Particle Accelerators Test Cosmological Theory.
ERIC Educational Resources Information Center
Schramm, David N.; Steigman, Gary
1988-01-01
Discusses the symbiotic relationship of cosmology and elementary-particle physics. Presents a brief overview of particle physics. Explains how cosmological considerations set limits on the number of types of elementary particles. (RT)
Particle Accelerators Test Cosmological Theory.
ERIC Educational Resources Information Center
Schramm, David N.; Steigman, Gary
1988-01-01
Discusses the symbiotic relationship of cosmology and elementary-particle physics. Presents a brief overview of particle physics. Explains how cosmological considerations set limits on the number of types of elementary particles. (RT)
Colliding-beam-accelerator lattice
Claus, J.; Cornacchia, M.; Courant, E.D.; Parzen, G.
1983-01-01
We describe the lattice of the Colliding Beam Accelerator, a 400 x 400 GeV pp facility proposed for construction at Brookhaven National Laboratory. The structure adopted is very versatile, in part in consequence of its desirable behavior as function of momentum deviation and as function of the betatron tunes. Each of the six insertions can be arranged to meet specific requirements at the crossing points as illustrated by a discussion of the tuneable low-beta insertions. The luminosity in these low-beta insertions (2 x 10/sup 33/ cm/sup -2/ sec/sup -1/) would be an order of magnitude larger than the standard insertions.
Lattice QCD input for axion cosmology
NASA Astrophysics Data System (ADS)
Berkowitz, Evan; Buchoff, Michael I.; Rinaldi, Enrico
2015-08-01
One intriguing beyond-the-Standard-Model particle is the QCD axion, which could simultaneously provide a solution to the Strong C P Problem and account for some, if not all, of the dark matter density in the Universe. This particle is a pseudo-Nambu-Goldstone boson of the conjectured Peccei-Quinn symmetry of the Standard Model. Its mass and interactions are suppressed by a heavy symmetry-breaking scale, fa, the value of which is roughly greater than 109 GeV (or, conversely, the axion mass, ma, is roughly less than 104 μ eV ). The density of axions in the Universe, which cannot exceed the relic dark matter density and is a quantity of great interest in axion experiments like ADMX, is a result of the early Universe interplay between cosmological evolution and the axion mass as a function of temperature. The latter quantity is proportional to the second derivative of the temperature-dependent QCD free energy with respect to the C P -violating phase, θ . However, this quantity is generically nonperturbative, and previous calculations have only employed instanton models at the high temperatures of interest (roughly 1 GeV). In this and future works, we aim to calculate the temperature-dependent axion mass at small θ from first-principle lattice calculations, with controlled statistical and systematic errors. Once calculated, this temperature-dependent axion mass is input for the classical evolution equations of the axion density of the Universe, which is required to be less than or equal to the dark matter density. Due to a variety of lattice systematic effects at the very high temperatures required, we perform a calculation of the leading small-θ cumulant of the theta vacua on large volume lattices for SU(3) Yang-Mills with high statistics as a first proof of concept, before attempting a full QCD calculation in the future. From these pure glue results, the misalignment mechanism yields the axion mass bound ma≥(14.6 ±0.1 ) μ eV when Peccei-Quinn breaking occurs
Scaling FFAG lattices for muon acceleration
Planche, T.; Lagrange, J. B.; Mori, Y.; Uesugi, T.
2010-03-30
Harmonic number jump acceleration of muon beams in scaling FFAG rings is studied. General considerations about harmonic number jump acceleration lead to the necessity of designing rings with dispersion suppressed insertions, and in which both mu{sup +} and mu{sup -} can be circulated in the same direction. Design principles of such a scaling FFAG ring are described. Example of a 3 to 10 GeV lattice is given, and 4D acceleration tracking is done in it.
Accelerating Cosmological Expansion from Shear and Bulk Viscosity
NASA Astrophysics Data System (ADS)
Floerchinger, Stefan; Tetradis, Nikolaos; Wiedemann, Urs Achim
2015-03-01
The dissipation of energy from local velocity perturbations in the cosmological fluid affects the time evolution of spatially averaged fluid dynamic fields and the cosmological solution of Einstein's field equations. We show how this backreaction effect depends on shear and bulk viscosity and other material properties of the dark sector, as well as the spectrum of perturbations. If sufficiently large, this effect could account for the acceleration of the cosmological expansion.
Cosmological consistency tests of gravity theory and cosmic acceleration
NASA Astrophysics Data System (ADS)
Ishak-Boushaki, Mustapha B.
2017-01-01
Testing general relativity at cosmological scales and probing the cause of cosmic acceleration are among the important objectives targeted by incoming and future astronomical surveys and experiments. I present our recent results on consistency tests that can provide insights about the underlying gravity theory and cosmic acceleration using cosmological data sets. We use statistical measures, the rate of cosmic expansion, the growth rate of large scale structure, and the physical consistency of these probes with one another.
Precision cosmology defeats void models for acceleration
Moss, Adam; Zibin, James P.; Scott, Douglas
2011-05-15
The suggestion that we occupy a privileged position near the center of a large, nonlinear, and nearly spherical void has recently attracted much attention as an alternative to dark energy. Putting aside the philosophical problems with this scenario, we perform the most complete and up-to-date comparison with cosmological data. We use supernovae and the full cosmic microwave background spectrum as the basis of our analysis. We also include constraints from radial baryonic acoustic oscillations, the local Hubble rate, age, big bang nucleosynthesis, the Compton y distortion, and for the first time include the local amplitude of matter fluctuations, {sigma}{sub 8}. These all paint a consistent picture in which voids are in severe tension with the data. In particular, void models predict a very low local Hubble rate, suffer from an ''old age problem,'' and predict much less local structure than is observed.
Cosmological zoo—accelerating models with dark energy
NASA Astrophysics Data System (ADS)
Szydlowski, Marek
2007-09-01
Recent observations of type Ia supernovae indicate that the Universe is in an accelerating phase of expansion. The fundamental quest in theoretical cosmology is to identify the origin of this phenomenon. In principle there are two possibilities: (1) the presence of matter which violates the strong energy condition (a substantial form of dark energy) or (2) modified Friedmann equations (Cardassian models—a non-substantial form of dark matter). We classify all these models in terms of two-dimensional dynamical systems of the Newtonian type. We search for generic properties of the models. It is achieved with the help of Peixoto's theorem for dynamical systems on the Poincaré sphere. We find that the notion of structural stability can be useful to distinguish the generic cases of evolutional paths with acceleration. We find that, while the ΛCDM models and phantom models are typical accelerating models, the cosmological models with bouncing phase are non-generic in the space of all planar dynamical systems. We derive the universal shape of the potential function which gives rise to presently accelerating models. Our results show explicitly the advantages of using the potential function (instead of the equation of state) to probe the origin of the present acceleration. We argue that simplicity and genericity are the best guide in understanding our Universe and its acceleration.
Learn-as-you-go acceleration of cosmological parameter estimates
Aslanyan, Grigor; Easther, Richard; Price, Layne C. E-mail: r.easther@auckland.ac.nz
2015-09-01
Cosmological analyses can be accelerated by approximating slow calculations using a training set, which is either precomputed or generated dynamically. However, this approach is only safe if the approximations are well understood and controlled. This paper surveys issues associated with the use of machine-learning based emulation strategies for accelerating cosmological parameter estimation. We describe a learn-as-you-go algorithm that is implemented in the Cosmo++ code and (1) trains the emulator while simultaneously estimating posterior probabilities; (2) identifies unreliable estimates, computing the exact numerical likelihoods if necessary; and (3) progressively learns and updates the error model as the calculation progresses. We explicitly describe and model the emulation error and show how this can be propagated into the posterior probabilities. We apply these techniques to the Planck likelihood and the calculation of ΛCDM posterior probabilities. The computation is significantly accelerated without a pre-defined training set and uncertainties in the posterior probabilities are subdominant to statistical fluctuations. We have obtained a speedup factor of 6.5 for Metropolis-Hastings and 3.5 for nested sampling. Finally, we discuss the general requirements for a credible error model and show how to update them on-the-fly.
Is cosmic acceleration proven by local cosmological probes?
NASA Astrophysics Data System (ADS)
Tutusaus, I.; Lamine, B.; Dupays, A.; Blanchard, A.
2017-06-01
Context. The cosmological concordance model (ΛCDM) matches the cosmological observations exceedingly well. This model has become the standard cosmological model with the evidence for an accelerated expansion provided by the type Ia supernovae (SNIa) Hubble diagram. However, the robustness of this evidence has been addressed recently with somewhat diverging conclusions. Aims: The purpose of this paper is to assess the robustness of the conclusion that the Universe is indeed accelerating if we rely only on low-redshift (z ≲ 2) observations, that is to say with SNIa, baryonic acoustic oscillations, measurements of the Hubble parameter at different redshifts, and measurements of the growth of matter perturbations. Methods: We used the standard statistical procedure of minimizing the χ2 function for the different probes to quantify the goodness of fit of a model for both ΛCDM and a simple nonaccelerated low-redshift power law model. In this analysis, we do not assume that supernovae intrinsic luminosity is independent of the redshift, which has been a fundamental assumption in most previous studies that cannot be tested. Results: We have found that, when SNIa intrinsic luminosity is not assumed to be redshift independent, a nonaccelerated low-redshift power law model is able to fit the low-redshift background data as well as, or even slightly better, than ΛCDM. When measurements of the growth of structures are added, a nonaccelerated low-redshift power law model still provides an excellent fit to the data for all the luminosity evolution models considered. Conclusions: Without the standard assumption that supernovae intrinsic luminosity is independent of the redshift, low-redshift probes are consistent with a nonaccelerated universe.
PyCOOL — A Cosmological Object-Oriented Lattice code written in Python
Sainio, J.
2012-04-01
There are a number of different phenomena in the early universe that have to be studied numerically with lattice simulations. This paper presents a graphics processing unit (GPU) accelerated Python program called PyCOOL that solves the evolution of scalar fields in a lattice with very precise symplectic integrators. The program has been written with the intention to hit a sweet spot of speed, accuracy and user friendliness. This has been achieved by using the Python language with the PyCUDA interface to make a program that is easy to adapt to different scalar field models. In this paper we derive the symplectic dynamics that govern the evolution of the system and then present the implementation of the program in Python and PyCUDA. The functionality of the program is tested in a chaotic inflation preheating model, a single field oscillon case and in a supersymmetric curvaton model which leads to Q-ball production. We have also compared the performance of a consumer graphics card to a professional Tesla compute card in these simulations. We find that the program is not only accurate but also very fast. To further increase the usefulness of the program we have equipped it with numerous post-processing functions that provide useful information about the cosmological model. These include various spectra and statistics of the fields. The program can be additionally used to calculate the generated curvature perturbation. The program is publicly available under GNU General Public License at https://github.com/jtksai/PyCOOL. Some additional information can be found from http://www.physics.utu.fi/tiedostot/theory/particlecosmology/pycool/.
PyCOOL — A Cosmological Object-Oriented Lattice code written in Python
NASA Astrophysics Data System (ADS)
Sainio, J.
2012-04-01
There are a number of different phenomena in the early universe that have to be studied numerically with lattice simulations. This paper presents a graphics processing unit (GPU) accelerated Python program called PyCOOL that solves the evolution of scalar fields in a lattice with very precise symplectic integrators. The program has been written with the intention to hit a sweet spot of speed, accuracy and user friendliness. This has been achieved by using the Python language with the PyCUDA interface to make a program that is easy to adapt to different scalar field models. In this paper we derive the symplectic dynamics that govern the evolution of the system and then present the implementation of the program in Python and PyCUDA. The functionality of the program is tested in a chaotic inflation preheating model, a single field oscillon case and in a supersymmetric curvaton model which leads to Q-ball production. We have also compared the performance of a consumer graphics card to a professional Tesla compute card in these simulations. We find that the program is not only accurate but also very fast. To further increase the usefulness of the program we have equipped it with numerous post-processing functions that provide useful information about the cosmological model. These include various spectra and statistics of the fields. The program can be additionally used to calculate the generated curvature perturbation. The program is publicly available under GNU General Public License at https://github.com/jtksai/PyCOOL. Some additional information can be found from http://www.physics.utu.fi/tiedostot/theory/particlecosmology/pycool/.
NASA Astrophysics Data System (ADS)
Demianski, Marek; Piedipalumbo, Ester; Sawant, Disha; Amati, Lorenzo
2017-02-01
Context. Explaining the accelerated expansion of the Universe is one of the fundamental challenges in physics today. Cosmography provides information about the evolution of the universe derived from measured distances, assuming only that the space time geometry is described by the Friedman-Lemaitre-Robertson-Walker metric, and adopting an approach that effectively uses only Taylor expansions of basic observables. Aims: We perform a high-redshift analysis to constrain the cosmographic expansion up to the fifth order. It is based on the Union2 type Ia supernovae data set, the gamma-ray burst Hubble diagram, a data set of 28 independent measurements of the Hubble parameter, baryon acoustic oscillations measurements from galaxy clustering and the Lyman-α forest in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), and some Gaussian priors on h and ΩM. Methods: We performed a statistical analysis and explored the probability distributions of the cosmographic parameters. By building up their regions of confidence, we maximized our likelihood function using the Markov chain Monte Carlo method. Results: Our high-redshift analysis confirms that the expansion of the Universe currently accelerates; the estimation of the jerk parameter indicates a possible deviation from the standard ΛCDM cosmological model. Moreover, we investigate implications of our results for the reconstruction of the dark energy equation of state (EOS) by comparing the standard technique of cosmography with an alternative approach based on generalized Padé approximations of the same observables. Because these expansions converge better, is possible to improve the constraints on the cosmographic parameters and also on the dark matter EOS. Conclusions: The estimation of the jerk and the DE parameters indicates at 1σ a possible deviation from the ΛCDM cosmological model.
New Low Emittance Lattice for the Super-B Accelerator
Biagini, M.E.; Boscolo, M.; Raimondi, P.; Tomassini, S.; Zobov, M.; Seeman, J.; Sullivan, M.; Wienands, U.; Wittmer, W.; Bettoni, S.; Paoloni, E.; Bogomyagkov, A.; Koop, I.; Levichev, E.; Nikitin, S.; Piminov, P.; Shatilov, D.; /Novosibirsk, IYF
2011-10-21
New low emittance lattices have been designed for the asymmetric SuperB accelerator, aiming at a luminosity of 10{sup 36} cm{sup -2} s{sup -1}. Main optics features are two alternating arc cells with different horizontal phase advance, decreasing beam emittance and allowing at the same time for easy chromaticity correction in the arcs. Emittance can be further reduced by a factor of two for luminosity upgrade. Spin rotation schemes for the e{sup -} beam have been studied to provide longitudinal polarization at the IP, and implementation into the lattice is in progress.
Some Cosmological Models for Poincare Gauge Gravity and Accelerated Expansion of the Universe
Mebarki, N.
2010-10-31
Two cosmological Models for the Poincare Gauge Gravity theory with a non vanishing torsion are proposed. It is shown that the torsion plays an important role in explaining the accelerated expansion of the universe. Some of the cosmological parameters are also expressed in terms of the redshift and the dark energy scenarios are discussed.
Deformed phase space Kaluza-Klein cosmology and late time acceleration
NASA Astrophysics Data System (ADS)
Sabido, M.; Yee-Romero, C.
2016-06-01
The effects of phase space deformations on Kaluza-Klein cosmology are studied. The deformation is introduced by modifying the symplectic structure of the minisuperspace variables. In the deformed model, we find an accelerating scale factor and therefore infer the existence of an effective cosmological constant from the phase space deformation parameter β.
The SuperB Accelerator: Overview and Lattice Studies
Biagini, M.E.; Boni, R.; Boscolo, M.; Drago, A.; Guiducci, S.; Preger, M.; Raimondi, P.; Tomassini, S.; Vaccarezza, C.; Zobov, M.; Cai, Y.; Fisher, A.; Heifets, S.; Novokhatski, A.; Pivi, M.T.; Seeman, J.; Sullivan, M.; Wienands, U.; Paoloni, E.; Marchiori, G.; Koop, I.; /Novosibirsk, IYF /Daresbury /LBL, Berkeley /CERN /Orsay, LAL /KEK, Tsukuba
2011-11-22
SuperB aims at the construction of a very high luminosity (10{sup 36} cm{sup -2} s{sup -1}) asymmetric e{sup +}e{sup -} Flavour Factory, with possible location at the campus of the University of Rome Tor Vergata, near the INFN Frascati National Laboratory. In this paper the basic principles of the design and details on the lattice are given. SuperB is a new machine that can exploit novel very promising design approaches: (1) large Piwinski angle scheme will allow for peak luminosity of the order of 10{sup 36} cm{sup -2} s{sup -1}, well beyond the current state-of-the-art, without a significant increase in beam currents or shorter bunch lengths; (2) 'crab waist' sextupoles will be used for suppression of dangerous resonances; (3) the low beam currents design presents reduced detector and background problems, and affordable operating costs; (4) a polarized electron beam can produce polarized {tau} leptons, opening an entirely new realm of exploration in lepton flavor physics. SuperB studies are already proving useful to the accelerator and particle physics communities. The principle of operation is being tested at DAFNE. The baseline lattice, based on the reuse of all PEP-II hardware, fits in the Tor Vergata University campus site, near Frascati. A CDR is being reviewed by an International Review Committee, chaired by J. Dainton (UK). A Technical Design Report will be prepared to be ready by beginning of 2010.
Farooq, Omer; Ratra, Bharat E-mail: ratra@phys.ksu.edu
2013-03-20
We compile a list of 28 independent measurements of the Hubble parameter between redshifts 0.07 {<=} z {<=} 2.3 and use this to place constraints on model parameters of constant and time-evolving dark energy cosmologies. These H(z) measurements by themselves require a currently accelerating cosmological expansion at about, or better than, 3{sigma} confidence. The mean and standard deviation of the six best-fit model deceleration-acceleration transition redshifts (for the three cosmological models and two Hubble constant priors we consider) are z{sub da} = 0.74 {+-} 0.05, in good agreement with the recent Busca et al. determination of z{sub da} = 0.82 {+-} 0.08 based on 11 H(z) measurements between redshifts 0.2 {<=} z {<=} 2.3, almost entirely from baryon-acoustic-oscillation-like data.
NASA Astrophysics Data System (ADS)
Farooq, Omer; Ratra, Bharat
2013-03-01
We compile a list of 28 independent measurements of the Hubble parameter between redshifts 0.07 <= z <= 2.3 and use this to place constraints on model parameters of constant and time-evolving dark energy cosmologies. These H(z) measurements by themselves require a currently accelerating cosmological expansion at about, or better than, 3σ confidence. The mean and standard deviation of the six best-fit model deceleration-acceleration transition redshifts (for the three cosmological models and two Hubble constant priors we consider) are z da = 0.74 ± 0.05, in good agreement with the recent Busca et al. determination of z da = 0.82 ± 0.08 based on 11 H(z) measurements between redshifts 0.2 <= z <= 2.3, almost entirely from baryon-acoustic-oscillation-like data.
Supernovae, an accelerating universe and the cosmological constant.
Kirshner, R P
1999-04-13
Observations of supernova explosions halfway back to the Big Bang give plausible evidence that the expansion of the universe has been accelerating since that epoch, approximately 8 billion years ago and suggest that energy associated with the vacuum itself may be responsible for the acceleration.
Supernovae, an accelerating universe and the cosmological constant
Kirshner, Robert P.
1999-01-01
Observations of supernova explosions halfway back to the Big Bang give plausible evidence that the expansion of the universe has been accelerating since that epoch, approximately 8 billion years ago and suggest that energy associated with the vacuum itself may be responsible for the acceleration. PMID:10200242
Scalar speed limits and cosmology: Acceleration from D-cceleration
NASA Astrophysics Data System (ADS)
Silverstein, Eva; Tong, David
2004-11-01
Causality on the gravity side of the AdS/CFT correspondence restricts motion on the moduli space of the N=4 super Yang-Mills theory by imposing a speed limit on how fast the scalar field may roll. This effect can be traced to higher-derivative operators arising from integrating out light degrees of freedom near the origin. In the strong coupling limit of the theory, the dynamics is well approximated by the Dirac-Born-Infeld Lagrangian for a probe D3-brane moving toward the horizon of the AdS Poincaré patch, combined with an estimate of the (ultimately suppressed) rate of particle and string production in the system. We analyze the motion of a rolling scalar field explicitly in the strong coupling regime of the field theory and extend the analysis to cosmological systems obtained by coupling this type of field theory to four-dimensional gravity. This leads to a mechanism for slow roll inflation for a massive scalar at sub-Planckian vacuum expectation value without need for a flat potential (realizing a version of k inflation in a microphysical framework). It also leads to a variety of novel Friedman-Roberston-Walker cosmologies, some of which are related to those obtained with tachyon matter.
Scalar Speed Limits and Cosmology: Acceleration from Deceleration
Silverstein, E
2003-11-21
Causality on the gravity side of the AdS/CFT correspondence restricts motion on the moduli space of the N = 4 super Yang Mills theory by imposing a speed limit on how fast the scalar field may roll. This effect can be traced to higher derivative operators arising from integrating out light degrees of freedom near the origin. In the strong coupling limit of the theory, the dynamics is well approximated by the Dirac-Born-Infeld Lagrangian for a probe D3-brane moving toward the horizon of the AdS Poincare patch, combined with an estimate of the (ultimately suppressed) rate of particle and string production in the system. We analyze the motion of a rolling scalar field explicitly in the strong coupling regime of the field theory, and extend the analysis to cosmological systems obtained by coupling this type of field theory to four dimensional gravity. This leads to a mechanism for slow roll inflation for a massive scalar at subPlanckian VEV without need for a flat potential (realizing a version of k-inflation in a microphysical framework). It also leads to a variety of novel FRW cosmologies, some of which are related to those obtained with tachyon matter.
NASA Astrophysics Data System (ADS)
Marochnik, Leonid
2017-07-01
We show that on the average, homogeneous and isotropic scalar field and on the average homogeneous and isotropic ensembles of classical and quantum gravitational waves generate the de Sitter expansion of the empty (with no matter) space-time. At the start and by the end of its cosmological evolution the Universe is empty. The contemporary Universe is about 70% empty, so the effect of cosmological acceleration should be very noticeable. One can assume that it manifests itself as dark energy. At the start of the cosmological evolution, before the first matter was born, the Universe is also empty. The cosmological acceleration of such an empty space-time can manifests itself as inflation. To get the de Sitter accelerated expansion of the empty space-time under influence of scalar fields and classical and quantum gravitational waves, one needs to make a mandatory Wick rotation, i.e. one needs to make a transition to the Euclidean space of imaginary time. One can assume that the very existence of inflation and dark energy could be considered as a possible observable evidence of the fact that time by its nature could be a complex value which manifests itself precisely at the start and by the end of the evolution of the Universe, i.e. in those periods when the Universe is empty (or nearly empty).
NASA Astrophysics Data System (ADS)
Harrison, Edward
2000-03-01
Cosmology: The Science of the Universe is a broad introduction to the science of modern cosmology, with emphasis on its historical origins. The first edition of this best-selling book received worldwide acclaim for its lucid style and wide-ranging exploration of the universe. This eagerly awaited second edition updates and greatly extends the first with seven new chapters that explore early scientific cosmology, Cartesian and Newtonian world systems, cosmology after Newton and before Einstein, special relativity, observational cosmology, inflation and creation of the universe. All chapters conclude with a section entitled Reflections containing provocative topics that will foster lively debate. The new Projects section, also at the end of each chapter, raises questions and issues to challenge the reader.
Observation of Stueckelberg oscillations in accelerated optical lattices
Zenesini, A.; Ciampini, D.; Arimondo, E.; Morsch, O.
2010-12-15
We report the experimental observation of Stueckelberg oscillations of matter waves in optical lattices. Extending previous work on Landau-Zener tunneling of Bose-Einstein condensates in optical lattices, we study the effects of the accumulated phase between two successive crossings of the Brillouin zone edge. Our results agree well with a simple model for multiple Landau-Zener tunneling events taking into account the band structure of the optical lattice.
