and real objects towards a more meaningful interpretation of results. In an attempt to go in that direction, the string-based model SSE ("steady state evolution") was developed, where abstract molecules (strings) and catalytic interaction rules are based on some of the most important features of carbon compounds in biological chemistry. The system is open with a random inflow and outflow of strings but also with a permanent string food source. Although specific catalysis is a key aspect of the model, used to define reaction rules, the focus is on energetics rather than kinetics. Standard energy change tables were constructed and used with standard formation reactions to track energy flows through the interpretation of equilibrium constant values. Detection of metabolic networks on the reaction system was done with elementary flux mode (EFM) analysis. The combination of these model design and analysis options enabled obtaining metabolic and catalytic networks showing several central features of biological metabolism, some more clearly than in previous models: metabolic networks with stepwise synthesis, energy coupling, catalysts regulation, SN2 coupling, redox coupling, intermediate cycling, coupled inverse pathways (metabolic cycling), autocatalytic cycles and catalytic cascades. The results strongly suggest that the main biological metabolism features, including the genotype-phenotype interpretation, are caused by the principles of catalytic systems and are prior to modern genetic systems principles. It also gives further theoretical support to the thesis that the basic features of biologic metabolism are a consequence of the time evolution of a random catalyst search working on an open system with a permanent food source. The importance of the food source characteristics and evolutionary possibilities are discussed. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Elemental composition and energy spectra of galactic cosmic rays

NASA Technical Reports Server (NTRS)

Mewaldt, R. A.

1988-01-01

A brief review is presented of the major features of the elemental composition and energy spectra of galactic cosmic rays. The requirements for phenomenological models of cosmic ray composition and energy spectra are discussed, and possible improvements to an existing model are suggested.

Post processing for offline Chinese handwritten character string recognition

NASA Astrophysics Data System (ADS)

Wang, YanWei; Ding, XiaoQing; Liu, ChangSong

2012-01-01

Offline Chinese handwritten character string recognition is one of the most important research fields in pattern recognition. Due to the free writing style, large variability in character shapes and different geometric characteristics, Chinese handwritten character string recognition is a challenging problem to deal with. However, among the current methods over-segmentation and merging method which integrates geometric information, character recognition information and contextual information, shows a promising result. It is found experimentally that a large part of errors are segmentation error and mainly occur around non-Chinese characters. In a Chinese character string, there are not only wide characters namely Chinese characters, but also narrow characters like digits and letters of the alphabet. The segmentation error is mainly caused by uniform geometric model imposed on all segmented candidate characters. To solve this problem, post processing is employed to improve recognition accuracy of narrow characters. On one hand, multi-geometric models are established for wide characters and narrow characters respectively. Under multi-geometric models narrow characters are not prone to be merged. On the other hand, top rank recognition results of candidate paths are integrated to boost final recognition of narrow characters. The post processing method is investigated on two datasets, in total 1405 handwritten address strings. The wide character recognition accuracy has been improved lightly and narrow character recognition accuracy has been increased up by 10.41% and 10.03% respectively. It indicates that the post processing method is effective to improve recognition accuracy of narrow characters.

Black string corrections in variable tension braneworld scenarios

NASA Astrophysics Data System (ADS)

Da Rocha, Roldão; Hoff da Silva, J. M.

2012-02-01

Braneworld models with variable tension are investigated, and the corrections on the black string horizon along the extra dimension are provided. Such corrections are encrypted in additional terms involving the covariant derivatives of the variable tension on the brane, providing profound consequences concerning the black string horizon variation along the extra dimension, near the brane. The black string horizon behavior is shown to be drastically modified by the terms corrected by the brane variable tension. In particular, a model motivated by the phenomenological interesting case regarding Eötvös branes is investigated. It forthwith provides further physical features regarding variable tension braneworld scenarios, heretofore concealed in all previous analysis in the literature. All precedent analysis considered uniquely the expansion of the metric up to the second order along the extra dimension, which is able to evince solely the brane variable tension absolute value. Notwithstanding, the expansion terms aftermath, further accomplished in this paper from the third order on, elicits the successive covariant derivatives of the brane variable tension, and their respective coupling with the extrinsic curvature, the Weyl tensor, and the Riemann and Ricci tensors, as well as the scalar curvature. Such additional terms are shown to provide sudden modifications in the black string horizon in a variable tension braneworld scenario.

Anomalous Transport of Cosmic Rays in a Nonlinear Diffusion Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Litvinenko, Yuri E.; Fichtner, Horst; Walter, Dominik

2017-05-20

We investigate analytically and numerically the transport of cosmic rays following their escape from a shock or another localized acceleration site. Observed cosmic-ray distributions in the vicinity of heliospheric and astrophysical shocks imply that anomalous, superdiffusive transport plays a role in the evolution of the energetic particles. Several authors have quantitatively described the anomalous diffusion scalings, implied by the data, by solutions of a formal transport equation with fractional derivatives. Yet the physical basis of the fractional diffusion model remains uncertain. We explore an alternative model of the cosmic-ray transport: a nonlinear diffusion equation that follows from a self-consistent treatmentmore » of the resonantly interacting cosmic-ray particles and their self-generated turbulence. The nonlinear model naturally leads to superdiffusive scalings. In the presence of convection, the model yields a power-law dependence of the particle density on the distance upstream of the shock. Although the results do not refute the use of a fractional advection–diffusion equation, they indicate a viable alternative to explain the anomalous diffusion scalings of cosmic-ray particles.« less

A Simple Introduction to Gröbner Basis Methods in String Phenomenology

NASA Astrophysics Data System (ADS)

Gray, James

In this talk I give an elementary introduction to the key algorithm used in recent applications of computational algebraic geometry to the subject of string phenomenology. I begin with a simple description of the algorithm itself and then give 3 examples of its use in physics. I describe how it can be used to obtain constraints on flux parameters, how it can simplify the equations describing vacua in 4d string models and lastly how it can be used to compute the vacuum space of the electroweak sector of the MSSM.