Anisotropic SD2 brane: accelerating cosmology and Kasner-like space-time from compactification
NASA Astrophysics Data System (ADS)
Nayek, Kuntal; Roy, Shibaji
2017-07-01
Starting from an anisotropic (in all directions including the time direction of the brane) non-SUSY D2 brane solution of type IIA string theory we construct an anisotropic space-like D2 brane (or SD2 brane, for short) solution by the standard trick of a double Wick rotation. This solution is characterized by five independent parameters. We show that compactification on six-dimensional hyperbolic space (H_6) of a time-dependent volume of this SD2 brane solution leads to accelerating cosmologies (for some time t˜ t_0, with t_0 some characteristic time) where both the expansions and the accelerations are different in three spatial directions of the resultant four-dimensional universe. On the other hand at early times (t ≪ t_0) this four-dimensional space, in certain situations, leads to four-dimensional Kasner-like cosmology, with two additional scalars, namely, the dilaton and a volume scalar of H_6. Unlike in the standard four-dimensional Kasner cosmology here all three Kasner exponents could be positive definite, leading to expansions in all three directions.
NASA Astrophysics Data System (ADS)
Livio, Mario
2000-12-01
Advance Praise for The Accelerating Universe "The Accelerating Universe is not only an informative book about modern cosmology. It is rich storytelling and, above all, a celebration of the human mind in its quest for beauty in all things." -Alan Lightman, author of Einstein's Dreams "This is a wonderfully lucid account of the extraordinary discoveries that have made the last years a golden period for observational cosmology. But Mario Livio has not only given the reader one clear explanation after another of what astronomers are up to, he has used them to construct a provocative argument for the importance of aesthetics in the development of science and for the inseparability of science, art, and culture." -Lee Smolin, author of The Life of the Cosmos "What a pleasure to read! An exciting, simple account of the universe revealed by modern astronomy. Beautifully written, clearly presented, informed by scientific and philosophical insights." -John Bahcall, Institute for Advanced Study "A book with charm, beauty, elegance, and importance. As authoritative a journey as can be taken through modern cosmology." -Allan Sandage, Observatories of the Carnegie Institution of Washington
Low-acceleration instability of a Bose-Einstein condensate in an optical lattice.
Zheng, Yi; Kostrun, Marijan; Javanainen, Juha
2004-12-03
We study a Bose-Einstein condensate in a one-dimensional accelerated optical lattice using the mean-field version of the Bose-Hubbard model. Reminiscent of recent experiments [M. Cristiani et al., Opt. Express 12, 4 (2004)], we find a new type of an instability in this system that occurs in the limit when the acceleration is small.
Cosmological Relativity: A General-Relativistic Theory for the Accelerating Expanding Universe
NASA Astrophysics Data System (ADS)
Carmeli, M.; Behar, S.
Recent observations of distant supernovae imply, in defiance of expectations, that the universe growth is accelerating, contrary to what has always been assumed that the expansion is slowing down due to gravity. In this paper a general-relativistic cosmological theory that gives a direct relationship between distances and redshifts in an expanding universe is presented. The theory is actually a generalization of Hubble's law taking gravity into account by means of Einstein's theory of general relativity. The theory predicts that the universe can have three phases of expansion, decelerating, constant and accelerating, but it is shown that at present the first two cases are excluded, although in the past it had experienced them. Our theory shows that the universe now is definitely in the stage of accelerating expansion, confirming the recent experimental results.
NASA Astrophysics Data System (ADS)
Capozziello, Salvatore; Farooq, Omer; Luongo, Orlando; Ratra, Bharat
2014-08-01
We examine the observational viability of a class of f(R) gravity cosmological models. Particular attention is devoted to constraints from the recent observational determination of the redshift of the cosmological deceleration-acceleration transition. Making use of the fact that the Ricci scalar is a function of redshift z in these models, R =R(z), and so is f(z), we use cosmography to relate a f(z) test function evaluated at higher z to late-time cosmographic bounds. First, we consider a model-independent procedure to build up a numerical f(z) by requiring that at z=0 the corresponding cosmological model reduces to standard ΛCDM. We then infer late-time observational constraints on f(z) in terms of bounds on the Taylor expansion cosmographic coefficients. In doing so we parametrize possible departures from the standard ΛCDM model in terms of a two-parameter logarithmic correction. The physical meaning of the two parameters is also discussed in terms of the post-Newtonian approximation. Second, we provide numerical estimates of the cosmographic series terms by using type Ia supernova apparent magnitude data and Hubble parameter measurements. Finally, we use these estimates to bound the two parameters of the logarithmic correction. We find that the deceleration parameter in our model changes sign at a redshift consistent with what is observed.
Implications of an absolute simultaneity theory for cosmology and universe acceleration.
Kipreos, Edward T
2014-01-01
An alternate Lorentz transformation, Absolute Lorentz Transformation (ALT), has similar kinematics to special relativity yet maintains absolute simultaneity in the context of a preferred reference frame. In this study, it is shown that ALT is compatible with current experiments to test Lorentz invariance only if the proposed preferred reference frame is locally equivalent to the Earth-centered non-rotating inertial reference frame, with the inference that in an ALT framework, preferred reference frames are associated with centers of gravitational mass. Applying this theoretical framework to cosmological data produces a scenario of universal time contraction in the past. In this scenario, past time contraction would be associated with increased levels of blueshifted light emissions from cosmological objects when viewed from our current perspective. The observation that distant Type Ia supernovae are dimmer than predicted by linear Hubble expansion currently provides the most direct evidence for an accelerating universe. Adjusting for the effects of time contraction on a redshift-distance modulus diagram produces a linear distribution of supernovae over the full redshift spectrum that is consistent with a non-accelerating universe.
Implications of an Absolute Simultaneity Theory for Cosmology and Universe Acceleration
Kipreos, Edward T.
2014-01-01
An alternate Lorentz transformation, Absolute Lorentz Transformation (ALT), has similar kinematics to special relativity yet maintains absolute simultaneity in the context of a preferred reference frame. In this study, it is shown that ALT is compatible with current experiments to test Lorentz invariance only if the proposed preferred reference frame is locally equivalent to the Earth-centered non-rotating inertial reference frame, with the inference that in an ALT framework, preferred reference frames are associated with centers of gravitational mass. Applying this theoretical framework to cosmological data produces a scenario of universal time contraction in the past. In this scenario, past time contraction would be associated with increased levels of blueshifted light emissions from cosmological objects when viewed from our current perspective. The observation that distant Type Ia supernovae are dimmer than predicted by linear Hubble expansion currently provides the most direct evidence for an accelerating universe. Adjusting for the effects of time contraction on a redshift–distance modulus diagram produces a linear distribution of supernovae over the full redshift spectrum that is consistent with a non-accelerating universe. PMID:25536116
LATTICES FOR HIGH-POWER PROTON BEAM ACCELERATION AND SECONDARY BEAM COLLECTION AND COOLING.
WANG, S.; WEI, J.; BROWN, K.; GARDNER, C.; LEE, Y.Y.; LOWENSTEIN, D.; PEGGS, S.; SIMOS, N.
2006-06-23
Rapid cycling synchrotrons are used to accelerate high-intensity proton beams to energies of tens of GeV for secondary beam production. After primary beam collision with a target, the secondary beam can be collected, cooled, accelerated or decelerated by ancillary synchrotrons for various applications. In this paper, we first present a lattice for the main synchrotron. This lattice has: (a) flexible momentum compaction to avoid transition and to facilitate RF gymnastics (b) long straight sections for low-loss injection, extraction, and high-efficiency collimation (c) dispersion-free straights to avoid longitudinal-transverse coupling, and (d) momentum cleaning at locations of large dispersion with missing dipoles. Then, we present a lattice for a cooler ring for the secondary beam. The momentum compaction across half of this ring is near zero, while for the other half it is normal. Thus, bad mixing is minimized while good mixing is maintained for stochastic beam cooling.
Late time acceleration in a non-commutative model of modified cosmology
NASA Astrophysics Data System (ADS)
Malekolkalami, B.; Atazadeh, K.; Vakili, B.
2014-12-01
We investigate the effects of non-commutativity between the position-position, position-momentum and momentum-momentum of a phase space corresponding to a modified cosmological model. We show that the existence of such non-commutativity results in a Moyal Poisson algebra between the phase space variables in which the product law between the functions is of the kind of an α-deformed product. We then transform the variables in such a way that the Poisson brackets between the dynamical variables take the form of a usual Poisson bracket but this time with a noncommutative structure. For a power law expression for the function of the Ricci scalar with which the action of the gravity model is modified, the exact solutions in the commutative and noncommutative cases are presented and compared. In terms of these solutions we address the issue of the late time acceleration in cosmic evolution.
Aissaoui, H.; Bouhalouf, H.; Mebarki, N.
2010-10-31
An FRW like cosmological model in the non commutative Seiberg-Witten space-time is proposed. The pure NCG dynamical apparent horizon and Hawking temperature are obtained and explicit expressions of the scale factor, Hubble and deceleration parameters are derived. The accelerated expansion of the universe scenario is also discussed.
Probing lattice dynamics in silicon with laser-wakefield accelerated electrons
NASA Astrophysics Data System (ADS)
Nees, John; He, Z.-H.; Thomas, A. G. R.; Krushelnick, Karl; Scott, S.; Legally, M.; Beaurepaire, B.; Gallé, G.; Faure, J.
2016-10-01
Laser wakefield acceleration is the key technology in a new breed of electron and photon beam sources that operate in the ultrafast domain. We show that the spatial and temporal properties of wakefield-generated electron beams can be manipulated to enable them interrogate ultrafast lattice dynamics in freestanding single-crystal silicon membranes, while maintaining spatial resolution on the atomic scale. In particular, picosecond resolution of Si lattice dynamics is obtained by recording streaked electron diffraction peaks using static magnetic fields. We will also discuss the role of wave front control in establishing optimal beam characteristics and the significance of single-shot measurements. Michigan support from NSF PHY-1535628.
Low-Acceleration Instability of a Bose-Einstein Condensate in an Optical Lattice
NASA Astrophysics Data System (ADS)
Zheng, Yi; Kos̆Trun, Marijan; Javanainen, Juha
2004-11-01
We study a Bose-Einstein condensate in a one-dimensional accelerated optical lattice using the mean-field version of the Bose-Hubbard model. Reminiscent of recent experiments [
Liang Nan; Wu Puxun; Zhang Shuangnan
2010-04-15
Gamma-ray bursts (GRBs) have been regarded as standard candles at very high redshift for cosmology research. We have proposed a new method to calibrate GRB distance indicators with Type Ia supernova (SNe Ia) data in a completely cosmology-independent way to avoid the circularity problem that had limited the direct use of GRBs to probe cosmology [N. Liang, W. K. Xiao, Y. Liu, and S. N. Zhang, Astrophys. J. 685, 354 (2008).]. In this paper, a simple method is provided to combine GRB data into the joint observational data analysis to constrain cosmological models; in this method those SNe Ia data points used for calibrating the GRB data are not used to avoid any correlation between them. We find that the {Lambda}CDM model is consistent with the joint data in the 1-{sigma} confidence region, using the GRB data at high redshift calibrated with the interpolating method, the Constitution set of SNe Ia, the cosmic microwave background radiation from Wilkinson Microwave Anisotropy Probe five year observation, the baryonic acoustic oscillation from the spectroscopic Sloan Digital Sky Survey Data Release 7 galaxy sample, the x-ray baryon mass fraction in clusters of galaxies, and the observational Hubble parameter versus redshift data. Comparing to the joint constraints with GRBs and without GRBs, we find that the contribution of GRBs to the joint cosmological constraints is a slight shift in the confidence regions of cosmological parameters to better enclose the {Lambda}CDM model. Finally, we reconstruct the acceleration history of the Universe up to z>6 with the distance moduli of SNe Ia and GRBs and find some features that deviate from the {Lambda}CDM model and seem to favor oscillatory cosmology models; however, further investigations are needed to better understand the situation.
NASA Astrophysics Data System (ADS)
Odintsov, S. D.; Oikonomou, V. K.
2016-06-01
We present some cosmological models which unify the late- and early-time acceleration eras with the radiation and the matter domination era, and we realize the cosmological models by using the theoretical framework of F(R) gravity. Particularly, the first model unifies the late- and early-time acceleration with the matter domination era, and the second model unifies all the evolution eras of our Universe. The two models are described in the same way at early and late times, and only the intermediate stages of the evolution have some differences. Each cosmological model contains two Type IV singularities which are chosen to occur one at the end of the inflationary era and one at the end of the matter domination era. The cosmological models at early times are approximately identical to the R 2 inflation model, so these describe a slow-roll inflationary era which ends when the slow-roll parameters become of order one. The inflationary era is followed by the radiation era and after that the matter domination era follows, which lasts until the second Type IV singularity, and then the late-time acceleration era follows. The models have two appealing features: firstly they produce a nearly scale invariant power spectrum of primordial curvature perturbations and a scalar-to-tensor ratio which are compatible with the most recent observational data and secondly, it seems that the deceleration-acceleration transition is crucially affected by the presence of the second Type IV singularity which occurs at the end of the matter domination era. As we demonstrate, the Hubble horizon at early times shrinks, as expected for an initially accelerating Universe, then during the matter domination era, it expands and finally after the Type IV singularity, the Hubble horizon starts to shrink again, during the late-time acceleration era. Intriguingly enough, the deceleration-acceleration transition, occurs after the second Type IV singularity. In addition, we investigate which F(R) gravity
Redshift remapping and cosmic acceleration in dark-matter-dominated cosmological models
NASA Astrophysics Data System (ADS)
Wojtak, Radosław; Prada, Francisco
2017-10-01
The standard relation between the cosmological redshift and cosmic scalefactor underlies cosmological inference from virtually all kinds of cosmological observations, leading to the emergence of the Λ cold-dark-matter (ΛCDM) cosmological model. This relation is not a fundamental theory and thus observational determination of this function (redshift remapping) should be regarded as an insightful alternative to holding its standard form in analyses of cosmological data. Here we present non-parametric reconstructions of redshift remapping in dark-matter-dominated models and constraints on cosmological parameters from a joint analysis of all primary cosmological probes including the local measurement of the Hubble constant, Type Ia supernovae, baryon acoustic oscillations (BAO), Planck observations of the cosmic microwave background (CMB) radiation (temperature power spectrum) and cosmic chronometers. The reconstructed redshift remapping points to an additional boost of redshift operating in late epoch of cosmic evolution, but affecting both low-redshift observations and the CMB. The model predicts a significant difference between the actual Hubble constant, h = 0.48 ± 0.02, and its local determination, hobs = 0.73 ± 0.02. The ratio of these two values coincides closely with the maximum expansion rate inside voids formed in the corresponding open cosmological model with Ωm = 0.87 ± 0.03, whereas the actual value of the Hubble constant implies the age of the Universe that is compatible with the Planck ΛCDM cosmology. The model with redshift remapping provides excellent fits to all data and eliminates recently reported tensions between the PlanckΛCDM cosmology, the local determination of the Hubble constant and the BAO measurements from the Ly α forest of high-redshift quasars.
A Lattice for a Hybrid Fast-Ramping Muon Accelerator to 750 GeV
Garren, A.A.; Berg, J.
2011-09-06
We describe a lattice for accelerating muons from 375 GeV to 750 GeV. The lattice is a fast-ramping synchrotron with a mixture of fixed-field superconducting dipoles and warm dipoles, so as to have a high average bending field while still being able to rapidly change the average bending field as the beam momentum increases. For a 1.5 TeV center of mass muon collider, muons must be rapidly accelerated to 750 GeV. To accomplish this efficiently, we wish to make as many passes through the RF cavities as possible, while keeping the average RF gradients sufficiently high to avoid excess muon decays. A synchrotron where the magnets are very rapidly ramped has been envisioned as one option to accomplish this. The entire acceleration cycle takes place in less than 1 ms, presenting a technological challenge for the magnets. Clearly superconducting magnets cannot be ramped on this time scale, so instead room-temperature magnets will be ramped. To keep losses low, dipoles can use grain-oriented silicon steel, but quadrupoles will probably need to use more conventional steel, giving a lower maximum field for these high ramping rates. If we want to have a large average RF gradient and simultaneously make a large number of passes through the RF cavities, the average bending field must be high. To achieve such a large bending field while rapidly ramping magnets, it has been proposed to use a hybrid lattice consisting of interleaved superconducting dipoles and bipolar ramped dipoles. Due to the large single-bunch current and the relatively small apertures we desire (both because we would like to use high-frequency RF, and because power requirements and heating will be more reasonable for smaller aperture ramped magnets), collective effects are expected to be very significant. To reduce their effects, we propose to have strong synchrotron oscillations (a synchrotron tune of over 1). To have such a high synchrotron tune, a large number of superperiods are needed. Putting together
Ishak, Mustapha; Peel, Austin; Troxel, M A
2013-12-20
Probes of cosmic expansion constitute the main basis for arguments to support or refute a possible apparent acceleration due to different expansion rates in the Universe as described by inhomogeneous cosmological models. We present in this Letter a separate argument based on results from an analysis of the growth rate of large-scale structure in the Universe as modeled by the inhomogeneous cosmological models of Szekeres. We use the models with no assumptions of spherical or axial symmetries. We find that while the Szekeres models can fit very well the observed expansion history without a Λ, they fail to produce the observed late-time suppression in the growth unless Λ is added to the dynamics. A simultaneous fit to the supernova and growth factor data shows that the cold dark matter model with a cosmological constant (ΛCDM) provides consistency with the data at a confidence level of 99.65%, while the Szekeres model without Λ achieves only a 60.46% level. When the data sets are considered separately, the Szekeres with no Λ fits the supernova data as well as the ΛCDM does, but provides a very poor fit to the growth data with only 31.31% consistency level compared to 99.99% for the ΛCDM. This absence of late-time growth suppression in inhomogeneous models without a Λ is consolidated by a physical explanation.
NASA Astrophysics Data System (ADS)
Odintsov, S. D.; Oikonomou, V. K.
2016-01-01
We study mimetic F (R ) gravity with a potential and Lagrange multiplier constraint. In the context of these theories, we introduce a reconstruction technique which enables us to realize arbitrary cosmologies, given the Hubble rate and an arbitrarily chosen F (R ) gravity. We exemplify our method by realizing cosmologies that are in concordance with current observations (Planck data) and also well-known bouncing cosmologies. The attribute of our method is that the F (R ) gravity can be arbitrarily chosen, so we can have the appealing features of the mimetic approach combined with the known features of some F (R ) gravities, which unify early-time with late-time acceleration. Moreover, we study the existence and the stability of de Sitter points in the context of mimetic F (R ) gravity. In the case of unstable de Sitter points, it is demonstrated that graceful exit from inflation occurs. We also study the Einstein-frame counterpart theory of the Jordan-frame mimetic F (R ) gravity, and we discuss the general properties of the theory and exemplify our analysis by studying a quite interesting (from a phenomenological point of view) model with two scalar fields. We also calculate the observational indices of the two-scalar-field model, by using the two-scalar-field formalism. Furthermore, we extensively study the dynamical system that corresponds to the mimetic F (R ) gravity, by finding the fixed points and studying their stability. Finally, we modify our reconstruction method to function in the inverse way and thus yield which F (R ) gravity can realize a specific cosmological evolution, given the mimetic potential and the Lagrange multiplier.
NASA Astrophysics Data System (ADS)
Yu, H.; Wang, Z.; Zhang, C.; Chen, N.; Zhao, Y.; Sawchuk, A. P.; Dalsing, M. C.; Teague, S. D.; Cheng, Y.
2014-11-01
Existing research of patient-specific computational hemodynamics (PSCH) heavily relies on software for anatomical extraction of blood arteries. Data reconstruction and mesh generation have to be done using existing commercial software due to the gap between medical image processing and CFD, which increases computation burden and introduces inaccuracy during data transformation thus limits the medical applications of PSCH. We use lattice Boltzmann method (LBM) to solve the level-set equation over an Eulerian distance field and implicitly and dynamically segment the artery surfaces from radiological CT/MRI imaging data. The segments seamlessly feed to the LBM based CFD computation of PSCH thus explicit mesh construction and extra data management are avoided. The LBM is ideally suited for GPU (graphic processing unit)-based parallel computing. The parallel acceleration over GPU achieves excellent performance in PSCH computation. An application study will be presented which segments an aortic artery from a chest CT dataset and models PSCH of the segmented artery.
Tunneling dynamics of superfluid Fermi gases in an accelerating optical lattice
Tie Lu; Xue Jukui
2010-11-15
The nonlinear Landau-Zener tunneling and the nonlinear Rabi oscillations of superfluid Fermi gases between Bloch bands in an accelerating optical lattice are discussed. Within the hydrodynamic theory and a two-level model, the tunneling probability of superfluid Fermi gases between Bloch bands is obtained. We find that, as the system crosses from the Bose-Einstein condensation (BEC) side to the BCS side, the tunneling rate is closely related to the particle density: when the density is smaller (larger) than a critical value, the tunneling rate at unitarity is larger (smaller) than that in the BEC limit. This is well explained in terms of an effective interaction and an effective potential. Furthermore, the nonlinear Rabi oscillations of superfluid Fermi gases between the bands are discussed by imposing a periodic modulation on the level bias and the strength of the lattice. Analytical expressions of the critical density for suppressing or enhancing the Rabi oscillations are obtained. It is shown that, as the system crosses from the BEC side to the BCS side, the critical density strongly depends on the modulation parameters (i.e., the modulation amplitude and the modulation frequency). For a fixed density, a high-frequency or low-frequency modulation can suppress or enhance the Rabi oscillations both at unitarity and in the BEC limit. For an intermediate modulation frequency, the Rabi oscillations are chaotic along the entire BEC-BCS crossover, especially, on the BCS side. Interestingly, we find that the modulation of the lattice strength only with an intermediate modulation frequency has significant effect on the Rabi oscillations both in the BEC limit and at unitarity; that is, an intermediate-frequency modulation can enhance the Rabi oscillations, especially on the BCS side.
Single Particle Dynamics in a Quasi-Integrable Nonlinear Accelerator Lattice
Antipov, Sergey A.; Nagaitsev, Sergei; Valishev, Alexander
2016-04-28
Fermilab is constructing the Integrable Optics Test Accelerator (IOTA) as the centerpiece of the Accelerator R&D Program towards high-intensity circular machines. One of the factors limiting the beam intensity in present circular accelerators is collective instabilities, which can be suppressed by a spread of betatron frequencies (tunes) through the Landau damping mechanism or by an external damper, if the instability is slow enough. The spread is usually created by octupole magnets, which introduce the tune dependence on the amplitude and, in some cases, by a chromatic spread (tune dependence on particle's momentum). The introduction of octupoles usually lead to a resonant behavior and a reduction of the dynamic aperture. One of the goals of the IOTA research program is to achieve a high betatron tune spread, while retaining a large dynamic aperture using conventional octupole magnets in a special but realistic accelerator configuration. In this report, we present results of computer simulations of an electron beam in the IOTA by particle tracking and the Frequency Map Analysis. The results show that the ring's octupole magnets can be configured to provide a betatron tune shift of 0.08 (for particles at large amplitudes) with the dynamical aperture of over 20 beam sigma for a 150-MeV electron beam. The influence of the synchrotron motion, lattice errors, and magnet imperfections is insignificant for the parameters and levels of tolerances set by the design of the ring. The described octupole insert could be beneficial for suppression of space-charge induced instabilities in high intensity machines.
Temple, Blake; Smoller, Joel
2009-08-25
We derive a system of three coupled equations that implicitly defines a continuous one-parameter family of expanding wave solutions of the Einstein equations, such that the Friedmann universe associated with the pure radiation phase of the Standard Model of Cosmology is embedded as a single point in this family. By approximating solutions near the center to leading order in the Hubble length, the family reduces to an explicit one-parameter family of expanding spacetimes, given in closed form, that represents a perturbation of the Standard Model. By introducing a comoving coordinate system, we calculate the correction to the Hubble constant as well as the exact leading order quadratic correction to the redshift vs. luminosity relation for an observer at the center. The correction to redshift vs. luminosity entails an adjustable free parameter that introduces an anomalous acceleration. We conclude (by continuity) that corrections to the redshift vs. luminosity relation observed after the radiation phase of the Big Bang can be accounted for, at the leading order quadratic level, by adjustment of this free parameter. The next order correction is then a prediction. Since nonlinearities alone could actuate dissipation and decay in the conservation laws associated with the highly nonlinear radiation phase and since noninteracting expanding waves represent possible time-asymptotic wave patterns that could result, we propose to further investigate the possibility that these corrections to the Standard Model might be the source of the anomalous acceleration of the galaxies, an explanation not requiring the cosmological constant or dark energy.