Twistor approach to string compactifications: A review

NASA Astrophysics Data System (ADS)

Alexandrov, Sergei

2013-01-01

We review a progress in obtaining the complete non-perturbative effective action of type II string theory compactified on a Calabi-Yau manifold. This problem is equivalent to understanding quantum corrections to the metric on the hypermultiplet moduli space. We show how all these corrections, which include D-brane and NS5-brane instantons, are incorporated in the framework of the twistor approach, which provides a powerful mathematical description of hyperkähler and quaternion-Kähler manifolds. We also present new insights on S-duality, quantum mirror symmetry, connections to integrable models and topological strings.

Fermi-LAT observations of the diffuse γ-ray emission: Implications for cosmic rays and the interstellar medium

DOE PAGES

Ackermann, M.; Ajello, M.; Atwood, W. B.; ...

2012-04-09

The γ-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Our observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi Large Area Telescope (Fermi-LAT) mission and compare with models of the diffuse γ-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas, and radiation fields. In ordermore » to assess uncertainties associated with the astrophysical input, a grid of models is created by varying within observational limits the distribution of cosmic-ray sources, the size of the cosmic-ray confinement volume (halo), and the distribution of interstellar gas. An all-sky maximum-likelihood fit is used to determine the X CO factor, the ratio between integrated CO-line intensity and H2 column density, the fluxes and spectra of the γ-ray point sources from the first Fermi-LAT catalog, and the intensity and spectrum of the isotropic background including residual cosmic rays that were misclassified as γ-rays, all of which have some dependency on the assumed diffuse emission model. The models are compared on the basis of their maximum-likelihood ratios as well as spectra, longitude, and latitude profiles. Here, we provide residual maps for the data following subtraction of the diffuse emission models. The models are consistent with the data at high and intermediate latitudes but underpredict the data in the inner Galaxy for energies above a few GeV. Possible explanations for this discrepancy are discussed, including the contribution by undetected point-source populations and spectral variations of cosmic rays throughout the Galaxy. In the outer Galaxy, we find that the data prefer models with a flatter distribution of cosmic-ray sources, a larger cosmic-ray halo, or greater gas density than is usually assumed. Our results in the outer Galaxy are consistent with other Fermi-LAT studies of this region that used different analysis methods than employed in this paper.« less

Fermi-LAT Observations of the Diffuse γ-Ray Emission: Implications for Cosmic Rays and the Interstellar Medium

NASA Astrophysics Data System (ADS)

Ackermann, M.; Ajello, M.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; de Angelis, A.; de Palma, F.; Dermer, C. D.; Digel, S. W.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Falletti, L.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gaggero, D.; Gargano, F.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grove, J. E.; Guiriec, S.; Gustafsson, M.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Horan, D.; Hou, X.; Hughes, R. E.; Jóhannesson, G.; Johnson, A. S.; Johnson, R. P.; Kamae, T.; Katagiri, H.; Kataoka, J.; Knödlseder, J.; Kuss, M.; Lande, J.; Latronico, L.; Lee, S.-H.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Parent, D.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Sadrozinski, H. F.-W.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Strong, A. W.; Suson, D. J.; Takahashi, H.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Wood, M.; Yang, Z.; Ziegler, M.; Zimmer, S.

2012-05-01

The γ-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi Large Area Telescope (Fermi-LAT) mission and compare with models of the diffuse γ-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas, and radiation fields. To assess uncertainties associated with the astrophysical input, a grid of models is created by varying within observational limits the distribution of cosmic-ray sources, the size of the cosmic-ray confinement volume (halo), and the distribution of interstellar gas. An all-sky maximum-likelihood fit is used to determine the X CO factor, the ratio between integrated CO-line intensity and H2 column density, the fluxes and spectra of the γ-ray point sources from the first Fermi-LAT catalog, and the intensity and spectrum of the isotropic background including residual cosmic rays that were misclassified as γ-rays, all of which have some dependency on the assumed diffuse emission model. The models are compared on the basis of their maximum-likelihood ratios as well as spectra, longitude, and latitude profiles. We also provide residual maps for the data following subtraction of the diffuse emission models. The models are consistent with the data at high and intermediate latitudes but underpredict the data in the inner Galaxy for energies above a few GeV. Possible explanations for this discrepancy are discussed, including the contribution by undetected point-source populations and spectral variations of cosmic rays throughout the Galaxy. In the outer Galaxy, we find that the data prefer models with a flatter distribution of cosmic-ray sources, a larger cosmic-ray halo, or greater gas density than is usually assumed. Our results in the outer Galaxy are consistent with other Fermi-LAT studies of this region that used different analysis methods than employed in this paper.

FERMI-LAT OBSERVATIONS OF THE DIFFUSE {gamma}-RAY EMISSION: IMPLICATIONS FOR COSMIC RAYS AND THE INTERSTELLAR MEDIUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackermann, M.; Ajello, M.; Bechtol, K.

The {gamma}-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi Large Area Telescope (Fermi-LAT) mission and compare with models of the diffuse {gamma}-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas, and radiation fields. To assess uncertaintiesmore » associated with the astrophysical input, a grid of models is created by varying within observational limits the distribution of cosmic-ray sources, the size of the cosmic-ray confinement volume (halo), and the distribution of interstellar gas. An all-sky maximum-likelihood fit is used to determine the X{sub CO} factor, the ratio between integrated CO-line intensity and H{sub 2} column density, the fluxes and spectra of the {gamma}-ray point sources from the first Fermi-LAT catalog, and the intensity and spectrum of the isotropic background including residual cosmic rays that were misclassified as {gamma}-rays, all of which have some dependency on the assumed diffuse emission model. The models are compared on the basis of their maximum-likelihood ratios as well as spectra, longitude, and latitude profiles. We also provide residual maps for the data following subtraction of the diffuse emission models. The models are consistent with the data at high and intermediate latitudes but underpredict the data in the inner Galaxy for energies above a few GeV. Possible explanations for this discrepancy are discussed, including the contribution by undetected point-source populations and spectral variations of cosmic rays throughout the Galaxy. In the outer Galaxy, we find that the data prefer models with a flatter distribution of cosmic-ray sources, a larger cosmic-ray halo, or greater gas density than is usually assumed. Our results in the outer Galaxy are consistent with other Fermi-LAT studies of this region that used different analysis methods than employed in this paper.« less

Fermi-LAT observations of the diffuse γ-ray emission: Implications for cosmic rays and the interstellar medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackermann, M.; Ajello, M.; Atwood, W. B.

The γ-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Our observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi Large Area Telescope (Fermi-LAT) mission and compare with models of the diffuse γ-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas, and radiation fields. In ordermore » to assess uncertainties associated with the astrophysical input, a grid of models is created by varying within observational limits the distribution of cosmic-ray sources, the size of the cosmic-ray confinement volume (halo), and the distribution of interstellar gas. An all-sky maximum-likelihood fit is used to determine the X CO factor, the ratio between integrated CO-line intensity and H2 column density, the fluxes and spectra of the γ-ray point sources from the first Fermi-LAT catalog, and the intensity and spectrum of the isotropic background including residual cosmic rays that were misclassified as γ-rays, all of which have some dependency on the assumed diffuse emission model. The models are compared on the basis of their maximum-likelihood ratios as well as spectra, longitude, and latitude profiles. Here, we provide residual maps for the data following subtraction of the diffuse emission models. The models are consistent with the data at high and intermediate latitudes but underpredict the data in the inner Galaxy for energies above a few GeV. Possible explanations for this discrepancy are discussed, including the contribution by undetected point-source populations and spectral variations of cosmic rays throughout the Galaxy. In the outer Galaxy, we find that the data prefer models with a flatter distribution of cosmic-ray sources, a larger cosmic-ray halo, or greater gas density than is usually assumed. Our results in the outer Galaxy are consistent with other Fermi-LAT studies of this region that used different analysis methods than employed in this paper.« less

Gauge fields and inflation

NASA Astrophysics Data System (ADS)

Maleknejad, A.; Sheikh-Jabbari, M. M.; Soda, J.

2013-07-01

The isotropy and homogeneity of the cosmic microwave background (CMB) favors “scalar driven” early Universe inflationary models. However, gauge fields and other non-scalar fields are far more common at all energy scales, in particular at high energies seemingly relevant to inflation models. Hence, in this review we consider the role and consequences, theoretical and observational, that gauge fields can have during the inflationary era. Gauge fields may be turned on in the background during inflation, or may become relevant at the level of cosmic perturbations. There have been two main classes of models with gauge fields in the background, models which show violation of the cosmic no-hair theorem and those which lead to isotropic FLRW cosmology, respecting the cosmic no-hair theorem. Models in which gauge fields are only turned on at the cosmic perturbation level, may source primordial magnetic fields. We also review specific observational features of these models on the CMB and/or the primordial cosmic magnetic fields. Our discussions will be mainly focused on the inflation period, with only a brief discussion on the post inflationary (p)reheating era. Large field models: The initial value of the inflaton field is large, generically super-Planckian, and it rolls slowly down toward the potential minimum at smaller φ values. For instance, chaotic inflation is one of the representative models of this class. The typical potential of large-field models has a monomial form as V(φ)=V0φn. A simple analysis using the dynamical equations reveals that for number of e-folds Ne larger than 60, we require super-Planckian initial field values,5φ0>3M. For these models typically ɛ˜η˜Ne-1. Small field models: Inflaton field is initially small and slowly evolves toward the potential minimum at larger φ values. The small field models are characterized by the following potential V(φ)=V0(1-(), which corresponds to a Taylor expansion about the origin, but more realistic small field models also have a potential minimum at φ≠0 which the system falls in at the end of inflation. A typical property of small field models is that a sufficient number of e-folds, requires a sub-Planckian inflaton initial value. For this reason they are called small field models. Natural inflation is an example of this type [12]. Hybrid inflation models: These models involve more than one scalar field while inflation is mainly driven by a single inflaton field ϕ. Inflaton starts from a large value rolling down until it reaches a bifurcation point, ϕ=ϕe, after which the field becomes unstable and undergoes a waterfall transition toward its global minimum. Its prime example is the Linde’s hybrid inflation model with the following potential [13] V(ϕ,χ)={λ}/{4}(+{1}/{2}g2ϕ2χ2+{1}/{2}m2ϕ2. During the initial inflationary phase the potential of the hybrid inflation is effectively described by a single field ϕ while inflation ends by a phase transition triggered by the presence of the second scalar field, the waterfall field χ. In other words, when the effective mass squared of a waterfall field becomes negative, the tachyonic instability makes waterfall field roll down toward the true vacuum state and the inflation suddenly ends.Number of e-folds Ne is given as Ne≃{M4}/{4λm2}ln({ϕ0}/{ϕe}), where ϕe={M}/{g} is the critical value of the inflaton below which, due to tachyonic instability, χ=0 becomes unstable and mχ2 gets negative. K-inflation: This is the prime example of models with non-canonical Kinetic term we discuss here. They are described by the action [14] S=∫d4x√{-g}({R}/{2}+P(φ,X)), where φ is a scalar field and X≔-{1}/{2}(. Here, P plays the rule of the effective pressure, while the energy density is given by ρ=2XP-P. Thus, the slow-roll parameter is given as ɛ={3XP}/{2XP-P}. The characteristic feature of these models is that in general they have a non-trivial sound speed cs2 for the propagation of perturbations (cf. our discussion in Section 2.2) cs2≡{P}/{P+2XP}. Finding K-inflation actions P(φ,X) which are well-motivated and consistently embedded in high-energy theories is the main challenge of this class of models [9]. Nonetheless, DBI inflation is a special kind of K-inflation, which is well-motivated from string theory with the action [15] S=∫d4x√{-g}[{R}/{2}-{1}/{f(φ)}((√{D}-1)+V(φI))], where D=1-2f(φ)X. In the presence of another natural cutoff Λ in the model, smallness or largeness of the inflaton field should be compared to Λ; Λ could be sub-Planckian and in general Λ≲M. For a discussion on this see [10,11].

Cosmic Ray Propagation through the Magnetic Fields of the Galaxy with Extended Halo

NASA Technical Reports Server (NTRS)

Zhang, Ming

2005-01-01

In this project we perform theoretical studies of 3-dimensional cosmic ray propagation in magnetic field configurations of the Galaxy with an extended halo. We employ our newly developed Markov stochastic process methods to solve the diffusive cosmic ray transport equation. We seek to understand observations of cosmic ray spectra, composition under the constraints of the observations of diffuse gamma ray and radio emission from the Galaxy. The model parameters are directly are related to properties of our Galaxy, such as the size of the Galactic halo, particle transport in Galactic magnetic fields, distribution of interstellar gas, primary cosmic ray source distribution and their confinement in the Galaxy. The core of this investigation is the development of software for cosmic ray propagation models with the Markov stochastic process approach. Values of important model parameters for the halo diffusion model are examined in comparison with observations of cosmic ray spectra, composition and the diffuse gamma-ray background. This report summarizes our achievement in the grant period at the Florida Institute of Technology. Work at the co-investigator's institution, the University of New Hampshire, under a companion grant, will be covered in detail by a separate report.