Temple, Blake; Smoller, Joel
2009-01-01
We derive a system of three coupled equations that implicitly defines a continuous one-parameter family of expanding wave solutions of the Einstein equations, such that the Friedmann universe associated with the pure radiation phase of the Standard Model of Cosmology is embedded as a single point in this family. By approximating solutions near the center to leading order in the Hubble length, the family reduces to an explicit one-parameter family of expanding spacetimes, given in closed form, that represents a perturbation of the Standard Model. By introducing a comoving coordinate system, we calculate the correction to the Hubble constant as well as the exact leading order quadratic correction to the redshift vs. luminosity relation for an observer at the center. The correction to redshift vs. luminosity entails an adjustable free parameter that introduces an anomalous acceleration. We conclude (by continuity) that corrections to the redshift vs. luminosity relation observed after the radiation phase of the Big Bang can be accounted for, at the leading order quadratic level, by adjustment of this free parameter. The next order correction is then a prediction. Since nonlinearities alone could actuate dissipation and decay in the conservation laws associated with the highly nonlinear radiation phase and since noninteracting expanding waves represent possible time-asymptotic wave patterns that could result, we propose to further investigate the possibility that these corrections to the Standard Model might be the source of the anomalous acceleration of the galaxies, an explanation not requiring the cosmological constant or dark energy. PMID:19706502
NASA Technical Reports Server (NTRS)
Muller, P. M.
1976-01-01
The theory and numerical analysis of ancient astronomical observations (1374 to 1715) are combined with modern data in a simultaneous solution for: the tidal acceleration of the lunar longitude; the observed apparent acceleration of the earth's rotation; the true nontidal geophysical part of this acceleration; and the rate of change in the gravitational constant. Provided are three independent determinations of a rate of change of G consistent with the Hubble Constant and a near zero nontidal rotational acceleration of the earth. The tidal accelerations are shown to have remained constant during the historical period within uncertainties. Ancient and modern solar system data, and extragalactic observations provided a completely consistent astronomical and cosmological scheme.
Kafka, Gene
2015-05-01
The Integrable Optics Test Accelerator (IOTA) storage ring at Fermilab will serve as the backbone for a broad spectrum of Advanced Accelerator R&D (AARD) experiments, and as such, must be designed with signi cant exibility in mind, but without compromising cost e ciency. The nonlinear experiments at IOTA will include: achievement of a large nonlinear tune shift/spread without degradation of dynamic aperture; suppression of strong lattice resonances; study of stability of nonlinear systems to perturbations; and studies of di erent variants of nonlinear magnet design. The ring optics control has challenging requirements that reach or exceed the present state of the art. The development of a complete self-consistent design of the IOTA ring optics, meeting the demands of all planned AARD experiments, is presented. Of particular interest are the precise control for nonlinear integrable optics experiments and the transverse-to-longitudinal coupling and phase stability for the Optical Stochastic Cooling Experiment (OSC). Since the beam time-of- ight must be tightly controlled in the OSC section, studies of second order corrections in this section are presented.
Accelerating anisotropic cosmological model in f(R,T) theory of gravity
NASA Astrophysics Data System (ADS)
Santhi Kumar, R.; Satyannarayana, B.
2017-10-01
Field equations in a modified theory of gravitation proposed by Harko et al. (Phys Rev D 84:024020, 8) are obtained with the aid of a spatially homogeneous and anisotropic LRS Bianchi type-I metric. Cosmological models corresponding to false vacuum and dust universe are obtained. Some physical and kinematical properties of each of the models are discussed. These models may be physically significant for discussion at an early stage of evolution of the universe.
GPU accelerated study of heat transfer and fluid flow by lattice Boltzmann method on CUDA
NASA Astrophysics Data System (ADS)
Ren, Qinlong
Lattice Boltzmann method (LBM) has been developed as a powerful numerical approach to simulate the complex fluid flow and heat transfer phenomena during the past two decades. As a mesoscale method based on the kinetic theory, LBM has several advantages compared with traditional numerical methods such as physical representation of microscopic interactions, dealing with complex geometries and highly parallel nature. Lattice Boltzmann method has been applied to solve various fluid behaviors and heat transfer process like conjugate heat transfer, magnetic and electric field, diffusion and mixing process, chemical reactions, multiphase flow, phase change process, non-isothermal flow in porous medium, microfluidics, fluid-structure interactions in biological system and so on. In addition, as a non-body-conformal grid method, the immersed boundary method (IBM) could be applied to handle the complex or moving geometries in the domain. The immersed boundary method could be coupled with lattice Boltzmann method to study the heat transfer and fluid flow problems. Heat transfer and fluid flow are solved on Euler nodes by LBM while the complex solid geometries are captured by Lagrangian nodes using immersed boundary method. Parallel computing has been a popular topic for many decades to accelerate the computational speed in engineering and scientific fields. Today, almost all the laptop and desktop have central processing units (CPUs) with multiple cores which could be used for parallel computing. However, the cost of CPUs with hundreds of cores is still high which limits its capability of high performance computing on personal computer. Graphic processing units (GPU) is originally used for the computer video cards have been emerged as the most powerful high-performance workstation in recent years. Unlike the CPUs, the cost of GPU with thousands of cores is cheap. For example, the GPU (GeForce GTX TITAN) which is used in the current work has 2688 cores and the price is only 1
NASA Astrophysics Data System (ADS)
Miniati, Francesco; Ryu, Dongsu; Kang, Hyesung; Jones, T. W.
2001-09-01
We investigate the production of cosmic-ray (CR) protons at cosmological shocks by performing, for the first time, numerical simulations of large-scale structure formation that include directly the acceleration, transport, and energy losses of the high-energy particles. CRs are injected at shocks according to the thermal leakage model and, thereafter, accelerated to a power-law distribution as indicated by the test particle limit of the diffusive shock acceleration theory. The evolution of the CR protons accounts for losses owing to adiabatic expansion/compression, Coulomb collisions, and inelastic p-p scattering. Our results suggest that CR protons produced at shocks formed in association with the process of large-scale structure formation could amount to a substantial fraction of the total pressure in the intracluster medium. Their presence should be easily revealed by GLAST (Gamma-Ray Large-Area Space Telescope) through detection of γ-ray flux from the decay of π0 produced in inelastic p-p collisions of such CR protons with nuclei of the intracluster gas. This measurement will allow a direct determination of the CR pressure contribution in the intracluster medium. We also find that the spatial distribution of CR is typically more irregular than that of the thermal gas because it is more influenced by the underlying distribution of shocks. This feature is reflected in the appearance of our γ-ray synthetic images. Finally, the average CR pressure distribution appears statistically slightly more extended than the thermal pressure.
Study of the possibility of solving cosmological lithium problem in an accelerator experiment
NASA Astrophysics Data System (ADS)
Bystritsky, V. M.; Varlachev, V. A.; Dudkin, G. N.; Krylov, A. R.; Gazi, S.; Guran, J.; Nechaev, B. A.; Padalko, V. N.; Sadovsky, A. B.; Tuleushev, Yu. Zh.; Filipowicz, M.; Philippov, A. V.
2017-03-01
Within the standar dmodel of Big Bang Nucleosynthesis (BBN), there is a cosmological lithium problem, which consists in a substantial difference between calculated data on the abundances of the isotopes 6Li and 7Li and those that were found from observational astronomy. An attempt at measuring the cross section for the main 6Li production reaction 2H(4He, γ)6Li induced by the interaction of 4He+ ions with deuterons at collision energies less than the lower boundary of the BBN energy range was made in the present study. Upper limits on the cross sections for the reaction in question were set.
Lattice Boltzmann accelerated direct simulation Monte Carlo for dilute gas flow simulations
NASA Astrophysics Data System (ADS)
Di Staso, G.; Clercx, H. J. H.; Succi, S.; Toschi, F.
2016-11-01
Hybrid particle-continuum computational frameworks permit the simulation of gas flows by locally adjusting the resolution to the degree of non-equilibrium displayed by the flow in different regions of space and time. In this work, we present a new scheme that couples the direct simulation Monte Carlo (DSMC) with the lattice Boltzmann (LB) method in the limit of isothermal flows. The former handles strong non-equilibrium effects, as they typically occur in the vicinity of solid boundaries, whereas the latter is in charge of the bulk flow, where non-equilibrium can be dealt with perturbatively, i.e. according to Navier-Stokes hydrodynamics. The proposed concurrent multiscale method is applied to the dilute gas Couette flow, showing major computational gains when compared with the full DSMC scenarios. In addition, it is shown that the coupling with LB in the bulk flow can speed up the DSMC treatment of the Knudsen layer with respect to the full DSMC case. In other words, LB acts as a DSMC accelerator. This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'.
Lattice Boltzmann accelerated direct simulation Monte Carlo for dilute gas flow simulations.
Di Staso, G; Clercx, H J H; Succi, S; Toschi, F
2016-11-13
Hybrid particle-continuum computational frameworks permit the simulation of gas flows by locally adjusting the resolution to the degree of non-equilibrium displayed by the flow in different regions of space and time. In this work, we present a new scheme that couples the direct simulation Monte Carlo (DSMC) with the lattice Boltzmann (LB) method in the limit of isothermal flows. The former handles strong non-equilibrium effects, as they typically occur in the vicinity of solid boundaries, whereas the latter is in charge of the bulk flow, where non-equilibrium can be dealt with perturbatively, i.e. according to Navier-Stokes hydrodynamics. The proposed concurrent multiscale method is applied to the dilute gas Couette flow, showing major computational gains when compared with the full DSMC scenarios. In addition, it is shown that the coupling with LB in the bulk flow can speed up the DSMC treatment of the Knudsen layer with respect to the full DSMC case. In other words, LB acts as a DSMC accelerator.This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'. © 2016 The Author(s).
NASA Astrophysics Data System (ADS)
Edmonds, C. S.; Gratus, J.; Hock, K. M.; Machida, S.; Muratori, B. D.; Torromé, R. G.; Wolski, A.
2014-05-01
In high chromaticity circular accelerators, rapid decoherence of the betatron motion of a particle beam can make the measurement of lattice and bunch values, such as Courant-Snyder parameters and betatron amplitude, difficult. A method for reconstructing the momentum distribution of a beam from beam position measurements is presented. Further analysis of the same beam position monitor data allows estimates to be made of the Courant-Snyder parameters and the amplitude of coherent betatron oscillation of the beam. The methods are tested through application to data taken on the linear nonscaling fixed field alternating gradient accelerator, EMMA.
NASA Astrophysics Data System (ADS)
Chen, P.
2014-05-01
Recent years have witnessed tremendous progress in our understanding of the cosmos, which in turn points to even deeper questions to be further addressed. Concurrently the laser technology has undergone dramatic revolutions, providing exciting opportunity for science applications. History has shown that the symbiosis between direct observations and laboratory investigation is instrumental in the progress of astrophysics. We believe that this remains true in cosmology. Current frontier phenomena related to particle astrophysics and cosmology typically involve one or more of the following conditions: (1) extremely high energy events;(2) very high density, high temperature processes; (3) super strong field environments. Laboratory experiments using high intensity lasers can calibrate astrophysical observations, investigate underlying dynamics of astrophysical phenomena, and probe fundamental physics in extreme limits. In this article we give an overview of the exciting prospect of laser cosmology. In particular, we showcase its unique capability of investigating frontier cosmology issues such as cosmic accelerator and quantum gravity.
ENTROPY AT THE OUTSKIRTS OF GALAXY CLUSTERS AS IMPLICATIONS FOR COSMOLOGICAL COSMIC-RAY ACCELERATION
Fujita, Yutaka; Ohira, Yutaka; Yamazaki, Ryo
2013-04-10
Recently, gas entropy at the outskirts of galaxy clusters has attracted much attention. We propose that the entropy profiles could be used to study cosmic-ray (CR) acceleration around the clusters. If the CRs are effectively accelerated at the formation of clusters, the kinetic energy of infalling gas is consumed by the acceleration and the gas entropy should decrease. As a result, the entropy profiles become flat at the outskirts. If the acceleration is not efficient, the entropy should continue to increase outward. By comparing model predictions with X-ray observations with Suzaku, which show flat entropy profiles, we find that the CRs have carried {approx}< 7% of the kinetic energy of the gas away from the clusters. Moreover, the CR pressure at the outskirts can be {approx}< 40% of the total pressure. On the other hand, if the entropy profiles are not flat at the outskirts, as indicated by combined Plank and ROSAT observations, the carried energy and the CR pressure should be much smaller than the above estimations.
Doolin, Ciaran; Neupane, Ishwaree P
2013-04-05
A late epoch cosmic acceleration may be naturally entangled with cosmic coincidence--the observation that at the onset of acceleration the vacuum energy density fraction nearly coincides with the matter density fraction. In this Letter we show that this is indeed the case with the cosmology of a Friedmann-Lamaître-Robertson-Walker (FLRW) 3-brane in a five-dimensional anti-de Sitter spacetime. We derive the four-dimensional effective action on a FLRW 3-brane, from which we obtain a mass-reduction formula, namely, M(P)(2) = ρ(b)/|Λ(5)|, where M(P) is the effective (normalized) Planck mass, Λ(5) is the five-dimensional cosmological constant, and ρ(b) is the sum of the 3-brane tension V and the matter density ρ. Although the range of variation in ρ(b) is strongly constrained, the big bang nucleosynthesis bound on the time variation of the effective Newton constant G(N) = (8πM(P)(2))(-1) is satisfied when the ratio V/ρ ≳ O(10(2)) on cosmological scales. The same bound leads to an effective equation of state close to -1 at late epochs in accordance with astrophysical and cosmological observations.
NASA Astrophysics Data System (ADS)
Iorio, Lorenzo
2014-01-01
By phenomenologically assuming a slow temporal variation of the percent acceleration rate S̈S -1 of the cosmic scale factor S(t), it is shown that the orbit of a local binary undergoes a secular expansion. To first order in the power expansion of S̈S -1 around the present epoch t0, a non-vanishing shift per orbit (Δr) of the two-body relative distance r occurs for eccentric trajectories. A general relativistic expression, which turns out to be cubic in the Hubble parameter H0 at the present epoch, is explicitly calculated for it in the case of matter-dominated epochs with Dark Energy. For a highly eccentric Oort comet orbit with period Pb ≈ 31 Myr, the general relativistic distance shift per orbit turns out to be of the order of (Δr) ≈ 70 km. For the Large Magellanic Cloud, assumed on a bound elliptic orbit around the Milky Way, the shift per orbit is of the order of (Δr) ≈ 2-4 pc. Our result has a general validity since it holds in any cosmological model admitting the Hubble law and a slowly varying S̈S-1(t). More generally, it is valid for an arbitrary Hooke-like extra-acceleration whose "elastic" parameter κ is slowly time-dependent, irrespectively of the physical mechanism which may lead to it. The coefficient κ1 of the first-order term of the power expansion of κ(t) can be preliminarily constrained in a model-independent way down to a κ1 ≤ 2 x 10-13 year-3 level from latest Solar System's planetary observations. The radial velocities of the double lined spectroscopic binary ALPHA Cen AB yield κ1 ≤ 10-8 year-3.
NASA Astrophysics Data System (ADS)
Antipov, S. A.; Nagaitsev, S.; Valishev, A.
2017-04-01
Fermilab is constructing the Integrable Optics Test Accelerator (IOTA) as the centerpiece of the Accelerator R&D Program towards high-intensity circular machines. One of the factors limiting the beam intensity in present circular accelerators is collective instabilities, which can be suppressed by a spread of betatron frequencies (tunes) through the Landau damping mechanism or by an external damper, if the instability is slow enough. The spread is usually created by octupole magnets, which introduce the tune dependence on the amplitude and, in some cases, by a chromatic spread (tune dependence on particle's momentum). The introduction of octupoles usually has both beneficial (improved Landau damping) and harmful properties, such as a resonant behavior and a reduction of the dynamic aperture. One of the research goals at the IOTA ring is to achieve a large betatron tune spread, while retaining a large dynamic aperture, using conventional octupole magnets in a special but realistic accelerator configuration. The configuration, although not integrable by design, approximates an autonomous 2D Hamiltonian system. In this paper, we present results of computer simulations of an electron beam in the IOTA by particle tracking and the Frequency Map Analysis. The results show that the ring's octupole magnets can be configured to provide a betatron tune shift of 0.08 (for particles at large amplitudes) with the dynamical aperture of over 20 beam sigma for a 150-MeV electron beam. The influence of the synchrotron motion, lattice errors, and magnet imperfections is insignificant for the parameters and levels of tolerances set by the design of the ring. The described octupole insert could be beneficial for enhancing Landau damping in high intensity machines.
Gumjudpai, Burin E-mail: buring@nu.ac.th
2008-09-15
Aspects of the non-linear Schroedinger (NLS) type of formulation of scalar (phantom) field cosmology for slow-roll, acceleration, the Wentzel-Kramers-Brillouin (WKB) approximation and the big rip singularity are presented. Slow-roll parameters for the curvature and barotropic density terms are introduced. We re-express all slow-roll parameters, slow-roll conditions and the acceleration condition in NLS form. The WKB approximation in the NLS formulation is also discussed while simplifying to the linear case. Most of the Schroedinger potentials in the NLS formulation are very slowly varying; hence the WKB approximation is valid in some ranges. In the NLS form of the big rip singularity, two quantities are infinite instead of three. We also found that approaching the big rip, w{sub eff}{yields}-1+2/3q (q<0), which is the same as the effective phantom equation of state in the flat case.
Accelerated lattice Boltzmann model for colloidal suspensions rheology and interface morphology
NASA Astrophysics Data System (ADS)
Farhat, Hassan
Colloids are ubiquitous in the food, medical, cosmetic, polymer, water purification and pharmaceutical industries. Colloids thermal, mechanical and storage properties are highly dependent on their interface morphology and their rheological behavior. Numerical methods provide a cheap and reliable virtual laboratory for the study of colloids. However efficiency is a major concern to address when using numerical methods for practical applications. This work introduces the main building-blocks for an improved lattice Boltzmann-based numerical tool designed for the study of colloidal rheology and interface morphology. The efficiency of the proposed model is enhanced by using the recently developed and validated migrating multi-block algorithms for the lattice Boltzmann method (LBM). The migrating multi-block was used to simulate single component, multi-component, multiphase and single component multiphase flows. Results were validated by experimental, numerical and analytical solutions. The contamination of the fluid-fluid interface influences the colloids morphology. This issue was addressed by the introduction of the hybrid LBM for surfactant-covered droplets. The module was used for the simulation of surfactant-covered droplet deformation under shear and uniaxial extensional flows respectively and under buoyancy. Validation with experimental and theoretical results was provided. Colloids are non-Newtonian fluids which exhibit rich rheological behavior. The suppression of coalescence module is the part of the proposed model which facilitates the study of colloids rheology. The model results for the relative viscosity were in agreement with some theoretical results. Biological suspensions such as blood are macro-colloids by nature. The study of the blood flow in the microvasculature was heuristically approached by assuming the red blood cells as surfactant covered droplets. The effects of interfacial tension on the flow velocity and the droplet exclusion from the walls
NASA Astrophysics Data System (ADS)
Borovský, Michal; Weigel, Martin; Barash, Lev Yu.; Žukovič, Milan
2016-02-01
The population annealing algorithm is a novel approach to study systems with rough free-energy landscapes, such as spin glasses. It combines the power of simulated annealing, Boltzmann weighted differential reproduction and sequential Monte Carlo process to bring the population of replicas to the equilibrium even in the low-temperature region. Moreover, it provides a very good estimate of the free energy. The fact that population annealing algorithm is performed over a large number of replicas with many spin updates, makes it a good candidate for massive parallelism. We chose the GPU programming using a CUDA implementation to create a highly optimized simulation. It has been previously shown for the frustrated Ising antiferromagnet on the stacked triangular lattice with a ferromagnetic interlayer coupling, that standard Markov Chain Monte Carlo simulations fail to equilibrate at low temperatures due to the effect of kinetic freezing of the ferromagnetically ordered chains. We applied the population annealing to study the case with the isotropic intra- and interlayer antiferromagnetic coupling (J2/|J1| = -1). The reached ground states correspond to non-magnetic degenerate states, where chains are antiferromagnetically ordered, but there is no long-range ordering between them, which is analogical with Wannier phase of the 2D triangular Ising antiferromagnet.
Carloni, Sante; Chaichian, Masud; Tureanu, Anca; Nojiri, Shin'ichi; Odintsov, Sergei D.; Oksanen, Markku
2010-09-15
We propose the most general modified first-order Horava-Lifshitz gravity, whose action does not contain time derivatives higher than the second order. The Hamiltonian structure of this theory is studied in all the details in the case of the spatially-flat Friedmann-Robertson-Walker (FRW) space-time, demonstrating many of the features of the general theory. It is shown that, with some plausible assumptions, including the projectability of the lapse function, this model is consistent. As a large class of such theories, the modified Horava-Lifshitz F(R) gravity is introduced. The study of its ultraviolet properties shows that its z=3 version seems to be renormalizable in the same way as the original Horava-Lifshitz proposal. The Hamiltonian analysis of the modified Horava-Lifshitz F(R) gravity shows that it is in general a consistent theory. The F(R) gravity action is also studied in the fixed-gauge form, where the appearance of a scalar field is particularly illustrative. Then the spatially-flat FRW cosmology for this F(R) gravity is investigated. It is shown that a special choice of parameters for this theory leads to the same equations of motion as in the case of traditional F(R) gravity. Nevertheless, the cosmological structure of the modified Horava-Lifshitz F(R) gravity turns out to be much richer than for its traditional counterpart. The emergence of multiple de Sitter solutions indicates the possibility of unification of early-time inflation with late-time acceleration within the same model. Power-law F(R) theories are also investigated in detail. It is analytically shown that they have a quite rich cosmological structure: early-/late-time cosmic acceleration of quintessence, as well as of phantom types. Also it is demonstrated that all the four known types of finite-time future singularities may occur in the power-law Horava-Lifshitz F(R) gravity. Finally, a covariant proposal for (renormalizable) F(R) gravity within the Horava-Lifshitz spirit is presented.
Precision cosmology, Accuracy cosmology and Statistical cosmology
NASA Astrophysics Data System (ADS)
Verde, Licia
2014-05-01
The avalanche of data over the past 10-20 years has propelled cosmology into the ``precision era''. The next challenge cosmology has to meet is to enter the era of accuracy. Because of the intrinsic nature of studying the Cosmos and the sheer amount of data available now and coming soon, the only way to meet this challenge is by developing suitable and specific statistical techniques. The road from precision Cosmology to accurate Cosmology goes through statistical Cosmology. I will outline some open challenges and discuss some specific examples.
Krioukov, Dmitri; Kitsak, Maksim; Sinkovits, Robert S; Rideout, David; Meyer, David; Boguñá, Marián
2012-01-01
Prediction and control of the dynamics of complex networks is a central problem in network science. Structural and dynamical similarities of different real networks suggest that some universal laws might accurately describe the dynamics of these networks, albeit the nature and common origin of such laws remain elusive. Here we show that the causal network representing the large-scale structure of spacetime in our accelerating universe is a power-law graph with strong clustering, similar to many complex networks such as the Internet, social, or biological networks. We prove that this structural similarity is a consequence of the asymptotic equivalence between the large-scale growth dynamics of complex networks and causal networks. This equivalence suggests that unexpectedly similar laws govern the dynamics of complex networks and spacetime in the universe, with implications to network science and cosmology.
Krioukov, Dmitri; Kitsak, Maksim; Sinkovits, Robert S.; Rideout, David; Meyer, David; Boguñá, Marián
2012-01-01
Prediction and control of the dynamics of complex networks is a central problem in network science. Structural and dynamical similarities of different real networks suggest that some universal laws might accurately describe the dynamics of these networks, albeit the nature and common origin of such laws remain elusive. Here we show that the causal network representing the large-scale structure of spacetime in our accelerating universe is a power-law graph with strong clustering, similar to many complex networks such as the Internet, social, or biological networks. We prove that this structural similarity is a consequence of the asymptotic equivalence between the large-scale growth dynamics of complex networks and causal networks. This equivalence suggests that unexpectedly similar laws govern the dynamics of complex networks and spacetime in the universe, with implications to network science and cosmology. PMID:23162688
Testing fractional action cosmology
NASA Astrophysics Data System (ADS)
Shchigolev, V. K.
2016-08-01
The present work deals with a combined test of the so-called Fractional Action Cosmology (FAC) on the example of a specific model obtained by the author earlier. In this model, the effective cosmological term is proportional to the Hubble parameter squared through the so-called kinematic induction. The reason of studying this cosmological model could be explained by its ability to describe two periods of accelerated expansion, that is in agreement with the recent observations and the cosmological inflation paradigm. First of all, we put our model through the theoretical tests, which gives a general conception of the influence of the model parameters on its behavior. Then, we obtain some restrictions on the principal parameters of the model, including the fractional index, by means of the observational data. Finally, the cosmography parameters and the observational data compared to the theoretical predictions are presented both analytically and graphically.
Yagi, Kent; Nishizawa, Atsushi; Yoo, Chul-Moon E-mail: anishi@yukawa.kyoto-u.ac.jp
2012-04-01
One possibility for explaining the apparent accelerating expansion of the universe is that we live in the center of a spherically inhomogeneous universe. Although current observations cannot fully distinguish ΛCDM and these inhomogeneous models, direct measurement of the acceleration of the universe can be a powerful tool in probing them. We have shown that, if ΛCDM is the correct model, DECIGO/BBO would be able to detect the positive redshift drift (which is the time evolution of the source redshift z) in 3–5 year gravitational wave (GW) observations from neutron-star binaries, which enables us to rule out any Lemaître-Tolman-Bondi (LTB) void model with monotonically increasing density profile. We may even be able to rule out any LTB model unless we allow unrealistically steep density profile at z ∼ 0. This test can be performed with GW observations alone, without any reference to electromagnetic observations, and is more powerful than the redshift drift measurement using Lyman α forest.
NASA Astrophysics Data System (ADS)
Shababi, Homa; Pedram, Pouria
In this paper, we obtain new exact solutions and first-order late-time solutions for the generalized Chaplygin gas Hořava-Lifshitz quantum cosmology with the equation-of-state p = -Aρ-α. Based on the Schutz formalism, we use the matter degree of freedom to recover the notion of time in quantum domain. This enables us to study time evolution of wave functions (wave packets) as well as their corresponding classical solutions. In particular, for α = 0, we obtain new exact classical and quantum mechanical solutions for various gravitational cases which are valid for both early and late times. For α = 1/3 and α = 1 (the standard Chaplygin gas), and up to the first-order approximation, we solve the corresponding Schrödinger-Wheeler-DeWitt equation and find the late-time solutions in the classical and quantum domains. Also, we study the accelerating behavior of solutions at the late times and we compare the results with solutions raised from general relativity.
Cosmology from start to finish.
Bennett, Charles L
2006-04-27
Cosmology is undergoing a revolution. With recent precise measurements of the cosmic microwave background radiation, large galaxy redshift surveys, better measurements of the expansion rate of the Universe and a host of other astrophysical observations, there is now a standard, highly constrained cosmological model. It is not a cosmology that was predicted. Unidentified dark particles dominate the matter content of our Universe, and mysteries surround the processes responsible for the accelerated expansion at its earliest moments (inflation?) and for its recent acceleration (dark energy?). New measurements must address the fundamental questions: what happened at the birth of the Universe, and what is its ultimate fate?
NASA Astrophysics Data System (ADS)
Zhu, B.; Lin, J.; Yuan, X.; Li, Y.; Shen, C.
2016-12-01
The role of turbulent acceleration and heating in the fractal magnetic reconnection of solar flares is still not clear, especially at the X-point in the diffusion region. At virtual test aspect, it is hardly to quantitatively analyze the vortex generation, turbulence evolution, particle acceleration and heating in the magnetic islands coalesce in fractal manner, formatting into largest plasmid and ejection process in diffusion region through classical magnetohydrodynamics numerical method. With the development of physical particle numerical method (particle in cell method [PIC], Lattice Boltzmann method [LBM]) and high performance computing technology in recently two decades. Kinetic simulation has developed into an effectively manner to exploring the role of magnetic field and electric field turbulence in charged particles acceleration and heating process, since all the physical aspects relating to turbulent reconnection are taken into account. In this paper, the LBM based lattice DxQy grid and extended distribution are added into charged-particles-to-grid-interpolation of PIC based finite difference time domain scheme and Yee Grid, the hybrid PIC-LBM simulation tool is developed to investigating turbulence acceleration on TIANHE-2. The actual solar coronal condition (L≈105Km,B≈50-500G,T≈5×106K, n≈108-109, mi/me≈500-1836) is applied to study the turbulent acceleration and heating in solar flare fractal current sheet. At stage I, magnetic islands shrink due to magnetic tension forces, the process of island shrinking halts when the kinetic energy of the accelerated particles is sufficient to halt the further collapse due to magnetic tension forces, the particle energy gain is naturally a large fraction of the released magnetic energy. At stage II and III, the particles from the energized group come in to the center of the diffusion region and stay longer in the area. In contract, the particles from non energized group only skim the outer part of the
NASA Astrophysics Data System (ADS)
Girdhar, Parth; Kobakhidze, Archil
2013-10-01
We describe a new phenomenon of zitterbewegung of a free Dirac particle in cosmological spacetimes. Unlike the similar effect theorized by Schrödinger in 1930, the cosmological zitterbewegung is a real, physically attainable effect, which originates from the mixing of positive and negative frequency modes of a field operator in cosmological spacetimes. We briefly discuss the potential for observing this effect in laboratory experiments with trapped ions.
NASA Astrophysics Data System (ADS)
Jones, Bernard J. T.
2017-04-01
Preface; Notation and conventions; Part I. 100 Years of Cosmology: 1. Emerging cosmology; 2. The cosmic expansion; 3. The cosmic microwave background; 4. Recent cosmology; Part II. Newtonian Cosmology: 5. Newtonian cosmology; 6. Dark energy cosmological models; 7. The early universe; 8. The inhomogeneous universe; 9. The inflationary universe; Part III. Relativistic Cosmology: 10. Minkowski space; 11. The energy momentum tensor; 12. General relativity; 13. Space-time geometry and calculus; 14. The Einstein field equations; 15. Solutions of the Einstein equations; 16. The Robertson–Walker solution; 17. Congruences, curvature and Raychaudhuri; 18. Observing and measuring the universe; Part IV. The Physics of Matter and Radiation: 19. Physics of the CMB radiation; 20. Recombination of the primeval plasma; 21. CMB polarisation; 22. CMB anisotropy; Part V. Precision Tools for Precision Cosmology: 23. Likelihood; 24. Frequentist hypothesis testing; 25. Statistical inference: Bayesian; 26. CMB data processing; 27. Parametrising the universe; 28. Precision cosmology; 29. Epilogue; Appendix A. SI, CGS and Planck units; Appendix B. Magnitudes and distances; Appendix C. Representing vectors and tensors; Appendix D. The electromagnetic field; Appendix E. Statistical distributions; Appendix F. Functions on a sphere; Appendix G. Acknowledgements; References; Index.
Cosmology and Particle Physics
NASA Astrophysics Data System (ADS)
Steigman, G.
1982-01-01
The cosmic connections between physics on the very largest and very smallest scales are reviewed with an emphasis on the symbiotic relation between elementary particle physics and cosmology. After a review of the early Universe as a cosmic accelerator, various cosmological and astrophysical constraints on models of particle physics are outlined. To illustrate this approach to particle physics via cosmology, reference is made to several areas of current research: baryon non-conservation and baryon asymmetry; free quarks, heavy hadrons and other exotic relics; primordial nucleosynthesis and neutrino masses. In the last few years we have witnessed the birth and growth to healthy adolescence of a new collaboration between astrophysicists and particle physicists. The most notable success of this cooperative effort has been to provide the framework for understanding, within the context of GUTs and the hot big-bang cosmology, the universal baryon asymmetry. The most exciting new predictions this effort has spawned are that exotic relics may exist in detectable abundances. In particular, we may live in a neutrino-dominated Universe. In the next few years, accummulating laboratory data (for example proton decay, neutrino masses and oscillations) coupled with theoritical work in particle physics and cosmology will ensure the growth to maturity of this joint effort.
Lin, Guang; Bao, Jie; Xu, Zhijie
2014-11-01
In this study, which builds on other related work, we present a new three-dimensional numerical model for crystal growth in a vertical solidification system. This model accounts for buoyancy, accelerated crucible rotation technique (ACRT), and traveling magnetic field (TMF) induced convective flow and their effect on crystal growth and the chemical component's transport process. The evolution of the crystal growth interface is simulated using the phase field method. A semi-implicit lattice kinetics solver based on the Boltzmann equation is employed to model the unsteady incompressible flow. A one-way coupled concentration transport model is used to simulate the component fraction variation in both the liquid and solid phases, which can be used to check the quality of the crystal growth.
The screening Horndeski cosmologies
NASA Astrophysics Data System (ADS)
Starobinsky, Alexei A.; Sushkov, Sergey V.; Volkov, Mikhail S.
2016-06-01
We present a systematic analysis of homogeneous and isotropic cosmologies in a particular Horndeski model with Galileon shift symmetry, containing also a Λ-term and a matter. The model, sometimes called Fab Five, admits a rich spectrum of solutions. Some of them describe the standard late time cosmological dynamic dominated by the Λ-term and matter, while at the early times the universe expands with a constant Hubble rate determined by the value of the scalar kinetic coupling. For other solutions the Λ-term and matter are screened at all times but there are nevertheless the early and late accelerating phases. The model also admits bounces, as well as peculiar solutions describing ``the emergence of time''. Most of these solutions contain ghosts in the scalar and tensor sectors. However, a careful analysis reveals three different branches of ghost-free solutions, all showing a late time acceleration phase. We analyse the dynamical stability of these solutions and find that all of them are stable in the future, since all their perturbations stay bounded at late times. However, they all turn out to be unstable in the past, as their perturbations grow violently when one approaches the initial spacetime singularity. We therefore conclude that the model has no viable solutions describing the whole of the cosmological history, although it may describe the current acceleration phase. We also check that the flat space solution is ghost-free in the model, but it may acquire ghost in more general versions of the Horndeski theory.
NASA Astrophysics Data System (ADS)
Crawford, David F.
Curvature Cosmology proposes a new cosmological model very different from, and more elegant than, the Big-Bang Theory. Curvature Cosmology is based on two major hypotheses that Hubble redshift is due to an interaction of photons with curved spacetime and that there is a pressure that acts to stabilise expansion and provides a static, stable universe. The main focus of this book is to describe these two hypotheses in detail and to examine all relevant cosmological data in the context of this new model of the universe. This model proposes that, though evolution of stars and galaxies is evident, the statistical properties of the universe are the same at all places and at all times. In short, the universe is ageless, has no defined beginning (unlike the Big-Bang model), and carries no evidence of expansion, despite the changeability of its components. Curvature Cosmology calls for a paradigm shift in current cosmology and requires at least basic (if not more complex) knowledge of past and current cosmological models and equations.
NASA Astrophysics Data System (ADS)
Berg, J. Scott
2008-02-01
EMMA is a 10 to 20 MeV electron ring designed to test our understanding of beam dynamics in a relativistic linear non-scaling fixed field alternating gradient accelerator (FFAG). I will give a basic review of the EMMA lattice parameters. Then I will review the different lattice configurations that we would like to have for EMMA. Finally, I will briefly discuss the process of commissioning each lattice configuration.
Beyond lensing by the cosmological constant
NASA Astrophysics Data System (ADS)
Faraoni, Valerio; Lapierre-Léonard, Marianne
2017-01-01
The long-standing problem of whether the cosmological constant affects directly the deflection of light caused by a gravitational lens is reconsidered. We use a new approach based on the Hawking quasilocal mass of a sphere grazed by light rays and on its splitting into local and cosmological parts. Previous literature restricted to the cosmological constant is extended to any form of dark energy accelerating the universe in which the gravitational lens is embedded.
Accelerated kinetics of amorphous silicon using an on-the-fly off-lattice kinetic Monte-Carlo method
NASA Astrophysics Data System (ADS)
Joly, Jean-Francois; El-Mellouhi, Fedwa; Beland, Laurent Karim; Mousseau, Normand
2011-03-01
The time evolution of a series of well relaxed amorphous silicon models was simulated using the kinetic Activation-RelaxationTechnique (kART), an on-the-fly off-lattice kinetic Monte Carlo method. This novel algorithm uses the ART nouveau algorithm to generate activated events and links them with local topologies. It was shown to work well for crystals with few defects but this is the first time it is used to study an amorphous material. A parallel implementation allows us to increase the speed of the event generation phase. After each KMC step, new searches are initiated for each new topology encountered. Well relaxed amorphous silicon models of 1000 atoms described by a modified version of the empirical Stillinger-Weber potential were used as a starting point for the simulations. Initial results show that the method is faster by orders of magnitude compared to conventional MD simulations up to temperatures of 500 K. Vacancy-type defects were also introduced in this system and their stability and lifetimes are calculated.
NASA Astrophysics Data System (ADS)
Krauss, L. M.
1999-01-01
The long-derided cosmological constant - a contrivance of Albert Einstein's that represents a bizarre form of energy inherent in space itself - is one of two contenders for explaining changes in the expansion rate of the Universe.
NASA Astrophysics Data System (ADS)
Silk, Joseph
2008-11-01
The field of cosmology has been transformed since the glorious decades of the 1920's and 1930's when theory and observation converged to develop the current model of the expanding universe. It was a triumph of the theory of general relativity and astronomy. The first revolution came when the nuclear physicists entered the fray. This marked the debut of the hot big bang, in which the light elements were synthesized in the first three minutes. It was soon realised that elements like carbon and iron were synthesized in exploding stars. However helium, as well as deuterium and lithium, remain as George Gamow envisaged, the detritus of the big bang. The climax arrived with one of the most remarkable discoveries of the twentieth century, the cosmic microwave background radiation, in 1964. The fossil glow turned out to have the spectrum of an ideal black body. One could not imagine a stronger confirmation of the hot and dense origin of the universe. This discovery set the scene for the next major advance. It was now the turn of the particle physicists, who realized that the energies attained near the beginning of the universe, and unachievable in any conceivable terrestrial accelerator, provided a unique testing ground for theories of grand unification of the fundamental forces. This led Alan Guth and Andrei Linde in 1980 to propose the theory of inflation, which solved outstanding puzzles of the big bang. One could now understand why the universe is so large and homogeneous, and the origin of the seed fluctuations that gave rise to large-scale structure. A key prediction was that the universe should have Euclidean geometry, now verified to a precision of a few percent. Modern cosmology is firmly embedded in particle physics. It merits a text written by a particle physicist who can however appreciate the contributions of astronomy that provide the foundation and infrastructure for the theory of the expanding universe. There are now several such texts available. The most
NASA Astrophysics Data System (ADS)
Blau, S. K.; Guth, A. H.
Contents: 1. Introduction. 2. Summary of the standard cosmological model. 3. Problems of the standard cosmological model. 4. The original inflationary universe. 5. Successes of the original inflationary model. 6. Problems of the original inflationary model. 7. The new inflationary universe. 8. Density perturbations in the new inflationary universe. 9. Quantum theory of the new inflationary universe phase transition. 10. Inflation in the minimal SU(5) grand unified theory. 11. False vacuum bubbles and child universes. 12. Conclusion.
Unstable anisotropic loop quantum cosmology
Nelson, William; Sakellariadou, Mairi
2009-09-15
We study stability conditions of the full Hamiltonian constraint equation describing the quantum dynamics of the diagonal Bianchi I model in the context of loop quantum cosmology. Our analysis has shown robust evidence of an instability in the explicit implementation of the difference equation, implying important consequences for the correspondence between the full loop quantum gravity theory and loop quantum cosmology. As a result, one may question the choice of the quantization approach, the model of lattice refinement, and/or the role of the ambiguity parameters; all these should, in principle, be dictated by the full loop quantum gravity theory.
Cosmological Inflation: A Personal Perspective
NASA Technical Reports Server (NTRS)
Kazanas, Demos
2008-01-01
We present a brief review of Cosmological Inflation from the personal perspective of the speaker who almost 30 years ago proposed a way of resolving the problem of Cosmological Horizon by employing certain notions and developments from the field of High Energy Physics. Along with a brief introduction of the Horizon and Flatness problems of standard cosmology, this lecture concentrates on personal reminiscing of the notions and ideas that prevailed and influenced the author's thinking at the time. The lecture then touches upon some more recent developments related to the subject including exact solutions to conformal gravity that provide a first principles emergence of a characteristic acceleration in the universe and concludes with some personal views concerning the direction that the cosmology field has taken in the past couple of decades and certain speculations some notions that may indicate future directions of research.
Cosmological Inflation: A Personal Perspective
NASA Technical Reports Server (NTRS)
Kazanas, Demos
2008-01-01
We present a brief review of Cosmological Inflation from the personal perspective of the speaker who almost 30 years ago proposed a way of resolving the problem of Cosmological Horizon by employing certain notions and developments from the field of High Energy Physics. Along with a brief introduction of the Horizon and Flatness problems of standard cosmology, this lecture concentrates on personal reminiscing of the notions and ideas that prevailed and influenced the author's thinking at the time. The lecture then touches upon some more recent developments related to the subject including exact solutions to conformal gravity that provide a first principles emergence of a characteristic acceleration in the universe and concludes with some personal views concerning the direction that the cosmology field has taken in the past couple of decades and certain speculations some notions that may indicate future directions of research.
Cosmological tests of modified gravity.
Koyama, Kazuya
2016-04-01
We review recent progress in the construction of modified gravity models as alternatives to dark energy as well as the development of cosmological tests of gravity. Einstein's theory of general relativity (GR) has been tested accurately within the local universe i.e. the Solar System, but this leaves the possibility open that it is not a good description of gravity at the largest scales in the Universe. This being said, the standard model of cosmology assumes GR on all scales. In 1998, astronomers made the surprising discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown dark energy. Alternatively, it could be that there is no dark energy and GR itself is in error on cosmological scales. In this review, we first give an overview of recent developments in modified gravity theories including f(R) gravity, braneworld gravity, Horndeski theory and massive/bigravity theory. We then focus on common properties these models share, such as screening mechanisms they use to evade the stringent Solar System tests. Once armed with a theoretical knowledge of modified gravity models, we move on to discuss how we can test modifications of gravity on cosmological scales. We present tests of gravity using linear cosmological perturbations and review the latest constraints on deviations from the standard [Formula: see text]CDM model. Since screening mechanisms leave distinct signatures in the non-linear structure formation, we also review novel astrophysical tests of gravity using clusters, dwarf galaxies and stars. The last decade has seen a number of new constraints placed on gravity from astrophysical to cosmological scales. Thanks to on-going and future surveys, cosmological tests of gravity will enjoy another, possibly even more, exciting ten years.
Cosmological tests of modified gravity
NASA Astrophysics Data System (ADS)
Koyama, Kazuya
2016-04-01
We review recent progress in the construction of modified gravity models as alternatives to dark energy as well as the development of cosmological tests of gravity. Einstein’s theory of general relativity (GR) has been tested accurately within the local universe i.e. the Solar System, but this leaves the possibility open that it is not a good description of gravity at the largest scales in the Universe. This being said, the standard model of cosmology assumes GR on all scales. In 1998, astronomers made the surprising discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown dark energy. Alternatively, it could be that there is no dark energy and GR itself is in error on cosmological scales. In this review, we first give an overview of recent developments in modified gravity theories including f(R) gravity, braneworld gravity, Horndeski theory and massive/bigravity theory. We then focus on common properties these models share, such as screening mechanisms they use to evade the stringent Solar System tests. Once armed with a theoretical knowledge of modified gravity models, we move on to discuss how we can test modifications of gravity on cosmological scales. We present tests of gravity using linear cosmological perturbations and review the latest constraints on deviations from the standard Λ CDM model. Since screening mechanisms leave distinct signatures in the non-linear structure formation, we also review novel astrophysical tests of gravity using clusters, dwarf galaxies and stars. The last decade has seen a number of new constraints placed on gravity from astrophysical to cosmological scales. Thanks to on-going and future surveys, cosmological tests of gravity will enjoy another, possibly even more, exciting ten years.
Quantum Gravity and Cosmology: an intimate interplay
NASA Astrophysics Data System (ADS)
Sakellariadou, Mairi
2017-08-01
I will briefly discuss three cosmological models built upon three distinct quantum gravity proposals. I will first highlight the cosmological rôle of a vector field in the framework of a string/brane cosmological model. I will then present the resolution of the big bang singularity and the occurrence of an early era of accelerated expansion of a geometric origin, in the framework of group field theory condensate cosmology. I will then summarise results from an extended gravitational model based on non-commutative spectral geometry, a model that offers a purely geometric explanation for the standard model of particle physics.
NASA Astrophysics Data System (ADS)
Tsamis, N. C.; Woodard, R. P.
2016-08-01
We study a class of nonlocal, action-based, and purely gravitational models. These models seek to describe a cosmology in which inflation is driven by a large, bare cosmological constant that is screened by the self-gravitation between the soft gravitons that inflation rips from the vacuum. Inflation ends with the Universe poised on the verge of gravitational collapse, in an oscillating phase of expansion and contraction that should lead to rapid reheating when matter is included. After the attainment of a hot, dense Universe the nonlocal screening terms become constant as the Universe evolves through a conventional phase of radiation domination. The onset of matter domination triggers a much smaller antiscreening effect that could explain the current phase of acceleration.
NASA Astrophysics Data System (ADS)
Lattanzi, M. G.
The accurate measurement of the motions of stars in our Galaxy can provide access to the cosmological signatures in the disk and halo, while astrometric experiments from within our Solar System can uniquely probe possible deviations from General Relativity. This article will introduce to the fact that astrometry has the potential, thanks also to impressive technological advancements, to become a key player in the field of local cosmology. For example, accurate absolute kinematics at the scale of the Milky Way can, for the first time in situ, account for the predictions made by the cold dark matter model for the Galactic halo, and eventually map out the distribution of dark matter, or other formation mechanisms, required to explain the signatures recently identified in the old component of the thick disk. Final notes dwell on to what extent Gaia can fulfill the expectations of astrometric cosmology and on what must instead be left to future, specifically designed, astrometric experiments.
NASA Astrophysics Data System (ADS)
Harvey, Alex
1993-10-01
Two of the most common terms employed in discussing cosmological models are open and closed. They are occasionally misused either by not recognizing or by not making it clear that each term may be used to characterize, independently and simultaneously, both the dynamic behavior and spatial geometric structure of the model under discussion. In addition, the spatial geometric structure implied by the terms open and closed is itself often either misunderstood or misused. Lastly, the role played by the cosmological constant is often improperly slighted. This paper is intended to give several examples of the abuse of terminology and clarify the distinction by means of a brief, elementary overview of Friedmann-Robertson-Walker cosmological models.
NASA Astrophysics Data System (ADS)
Narimani, Ali; Moss, Adam; Scott, Douglas
2012-10-01
Although it is well known that any consideration of the variations of fundamental constants should be restricted to their dimensionless combinations, the literature on variations of the gravitational constant G is entirely dimensionfull. To illustrate applications of this to cosmology, we explicitly give a dimensionless version of the parameters of the standard cosmological model, and describe the physics of both Big Bang Nucleosynthesis and recombination in a dimensionless manner. Rigorously determining how to talk about the model in a way which avoids physical dimensions is a requirement for proceeding with a calculation to constrain time-varying fundamental constants. The issue that appears to have been missed in many studies is that in cosmology the strength of gravity is bound up in the cosmological equations, and the epoch at which we live is a crucial part of the model. We argue that it is useful to consider the hypothetical situation of communicating with another civilization (with entirely different units), comparing only dimensionless constants, in order to decide if we live in a Universe governed by precisely the same physical laws. In this thought experiment, we would also have to compare epochs, which can be defined by giving the value of any one of the evolving cosmological parameters. By setting things up carefully in this way one can avoid inconsistent results when considering variable constants, caused by effectively fixing more than one parameter today. We show examples of this effect by considering microwave background anisotropies, being careful to maintain dimensionlessness throughout. We present Fisher matrix calculations to estimate how well the fine structure constants for electromagnetism and gravity can be determined with future microwave background experiments. We highlight how one can be misled by simply adding G to the usual cosmological parameter set.
Multi-dimensional cosmology and GUP
Zeynali, K.; Motavalli, H.; Darabi, F. E-mail: f.darabi@azaruniv.edu
2012-12-01
We consider a multidimensional cosmological model with FRW type metric having 4-dimensional space-time and d-dimensional Ricci-flat internal space sectors with a higher dimensional cosmological constant. We study the classical cosmology in commutative and GUP cases and obtain the corresponding exact solutions for negative and positive cosmological constants. It is shown that for negative cosmological constant, the commutative and GUP cases result in finite size universes with smaller size and longer ages, and larger size and shorter age, respectively. For positive cosmological constant, the commutative and GUP cases result in infinite size universes having late time accelerating behavior in good agreement with current observations. The accelerating phase starts in the GUP case sooner than the commutative case. In both commutative and GUP cases, and for both negative and positive cosmological constants, the internal space is stabilized to the sub-Planck size, at least within the present age of the universe. Then, we study the quantum cosmology by deriving the Wheeler-DeWitt equation, and obtain the exact solutions in the commutative case and the perturbative solutions in GUP case, to first order in the GUP small parameter, for both negative and positive cosmological constants. It is shown that good correspondence exists between the classical and quantum solutions.