Evaluating Galactic Cosmic Ray Environment Models Using RaD-X Flight Data

NASA Technical Reports Server (NTRS)

Norman, R. B.; Mertens, C. J.; Slaba, T. C.

2016-01-01

Galactic cosmic rays enter Earth's atmosphere after interacting with the geomagnetic field. The primary galactic cosmic rays spectrum is fundamentally changed as it interacts with Earth's atmosphere through nuclear and atomic interactions. At points deeper in the atmosphere, such as at airline altitudes, the radiation environment is a combination of the primary galactic cosmic rays and the secondary particles produced through nuclear interactions. The RaD-X balloon experiment measured the atmospheric radiation environment above 20 km during 2 days in September 2015. These experimental measurements were used to validate and quantify uncertainty in physics-based models used to calculate exposure levels for commercial aviation. In this paper, the Badhwar-O'Neill 2014, the International Organization for Standardization 15390, and the German Aerospace Company galactic cosmic ray environment models are used as input into the same radiation transport code to predict and compare dosimetric quantities to RaD-X measurements. In general, the various model results match the measured tissue equivalent dose well, with results generated by the German Aerospace Center galactic cosmic ray environment model providing the best comparison. For dose equivalent and dose measured in silicon, however, the models were compared less favorably to the measurements.

Big bang nucleosynthesis, the CMB, and the origin of matter and space-time

NASA Astrophysics Data System (ADS)

Mathews, Grant J.; Gangopadhyay, Mayukh; Sasankan, Nishanth; Ichiki, Kiyotomo; Kajino, Toshitaka

2018-04-01

We summarize some applications of big bang nucleosythesis (BBN) and the cosmic microwave background (CMB) to constrain the first moments of the creation of matter in the universe. We review the basic elements of BBN and how it constraints physics of the radiation-dominated epoch. In particular, how the existence of higher dimensions impacts the cosmic expansion through the projection of curvature from the higher dimension in the "dark radiation" term. We summarize current constraints from BBN and the CMB on this brane-world dark radiation term. At the same time, the existence of extra dimensions during the earlier inflation impacts the tensor to scalar ratio and the running spectral index as measured in the CMB. We summarize how the constraints on inflation shift when embedded in higher dimensions. Finally, one expects that the universe was born out of a complicated multiverse landscape near the Planck time. In these moments the energy scale of superstrings was obtainable during the early moments of chaotic inflation. We summarize the quest for cosmological evidence of the birth of space-time out of the string theory landscape. We will explore the possibility that a superstring excitations may have made itself known via a coupling to the field of inflation. This may have left an imprint of "dips" in the power spectrum of temperature fluctuations in the cosmic microwave background. The identification of this particle as a superstring is possible because there may be evidence for different oscillator states of the same superstring that appear on different scales on the sky. It will be shown that from this imprint one can deduce the mass, number of oscillations, and coupling constant for the superstring. Although the evidence is marginal, this may constitute the first observation of a superstring in Nature.

Study of baryon production mechanism in e+e- annihilation into hadrons

NASA Astrophysics Data System (ADS)

Topaz Collaboration; Aoki, M.; Itoh, R.; Watanabe, Y.; Kaneyuki, K.; Ohshima, Y.; Ochi, A.; Tanimori, T.; Abe, K.; Abe, T.; Adachi, I.; Adachi, K.; Aoki, M.; Emi, K.; Enomoto, R.; Fujii, H.; Fujii, T.; Fujii, K.; Fujimoto, J.; Fujiwara, N.; Hayashii, H.; Hirano, H.; Howell, B.; Ikeda, H.; Inoue, Y.; Itami, S.; Iwasaki, H.; Iwasaki, M.; Kajikawa, R.; Kato, S.; Kawabata, S.; Kichimi, H.; Kobayashi, M.; Koltick, D.; Levine, I.; Mamada, H.; Miyabayashi, K.; Miyamoto, A.; Nagai, K.; Nakabayashi, K.; Nakamura, M.; Nakano, E.; Nitoh, O.; Noguchi, S.; Ochiai, F.; Ohishi, N.; Ohnishi, Y.; Okuno, H.; Okusawa, T.; Shibata, E.; Sugiyama, A.; Suzuki, S.; Takahashi, K.; Takahashi, T.; Teramoto, Y.; Tauchi, T.; Tomoto, M.; Tsukamoto, T.; Tsumura, T.; Uno, S.; Yamamoto, A.; Yamauchi, M.

1998-11-01

The mechanism of baryon-anti-baryon pair production in e+e- annihilation into hadrons has been studied using the TOPAZ detector at the TRISTAN e+e- collider at an average center-of-mass energy of 58 GeV. The distributions of various p¯p correlations were compared with two prominent models: the cluster-fragmentation model and the string-fragmentation model. We rejected the cluster-fragmentation model at the 90% C.L. Furthermore, in the context of the string-fragmentation model, we favor the ``popcorn'' model, rejecting the ``diquark'' model, where a diquark is considered to be a fundamental entity, at the 95% C.L.

Black holes and black strings of N = 2, d = 5 supergravity in the H-FGK formalism

NASA Astrophysics Data System (ADS)

Meessen, Patrick; Ortín, Tomás; Perz, Jan; Shahbazi, C. S.

2012-09-01

We study general classes and properties of extremal and non-extremal static black-hole solutions of N = 2, d = 5 supergravity coupled to vector multiplets using the recently proposed H-FGK formalism, which we also extend to static black strings. We explain how to determine the integration constants and physical parameters of the blackhole and black-string solutions. We derive some model-independent statements, including the transformation of non-extremal flow equations to the form of those for the extremal flow. We apply our methods to the construction of example solutions (among others a new extremal string solution of heterotic string theory on K 3 × S 1). In the cases where we have calculated it explicitly, the product of areas of the inner and outer horizon of a non-extremal solution coincides with the square of the moduli-independent area of the horizon of the extremal solution with the same charges.