New Cosmological Solutions in Massive Gravity Theory
NASA Astrophysics Data System (ADS)
Pinho, S. S. A.; Pereira, S. H.; Mendonça, E. L.
2017-04-01
In this paper we present some new cosmological solutions in massive gravity theory. Some homogeneous and isotropic solutions correctly describe accelerated evolutions for the universe. The study was realized considering a specific form to the fiducial metric and found different functions and constant parameters of the theory that guarantee the conservation of the energy momentum tensor. Several accelerating cosmologies were found, all of them reproducing a cosmological constant term proportional to the graviton mass, with a de Sitter type solution for the scale factor. We have also verified that when the fiducial metric is close to the physical metric the solutions are absent, except for some specific open cases.
Cosmology with the Square Kilometre Array by SKA-Japan
Yamauchi, Daisuke; Ichiki, Kiyotomo; Kohri, Kazunori; ...
2016-10-17
In the past several decades, the standard cosmological model has been established and its parameters have been measured to a high precision, while there are still many fundamental questions in cosmology; such as the physics in the very early universe, the origin of the cosmic acceleration, and the nature of dark matter. The forthcoming radio telescope, the Square Kilometre Array (SKA), which will be the world's largest, will be able to open a new frontier in cosmology and will be one of the most powerful tools for cosmology in the coming decade. The cosmological surveys conducted by the SKA wouldmore » have the potential not only to answer these fundamental questions but also deliver precision cosmology. In this article we briefly review the role of the SKA from the viewpoint of modern cosmology. Furthermore, the cosmological science led by the SKA-Japan Consortium (SKA-JP) Cosmology Science Working Group is also discussed.« less
Cosmology with the Square Kilometre Array by SKA-Japan
Yamauchi, Daisuke; Ichiki, Kiyotomo; Kohri, Kazunori; Namikawa, Toshiya; Oyama, Yoshihiko; Sekiguchi, Toyokazu; Shimabukuro, Hayato; Takahashi, Keitaro; Takahashi, Tomo; Yokoyama, Shuichiro; Yoshikawa, Kohji
2016-10-17
In the past several decades, the standard cosmological model has been established and its parameters have been measured to a high precision, while there are still many fundamental questions in cosmology; such as the physics in the very early universe, the origin of the cosmic acceleration, and the nature of dark matter. The forthcoming radio telescope, the Square Kilometre Array (SKA), which will be the world's largest, will be able to open a new frontier in cosmology and will be one of the most powerful tools for cosmology in the coming decade. The cosmological surveys conducted by the SKA would have the potential not only to answer these fundamental questions but also deliver precision cosmology. In this article we briefly review the role of the SKA from the viewpoint of modern cosmology. Furthermore, the cosmological science led by the SKA-Japan Consortium (SKA-JP) Cosmology Science Working Group is also discussed.
Cosmology with the Square Kilometre Array by SKA-Japan
NASA Astrophysics Data System (ADS)
Yamauchi, Daisuke; Ichiki, Kiyotomo; Kohri, Kazunori; Namikawa, Toshiya; Oyama, Yoshihiko; Sekiguchi, Toyokazu; Shimabukuro, Hayato; Takahashi, Keitaro; Takahashi, Tomo; Yokoyama, Shuichiro; Yoshikawa, Kohji
2016-12-01
In the past several decades, the standard cosmological model has been established and its parameters have been measured to a high precision, while there are still many fundamental questions in cosmology; such as the physics in the very early universe, the origin of the cosmic acceleration, and the nature of dark matter. The forthcoming radio telescope, the Square Kilometre Array (SKA), which will be the world's largest, will be able to open a new frontier in cosmology and will be one of the most powerful tools for cosmology in the coming decade. The cosmological surveys conducted by the SKA would have the potential not only to answer these fundamental questions but also deliver precision cosmology. In this article we briefly review the role of the SKA from the viewpoint of modern cosmology. The cosmological science led by the SKA-Japan Consortium (SKA-JP) Cosmology Science Working Group is also discussed.
NASA Astrophysics Data System (ADS)
Plionis, M.
2004-07-01
The recent scientific efforts in Astrophysics & Cosmology have brought a revolution to our understanding of the Cosmos. Amazing results is the outcome of amazing experiments! The huge scientific, technological & financial effort that has gone into building the 10-m class telescopes as well as many space and balloon observatories, essential to observe the multitude of cosmic phenomena in their manifestations at different wavelengths, from gamma-rays to the millimetre and the radio, has given and is still giving its fruits of knowledge. These recent scientific achievements in Observational and Theoretical Cosmology were presented in the "Multiwavelength Cosmology" conference that took place on beautiful Mykonos island in the Aegean between 17 and 20 June 2003. More than 180 Cosmologists from all over the world gathered for a four-day intense meeting in which recent results from large ground based surveys (AAT/2-df, SLOAN) and space missions (WMAP, Chandra, XMM, ISO, HST) were presented and debated, providing a huge impetus to our knowledge of the Cosmos. The future of the subject (experiments, and directions of research) was also discussed. The conference was devoted mostly on the constraints on Cosmological models and galaxy formation theories that arise from the study of the high redshift Universe, from clusters of galaxies, and their evolution, from the cosmic microwave background, the large-scale structure and star-formation history. Link: Multidimensional cosmology
NASA Astrophysics Data System (ADS)
Alvarez, Enrique
This paper briefly reports on some recent attempts to construct a cosmology consistent with present ideas about the fundamental theories of nature, which generally involve extra dimensions. The decoupling of the extra dimensions from the usual ones is analyzed, as well as the possiblity of phase transitions in a "superstring universe".
The screening Horndeski cosmologies
Starobinsky, Alexei A.; Sushkov, Sergey V.; Volkov, Mikhail S.
2016-06-06
We present a systematic analysis of homogeneous and isotropic cosmologies in a particular Horndeski model with Galileon shift symmetry, containing also a Λ-term and a matter. The model, sometimes called Fab Five, admits a rich spectrum of solutions. Some of them describe the standard late time cosmological dynamic dominated by the Λ-term and matter, while at the early times the universe expands with a constant Hubble rate determined by the value of the scalar kinetic coupling. For other solutions the Λ-term and matter are screened at all times but there are nevertheless the early and late accelerating phases. The model also admits bounces, as well as peculiar solutions describing “the emergence of time”. Most of these solutions contain ghosts in the scalar and tensor sectors. However, a careful analysis reveals three different branches of ghost-free solutions, all showing a late time acceleration phase. We analyse the dynamical stability of these solutions and find that all of them are stable in the future, since all their perturbations stay bounded at late times. However, they all turn out to be unstable in the past, as their perturbations grow violently when one approaches the initial spacetime singularity. We therefore conclude that the model has no viable solutions describing the whole of the cosmological history, although it may describe the current acceleration phase. We also check that the flat space solution is ghost-free in the model, but it may acquire ghost in more general versions of the Horndeski theory.
Was Newtonian cosmology really inconsistent?
NASA Astrophysics Data System (ADS)
Vickers, Peter
This paper follows up a debate as to the consistency of Newtonian cosmology. Whereas Malament [(1995). Is Newtonian cosmology really inconsistent? Philosophy of Science 62, 489-510] has shown that Newtonian cosmology is not inconsistent, to date there has been no analysis of Norton's claim [(1995). The force of Newtonian cosmology: Acceleration is relative. Philosophy of Science 62, 511-522.] that Newtonian cosmology was inconsistent prior to certain advances in the 1930s, and in particular prior to Seeliger's seminal paper of Seeliger [(1895). Über das Newton'sche Gravitationsgesetz. Astronomische Nachrichten 137 (3273), 129-136.] In this paper I agree that there are assumptions, Newtonian and cosmological in character, and relevant to the real history of science, which are inconsistent. But there are some important corrections to make to Norton's account. Here I display for the first time the inconsistencies-four in total-in all their detail. Although this extra detail shows there to be several different inconsistencies, it also goes some way towards explaining why they went unnoticed for 200 years.
Anisotropic Weyl symmetry and cosmology
Moon, Taeyoon; Oh, Phillial; Sohn, Jongsu E-mail: ploh@skku.edu
2010-11-01
We construct an anisotropic Weyl invariant theory in the ADM formalism and discuss its cosmological consequences. It extends the original anisotropic Weyl invariance of Hořava-Lifshitz gravity using an extra scalar field. The action is invariant under the anisotropic transformations of the space and time metric components with an arbitrary value of the critical exponent z. One of the interesting features is that the cosmological constant term maintains the anisotropic symmetry for z = −3. We also include the cosmological fluid and show that it can preserve the anisotropic Weyl invariance if the equation of state satisfies P = zρ/3. Then, we study cosmology of the Einstein-Hilbert-anisotropic Weyl (EHaW) action including the cosmological fluid, both with or without anisotropic Weyl invariance. The correlation of the critical exponent z and the equation of state parameter ω-bar provides a new perspective of the cosmology. It is also shown that the EHaW action admits a late time accelerating universe for an arbitrary value of z when the anisotropic conformal invariance is broken, and the anisotropic conformal scalar field is interpreted as a possible source of dark energy.
NASA Astrophysics Data System (ADS)
Bothun, Greg
2011-10-01
Ever since Aristotle placed us, with certainty, in the Center of the Cosmos, Cosmological models have more or less operated from a position of known truths for some time. As early as 1963, for instance, it was ``known'' that the Universe had to be 15-17 billion years old due to the suspected ages of globular clusters. For many years, attempts to determine the expansion age of the Universe (the inverse of the Hubble constant) were done against this preconceived and biased notion. Not surprisingly when more precise observations indicated a Hubble expansion age of 11-13 billion years, stellar models suddenly changed to produce a new age for globular cluster stars, consistent with 11-13 billion years. Then in 1980, to solve a variety of standard big bang problems, inflation was introduced in a fairly ad hoc manner. Inflation makes the simple prediction that the net curvature of spacetime is zero (i.e. spacetime is flat). The consequence of introducing inflation is now the necessary existence of a dark matter dominated Universe since the known baryonic material could comprise no more than 1% of the necessary energy density to make spacetime flat. As a result of this new cosmological ``truth'' a significant world wide effort was launched to detect the dark matter (which obviously also has particle physics implications). To date, no such cosmological component has been detected. Moreover, all available dynamical inferences of the mass density of the Universe showed in to be about 20% of that required for closure. This again was inconsistent with the truth that the real density of the Universe was the closure density (e.g. Omega = 1), that the observations were biased, and that 99% of the mass density had to be in the form of dark matter. That is, we know the universe is two component -- baryons and dark matter. Another prevailing cosmological truth during this time was that all the baryonic matter was known to be in galaxies that populated our galaxy catalogs. Subsequent
NASA Astrophysics Data System (ADS)
Alvarez, Enrique
1985-01-01
Some cosmological consequences of the assumption that superstrings are more fundamental objects than ordinary local quantum fields are examined. We study, in particular, the dependence of both the string tension and the temperature of the primordial string soup on cosmic time. A particular scenario is proposed in which the universe undergoes a contracting ``string phase'' before the ordinary ``big bang,'' which according to this picture is nothing but the outcome of the transition from nonlocal to local fundamental physics.
NASA Astrophysics Data System (ADS)
Grant, E.; Murdin, P.
2000-11-01
During the early Middle Ages (ca 500 to ca 1130) scholars with an interest in cosmology had little useful and dependable literature. They relied heavily on a partial Latin translation of PLATO's Timaeus by Chalcidius (4th century AD), and on a series of encyclopedic treatises associated with the names of Pliny the Elder (ca AD 23-79), Seneca (4 BC-AD 65), Macrobius (fl 5th century AD), Martianus ...
NASA Astrophysics Data System (ADS)
Kirillov, A. A.; Savelova, E. P.
2016-05-01
We describe in details the procedure how the Lobachevsky space can be factorized to a space of the constant negative curvature filled with a gas of wormholes. We show that such wormholes have throat sections in the form of tori and are traversable and stable in the cosmological context. The relation of such wormholes to the dark matter phenomenon is briefly described. We also discuss the possibility of the existence of analogous factorizations for all types of homogeneous spaces.
Cosmological study in loop quantum cosmology through dark energy model
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Rani, Shamaila; Salako, Ines G.; Gulshan, Faiza
The interacting generalized ghost version of pilgrim dark energy (GGPDE) is discussed in the framework of loop quantum cosmology (LQC). We analyze the behavior of cosmological parameters (Hubble, equation of state (EoS), deceleration) and cosmological planes (ωD ‑ ωD‧ and r-s) in the present scenario (ωD represents the EoS parameter and ωD‧ indicates the evolution of the EoS parameter, r,s are statefinder parameters). It is observed that the deceleration parameter corresponds to the accelerated expansion of the universe. The EoS parameter lies in vacuum and phantom regions for all cases of u (pilgrim dark energy (PDE) parameter). The ωD ‑ ωD‧ plane lies in thawing region for all cases of u. The r ‑ s plane corresponds to Λ cold dark matter (CDM) and Chaplygin gas model. We have also mentioned the constraints on calculated cosmological parameters and found that all the trajectories of cosmological parameters and planes show the consistence behavior with the observational schemes.
The Cosmological Constant in Quantum Cosmology
Wu Zhongchao
2008-10-10
Hawking proposed that the cosmological constant is probably zero in quantum cosmology in 1984. By using the right configuration for the wave function of the universe, a complete proof is found very recently.
Asymptotic safety and the cosmological constant
NASA Astrophysics Data System (ADS)
Falls, Kevin
2016-01-01
We study the non-perturbative renormalisation of quantum gravity in four dimensions. Taking care to disentangle physical degrees of freedom, we observe the topological nature of conformal fluctuations arising from the functional measure. The resulting beta functions possess an asymptotically safe fixed point with a global phase structure leading to classical general relativity for positive, negative or vanishing cosmological constant. If only the conformal fluctuations are quantised we find an asymptotically safe fixed point predicting a vanishing cosmological constant on all scales. At this fixed point we reproduce the critical exponent, ν = 1/3, found in numerical lattice studies by Hamber. Returning to the full theory we find that by setting the cosmological constant to zero the critical exponent agrees with the conformally reduced theory. This suggests the fixed point may be physical while hinting at solution to the cosmological constant problem.
Modernized Newtonian Cosmology in Secondary Schools
NASA Astrophysics Data System (ADS)
Sigurdsson, Thorir
2007-08-01
Modern cosmology is founded on general relativity. Therefore, it lies outside the syllabus of classical physics and mathematics in most secondary schools. Nevertheless, it is desirable to introduce its concepts, methods and results to interested students. This is possible by assuming modified principles of homogeneity and isotropy and applying Newtonian dynamics with an extra repulsive force including Einstein's cosmological constant. With suitable simplifications and approximations several cosmological models can be derived with basic calculus from the Friedmann-Lemaitre equation, e.g. today's accelerating universe. The derivation is supplemented by examples of hypothetical universes to illustrate the theory.
Observational constraints on undulant cosmologies
Barenboim, Gabriela; Mena Requejo, Olga; Quigg, Chris; /Fermilab
2005-10-01
In an undulant universe, cosmic expansion is characterized by alternating periods of acceleration and deceleration. We examine cosmologies in which the dark-energy equation of state varies periodically with the number of e-foldings of the scale factor of the universe, and use observations to constrain the frequency of oscillation. We find a tension between a forceful response to the cosmic coincidence problem and the standard treatment of structure formation.
NASA Astrophysics Data System (ADS)
Petit, J. P.; D'Agostini, G.
2014-10-01
An extension of a previously published model of a bimetric Universe is presented, where the speeds of light associated to positive and negative mass species are different. As shown earlier, the asymmetry of the model explains the acceleration of the positive species, while the negative one slows down. Asymmetry affects scale factors linked to lengths, times and speeds of light; so that if a mass inversion of a craft can be achieved, then interstellar travels would become non-impossible at a velocity less than the speed of light of the negative sector, and possibly much higher than that of the positive sector.
NASA Astrophysics Data System (ADS)
Ross, Charles H.
2005-04-01
Aristotle thought that the universe was finite and Earth centered. Newton thought that it was infinite. Einstein guessed that the universe was finite, spherical, static, warped, and closed. Hubble's 1930 discovery of the expanding universe, Penzias and Wilson's 1968 discovery of the isotropic CMB, and measurements on light element abundances, however, established a big bang origin. Vera Rubin's 1980 dark matter discovery significantly impacted contending theories. However, 1998 is the year when sufficiently accurate supernova and primordial deuterium data was available to truly explore the universe. CMB anisotropy measurements further extended our cosmological database in 2003. On the theoretical side, Friedmann's 1922 perturbation solution of Einstein's general relativity equations for a static universe has shaped the thought and direction in cosmology for the past 80 years. It describes 3D space as a dynamic function of time. However, 80 years of trying to fit Friedmann's solution to observational data has been a bumpy road - resulting in such counter-intuitive, but necessary, features as rapid inflation, precision tuning, esoteric dark matter, and an accelerating input of esoteric dark energy.
Cosmological constraints on a classical limit of quantum gravity
Easson, Damien A.; Trodden, Mark; Schuller, Frederic P.; Wohlfarth, Mattias N.R.
2005-08-15
We investigate the cosmology of a recently proposed deformation of Einstein gravity, emerging from quantum gravity heuristics. The theory is constructed to have de Sitter space as a vacuum solution, and thus to be relevant to the accelerating universe. However, this solution turns out to be unstable, and the true phase space of cosmological solutions is significantly more complex, displaying two late-time power-law attractors - one accelerating and the other dramatically decelerating. It is also shown that nonaccelerating cosmologies sit on a separatrix between the two basins of attraction of these attractors. Hence it is impossible to pass from a decelerating cosmology to an accelerating one, as required in standard cosmology for consistency with nucleosynthesis and structure formation and compatibility with the data inferred from supernovae Ia. We point out that alternative models of the early universe, such as the one investigated here might provide possible ways to circumvent these requirements.
Stability of winding cosmic wall lattices with X type junctions
NASA Astrophysics Data System (ADS)
Carter, Brandon
2008-08-01
This work confirms the stability of a class of domain wall lattice models that can produce accelerated cosmological expansion, with pressure to density ratio w = -1/3 at early times, and with w = -2/3 at late times when the lattice scale becomes large compared to the wall thickness. For walls of tension TI, the relevant X type junctions could be unstable (for a sufficiently acute intersection angle α) against separation into a pair of Y type junctions joined by a compound wall, only if the tension {T}_{{\\bb I}} of the latter were less than 2TI (and for an approximately right-angled intersection if it were less than \\sqrt{2} {T}_I ) which cannot occur in the class considered here. In an extensive category of multicomponent scalar field models of forced harmonic (linear or nonlinear) type it is shown how the relevant tension—which is the same as the surface energy density U of the wall—can be calculated as the minimum (geodesic) distance between the relevant vacuum states as measured on the space of field values Φi using a positive definite (Riemannian) energy metric d{U}^2={\\tilde{{ G}}}_{ij}\\,d{\\Phi}^i\\, d{\\Phi}^j that is obtained from the usual kinetic metric (which is flat for a model with an ordinary linear kinetic part) by application of a conformal factor proportional to the relevant potential function V. For suitably periodic potential functions there will be corresponding periodic configurations—with parallel walls characterized by incrementation of a winding number—in which the condition for stability of large scale bunching modes is shown to be satisfied automatically. It is suggested that such a configuration—with a lattice lengthscale comparable to intergalactic separation distances—might have been produced by a late stage of cosmological inflation.
Fate of an accelerating universe
Gu, J.-A.; Hwang, W-Y. P.
2006-01-15
The presently accelerating universe may keep accelerating forever, eventually run into the event horizon problem, and thus be in conflict with the superstring idea. On the other hand, the current accelerating phase as well as the fate of the universe may be swayed by a negative cosmological constant, which dictates a big crunch. Based on the current observational data, in this paper we investigate how large the magnitude of a negative cosmological constant is allowed to be. In addition, for distinguishing the sign of the cosmological constant via observations, we point out that a measure of the evolution of the dark energy equation-of-state may be a good discriminator. Hopefully future observations will provide much more detailed information about dark energy and thereby indicate the sign of the cosmological constant as well as the fate of the presently accelerating universe.
Braneworld cosmology and noncommutative inflation
NASA Astrophysics Data System (ADS)
Calcagni, Gianluca
2005-03-01
In this work we develop the patch formalism, an approach providing a very simple and compact description of braneworld-motivated cosmologies with nonstandard effective Friedmann equations. In particular, the Hubble parameter is assumed to depend on some power of the brane energy density, H^2 propto rho^q. The high-energy limit of Randall-Sundrum (q=2) and Gauss-Bonnet (q=2/3) braneworlds are considered, during an accelerating era triggered by a single ordinary or tachyonic scalar field. The inflationary dynamics, solutions, and spectra are provided. Using the latest results from WMAP and other experiments for estimates of cosmological observables, it is shown that future data and missions can in principle discriminate between standard four-dimensional and braneworld scenarios. The issue of non-Gaussianity is also studied within nonlinear perturbation theory. The introduction of a fundamental energy scale reinforces these results. Several classes of noncommutative inflationary models are considered and their features analyzed in a number of ways and energy regimes. Finally, we establish dual relations between inflationary, cyclic/ekpyrotic and phantom cosmologies, as well as between scalar-driven and tachyon-driven cosmologies. The exact dualities relating the four-dimensional spectra are broken in favour of their braneworld counterparts. The dual solutions display new interesting features because of the modification of the effective Friedmann equation on the brane.
Koivisto, Tomi; Wills, Danielle; Zavala, Ivonne E-mail: d.e.wills@durham.ac.uk
2014-06-01
Disformally coupled cosmologies arise from Dirac-Born-Infeld actions in Type II string theories, when matter resides on a moving hidden sector D-brane. Since such matter interacts only very weakly with the standard model particles, this scenario can provide a natural origin for the dark sector of the universe with a clear geometrical interpretation: dark energy is identified with the scalar field associated to the D-brane's position as it moves in the internal space, acting as quintessence, while dark matter is identified with the matter living on the D-brane, which can be modelled by a perfect fluid. The coupling functions are determined by the (warped) extra-dimensional geometry, and are thus constrained by the theory. The resulting cosmologies are studied using both dynamical system analysis and numerics. From the dynamical system point of view, one free parameter controls the cosmological dynamics, given by the ratio of the warp factor and the potential energy scales. The disformal coupling allows for new scaling solutions that can describe accelerating cosmologies alleviating the coincidence problem of dark energy. In addition, this scenario may ameliorate the fine-tuning problem of dark energy, whose small value may be attained dynamically, without requiring the mass of the dark energy field to be unnaturally low.
NASA Astrophysics Data System (ADS)
Aref'eva, I. Ya.; Volovich, I. V.
2011-08-01
Classical versions of the Big Bang cosmological models of the universe contain a singularity at the start of time, hence the time variable in the field equations should run over a half-line. Nonlocal string field theory equations with infinite number of derivatives are considered and an important difference between nonlocal operators on the whole real line and on a half-line is pointed out. We use the heat equation method and show that on the half-line in addition to the usual initial data a new arbitrary function (external source) occurs that we call the daemon function. The daemon function governs the evolution of the universe similar to Maxwell's demon in thermodynamics. The universe and multiverse are open systems interacting with the daemon environment. In the simplest case the nonlocal scalar field reduces to the usual local scalar field coupled with an external source which is discussed in the stochastic approach to inflation. The daemon source can help to get the chaotic inflation scenario with a small scalar field.
Weinstein, M
2003-11-19
This paper discusses the problem of inflation in the context of Friedmann-Robertson-Walker Cosmology. We show how, after a simple change of variables, one can quantize the problem in a way which parallels the classical discussion. The result is that two of the Einstein equations arise as exact equations of motion; one of the usual Einstein equations (suitably quantized) survives as a constraint equation to be imposed on the space of physical states. However, the Friedmann equation, which is also a constraint equation and which is the basis of the Wheeler-DeWitt equation, acquires a welcome quantum correction that becomes significant for small scale factors. We then discuss the extension of this result to a full quantum mechanical derivation of the anisotropy ({delta}{rho}/{rho}) in the cosmic microwave background radiation and the possibility that the extra term in the Friedmann equation could have observable consequences. Finally, we suggest interesting ways in which these techniques can be generalized to cast light on the question of chaotic or eternal inflation. In particular, we suggest that one can put an experimental bound on how far away a universe with a scale factor very different from our own must be, by looking at its effects on our CMB radiation.
Cosmological constant from the emergent gravity perspective
NASA Astrophysics Data System (ADS)
Padmanabhan, T.; Padmanabhan, Hamsa
2014-05-01
Observations indicate that our universe is characterized by a late-time accelerating phase, possibly driven by a cosmological constant Λ, with the dimensionless parameter Λ {LP2} ˜= 10-122, where LP = (Għ/c3)1/2 is the Planck length. In this review, we describe how the emergent gravity paradigm provides a new insight and a possible solution to the cosmological constant problem. After reviewing the necessary background material, we identify the necessary and sufficient conditions for solving the cosmological constant problem. We show that these conditions are naturally satisfied in the emergent gravity paradigm in which (i) the field equations of gravity are invariant under the addition of a constant to the matter Lagrangian and (ii) the cosmological constant appears as an integration constant in the solution. The numerical value of this integration constant can be related to another dimensionless number (called CosMIn) that counts the number of modes inside a Hubble volume that cross the Hubble radius during the radiation and the matter-dominated epochs of the universe. The emergent gravity paradigm suggests that CosMIn has the numerical value 4π, which, in turn, leads to the correct, observed value of the cosmological constant. Further, the emergent gravity paradigm provides an alternative perspective on cosmology and interprets the expansion of the universe itself as a quest towards holographic equipartition. We discuss the implications of this novel and alternate description of cosmology.
NASA Astrophysics Data System (ADS)
Tipler, Frank J.
1996-09-01
I show that if Newtonian gravity is formulated in geometrical language, then Newtonian cosmology is as rigorous as relativistic cosmology. In homogeneous and isotropic universes, the geodesic deviation equation in Newtonian cosmology is proven to be exactly the same as the geodesic deviation equation in relativistic Friedmann cosmologies. This equation can be integrated to yield a constraint equation formally identical to the Friedmann equation. However, Newtonian cosmology is more general than Friedmann cosmology: by generalizing the flat-space Newtonian gravity force law to Riemannian metrics, I show that ever-expanding and recollapsing universes are allowed in any homogeneous and isotropic spatial geometry.
Cosmology with large galaxy redshift surveys
NASA Astrophysics Data System (ADS)
Sodré, Laerte, Jr.
2012-10-01
Galaxy redshift surveys are a major tool to address the most challenging cosmological problems facing cosmology, like the nature of dark energy and properties dark matter. The same observations are useful for a much larger variety of scientific applications, from the study of small bodies in the solar system, to properties of tidal streams in the Milky Way halo, to galaxy formation and evolution. Here I briefly discuss what is a redshift survey and how it can be used to attack astrophysical and cosmological problems. I finish with a brief description of a new survey, the Javalambre Physics of the Accelerating Universe Astrophysical Survey (JPAS), which will use an innovative system of 56 filters to map ~ 8000 square degrees on the sky. JPAS photometric system, besides providing accurate photometric redshifts useful for cosmological parameter estimation, will deliver a low-resolution spectrum at each pixel on the sky, allowing for the first time an almost all-sky IFU science.
The Age of Precision Cosmology
NASA Technical Reports Server (NTRS)
Chuss, David T.
2012-01-01
In the past two decades, our understanding of the evolution and fate of the universe has increased dramatically. This "Age of Precision Cosmology" has been ushered in by measurements that have both elucidated the details of the Big Bang cosmology and set the direction for future lines of inquiry. Our universe appears to consist of 5% baryonic matter; 23% of the universe's energy content is dark matter which is responsible for the observed structure in the universe; and 72% of the energy density is so-called "dark energy" that is currently accelerating the expansion of the universe. In addition, our universe has been measured to be geometrically flat to 1 %. These observations and related details of the Big Bang paradigm have hinted that the universe underwent an epoch of accelerated expansion known as Uinflation" early in its history. In this talk, I will review the highlights of modern cosmology, focusing on the contributions made by measurements of the cosmic microwave background, the faint afterglow of the Big Bang. I will also describe new instruments designed to measure the polarization of the cosmic microwave background in order to search for evidence of cosmic inflation.
Quintessence and Born-Infeld cosmology
NASA Astrophysics Data System (ADS)
Moniz, P. Vargas
2002-11-01
Recent observations suggest that the universe is in a state of accelerated cosmic expansion. Herewith we investigate this scenario within the Born-Infeld theory, which has been employed to describe open strings ending on D-branes. A multidimensional model with a topology R×S3×Sd, a cosmological constant, dust matter, and gauge fields is considered for that purpose. Two situations are subsequently discussed, according to whether string effects are (i) dominant or (ii) induce perturbations in the gauge field sector. Studying the set of equations governing the cosmological dynamics, we find that Born-Infeld cosmology can be compatible with the presently measured acceleration, together with a compactified internal space. This is shown to depend on the gauge field components in the internal dimensions as well as string modifications to the gauge matter sector. Furthermore, we argue regarding situation (i) that quintessence could constitute a transient stage.
Attractor behaviour in ELKO cosmology
Basak, Abhishek; Bhatt, Jitesh R.; Shankaranarayanan, S.; Varma, K.V. Prasantha E-mail: jeet@prl.res.in E-mail: varma@iisertvm.ac.in
2013-04-01
We study the dynamics of ELKO in the context of accelerated phase of our universe. To avoid the fine tuning problem associated with the initial conditions, it is required that the dynamical equations lead to an early-time attractor. In the earlier works, it was shown that the dynamical equations containing ELKO fields do not lead to early-time stable fixed points. In this work, using redefinition of variables, we show that ELKO cosmology admits early-time stable fixed points. More interestingly, we show that ELKO cosmology admit two sets of attractor points corresponding to slow and fast-roll inflation. The fast-roll inflation attractor point is unique for ELKO as it is independent of the form of the potential. We also discuss the plausible choice of interaction terms in these two sets of attractor points and constraints on the coupling constant.
Deser, S; Woodard, R P
2007-09-14
We explore nonlocally modified models of gravity, inspired by quantum loop corrections, as a mechanism for explaining current cosmic acceleration. These theories enjoy two major advantages: they allow a delayed response to cosmic events, here the transition from radiation to matter dominance, and they avoid the usual level of fine-tuning; instead, emulating Dirac's dictum, the required large numbers come from the large time scales involved. Their solar system effects are safely negligible, and they may even prove useful to the black hole information problem.
NASA Astrophysics Data System (ADS)
Gasperini, Maurizio
2011-03-01
Preface; Acknowledgements; Notation, units and conventions; 1. A short review of standard and inflationary cosmology; 2. The basic string cosmology equations; 3. Conformal invariance and string effective action; 4. Duality symmetries and cosmological solutions; 5. Inflationary kinematics; 6. The string phase; 7. The cosmic background of relic gravitational waves; 8. Scalar perturbations and the anisotropy of the CMB radiation; 9. Dilaton phenomenology; 10. Elements of brane cosmology; Index.
CONFERENCES AND SYMPOSIA: Lev Landau and the problem of singularities in cosmology
NASA Astrophysics Data System (ADS)
Khalatnikov, I. M.; Kamenshchik, A. Yu
2008-06-01
We consider different aspects of the problem of cosmological singularity such as the BKL oscillatory approach to singularity, the new features of the cosmological dynamics in the neighbourhood of the singularity in multidimensional and superstring cosmological models and their connections with such a modern branch of mathematics as infinite-dimensional Lie algebras. Besides, we consider some new types of cosmological singularities which were widely discussed during last decade after the discovery of the phenomenon of cosmic acceleration.
Superbounce and loop quantum cosmology ekpyrosis from modified gravity
NASA Astrophysics Data System (ADS)
Oikonomou, V. K.
2015-09-01
As is known, in modified cosmological theories of gravity many of the cosmologies which could not be generated by standard Einstein gravity, can be consistently described by theories. Using known reconstruction techniques, we investigate which theories can lead to a Hubble parameter describing two types of cosmological bounces, the superbounce model, related to supergravity and non-supersymmetric models of contracting ekpyrosis and also the Loop Quantum Cosmology modified ekpyrotic model. Since our method is an approximate method, we investigate the problem at large and small curvatures. As we evince, both models yield power law reconstructed gravities, with the most interesting new feature being that both lead to accelerating cosmologies, in the large curvature approximation. The mathematical properties of the some Friedmann-Robertson-Walker spacetimes , that describe superbounce-like cosmologies are also pointed out, with regards to the group of curvature collineations.
Duality gives rise to Chaplygin cosmologies with a big rip
NASA Astrophysics Data System (ADS)
Chimento, Luis P.; Lazkoz, Ruth
2006-05-01
We consider modifications to the Friedmann equation motivated by recent proposals along these lines pursuing an explanation to the observed late time acceleration. Here we show that these approaches can be framed within a theory with modified gravity, and we discuss the construction of the duals of the cosmologies generated within that framework. We then investigate the modifications required to generate extended, generalized and modified Chaplygin cosmologies, and then show that their duals belong to a larger family of cosmologies we call enlarged Chaplygin cosmologies. Finally, by letting the parameters of these models take values not earlier considered in the literature we show that some representatives of that family of cosmologies display sudden future singularities. This fact indicates that the behaviour of these spacetimes is rather different from that of generalized or modified Chaplygin gas cosmologies. This reinforces the idea that modifications of gravity can be responsible for unexpected evolutionary features in the universe.
NASA Astrophysics Data System (ADS)
Chamcham, Khalil; Silk, Joseph; Barrow, John D.; Saunders, Simon
2017-04-01
Part I. Issues in the Philosophy of Cosmology: 1. Cosmology, cosmologia and the testing of cosmological theories George F. R. Ellis; 2. Black holes, cosmology and the passage of time: three problems at the limits of science Bernard Carr; 3. Moving boundaries? – comments on the relationship between philosophy and cosmology Claus Beisbart; 4. On the question why there exists something rather than nothing Roderich Tumulka; Part II. Structures in the Universe and the Structure of Modern Cosmology: 5. Some generalities about generality John D. Barrow; 6. Emergent structures of effective field theories Jean-Philippe Uzan; 7. Cosmological structure formation Joel R. Primack; 8. Formation of galaxies Joseph Silk; Part III. Foundations of Cosmology: Gravity and the Quantum: 9. The observer strikes back James Hartle and Thomas Hertog; 10. Testing inflation Chris Smeenk; 11. Why Boltzmann brains do not fluctuate into existence from the de Sitter vacuum Kimberly K. Boddy, Sean M. Carroll and Jason Pollack; 12. Holographic inflation revised Tom Banks; 13. Progress and gravity: overcoming divisions between general relativity and particle physics and between physics and HPS J. Brian Pitts; Part IV. Quantum Foundations and Quantum Gravity: 14. Is time's arrow perspectival? Carlo Rovelli; 15. Relational quantum cosmology Francesca Vidotto; 16. Cosmological ontology and epistemology Don N. Page; 17. Quantum origin of cosmological structure and dynamical reduction theories Daniel Sudarsky; 18. Towards a novel approach to semi-classical gravity Ward Struyve; Part V. Methodological and Philosophical Issues: 19. Limits of time in cosmology Svend E. Rugh and Henrik Zinkernagel; 20. Self-locating priors and cosmological measures Cian Dorr and Frank Arntzenius; 21. On probability and cosmology: inference beyond data? Martin Sahlén; 22. Testing the multiverse: Bayes, fine-tuning and typicality Luke A. Barnes; 23. A new perspective on Einstein's philosophy of cosmology Cormac O
Kubicek, Markus; Cai, Zhuhua; Ma, Wen; Yildiz, Bilge; Hutter, Herbert; Fleig, Jürgen
2013-04-23
The influence of lattice strain on the oxygen exchange kinetics and diffusion in oxides was investigated on (100) epitaxial La1-xSrxCoO3-δ (LSC) thin films grown by pulsed laser deposition. Planar tensile and compressively strained LSC films were obtained on single-crystalline SrTiO3 and LaAlO3. 18O isotope exchange depth profiling with ToF-SIMS was employed to simultaneously measure the tracer surface exchange coefficient k* and the tracer diffusion coefficient D* in the temperature range 280-475 °C. In accordance with recent theoretical findings, much faster surface exchange (∼4 times) and diffusion (∼10 times) were observed for the tensile strained films compared to the compressively strained films in the entire temperature range. The same strain effect--tensile strain leading to higher k* and D*--was found for different LSC compositions (x=0.2 and x=0.4) and for surface-etched films. The temperature dependence of k* and D* is discussed with respect to the contributions of strain states, formation enthalpy of oxygen vacancies, and vacancy mobility at different temperatures. Our findings point toward the control of oxygen surface exchange and diffusion kinetics by means of lattice strain in existing mixed conducting oxides for energy conversion applications.
Bornyakov, V.G.
2005-06-01
Possibilities that are provided by a lattice regularization of QCD for studying nonperturbative properties of QCD are discussed. A review of some recent results obtained from computer calculations in lattice QCD is given. In particular, the results for the QCD vacuum structure, the hadron mass spectrum, and the strong coupling constant are considered.
Philosophical Roots of Cosmology
NASA Astrophysics Data System (ADS)
Ivanovic, M.
2008-10-01
We shall consider the philosophical roots of cosmology in the earlier Greek philosophy. Our goal is to answer the question: Are earlier Greek theories of pure philosophical-mythological character, as often philosophers cited it, or they have scientific character. On the bases of methodological criteria, we shall contend that the latter is the case. In order to answer the question about contemporary situation of the relation philosophy-cosmology, we shall consider the next question: Is contemporary cosmology completely independent of philosophical conjectures? The answer demands consideration of methodological character about scientific status of contemporary cosmology. We also consider some aspects of the relation contemporary philosophy-cosmology.
NASA Astrophysics Data System (ADS)
Tipler, Frank J.
1996-10-01
It is generally believed that it is not possible to rigorously analyze a homogeneous and isotropic cosmological model in Newtonian mechanics. I show on the contrary that if Newtonian gravity theory is rewritten in geometrical language in the manner outlined in 1923-1924 by Élie Cartan [Ann. Ecole Norm. Sup. 40, 325-412 (1923); 41, 1-25 (1924)], then Newtonian cosmology is as rigorous as Friedmann cosmology. In particular, I show that the equation of geodesic deviation in Newtonian cosmology is exactly the same as equation of geodesic deviation in the Friedmann universe, and that this equation can be integrated to yield a constraint equation formally identical to the Friedmann equation. However, Newtonian cosmology is more general than Friedmann cosmology: Ever-expanding and recollapsing universes are allowed in any noncompact homogeneous and isotropic spatial topology. I shall give a brief history of attempts to do cosmology in the framework of Newtonian mechanics.
BRS structure of simple model of cosmological constant and cosmology
NASA Astrophysics Data System (ADS)
Mori, Taisaku; Nitta, Daisuke; Nojiri, Shin'ichi
2017-07-01
In Mod. Phys. Lett. A 31, 1650213 (2016, 10.1142/S0217732316502138), Nojiri proposed a simple model in order to solve one of the problems related to the cosmological constant. The model is induced from a topological field theory, and the model has an infinite number of BRS symmetries. The BRS symmetries are, in general, spontaneously broken, however. We investigate the BRS symmetry in detail and show that there is one and only one BRS symmetry which is not broken, and the unitarity can be guaranteed. In the model, the quantum problem of the vacuum energy, which may be identified with the cosmological constant, reduces to the classical problem of the initial condition. We investigate the cosmology given by the model and specify the region of the initial conditions, which could be consistent with the evolution of the Universe. We also show that there is a stable solution describing the de Sitter space-time, which may explain the accelerating expansion in the current Universe.
Conformal cosmological model and SNe Ia data
NASA Astrophysics Data System (ADS)
Zakharov, A. F.; Pervushin, V. N.
2012-11-01
Now there is a huge scientific activity in astrophysical studies and cosmological ones in particular. Cosmology transforms from a pure theoretical branch of science into an observational one. All the cosmological models have to pass observational tests. The supernovae type Ia (SNe Ia) test is among the most important ones. If one applies the test to determine parameters of the standard Friedmann-Robertson-Walker cosmological model one can conclude that observations lead to the discovery of the dominance of the Λ term and as a result to an acceleration of the Universe. However, there are big mysteries connected with an origin and an essence of dark matter (DM) and the Λ term or dark energy (DE). Alternative theories of gravitation are treated as a possible solution of DM and DE puzzles. The conformal cosmological approach is one of possible alternatives to the standard ΛCDM model. As it was noted several years ago, in the framework of the conformal cosmological approach an introduction of a rigid matter can explain observational data without Λ term (or dark energy). We confirm the claim with much larger set of observational data.
Constraining holographic cosmology using Planck data
NASA Astrophysics Data System (ADS)
Afshordi, Niayesh; Gould, Elizabeth; Skenderis, Kostas
2017-06-01
Holographic cosmology offers a novel framework for describing the very early Universe in which cosmological predictions are expressed in terms of the observables of a three-dimensional quantum field theory (QFT). This framework includes conventional slow-roll inflation, which is described in terms of a strongly coupled QFT, but it also allows for qualitatively new models for the very early Universe, where the dual QFT may be weakly coupled. The new models describe a universe which is nongeometric at early times. While standard slow-roll inflation leads to a (near-) power-law primordial power spectrum, perturbative super-renormalizable QFTs yield a new holographic spectral shape. Here, we compare the two predictions against cosmological observations. We use CosmoMC to determine the best fit parameters, and MultiNest for Bayesian evidence, comparing the likelihoods. We find that the dual QFT should be nonperturbative at the very low multipoles (l ≲30 ), while for higher multipoles (l ≳30 ) the new holographic model, based on perturbative QFT, fits the data just as well as the standard power-law spectrum assumed in Λ CDM cosmology. This finding opens the door to applications of nonperturbative QFT techniques, such as lattice simulations, to observational cosmology on gigaparsec scales and beyond.
NASA Astrophysics Data System (ADS)
Berg, J. Scott
2008-11-01
The EMMA experiment will study beam dynamics in a linear non-scaling fixed-field alternating gradient (FFAG) accelerator. I give a brief introduction to the purpose and goals of the EMMA experiment and describe how they will impact the design of the main EMMA ring. I then describe the mathematical model that is used to describe the EMMA lattice. Finally, I show how the different lattice configurations were obtained and list their parameters.
Cosmology of Continuum Creation and Annihilation
NASA Astrophysics Data System (ADS)
Ierokomos, Nikiforos
2011-11-01
An extensive cosmology hypothesis is presented that was developed over decades and is based on the existence and evolution of the universe via Cosmic Symmetry Breaks (CSBs) or phases with our universe (Cosmos) describable by a Cosmology of Continuum Creation and Annihilation, or CCA Cosmology. The CCA cosmology hypothesis does not belong to a Standard Model Big Bang. This hypothesis not only describes the universe but also the realm of elementary particles and forces. It provides plausible answers to a large number of puzzles in Physics and Cosmology. These answers range from those that can be calculated and values checked by observations, such as: How much and what is dark energy? How much and what is dark matter? How much baryonic matter? How much and why is there a time-delay for GRB energetic photons? When (or did?) the universe started to accelerate? Are primordial galaxies smaller? Why are orbits non-Newtonian beyond an acceleration value, and other calculable parameters. Also, answers which are more fundamental in interpretation, such as: What is mass and gravity? How many families of elementary particles exist and why are there only three generations of each? Why did the universe start with such low entropy? Does the Cosmos violate the First or Second Law of Thermodynamics? Why is there an asymmetry of matter over antimatter in the universe and what is antimatter? These and other questions the CCA hypothesis is proposing to answer. This hypothesis requires minimum assumptions and can build a coherent theory that can arrive at today's complex universe with plausible evolutionary steps from one postulate and one particle. cosmogony, non-standard cosmology, dark energy, dark matter, new elementary particles, gravity, antimatter, accelerated universe.
Cosmology from High Redshift Supernovae
NASA Astrophysics Data System (ADS)
Garnavich, Peter
The discovery of a correlation between the light curve shape and intrinsic b rightness has made Type Ia supernovae exceptionally accurate distance indicators out to cosmologically interesting redshifts. Ground-based searches and follow-up as well as Hubble S pace Telescope observations of Type Ia supernovae have produced a significant number of object s with redshifts between 0.3 and 1.0. The distant SNe, when combined with a local samp le analyzed in the same way, provide reliable constraints on the deceleration and age of th e Universe. Early this year, an analysis of a handful of Type Ia events indicated that the deceleration was too small for gravitating matter alone to make a flat Universe. A larger sa mple of supernovae gives the surprising result that the Universe is accelerating, implying the exi stence of a cosmological constant or some other exotic form of energy. The success of this research has depended on the development of algorithms and software to register, scale and subtract CCD images taken weeks apart and to search for var iable objects. A good fraction of the point-sources identified are asteroids, variable stars, or AGN, so spectra are needed to confirm the identification as a Type Ia supernova and obt ain a redshift. The best candidates are followed photometrically to construct light curves. The steps to transform the observed light curves into cosmologically interestin g results will also be described.
TOPICAL REVIEW The cosmological constant puzzle
NASA Astrophysics Data System (ADS)
Bass, Steven D.
2011-04-01
The accelerating expansion of the Universe points to a small positive vacuum energy density and negative vacuum pressure. A strong candidate is the cosmological constant in Einstein's equations of general relativity. Possible contributions are zero-point energies and the condensates associated with spontaneous symmetry breaking. The vacuum energy density extracted from astrophysics is 1056 times smaller than the value expected from quantum fields and standard model particle physics. Is the vacuum energy density time dependent? We give an introduction to the cosmological constant puzzle and ideas how to solve it.
Cosmology of a covariant Galilean field.
De Felice, Antonio; Tsujikawa, Shinji
2010-09-10
We study the cosmology of a covariant scalar field respecting a Galilean symmetry in flat space-time. We show the existence of a tracker solution that finally approaches a de Sitter fixed point responsible for cosmic acceleration today. The viable region of model parameters is clarified by deriving conditions under which ghosts and Laplacian instabilities of scalar and tensor perturbations are absent. The field equation of state exhibits a peculiar phantomlike behavior along the tracker, which allows a possibility to observationally distinguish the Galileon gravity from the cold dark matter model with a cosmological constant.
Bousso, Raphael
2005-01-25
We study conditions for the existence of asymptotic observables in cosmology. With the exception of de Sitter space, the thermal properties of accelerating universes permit arbitrarily long observations, and guarantee the production of accessible states of arbitrarily large entropy. This suggests that some asymptotic observables may exist, despite the presence of an event horizon. Comparison with decelerating universes shows surprising similarities: Neither type suffers from the limitations encountered in de Sitter space, such as thermalization and boundedness of entropy. However, we argue that no realistic cosmology permits the global observations associated with an S-matrix.
General very special relativity in Finsler cosmology
Kouretsis, A. P.; Stathakopoulos, M.; Stavrinos, P. C.
2009-05-15
General very special relativity (GVSR) is the curved space-time of very special relativity (VSR) proposed by Cohen and Glashow. The geometry of general very special relativity possesses a line element of Finsler geometry introduced by Bogoslovsky. We calculate the Einstein field equations and derive a modified Friedmann-Robertson-Walker cosmology for an osculating Riemannian space. The Friedmann equation of motion leads to an explanation of the cosmological acceleration in terms of an alternative non-Lorentz invariant theory. A first order approach for a primordial-spurionic vector field introduced into the metric gives back an estimation of the energy evolution and inflation.
General very special relativity in Finsler cosmology
NASA Astrophysics Data System (ADS)
Kouretsis, A. P.; Stathakopoulos, M.; Stavrinos, P. C.
2009-05-01
General very special relativity (GVSR) is the curved space-time of very special relativity (VSR) proposed by Cohen and Glashow. The geometry of general very special relativity possesses a line element of Finsler geometry introduced by Bogoslovsky. We calculate the Einstein field equations and derive a modified Friedmann-Robertson-Walker cosmology for an osculating Riemannian space. The Friedmann equation of motion leads to an explanation of the cosmological acceleration in terms of an alternative non-Lorentz invariant theory. A first order approach for a primordial-spurionic vector field introduced into the metric gives back an estimation of the energy evolution and inflation.
Our Universe from the cosmological constant
Barrau, Aurélien; Linsefors, Linda E-mail: linda.linsefors@lpsc.in2p3.fr
2014-12-01
The issue of the origin of the Universe and of its contents is addressed in the framework of bouncing cosmologies, as described for example by loop quantum gravity. If the current acceleration is due to a true cosmological constant, this constant is naturally conserved through the bounce and the Universe should also be in a (contracting) de Sitter phase in the remote past. We investigate here the possibility that the de Sitter temperature in the contracting branch fills the Universe with radiation that causes the bounce and the subsequent inflation and reheating. We also consider the possibility that this gives rise to a cyclic model of the Universe and suggest some possible tests.