Moving heavy quarkonium entropy, effective string tension, and the QCD phase diagram

NASA Astrophysics Data System (ADS)

Chen, Xun; Feng, Sheng-Qin; Shi, Ya-Fei; Zhong, Yang

2018-03-01

The entropy and effective string tension of the moving heavy quark-antiquark pair in the strongly coupled plasmas are calculated by using a deformed an anti-de Sitter/Reissner-Nordström black hole metric. A sharp peak of the heavy-quarkonium entropy around the deconfinement transition can be realized in our model, which is consistent with the lattice QCD result. The effective string tension of the heavy quark-antiquark pair is related to the deconfinement phase transition. Thus, we investigate the deconfinement phase transition by analyzing the characteristics of the effective string tension with different temperatures, chemical potentials, and rapidities. It is found that the results of phase diagram calculated through effective string tension are in agreement with results calculated through a Polyakov loop. We argue that a moving system will reach the phase transition point at a lower temperature and chemical potential than a stationary system. It means that the lifetime of the moving quark-gluon plasma become longer than the static one.

Badhwar-O'Neil 2007 Galactic Cosmic Ray (GCR) Model Using Advanced Composition Explorer (ACE) Measurements for Solar Cycle 23

NASA Technical Reports Server (NTRS)

ONeill, P. M.

2007-01-01

Advanced Composition Explorer (ACE) satellite measurements of the galactic cosmic ray flux and correlation with the Climax Neutron Monitor count over Solar Cycle 23 are used to update the Badhwar O'Neill Galactic Cosmic Ray (GCR) model.

Constraints on axion inflation from the weak gravity conjecture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rudelius, Tom, E-mail: rudelius@physics.harvard.edu

2015-09-01

We derive constraints facing models of axion inflation based on decay constant alignment from a string-theoretic and quantum gravitational perspective. In particular, we investigate the prospects for alignment and 'anti-alignment' of C{sub 4} axion decay constants in type IIB string theory, deriving a strict no-go result in the latter case. We discuss the relationship of axion decay constants to the weak gravity conjecture and demonstrate agreement between our string-theoretic constraints and those coming from the 'generalized' weak gravity conjecture. Finally, we consider a particular model of decay constant alignment in which the potential of C{sub 4} axions in type IIBmore » compactifications on a Calabi-Yau three-fold is dominated by contributions from D7-branes, pointing out that this model evades some of the challenges derived earlier in our paper but is highly constrained by other geometric considerations.« less

Constraints on axion inflation from the weak gravity conjecture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rudelius, Tom

2015-09-08

We derive constraints facing models of axion inflation based on decay constant alignment from a string-theoretic and quantum gravitational perspective. In particular, we investigate the prospects for alignment and ‘anti-alignment’ of C{sub 4} axion decay constants in type IIB string theory, deriving a strict no-go result in the latter case. We discuss the relationship of axion decay constants to the weak gravity conjecture and demonstrate agreement between our string-theoretic constraints and those coming from the ‘generalized’ weak gravity conjecture. Finally, we consider a particular model of decay constant alignment in which the potential of C{sub 4} axions in type IIBmore » compactifications on a Calabi-Yau three-fold is dominated by contributions from D7-branes, pointing out that this model evades some of the challenges derived earlier in our paper but is highly constrained by other geometric considerations.« less

Meteorological Sensor Array (MSA)-Phase I. Volume 2 (Data Management Tool: Proof of Concept)

DTIC Science & Technology

2014-10-01

directory of next hourly file to read *** utcString = CStr (CInt(utcString) + 1) utcString = String(2 - Len(utcString), Ŕ...hourly file to read *** utcString = CStr (CInt(utcString) + 1) utcString = String(2 - Len(utcString), Ŕ") & utcString

Cosmic Ray Studies with the Fermi Gamma-ray Space Telescope Large Area Telescope

NASA Technical Reports Server (NTRS)

Thompson, David J.; Baldini, L.; Uchiyama, Y.

2012-01-01

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope provides both direct and indirect measurements of galactic cosmic rays (CR). The LAT high-statistics observations of the 7 GeV - 1 TeV electron plus positron spectrum and limits on spatial anisotropy constrain models for this cosmic-ray component. On a galactic scale, the LAT observations indicate that cosmic-ray sources may be more plentiful in the outer Galaxy than expected or that the scale height of the cosmic-ray diffusive halo is larger than conventional models. Production of cosmic rays in supernova remnants (SNR) is supported by the LAT gamma-ray studies of several of these, both young SNR and those interacting with molecular clouds.

Cosmic Ray Studies with the Fermi Gamma-ray Space Telescope Large Area Telescope

NASA Technical Reports Server (NTRS)

Thompson, D. J.; Baldini, L.; Uchiyama, Y.

2011-01-01

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope provides both direct and indirect measurements of Galactic cosmic rays (CR). The LAT high-statistics observations of the 7 GeV - 1 TcV electron plus positron spectrum and limits on spatial anisotropy constrain models for this cosmic-ray component. On a Galactic scale, the LAT observations indicate that cosmic-ray sources may be more plentiful in the outer Galaxy than expected or that the scale height of the cosmic-ray diffusive halo is larger than conventional models. Production of cosmic rays in supernova remnants (SNR) is supported by the LAT gamma-ray studies of several of these, both young SNR and those interacting with molecular clouds.

Ionization Processes in the Atmosphere of Titan (Research Note). III. Ionization by High-Z Nuclei Cosmic Rays

NASA Technical Reports Server (NTRS)

Gronoff, G.; Mertens, C.; Lilensten, J.; Desorgher, L.; Fluckiger, E.; Velinov, P.