NASA Astrophysics Data System (ADS)
Bojowald, Martin
The universe, ultimately, is to be described by quantum theory. Quantum aspects of all there is, including space and time, may not be significant for many purposes, but are crucial for some. And so a quantum description of cosmology is required for a complete and consistent worldview. At any rate, even if we were not directly interested in regimes where quantum cosmology plays a role, a complete physical description could not stop at a stage before the whole universe is reached. Quantum theory is essential in the microphysics of particles, atoms, molecules, solids, white dwarfs and neutron stars. Why should one expect this ladder of scales to end at a certain size? If regimes are sufficiently violent and energetic, quantum effects are non-negligible even on scales of the whole cosmos; this is realized at least once in the history of the universe: at the big bang where the classical theory of general relativity would make energy densities diverge.
Cosmological parallax-distance formula
NASA Astrophysics Data System (ADS)
Singal, Ashok K.
2015-09-01
The standard cosmological parallax-distance formula, as found in the literature, including text-books and reference books on cosmology, requires a correction. This correction stems from the fact that in the standard text-book derivation it has been ignored that any chosen baseline in a gravitationally bound system does not partake in the cosmological expansion. Though the correction is available in the literature for some time, the text-books still continue to use the older, incorrect formula, and its full implications are not yet fully realized. Apart from providing an alternate correct, closed-form expression that is more suitable and convenient for computations for certain limiting cases of FRW () world models, we also demonstrate how one can compute parallax distance for the currently favored flat-space accelerating-universe (, ) cosmologies. Further, we show that the correction in parallax distance at large redshifts could amount to a factor of three or even more. Moreover, even in an infinite universe the parallax distance does not increase indefinitely with redshift and that even the farthest possible observable point may have a finite parallax angle, a factor that needs to be carefully taken into account when using distant objects as the background field against which the parallax of a foreground object is to be measured. Some other complications that could arise in parallax measurements of a distant source, like that due to the deflection of incoming light by the gravitation field of the Sun and other planetary bodies in the solar system, are pointed out.
Schramm, D.N.
1992-03-01
The cosmological dark matter problem is reviewed. The Big Bang Nucleosynthesis constraints on the baryon density are compared with the densities implied by visible matter, dark halos, dynamics of clusters, gravitational lenses, large-scale velocity flows, and the {Omega} = 1 flatness/inflation argument. It is shown that (1) the majority of baryons are dark; and (2) non-baryonic dark matter is probably required on large scales. It is also noted that halo dark matter could be either baryonic or non-baryonic. Descrimination between cold'' and hot'' non-baryonic candidates is shown to depend on the assumed seeds'' that stimulate structure formation. Gaussian density fluctuations, such as those induced by quantum fluctuations, favor cold dark matter, whereas topological defects such as strings, textures or domain walls may work equally or better with hot dark matter. A possible connection between cold dark matter, globular cluster ages and the Hubble constant is mentioned. Recent large-scale structure measurements, coupled with microwave anisotropy limits, are shown to raise some questions for the previously favored density fluctuation picture. Accelerator and underground limits on dark matter candidates are also reviewed.
Schramm, D.N.
1992-03-01
The cosmological dark matter problem is reviewed. The Big Bang Nucleosynthesis constraints on the baryon density are compared with the densities implied by visible matter, dark halos, dynamics of clusters, gravitational lenses, large-scale velocity flows, and the {Omega} = 1 flatness/inflation argument. It is shown that (1) the majority of baryons are dark; and (2) non-baryonic dark matter is probably required on large scales. It is also noted that halo dark matter could be either baryonic or non-baryonic. Descrimination between ``cold`` and ``hot`` non-baryonic candidates is shown to depend on the assumed ``seeds`` that stimulate structure formation. Gaussian density fluctuations, such as those induced by quantum fluctuations, favor cold dark matter, whereas topological defects such as strings, textures or domain walls may work equally or better with hot dark matter. A possible connection between cold dark matter, globular cluster ages and the Hubble constant is mentioned. Recent large-scale structure measurements, coupled with microwave anisotropy limits, are shown to raise some questions for the previously favored density fluctuation picture. Accelerator and underground limits on dark matter candidates are also reviewed.
NASA Astrophysics Data System (ADS)
Verde, Licia; Bellini, Emilio; Pigozzo, Cassio; Heavens, Alan F.; Jimenez, Raul
2017-04-01
We investigate our knowledge of early universe cosmology by exploring how much additional energy density can be placed in different components beyond those in the ΛCDM model. To do this we use a method to separate early- and late-universe information enclosed in observational data, thus markedly reducing the model-dependency of the conclusions. We find that the 95% credibility regions for extra energy components of the early universe at recombination are: non-accelerating additional fluid density parameter ΩMR < 0.006 and extra radiation parameterised as extra effective neutrino species 2.3 < Neff < 3.2 when imposing flatness. Our constraints thus show that even when analyzing the data in this largely model-independent way, the possibility of hiding extra energy components beyond ΛCDM in the early universe is seriously constrained by current observations. We also find that the standard ruler, the sound horizon at radiation drag, can be well determined in a way that does not depend on late-time Universe assumptions, but depends strongly on early-time physics and in particular on additional components that behave like radiation. We find that the standard ruler length determined in this way is rs = 147.4 ± 0.7 Mpc if the radiation and neutrino components are standard, but the uncertainty increases by an order of magnitude when non-standard dark radiation components are allowed, to rs = 150 ± 5 Mpc.
NASA Astrophysics Data System (ADS)
Brynjolfsson, Ari
2011-04-01
The newly discovered plasma redshift cross section explains a long range of phenomena; including the cosmological redshift, and the intrinsic redshift of Sun, stars, galaxies and quasars. It explains the beautiful black body spectrum of the CMB, and it predicts correctly: a) the observed XRB, b) the magnitude redshift relation for supernovae, and c) the surface- brightness-redshift relation for galaxies. There is no need for Big Bang, Inflation, Dark Energy, Dark Matter, Accelerated Expansion, and Black Holes. The universe is quasi-static and can renew itself forever (for details, see: http://www.plasmaredshift.org). There is no cosmic time dilation. In intergalactic space, the average electron temperature is T = 2.7 million K, and the average electron density is N = 0.0002 per cubic cm. Plasma redshift is derived theoretically from conventional axioms of physics by using more accurate methods than those conventionally used. The main difference is: 1) the proper inclusion of the dielectric constant, 2) more exact calculations of imaginary part of the dielectric constant, and as required 3) a quantum mechanical treatment of the interactions.
Translational symmetry breaking in field theories and the cosmological constant
NASA Astrophysics Data System (ADS)
Evans, Nick; Morris, Tim R.; Scott, Marc
2016-01-01
We argue, at a very basic effective field theory level, that higher dimension operators in scalar theories that break symmetries at scales close to their ultraviolet completion cutoff include terms that favor the breaking of translation (Lorentz) invariance, potentially resulting in striped, checkerboard or general crystal-like phases. Such descriptions can be thought of as the effective low energy description of QCD-like gauge theories near their strong coupling scale where terms involving higher dimension operators are generated. Our low energy theory consists of scalar fields describing operators such as q ¯q and q ¯F(2 n )q . Such scalars can have kinetic mixing terms that generate effective momentum dependent contributions to the mass matrix. We show that these can destabilize the translationally invariant vacuum. It is possible that in some real gauge theory such operators could become sufficiently dominant to realize such phases, and it would be interesting to look for them in lattice simulations. We present a holographic model of the same phenomena which includes renormalization group running. A key phenomenological motive to look at such states is recent work that shows that the nonlinear response in R2 gravity to such short-range fluctuations can mimic a cosmological constant. Intriguingly in a cosmology with such a Starobinsky inflation term, to generate the observed value of the present day acceleration would require stripes at the electroweak scale. Unfortunately, low energy phenomenological constraints on Lorentz violation in the electron-photon system appear to strongly rule out any such possibility outside of a disconnected dark sector.
Wong, Yvonne Y. Y.
2008-01-24
I give an overview of the effects of neutrinos on cosmology, focussing in particular on the role played by neutrinos in the evolution of cosmological perturbations. I discuss how recent observations of the cosmic microwave background and the large-scale structure of galaxies can probe neutrino masses with greater precision than current laboratory experiments. I describe several new techniques that will be used to probe cosmology in the future.
Dark Energy and the Cosmological Constant: A Brief Introduction
ERIC Educational Resources Information Center
Harvey, Alex
2009-01-01
The recently observed acceleration of the expansion of the universe is a topic of intense interest. The favoured causes are the "cosmological constant" or "dark energy". The former, which appears in the Einstein equations as the term [lambda]g[subscript [mu]v], provides an extremely simple, well-defined mechanism for the acceleration. However,…
Dark Energy and the Cosmological Constant: A Brief Introduction
ERIC Educational Resources Information Center
Harvey, Alex
2009-01-01
The recently observed acceleration of the expansion of the universe is a topic of intense interest. The favoured causes are the "cosmological constant" or "dark energy". The former, which appears in the Einstein equations as the term [lambda]g[subscript [mu]v], provides an extremely simple, well-defined mechanism for the acceleration. However,…
Light propagation through black-hole lattices
NASA Astrophysics Data System (ADS)
Bentivegna, Eloisa; Korzyński, Mikołaj; Hinder, Ian; Gerlicher, Daniel
2017-03-01
The apparent properties of distant objects encode information about the way the light they emit propagates to an observer, and therefore about the curvature of the underlying spacetime. Measuring the relationship between the redshift z and the luminosity distance DL of a standard candle, for example, yields information on the Universe's matter content. In practice, however, in order to decode this information the observer needs to make an assumption about the functional form of the DL(z) relation; in other words, a cosmological model needs to be assumed. In this work, we use numerical-relativity simulations, equipped with a new ray-tracing module, to numerically obtain this relation for a few black-hole-lattice cosmologies and compare it to the well-known Friedmann-Lema{ȋtre-Robertson-Walker case, as well as to other relevant cosmologies and to the Empty-Beam Approximation. We find that the latter provides the best estimate of the luminosity distance and formulate a simple argument to account for this agreement. We also find that a Friedmann-Lema{ȋtre-Robertson-Walker model can reproduce this observable exactly, as long as a time-dependent cosmological constant is included in the fit. Finally, the dependence of these results on the lattice mass-to-spacing ratio μ is discussed: we discover that, unlike the expansion rate, the DL(z) relation in a black-hole lattice does not tend to that measured in the corresponding continuum spacetime as 0μ → .
Normal DGP in varying speed of light cosmology
NASA Astrophysics Data System (ADS)
Ravanpak, Arvin; Farajollahi, Hossein; Farpoor Fadakar, Golnaz
2017-02-01
Varying speed of light (VSL) has been used in cosmological models in which the physical constants vary over time. On the other hand, the Dvali, Gabadadze and Porrati (DGP) brane world model, especially its normal branch, has been extensively discussed to justify the current cosmic acceleration. In this article we show that the normal branch of DGP in VSL cosmology leads to a self-accelerating behavior and therefore can interpret cosmic acceleration. Applying statefinder diagnostics demonstrates that our result slightly deviates from the ΛCDM model.
NASA Astrophysics Data System (ADS)
López-Corredoira, M.
2009-08-01
Certain results of observational cosmology cast critical doubt on the foundations of standard cosmology but leave most cosmologists untroubled. Alternative cosmological models that differ from the Big Bang have been published and defended by heterodox scientists; however, most cosmologists do not heed these. This may be because standard theory is correct and all other ideas and criticisms are incorrect, but it is also to a great extent due to sociological phenomena such as the ``snowball effect'' or ``groupthink''. We might wonder whether cosmology, the study of the Universe as a whole, is a science like other branches of physics or just a dominant ideology.
Cosmology and neutrino properties
Dolgov, A. D.
2008-12-15
A brief review for particle physicists on the cosmological impact of neutrinos and on restrictions on neutrino properties from cosmology is given. The paper includes a discussion of upper bounds on neutrino mass and possible ways to relax them, methods to observe the cosmic-neutrino background, bounds on the cosmological lepton asymmetry which are strongly improved by neutrino oscillations, cosmological effects of breaking of the spin-statistics theorem for neutrinos, bounds on mixing parameters of active and possible sterile neutrinos with account of active-neutrino oscillations, bounds on right-handed currents and neutrino magnetic moments, and some more.
Inherent weaknesses of cosmology
NASA Technical Reports Server (NTRS)
Chiu, H.-Y.
1986-01-01
Sources of astrophysical evidence necessary to verify a cosmological model are reviewed. Cosmological history of the universe is divided into four epochs, each unique in its physical conditions related to observability at present. The current epoch, started after recombination of hydrogen in the universe, offers the most in observability. In earlier epochs, verifiable astrophysical evidence gradually disappeared. It seems that no astrophysical evidence has been left behind from the singularity epoch of the Universe. The gradual disappearance of astrophysical evidence ascertainable at present is the result of physical conditions structured within the cosmological models, hence indicating certain inherent weaknesses of cosmology as a verifiable physical theory.
Induced cosmological constant and other features of asymmetric brane embedding
Shtanov, Yuri; Sahni, Varun; Shafieloo, Arman; Toporensky, Alexey E-mail: varun@iucaa.ernet.in E-mail: lesha@xray.sai.msu.ru
2009-04-15
We investigate the cosmological properties of an 'induced gravity' brane scenario in the absence of mirror symmetry with respect to the brane. We find that brane evolution can proceed along one of four distinct branches. By contrast, when mirror symmetry is imposed, only two branches exist, one of which represents the self-accelerating brane, while the other is the so-called normal branch. This model incorporates many of the well-known possibilities of brane cosmology including phantom acceleration (w < -1), self-acceleration, transient acceleration, quiescent singularities, and cosmic mimicry. Significantly, the absence of mirror symmetry also provides an interesting way of inducing a sufficiently small cosmological constant on the brane. A small (positive) {Lambda}-term in this case is induced by a small asymmetry in the values of bulk fundamental constants on the two sides of the brane.
Cosmological 3-point correlators from holography
McFadden, Paul; Skenderis, Kostas E-mail: K.Skenderis@uva.nl
2011-06-01
We investigate the non-Gaussianity of primordial cosmological perturbations using holographic methods. In particular, we derive holographic formulae that relate all cosmological 3-point correlation functions, including both scalar and tensor perturbations, to stress-energy correlation functions of a holographically dual three-dimensional quantum field theory. These results apply to general single scalar inflationary universes that at late times approach either de Sitter spacetime or accelerating power-law cosmologies. We further show that in Einstein gravity all 3-point functions involving tensors may be obtained from correlators containing only positive helicity gravitons, with the ratios of these to the correlators involving one negative helicity graviton being given by universal functions of momenta, irrespectively of the potential of the scalar field. As a by-product of this investigation, we obtain holographic formulae for the full 3-point function of the stress-energy tensor along general holographic RG flows. These results should have applications in a wider holographic context.
Fundamental cosmology from precision spectroscopy: Varying couplings
NASA Astrophysics Data System (ADS)
Leite, A. C. O.; Martins, C. J. A. P.; Pedrosa, P. O. J.; Nunes, N. J.
2014-09-01
The observational evidence for the acceleration of the Universe demonstrates that canonical theories of cosmology and particle physics are incomplete, if not incorrect, and that new physics is out there, waiting to be discovered. Forthcoming high-resolution ultrastable spectrographs will play a crucial role in this quest for new physics, by enabling a new generation of precision consistency tests. Here we focus on astrophysical tests of the stability of nature's fundamental couplings, and by using principal component analysis techniques further calibrated by existing VLT data we discuss how the improvements that can be expected with ESPRESSO and ELT-HIRES will impact on fundamental cosmology. In particular we show that a 20 to 30 night program on ELT-HIRES will allow it to play a leading role in fundamental cosmology.
Multidimensional integrable models of gravitation and cosmology
NASA Astrophysics Data System (ADS)
Ivashchuk, V. D.; Melnikov, V. N.
Review of the motivation and main results in multidimentional gravitation and cosmology is presented. Special attention is devoted to results within the model with scalar fields and fields of forms in the billiard approach for obtaining cosmological solutions with branes and integrable configurations with fluxand black branes. In case of the quantum billiard with branes it is shown that the basis solutions for wave functions vanish in the limit of the formation of billiard walls (i.e., at the singularity) for the D = 11 model which mimics the D = 11 supergravitational cosmology. Another fruitful approach - to multidimensional gravity with higher derivatives is mentioned, which leads to a unified description of inflation and the present accelerated expansion of the Universe. Some of these models explain possible spatial and temporal variations of the fine structure and the gravitational constants.
Effective Friedmann model from multidimensional cosmologies
NASA Astrophysics Data System (ADS)
Zhuk, A.
2006-10-01
We investigate the possibility of the construction of the conventional Friedmann cosmology for our observable Universe if the underlying theory is the multidimensional Kaluza-Klein model. We show that the effective Friedmann model obtained by dynamic compactification of the multidimensional model is faced with too strong variations in the fundamental constants. On the other hand, models with stable compactification of the internal space are free from this problem and also result in conventional four-dimensonal cosmological behaviour for our Universe. We prove a no-go theorem, which shows that stable compactification of the internal spaces is possible only if the equations of state in the external and internal spaces are properly adjusted to each other. With a proper choice of parameters (fine tuning), the effective cosmological constant in this model provides the late-time acceleration of the Universe.
On the Convergence in Effective Loop Quantum Cosmology
Corichi, Alejandro; Vukasinac, Tatjana; Zapata, Jose Antonio
2010-07-12
In Loop Quantum Cosmology (LQC) there is a discreteness parameter {lambda}, that has been heuristically associated to a fundamental granularity of quantum geometry. It is also possible to consider {lambda} as a regulator in the same spirit as that used in lattice field theory, where it specifies a regular lattice in the real line. A particular quantization of the k = 0 FLRW loop cosmological model yields a completely solvable model, known as solvable loop quantum cosmology(sLQC). In this contribution, we consider effective classical theories motivated by sLQC and study their {lambda}-dependence, with a special interest on the limit {lambda}{yields}0 and the role of the evolution parameter in the convergence of such limit.
Brane-world cosmology with black strings
NASA Astrophysics Data System (ADS)
Gergely, László Á.
2006-07-01
We consider the simplest scenario when black strings/cigars penetrate the cosmological brane. As a result, the brane has a Swiss-cheese structure, with Schwarzschild black holes immersed in a Friedmann-Lemaître-Robertson-Walker brane. There is no dark radiation in the model, the cosmological regions of the brane are characterized by a cosmological constant Λ and flat spatial sections. Regardless of the value of Λ, these brane-world universes forever expand and forever decelerate. The totality of source terms in the modified Einstein equation sum up to a dust, establishing a formal equivalence with the general relativistic Einstein-Straus model. However in this brane-world scenario with black strings the evolution of the cosmological fluid strongly depends on Λ. For Λ≤0 it has positive energy density ρ and negative pressure p and at late times it behaves as in the Einstein-Straus model. For (not too high) positive values of Λ the cosmological evolution begins with positive ρ and negative p, but this is followed by an epoch with both ρ and p positive. Eventually, ρ becomes negative, while p stays positive. A similar evolution is present for high positive values of Λ, however in this case the evolution ends in a pressure singularity, accompanied by a regular behavior of the cosmic acceleration. This is a novel type of singularity appearing in brane-worlds.
Dissipative or conservative cosmology with dark energy?
NASA Astrophysics Data System (ADS)
Szydlowski, M.; Hrycyna, O.
2007-12-01
All evolutional paths for all admissible initial conditions of FRW cosmological models with dissipative dust fluid (described by dark matter, baryonic matter and dark energy) are analyzed using dynamical system approach. With that approach, one is able to see how generic the class of solutions leading to the desired property -- acceleration -- is. The theory of dynamical systems also offers a possibility of investigating all possible solutions and their stability with tools of Newtonian mechanics of a particle moving in a 1-dimensional potential which is parameterized by the cosmological scale factor. We demonstrate that flat cosmology with bulk viscosity can be treated as a conservative system with a potential function of the Chaplygin gas type. We also confront viscous models with SNIa observations. The best fitted models are obtained by minimizing the $\\chi^{2}$ function which is illustrated by residuals and $\\chi^{2}$ levels in the space of model independent parameters. The general conclusion is that SNIa data supports the viscous model without the cosmological constant. The obtained values of $\\chi^{2}$ statistic are comparable for both the viscous model and LCDM model. The Bayesian information criteria are used to compare the models with different power law parameterization of viscous effects. Our result of this analysis shows that SNIa data supports viscous cosmology more than the LCDM model if the coefficient in viscosity parameterization is fixed. The Bayes factor is also used to obtain the posterior probability of the model.
Quasars, clusters and cosmology
NASA Astrophysics Data System (ADS)
Dhanda, Neelam
PART A: Acceleration of the Universe and Modified Gravity: We study the power of next-generation galaxy cluster surveys (such as eROSITA and WFXT) in constraining the cosmological parameters and especially the growth history of the Universe, using the information from galaxy cluster redshift and mass-function evolution and from cluster power spectrum. We use the Fisher Matrix formalism to evaluate the potential for the galaxy cluster surveys to make predictions about cosmological parameters like the gravitational growth index gamma. The primary purpose of this study has been to check whether we can rule out one or the other of the underlying gravity theories in light of the present uncertainty of mass-observable relations and their scatter evolution. We found that these surveys will provide better constraints on various cosmological parameters even after we admit a lack of complete knowledge about the galaxy cluster structure, and when we combine the information from the cluster number count redshift and mass evolution with that from the cluster power spectrum. Based on this, we studied the ability of different surveys to constrain the growth history of the Universe. It was found that whereas eROSITA surveys will need strong priors on cluster structure evolution to conclusively rule out one or the other of the two gravity models, General Relativity and DGP Braneworld Gravity; WFXT surveys do hold the special promise of differentiating growth and telling us whether it is GR or not, with its wide-field survey having the ability to say so even with 99% confidence. PART B: Chemical Evolution in Quasars: We studied chemical evolution in the broad emission line region (BELR) of nitrogen rich quasars drawn from the SDSS Quasar Catalogue IV. Using tools of emission-line spectroscopy, we made detailed abundance measurements of ˜ 40 quasars and estimated their metallicities using the line-intensity ratio method. It was found that quasars with strong nitrogen lines are
Computational Cosmology at the Bleeding Edge
NASA Astrophysics Data System (ADS)
Habib, Salman
2013-04-01
Large-area sky surveys are providing a wealth of cosmological information to address the mysteries of dark energy and dark matter. Observational probes based on tracking the formation of cosmic structure are essential to this effort, and rely crucially on N-body simulations that solve the Vlasov-Poisson equation in an expanding Universe. As statistical errors from survey observations continue to shrink, and cosmological probes increase in number and complexity, simulations are entering a new regime in their use as tools for scientific inference. Changes in supercomputer architectures provide another rationale for developing new parallel simulation and analysis capabilities that can scale to computational concurrency levels measured in the millions to billions. In this talk I will outline the motivations behind the development of the HACC (Hardware/Hybrid Accelerated Cosmology Code) extreme-scale cosmological simulation framework and describe its essential features. By exploiting a novel algorithmic structure that allows flexible tuning across diverse computer architectures, including accelerated and many-core systems, HACC has attained a performance of 14 PFlops on the IBM BG/Q Sequoia system at 69% of peak, using more than 1.5 million cores.
McAllister, Liam P.; Silverstein, Eva
2007-10-22
We give an overview of the status of string cosmology. We explain the motivation for the subject, outline the main problems, and assess some of the proposed solutions. Our focus is on those aspects of cosmology that benefit from the structure of an ultraviolet-complete theory.
Cosmological Implications of Geometrothermodynamics
NASA Astrophysics Data System (ADS)
Luongo, O.; Quevedo, H.
2015-01-01
We use the formalism of Geometrothermodynamics to derive a series of fundamental equations for thermodynamic systems. It is shown that all these fundamental equations can be used in the context of relativistic cosmology to derive diverse scenarios which include the standard cosmological model, a unified model for dark energy and dark matter, and an effective inflationary model.
Klebanov, I.; Susskind, L.
1988-10-01
We review Coleman's wormhole mechanism for the vanishing of the cosmological constant. We find a discouraging result that wormholes much bigger than the Planck size are generated. We also consider the implications of the wormhole theory for cosmology. 7 refs., 2 figs.
NASA Astrophysics Data System (ADS)
Lusso, Elisabeta
2016-10-01
I will review previous methods that have tried to employ active galactic nuclei to measure cosmological parameters. I will introduce a novel technique able to test the cosmological model using quasars as “standard candles” by employing the non- linear relation between their intrinsic UV and X-ray emission as an absolute distance indicator.