2011-01-01

Context. The Cassini-Huygens mission has revealed the importance of particle precipitation in the atmosphere of Titan thanks to in-situ measurements. These ionizing particles (electrons, protons, and cosmic rays) have a strong impact on the chemistry, hence must be modeled. Aims. We revisit our computation of ionization in the atmosphere of Titan by cosmic rays. The high-energy high-mass ions are taken into account to improve the precision of the calculation of the ion production profile. Methods. The Badhwahr and O Neill model for cosmic ray spectrum was adapted for the Titan model. We used the TransTitan model coupled with the Planetocosmics model to compute the ion production by cosmic rays. We compared the results with the NAIRAS/HZETRN ionization model used for the first time for a body that differs from the Earth. Results. The cosmic ray ionization is computed for five groups of cosmic rays, depending on their charge and mass: protons, alpha, Z = 8 (oxygen), Z = 14 (silicon), and Z = 26 (iron) nucleus. Protons and alpha particles ionize mainly at 65 km altitude, while the higher mass nucleons ionize at higher altitudes. Nevertheless, the ionization at higher altitude is insufficient to obscure the impact of Saturn s magnetosphere protons at a 500 km altitude. The ionization rate at the peak (altitude: 65 km, for all the different conditions) lies between 30 and 40/cu cm/s. Conclusions. These new computations show for the first time the importance of high Z cosmic rays on the ionization of the Titan atmosphere. The updated full ionization profile shape does not differ significantly from that found in our previous calculations (Paper I: Gronoff et al. 2009, 506, 955) but undergoes a strong increase in intensity below an altitude of 400 km, especially between 200 and 400 km altitude where alpha and heavier particles (in the cosmic ray spectrum) are responsible for 40% of the ionization. The comparison of several models of ionization and cosmic ray spectra (in intensity and composition) reassures us about the stability of the altitude of the ionization peak (65 km altitude) with respect to the solar activity.

REVIEWS OF TOPICAL PROBLEMS: Astrophysical aspects of cosmic-ray research (first 75 years and outlook for the future)

NASA Astrophysics Data System (ADS)

Ginzburg, Vitalii L.

1988-06-01

(Invited talk at the 20th International Cosmic Ray Conference, Moscow, 2-15 August 1987) The basic topics discussed here are the primary cosmic rays near the earth, cosmic rays in the universe, the origin of cosmic rays, a galactic model with a halo, and some prospects for future research.

A predictive analytic model for the solar modulation of cosmic rays

DOE PAGES

Cholis, Ilias; Hooper, Dan; Linden, Tim

2016-02-23

An important factor limiting our ability to understand the production and propagation of cosmic rays pertains to the effects of heliospheric forces, commonly known as solar modulation. The solar wind is capable of generating time- and charge-dependent effects on the spectrum and intensity of low-energy (≲10 GeV) cosmic rays reaching Earth. Previous analytic treatments of solar modulation have utilized the force-field approximation, in which a simple potential is adopted whose amplitude is selected to best fit the cosmic-ray data taken over a given period of time. Making use of recently available cosmic-ray data from the Voyager 1 spacecraft, along withmore » measurements of the heliospheric magnetic field and solar wind, we construct a time-, charge- and rigidity-dependent model of solar modulation that can be directly compared to data from a variety of cosmic-ray experiments. Here, we provide a simple analytic formula that can be easily utilized in a variety of applications, allowing us to better predict the effects of solar modulation and reduce the number of free parameters involved in cosmic-ray propagation models.« less

Galactic cosmic-ray mediation of a spherical solar wind flow. 1: The steady state cold gas hydrodynamical approximation

NASA Technical Reports Server (NTRS)

Le Roux, J. A.; Ptuskin, V. S.

1995-01-01

Realistic models of the outer heliosphere should consider that the interstellar cosmic-ray pressure becomes comparable to pressures in the solar wind at distances more than 100 AU from the Sun. The cosmic-ray pressure dynamically affects solar wind flow through deceleration. This effect, which occurs over a scale length of the order of the effective diffusion length at large radial distances, has important implications for cosmic-ray modulation and acceleration. As a first step toward solution of this nonlinear problem, a steady state numerical model was developed for a relatively cold spherical solar wind flow which encounters the confining isotropic pressure of the surrounding Galactic medium. This pressure is assumed to be dominated by energetic particles (Galactic cosmic rays). The system of equations, which are solved self-consistently, includes the relevant hydrodynamical equations for the solar wind flow and the spherical cosmic-ray transport equation. To avoid the closure parameter problem of the two-fluid model, the latter equation is solved for the energy-dependent cosmic-ray distribution function.

An improved cooperative adaptive cruise control (CACC) algorithm considering invalid communication

NASA Astrophysics Data System (ADS)

Wang, Pangwei; Wang, Yunpeng; Yu, Guizhen; Tang, Tieqiao

2014-05-01

For the Cooperative Adaptive Cruise Control (CACC) Algorithm, existing research studies mainly focus on how inter-vehicle communication can be used to develop CACC controller, the influence of the communication delays and lags of the actuators to the string stability. However, whether the string stability can be guaranteed when inter-vehicle communication is invalid partially has hardly been considered. This paper presents an improved CACC algorithm based on the sliding mode control theory and analyses the range of CACC controller parameters to maintain string stability. A dynamic model of vehicle spacing deviation in a platoon is then established, and the string stability conditions under improved CACC are analyzed. Unlike the traditional CACC algorithms, the proposed algorithm can ensure the functionality of the CACC system even if inter-vehicle communication is partially invalid. Finally, this paper establishes a platoon of five vehicles to simulate the improved CACC algorithm in MATLAB/Simulink, and the simulation results demonstrate that the improved CACC algorithm can maintain the string stability of a CACC platoon through adjusting the controller parameters and enlarging the spacing to prevent accidents. With guaranteed string stability, the proposed CACC algorithm can prevent oscillation of vehicle spacing and reduce chain collision accidents under real-world circumstances. This research proposes an improved CACC algorithm, which can guarantee the string stability when inter-vehicle communication is invalid.

Ecohydraulics of Strings and Beads in Bedrock Rivers

NASA Astrophysics Data System (ADS)

Wohl, E.

2016-12-01

Twenty years ago, Jack Stanford and others described rivers in bedrock canyons as resembling beads on a string when viewed in planform. The beads are relatively wide, low gradient river segments with floodplains, whereas the strings are the intervening steep, narrow river segments with minimal floodplain development. This pattern of longitudinal variations in channel and valley morphology along bedrock canyon rivers is very common, from small channels to major rivers such as the Colorado. Basic understanding of river ecosystems, as well as limited studies, indicates that the beads are more retentive and biologically productive. Although both strings and beads can provide habitat for diverse organisms, strings are more likely to serve as migration corridors, whereas beads provide spawning and nursery habitat, facilitate lateral (channel-floodplain) and vertical (channel-hyporheic) exchanges and associated habitat diversity, and retain dissolved and particulate organic matter. Recognition of the different characteristics and functions of strings and beads can be used to identify their spatial distribution along a river or within a river network and the hydraulically driven processes that sustain channel form, water quality, and biota within strings and beads. Diverse modeling approaches can then be used to quantify the fluxes of water and sediment needed to maintain these hydraulically driven processes. This conceptual framework is illustrated using examples from mountain streams in the Southern Rockies and canyon rivers in the southwestern United States.

A time-dependent diffusion convection model for the long term modulation of cosmic rays

NASA Technical Reports Server (NTRS)

Gallagher, J. J.

1974-01-01

A model is developed which incorporates to first order the direct effects of the time dependent diffusive propagation of interstellar cosmic rays in a slowly changing interplanetary medium. The model provides a physical explanation for observed rigidity-dependent phase lags in modulated spectra (cosmic ray hysteresis). The average distance to the modulating boundary during the last solar cycle is estimated.

Toric-boson model: Toward a topological quantum memory at finite temperature

NASA Astrophysics Data System (ADS)

Hamma, Alioscia; Castelnovo, Claudio; Chamon, Claudio

2009-06-01

We discuss the existence of stable topological quantum memory at finite temperature. At stake here is the fundamental question of whether it is, in principle, possible to store quantum information for macroscopic times without the intervention from the external world, that is, without error correction. We study the toric code in two dimensions with an additional bosonic field that couples to the defects, in the presence of a generic environment at finite temperature: the toric-boson model. Although the coupling constants for the bare model are not finite in the thermodynamic limit, the model has a finite spectrum. We show that in the topological phase, there is a finite temperature below which open strings are confined and therefore the lifetime of the memory can be made arbitrarily (polynomially) long in system size. The interaction with the bosonic field yields a long-range attractive force between the end points of open strings but leaves closed strings and topological order intact.

Pulsating strings with mixed three-form flux

NASA Astrophysics Data System (ADS)

Hernández, Rafael; Nieto, Juan Miguel; Ruiz, Roberto

2018-04-01

Circular strings pulsating in AdS 3 × S 3 × T 4 with mixed R-R and NS-NS three-form fluxes can be described by an integrable deformation of the one-dimensional Neumann-Rosochatius mechanical model. In this article we find a general class of pulsating solutions to this integrable system that can be expressed in terms of elliptic functions. In the limit of strings moving in AdS 3 with pure NS-NS three-form flux, where the action reduces to the SL(2, ℝ) WZW model, we find agreement with the analysis of the classical solutions of the system performed using spectral flow by Maldacena and Ooguri. We use our elliptic solutions in AdS 3 to extend the dispersion relation beyond the limit of pure NS-NS flux.

Super Yang Mills, matrix models and geometric transitions

NASA Astrophysics Data System (ADS)

Ferrari, Frank

2005-03-01

I explain two applications of the relationship between four-dimensional N=1 supersymmetric gauge theories, zero-dimensional gauged matrix models, and geometric transitions in string theory. The first is related to the spectrum of BPS domain walls or BPS branes. It is shown that one can smoothly interpolate between a D-brane state, whose weak coupling tension scales as N˜1/g, and a closed string solitonic state, whose weak coupling tension scales as N˜1/gs2. This is part of a larger theory of N=1 quantum parameter spaces. The second is a new purely geometric approach to sum exactly over planar diagrams in zero dimension. It is an example of open/closed string duality. To cite this article: F. Ferrari, C. R. Physique 6 (2005).

PREFACE: Gauge-string duality and integrability: progress and outlook Gauge-string duality and integrability: progress and outlook

NASA Astrophysics Data System (ADS)

Kristjansen, C.; Staudacher, M.; Tseytlin, A.

2009-06-01

The AdS/CFT correspondence, proposed a little more than a decade ago, has become a major subject of contemporary theoretical physics. One reason is that it suggests the exact identity of a certain ten-dimensional superstring theory, and a specific supersymmetric four-dimensional gauge field theory. This indicates that string theory, often thought of as a generalization of quantum field theory, can also lead to an alternative and computationally advantageous reformulation of gauge theory. This establishes the direct, down-to-earth relevance of string theory beyond loftier ideas of finding a theory of everything. Put differently, strings definitely lead to a theory of something highly relevant: a non-abelian gauge theory in a physical number of dimensions! A second reason for recent excitement around AdS/CFT is that it uncovers surprising novel connections between otherwise increasingly separate subdisciplines of theoretical physics, such as high energy physics and condensed matter theory. This collection of review articles concerns precisely such a link. About six years ago evidence was discovered showing that the AdS/CFT string/gauge system might actually be an exactly integrable model, at least in the so-called planar limit. Its spectrum appears to be described by (a generalization of) a Bethe ansatz, first proposed as an exact solution for certain one-dimensional magnetic spin chains in the early days of quantum mechanics. The field has been developing very rapidly, and a collection of fine review articles is needed. This special issue is striving to provide precisely that. The first article of the present collection, by Nick Dorey, is a pedagogical introduction to the subject. The second article, by Adam Rej, based on the translation of the author's PhD thesis, describes important techniques for analysing and interpreting the integrable structure of AdS/CFT, mostly from the point of view of the gauge theory. The third contribution, by Gleb Arutyunov and Sergey Frolov, explains in great detail the state-of-the-art of quantizing the AdS5 × S5 string theory's sigma model, gathering evidence for the conjectured integrability from the string side of the correspondence. The ensuing article by Nikolay Gromov starts with the full set of conjectured asymptotic Bethe equations of the model, and indicates how they relate to the firmly established classical integrabiliity of the string sigma model. The article by Benjamin Basso and Gregory Korchemsky discusses the issue of non-perturbative corrections in strong-coupling expansion and connections to the O(6) sigma model. The final article, by Fernando Alday, provides a link between the main topic of this special issue—the integrability of the spectrum of AdS/CFT—and other important observables of the model, such as the set of gluon scattering amplitudes, which may also lead to an exactly solvable problem. We feel that the whole subject of AdS/CFT integrability is still in its infancy, and that much remains to be understood, proved, and extended. It is furthermore quite possible that the underlying structures will prove important for progress on cutting-edge problems in condensed matter theory. This collection of articles by experts in the field should serve as an important assessment of the incomplete status quo of the subject. As such, we hope it will inspire further research activity by ambitious theorists!

Nonmonotonic Logic for Use in Information Retrieval: An Exploratory Paper.

ERIC Educational Resources Information Center

Hurt, C. D.

1998-01-01

Monotonic logic requires reexamination of the entire logic string when there is a contradiction. Nonmonotonic logic allows the user to withdraw conclusions in the face of contradiction without harm to the logic string, which has considerable application to the field of information searching. Artificial intelligence models and neural networks based…

Coupled dynamics of a viscoelastically supported infinite string and a number of discrete mechanical systems moving with uniform speed

NASA Astrophysics Data System (ADS)

Roy, Soumyajit; Chakraborty, G.; DasGupta, Anirvan

2018-02-01

The mutual interaction between a number of multi degrees of freedom mechanical systems moving with uniform speed along an infinite taut string supported by a viscoelastic layer has been studied using the substructure synthesis method when base excitations of a common frequency are given to the mechanical systems. The mobility or impedance matrices of the string have been calculated analytically by Fourier transform method as well as wave propagation technique. The above matrices are used to calculate the response of the discrete mechanical systems. Special attention is paid to the contact forces between the discrete and the continuous systems which are estimated by numerical simulation. The effects of phase difference, the distance between the systems and different base excitation amplitudes on the collective behaviour of the mechanical systems are also studied. The present study has relevance to the coupled dynamic problem of more than one railway pantographs and an overhead catenary system where the pantographs are modelled as discrete systems and the catenary is modelled as a taut string supported by continuous viscoelastic layer.

Thermodynamical string fragmentation

NASA Astrophysics Data System (ADS)

Fischer, Nadine; Sjöstrand, Torbjörn

2017-01-01

The observation of heavy-ion-like behaviour in pp collisions at the LHC suggests that more physics mechanisms are at play than traditionally assumed. The introduction e.g. of quark-gluon plasma or colour rope formation can describe several of the observations, but as of yet there is no established paradigm. In this article we study a few possible modifications to the Pythia event generator, which describes a wealth of data but fails for a number of recent observations. Firstly, we present a new model for generating the transverse momentum of hadrons during the string fragmentation process, inspired by thermodynamics, where heavier hadrons naturally are suppressed in rate but obtain a higher average transverse momentum. Secondly, close-packing of strings is taken into account by making the temperature or string tension environment-dependent. Thirdly, a simple model for hadron rescattering is added. The effect of these modifications is studied, individually and taken together, and compared with data mainly from the LHC. While some improvements can be noted, it turns out to be nontrivial to obtain effects as big as required, and further work is called for.

TOPICAL REVIEW: TeV mini black hole decay at future colliders

NASA Astrophysics Data System (ADS)

Casanova, Alex; Spallucci, Euro

2006-02-01

It is generally believed that mini black holes decay by emitting elementary particles with a black body energy spectrum. The original calculation leads to the conclusion that about the 90% of the black hole mass is radiated away in the form of photons, neutrinos and light leptons, mainly electrons and muons. With the advent of string theory, such a scenario must be updated by including new effects coming from the stringy nature of particles and interactions. The main modifications with respect to the original picture of black hole evaporation come from recent developments in non-perturbative string theory globally referred to as TeV-scale gravity. By taking for granted that black holes can be produced in hadronic collisions, then their decay must take into account that: (i) we live in a D3 brane embedded into a higher dimensional bulk spacetime; (ii) fundamental interactions, including gravity, are unified at the TeV energy scale. Thus, the formal description of the Hawking radiation mechanism has to be extended to the case of more than four spacetime dimensions and includes the presence of D-branes. This kind of topological defect in the bulk spacetime fabric acts as a sort of 'cosmic fly-paper' trapping electro-weak standard model elementary particles in our (3 + 1)-dimensional universe. Furthermore, unification of fundamental interactions at an energy scale many orders of magnitude lower than the Planck energy implies that any kind of fundamental particle, not only leptons, is expected to be emitted. A detailed understanding of the new scenario is instrumental for optimal tuning of detectors at future colliders, where, hopefully, this exciting new physics will be tested. In this review, we study higher dimensional black hole decay, considering not only the emission of particles according to the Hawking mechanism, but also their near-horizon QED/QCD interactions. The ultimate motivation is to build up a phenomenologically reliable scenario, allowing a clear experimental signature of the event.

Steady state and dynamical structure of a cosmic-ray-modified termination shock

NASA Technical Reports Server (NTRS)

Donohue, D. J.; Zank, G. P.

1993-01-01

A hydrodynamic model is developed for the structure of a cosmic-ray-modified termination shock. The model is based on the two-fluid equations of diffuse shock acceleration (Drury and Volk, 1981). Both the steady state structure of the shock and its interaction with outer heliospheric disturbances are considered. Under the assumption that the solar wind is decelerated by diffusing interstellar cosmic rates, it is shown that the natural state of the termination shock is a gradual deceleration and compression, followed by a discontinuous jump to a downstream state which is dominated by the pressure contribution of the cosmic rays. A representative model is calculated for the steady state which incorporates both interstellar cosmic ray mediation and diffusively accelerated anomalous ions through a proposed thermal leakage mechanism. The interaction of large-scale disturbances with the equilibrium termination shock model is shown to result in some unusual downstream structure, including transmitted shocks and cosmic-ray-modified contact discontinuities. The structure observed may be connected to the 2-kHz outer heliospheric radio emission (Cairns et al., 1992a, b). The time-dependent simulations also demonstrate that interaction with solar wind compressible turbulence (e.g., traveling interplanetary shocks, etc.) could induce the termination shock to continually fluctuate between cosmic-ray-dominated and gas-dynamic states. This fluctuation may represent a partial explanation of the galactic cosmic ray modulation effect and illustrates that the Pioneer and Voyager satellites will encounter an evolving shock whose structure and dynamic properties are strongly influence by the mediation of interstellar and anomalous cosmic rays.