Exploring bouncing cosmologies with cosmological surveys
NASA Astrophysics Data System (ADS)
Cai, Yi-Fu
2014-08-01
From recent observational data two significant directions have been made in the field of theoretical cosmology recently. First, we are now able to make use of present observations, such as the Planck and BICEP2 data, to examine theoretical predictions from the standard inflationary ΛCDM which were made decades of years ago. Second, we can search for new cosmological signatures as a way to explore physics beyond the standard cosmic paradigm. In particular, a subset of early universe models admit a nonsingular bouncing solution that attempts to address the issue of the big bang singularity. These models have achieved a series of considerable developments in recent years, in particular in their perturbative frameworks, which made brand-new predictions of cosmological signatures that could be visible in current and forthcoming observations. Herein we present two representative paradigms of early universe physics. The first is the reputed new matter (or matter-ekpyrotic) bounce scenario in which the universe starts with a matter-dominated contraction phase and transitions into an ekpyrotic phase. In the setting of this paradigm, we have proposed some possible mechanisms of generating a red tilt for primordial curvature perturbations and confront the general predictions with recent cosmological observations. The second is the matter-bounce inflation scenario which can be viewed as an extension of inflationary cosmology with a matter contraction before inflation. We present a class of possible model constructions and review the implications on the current CMB experiments. Lastly a review of significant achievements of these paradigms beyond the inflationary ΛCDM model is made, which is expected to shed new light on the future direction of observational cosmology.
NASA Astrophysics Data System (ADS)
Tseytlin, A. A.; Vafa, C.
1992-03-01
Aspects of string cosmology for critical and non-critical strings are discussed emphasizing the necessity to account for the dilaton dynamics for a proper incorporation of ``large-small'' duality. This drastically modifies the intuition one has with Einstein's gravity. For example winding modes, even though contributing to the energy density, oppose expansion and if not annihilated will stop the expansion. Moreover we find that the radiation dominated era of the standard cosmology emerges quite naturally in string cosmology. Our analysis of non-critical string cosmology provides a reinterpretation of the (universal cover of the) recently studied two-dimensional black hole solution as a conformal realization of cosmological solutions found previously by Mueller. Supported in part by Packard Foundation and NSF grants PHY-89-57162 and PHY-87-14654.
Cosmology and particle physics
NASA Technical Reports Server (NTRS)
Turner, Michael S.
1988-01-01
The interplay between cosmology and elementary particle physics is discussed. The standard cosmology is reviewed, concentrating on primordial nucleosynthesis and discussing how the standard cosmology has been used to place constraints on the properties of various particles. Baryogenesis is discussed, showing how a scenario in which the B-, C-, and CP-violating interactions in GUTs provide a dynamical explanation for the predominance of matter over antimatter and for the present baryon-to-photon ratio. It is shown how the very early dynamical evolution of a very weakly coupled scalar field which is initially displaced from the minimum of its potential may explain a handful of very fundamental cosmological facts which are not explained by the standard cosmology.
Cosmology and particle physics
NASA Technical Reports Server (NTRS)
Turner, Michael S.
1988-01-01
The interplay between cosmology and elementary particle physics is discussed. The standard cosmology is reviewed, concentrating on primordial nucleosynthesis and discussing how the standard cosmology has been used to place constraints on the properties of various particles. Baryogenesis is discussed, showing how a scenario in which the B-, C-, and CP-violating interactions in GUTs provide a dynamical explanation for the predominance of matter over antimatter and for the present baryon-to-photon ratio. It is shown how the very early dynamical evolution of a very weakly coupled scalar field which is initially displaced from the minimum of its potential may explain a handful of very fundamental cosmological facts which are not explained by the standard cosmology.
Testing loop quantum cosmology
NASA Astrophysics Data System (ADS)
Wilson-Ewing, Edward
2017-03-01
Loop quantum cosmology predicts that quantum gravity effects resolve the big-bang singularity and replace it by a cosmic bounce. Furthermore, loop quantum cosmology can also modify the form of primordial cosmological perturbations, for example by reducing power at large scales in inflationary models or by suppressing the tensor-to-scalar ratio in the matter bounce scenario; these two effects are potential observational tests for loop quantum cosmology. In this article, I review these predictions and others, and also briefly discuss three open problems in loop quantum cosmology: its relation to loop quantum gravity, the trans-Planckian problem, and a possible transition from a Lorentzian to a Euclidean space-time around the bounce point.
Exact scalar-tensor cosmological models
NASA Astrophysics Data System (ADS)
Belinchón, J. A.; Harko, T.; Mak, M. K.
Scalar-tensor gravitational theories are important extensions of standard general relativity, which can explain both the initial inflationary evolution, as well as the late accelerating expansion of the universe. In the present paper, we investigate the cosmological solution of a scalar-tensor gravitational theory, in which the scalar field ϕ couples to the geometry via an arbitrary function F(ϕ). The kinetic energy of the scalar field as well as its self-interaction potential V (ϕ) are also included in the gravitational action. By using a standard mathematical procedure, the Lie group approach, and Noether symmetry techniques, we obtain several exact solutions of the gravitational field equations describing the time evolutions of a flat Friedman-Robertson-Walker universe in the framework of the scalar-tensor gravity. The obtained solutions can describe both accelerating and decelerating phases during the cosmological expansion of the universe.
Creutz, M.
1984-01-01
After reviewing some recent developments in supercomputer access, the author discusses a few areas where perturbation theory and lattice gauge simulations make contact. The author concludes with a brief discussion of a deterministic dynamics for the Ising model. This may be useful for numerical studies of nonequilibrium phenomena. 13 references.
Scaling FFAG accelerator for muon acceleration
Lagrange, JB.; Planche, T.; Mori, Y.
2011-10-06
Recent developments in scaling fixed field alternating gradient (FFAG) accelerators have opened new ways for lattice design, with straight sections, and insertions like dispersion suppressors. Such principles and matching issues are detailed in this paper. An application of these new concepts is presented to overcome problems in the PRISM project.
Scaling FFAG accelerator for muon acceleration
NASA Astrophysics Data System (ADS)
Lagrange, JB.; Planche, T.; Mori, Y.
2011-10-01
Recent developments in scaling fixed field alternating gradient (FFAG) accelerators have opened new ways for lattice design, with straight sections, and insertions like dispersion suppressors. Such principles and matching issues are detailed in this paper. An application of these new concepts is presented to overcome problems in the PRISM project.
Stability analysis in tachyonic potential chameleon cosmology
Farajollahi, H.; Salehi, A.; Tayebi, F.; Ravanpak, A. E-mail: a.salehi@guilan.ac.ir E-mail: aravanpak@guilan.ac.ir
2011-05-01
We study general properties of attractors for tachyonic potential chameleon scalar-field model which possess cosmological scaling solutions. An analytic formulation is given to obtain fixed points with a discussion on their stability. The model predicts a dynamical equation of state parameter with phantom crossing behavior for an accelerating universe. We constrain the parameters of the model by best fitting with the recent data-sets from supernovae and simulated data points for redshift drift experiment generated by Monte Carlo simulations.
Phantom field dynamics in loop quantum cosmology
Samart, Daris; Gumjudpai, Burin
2007-08-15
We consider a dynamical system of phantom scalar field under exponential potential in the background of loop quantum cosmology. In our analysis, there is neither stable node nor repeller unstable node but only two saddle points, hence no big rip singularity. Physical solutions always possess potential energy greater than the magnitude of the negative kinetic energy. We found that the universe bounces after accelerating even in the domination of the phantom field. After bouncing, the universe finally enters the oscillatory regime.
Cosmological perturbations in teleparallel Loop Quantum Cosmology
NASA Astrophysics Data System (ADS)
Haro, Jaime
2013-11-01
Cosmological perturbations in Loop Quantum Cosmology (LQC) are usually studied incorporating either holonomy corrections, where the Ashtekar connection is replaced by a suitable sinus function in order to have a well-defined quantum analogue, or inverse-volume corrections coming from the eigenvalues of the inverse-volume operator. In this paper we will develop an alternative approach to calculate cosmological perturbations in LQC based on the fact that, holonomy corrected LQC in the flat Friedmann-Lemaître-Robertson-Walker (FLRW) geometry could be also obtained as a particular case of teleparallel F(T) gravity (teleparallel LQC). The main idea of our approach is to mix the simple bounce provided by holonomy corrections in LQC with the non-singular perturbation equations given by F(T) gravity, in order to obtain a matter bounce scenario as a viable alternative to slow-roll inflation. In our study, we have obtained an scale invariant power spectrum of cosmological perturbations. However, the ratio of tensor to scalar perturbations is of order 1, which does not agree with the current observations. For this reason, we suggest a model where a transition from the matter domination to a quasi de Sitter phase is produced in order to enhance the scalar power spectrum.
Newtonian and Relativistic Cosmologies
NASA Astrophysics Data System (ADS)
Green, Stephen; Wald, Robert
2012-03-01
Cosmological N-body simulations are now being performed using Newtonian gravity on scales larger than the Hubble radius. It is known that a uniformly expanding, homogeneous ball of dust in Newtonian gravity satisfies the Friedmann equations, and also that a correspondence between Newtonian and relativistic dust cosmologies holds in linearized perturbation theory. Nevertheless, it is not obvious that Newtonian gravity can provide a good global description of an inhomogeneous cosmology with significant nonlinear dynamical behavior at small scales. We investigate this issue in light of a perturbative framework that we have recently developed. We propose a straightforward dictionary---exact at the linearized level---that maps Newtonian dust cosmologies into GR dust cosmologies, and we use our ordering scheme to determine the degree to which the resulting metric and matter distribution solve Einstein's equation. We then find additional corrections needed to satisfy Einstein's equation to ``order 1'' at small scales and to ``order ɛ'' at large scales. We expect that, in realistic Newtonian cosmologies, these additional corrections will be very small; if so, this should provide strong justification for the use of Newtonian simulations to describe GR cosmologies.
Kehagias, A.; Riotto, A.
2016-05-25
Symmetries play an interesting role in cosmology. They are useful in characterizing the cosmological perturbations generated during inflation and lead to consistency relations involving the soft limit of the statistical correlators of large-scale structure dark matter and galaxies overdensities. On the other hand, in observational cosmology the carriers of the information about these large-scale statistical distributions are light rays traveling on null geodesics. Motivated by this simple consideration, we study the structure of null infinity and the associated BMS symmetry in a cosmological setting. For decelerating Friedmann-Robertson-Walker backgrounds, for which future null infinity exists, we find that the BMS transformations which leaves the asymptotic metric invariant to leading order. Contrary to the asymptotic flat case, the BMS transformations in cosmology generate Goldstone modes corresponding to scalar, vector and tensor degrees of freedom which may exist at null infinity and perturb the asymptotic data. Therefore, BMS transformations generate physically inequivalent vacua as they populate the universe at null infinity with these physical degrees of freedom. We also discuss the gravitational memory effect when cosmological expansion is taken into account. In this case, there are extra contribution to the gravitational memory due to the tail of the retarded Green functions which are supported not only on the light-cone, but also in its interior. The gravitational memory effect can be understood also from an asymptotic point of view as a transition among cosmological BMS-related vacua.
NASA Astrophysics Data System (ADS)
Kehagias, A.; Riotto, A.
2016-05-01
Symmetries play an interesting role in cosmology. They are useful in characterizing the cosmological perturbations generated during inflation and lead to consistency relations involving the soft limit of the statistical correlators of large-scale structure dark matter and galaxies overdensities. On the other hand, in observational cosmology the carriers of the information about these large-scale statistical distributions are light rays traveling on null geodesics. Motivated by this simple consideration, we study the structure of null infinity and the associated BMS symmetry in a cosmological setting. For decelerating Friedmann-Robertson-Walker backgrounds, for which future null infinity exists, we find that the BMS transformations which leaves the asymptotic metric invariant to leading order. Contrary to the asymptotic flat case, the BMS transformations in cosmology generate Goldstone modes corresponding to scalar, vector and tensor degrees of freedom which may exist at null infinity and perturb the asymptotic data. Therefore, BMS transformations generate physically inequivalent vacua as they populate the universe at null infinity with these physical degrees of freedom. We also discuss the gravitational memory effect when cosmological expansion is taken into account. In this case, there are extra contribution to the gravitational memory due to the tail of the retarded Green functions which are supported not only on the light-cone, but also in its interior. The gravitational memory effect can be understood also from an asymptotic point of view as a transition among cosmological BMS-related vacua.
Bouncing Cosmologies: Progress and Problems
NASA Astrophysics Data System (ADS)
Brandenberger, Robert; Peter, Patrick
2017-02-01
We review the status of bouncing cosmologies as alternatives to cosmological inflation for providing a description of the very early universe, and a source for the cosmological perturbations which are observed today. We focus on the motivation for considering bouncing cosmologies, the origin of fluctuations in these models, and the challenges which various implementations face.
Cosmic inhomogeneities and averaged cosmological dynamics.
Paranjape, Aseem; Singh, T P
2008-10-31
If general relativity (GR) describes the expansion of the Universe, the observed cosmic acceleration implies the existence of a "dark energy." However, while the Universe is on average homogeneous on large scales, it is inhomogeneous on smaller scales. While GR governs the dynamics of the inhomogeneous Universe, the averaged homogeneous Universe obeys modified Einstein equations. Can such modifications alone explain the acceleration? For a simple generic model with realistic initial conditions, we show the answer to be "no." Averaging effects negligibly influence the cosmological dynamics.
Mesoamerican Cosmology: Recent Finds
NASA Astrophysics Data System (ADS)
Trejo, J. G.
2009-08-01
The archaeological and ethnological research carried out in the last decades in Mesoamerica has allowed to know better diverse topics of the cosmology in regions little studied till now. Though one can distinguish a common substratum from the Mesoamerican living together throughout many centuries, the cultural local peculiarities frequently seem to dominate the message expressed in the Prehispanic art. In this work we present cosmological ideas from Olmec and Huaxtec regions which show distinctive features but at the same time suggest an obvious unity concerning calendrical concepts. The previous thing demonstrates clearly the richness of alternatives that followed the Mesoamerican cosmological thought.
Hamiltonian cosmology of bigravity
NASA Astrophysics Data System (ADS)
Soloviev, V. O.
2017-03-01
This article is written as a review of the Hamiltonian formalism for the bigravity with de Rham-Gabadadze-Tolley (dRGT) potential, and also of applications of this formalism to the derivation of the background cosmological equations. It is demonstrated that the cosmological scenarios are close to the standard ΛCDM model, but they also uncover the dynamical behavior of the cosmological term. This term arises in bigravity regardless on the choice of the dRGT potential parameters, and its scale is given by the graviton mass. Various matter couplings are considered.
Carol J. Johnstone and Shane Koscielniak
2002-09-30
When large transverse and longitudinal emittances are to be transported through a circular machine, extremely rapid acceleration holds the advantage that the beam becomes immune to nonlinear resonances because there is insufficient time for amplitudes to build up. Uncooled muon beams exhibit large emittances and require fast acceleration to avoid decay losses and would benefit from this style of acceleration. The approach here employs a fixed-field alternating gradient or FFAG magnet structure and a fixed frequency acceleration system. Acceptance is enhanced by the use only of linear lattice elements, and fixed-frequency rf enables the use of cavities with large shunt resistance and quality factor.
Computing tools for accelerator design
Parsa, Z.
1986-06-01
An algorithm has been developed that calculates and obtains information about nonlinear contributions in accelerators. The comparison of the results obtained from this program ''NONLIN'' and HARMON is discussed and illustrated for the SSC-CDR clustered lattices.
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.
Vector fields in multidimensional cosmology
NASA Astrophysics Data System (ADS)
Meierovich, Boris E.
2011-09-01
Vector fields in the expanding Universe are considered within the multidimensional theory of general relativity. Vector fields in general relativity form a three-parametric variety. Our consideration includes the fields with a nonzero covariant divergence. Depending on the relations between the particular parameters and the symmetry of a problem, the vector fields can be longitudinal and/or transverse, ultrarelativistic (i.e. massless) or nonrelativistic (massive), and so on. The longitudinal and transverse vector fields are considered separately in detail in the background of the de Sitter cosmological metric. In most cases the field equations reduce to Bessel equations, and their temporal evolution is analyzed analytically. The energy-momentum tensor of the most simple zero-mass longitudinal vector fields enters the Einstein equations as an additive to the cosmological constant. In this case the de Sitter metric is the exact solution of the Einstein equations. Hence, the most simple zero-mass longitudinal vector field pretends to be an adequate tool for macroscopic description of dark energy as a source of the expansion of the Universe at a constant rate. The zero-mass vector field does not vanish in the process of expansion. On the contrary, massive fields vanish with time. Though their amplitude is falling down, the massive fields make the expansion accelerated.
Growth of matter perturbation in quintessence cosmology
NASA Astrophysics Data System (ADS)
Mulki, Fargiza A. M.; Wulandari, Hesti R. T.
2017-01-01
Big bang theory states that universe emerged from singularity with very high temperature and density, then expands homogeneously and isotropically. This theory gives rise standard cosmological principle which declares that universe is homogeneous and isotropic on large scales. However, universe is not perfectly homogeneous and isotropic on small scales. There exist structures starting from clusters, galaxies even to stars and planetary system scales. Cosmological perturbation theory is a fundamental theory that explains the origin of structures. According to this theory, the structures can be regarded as small perturbations in the early universe, which evolves as the universe expands. In addition to the problem of inhomogeneities of the universe, observations of supernovae Ia suggest that our universe is being accelerated. Various models of dark energy have been proposed to explain cosmic acceleration, one of them is cosmological constant. Because of several problems arise from cosmological constant, the alternative models have been proposed, one of these models is quintessence. We reconstruct growth of structure model following quintessence scenario at several epochs of the universe, which is specified by the effective equation of state parameters for each stage. Discussion begins with the dynamics of quintessence, in which exponential potential is analytically derived, which leads to various conditions of the universe. We then focus on scaling and quintessence dominated solutions. Subsequently, we review the basics of cosmological perturbation theory and derive formulas to investigate how matter perturbation evolves with time in subhorizon scales which leads to structure formation, and also analyze the influence of quintessence to the structure formation. From analytical exploration, we obtain the growth rate of matter perturbation and the existence of quintessence as a dark energy that slows down the growth of structure formation of the universe.
NASA Technical Reports Server (NTRS)
Wilczek, Frank
1987-01-01
A simple heuristic proof of the Nielsen-Ninomaya theorem is given. A method is proposed whereby the multiplication of fermion species on a lattice is reduced to the minimal doubling, in any dimension, with retention of appropriate chiral symmetries. Also, it is suggested that use of spatially thinned fermion fields is likely to be a useful and appropriate approximation in QCD - in any case, it is a self-checking one.
Introduction to Microwave Linear [Accelerators
Whittum, David H
1999-01-04
The elements of microwave linear accelerators are introduced starting with the principles of acceleration and accelerating structures. Considerations for microwave structure modeling and design are developed from an elementary point of view. Basic elements of microwave electronics are described for application to the accelerator circuit and instrumentation. Concepts of beam physics are explored together with examples of common beamline instruments. Charged particle optics and lattice diagnostics are introduced. Considerations for fixed-target and colliding-beam experimentation are summarized.
Cosmological Inflation: A Personal Perspective
NASA Technical Reports Server (NTRS)
Kazanas, Demosthenes
2007-01-01
We present a review of the sequence of events/circumstances that led to the introduction of interplay between the physics associated with phase transitions in the early universe and their effects on its dynamics of expansion with the goal of resolving the horizon problem that it has since become known as Cosmological Inflation. We then provide a brief review of the fundamentals and the solutions of a theory of gravity based on local scale invariance, known as Weyl gravity that have been elaborated by the presenter and his collaborator P. D. Mannheim. We point out that this theory provides from first principles for a characteristic universal acceleration, whose value appears to be in agreement with observations across a vast range of length scales in the universe.
NASA Astrophysics Data System (ADS)
Ellis, George F. R.
2003-01-01
This article gives a brief survey of cosmology to the present day, and then explores a positive but critical approach, looking in turn at issues arising in observations, geometry, and physics, and at the foundational (philosophical) issues that necessarily arise.
Baryogenesis and cosmological antimatter
Dolgov, Alexander D.
2009-04-20
Possible mechanisms of baryogenesis are reviewed. Special attention is payed to those which allow for creation of astronomically significant domains or objects consisting of antimatter. Observational manifestations of cosmological antimatter are discussed.
The cosmological constant problem
Dolgov, A.D.
1989-05-01
A review of the cosmological term problem is presented. Baby universe model and the compensating field model are discussed. The importance of more accurate data on the Hubble constant and the Universe age is stressed. 18 refs.
NASA Astrophysics Data System (ADS)
Nelson, William
2014-03-01
I will discuss my transition from Quantum Gravity and Cosmology to the world of consulting and describe the differences and similarities between academia and industry. I will give some dos and don'ts for industry interviews and jobs searches.
NASA Astrophysics Data System (ADS)
Turner, Michael S.
1999-03-01
For two decades the hot big-bang model as been referred to as the standard cosmology - and for good reason. For just as long cosmologists have known that there are fundamental questions that are not answered by the standard cosmology and point to a grander theory. The best candidate for that grander theory is inflation + cold dark matter. It holds that the Universe is flat, that slowly moving elementary particles left over from the earliest moments provide the cosmic infrastructure, and that the primeval density inhomogeneities that seed all the structure arose from quantum fluctuations. There is now prima facie evidence that supports two basic tenets of this paradigm. An avalanche of high-quality cosmological observations will soon make this case stronger or will break it. Key questions remain to be answered; foremost among them are: identification and detection of the cold dark matter particles and elucidation of the dark-energy component. These are exciting times in cosmology!
A simple cosmology with a varying fine structure constant.
Sandvik, Håvard Bunes; Barrow, John D; Magueijo, João
2002-01-21
We investigate the cosmological consequences of a theory in which the electric charge e can vary. In this theory the fine structure "constant," alpha, remains almost constant in the radiation era, undergoes a small increase in the matter era, but approaches a constant value when the universe starts accelerating because of a positive cosmological constant. This model satisfies geonuclear, nucleosynthesis, and cosmic microwave background constraints on time variation in alpha, while fitting the observed accelerating Universe and evidence for small alpha variations in quasar spectra. It also places specific restrictions on the nature of the dark matter. Further tests, involving stellar spectra and Eötvös experiments, are proposed.
Lindquist-Wheeler formulation of lattice universes
NASA Astrophysics Data System (ADS)
Liu, Rex G.
2015-09-01
This paper examines the properties of "lattice universes" wherein point masses are arranged in a regular lattice on spacelike hypersurfaces; open, flat, and closed universes are considered. The universes are modeled using the Lindquist-Wheeler (LW) approximation scheme, which approximates the space-time in each lattice cell by Schwarzschild geometry. Extending Lindquist and Wheeler's work, we derive cosmological scale factors describing the evolution of all three types of universes, and we use these scale factors to show that the universes' dynamics strongly resemble those of Friedmann-Lemaître-Robertson-Walker (FLRW) universes. In particular, we use the scale factors to make more salient the resemblance between Clifton and Ferreira's Friedmann-like equations for the LW models and the actual Friedmann equations of FLRW space-times. Cosmological redshifts for such universes are then determined numerically, using a modification of Clifton and Ferreira's approach; the redshifts are found to closely resemble their FLRW counterparts, though with certain differences attributable to the "lumpiness" in the underlying matter content. Most notably, the LW redshifts can differ from their FLRW counterparts by as much as 30%, even though they increase linearly with FLRW redshifts, and they exhibit a nonzero integrated Sachs-Wolfe effect, something which would not be possible in matter-dominated FLRW universes without a cosmological constant.
Cosmology: A research briefing
NASA Technical Reports Server (NTRS)
1995-01-01
As part of its effort to update topics dealt with in the 1986 decadal physics survey, the Board on Physics and Astronomy of the National Research Council (NRC) formed a Panel on Cosmology. The Panel produced this report, intended to be accessible to science policymakers and nonscientists. The chapters include an overview ('What Is Cosmology?'), a discussion of cosmic microwave background radiation, the large-scale structure of the universe, the distant universe, and physics of the early universe.
Fernandez-Jambrina, L.
2010-12-15
In this paper we characterize barotropic index singularities of homogeneous isotropic cosmological models [M. P. Dabrowski and T. Denkiewicz, Phys. Rev. D 79, 063521 (2009).]. They are shown to appear in cosmologies for which the scale factor is analytical with a Taylor series in which the linear and quadratic terms are absent. Though the barotropic index of the perfect fluid is singular, the singularities are weak, as it happens for other models for which the density and the pressure are regular.
Classification of cosmological milestones
Fernandez-Jambrina, L.; Lazkoz, Ruth
2006-09-15
In this paper causal geodesic completeness of Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological models is analyzed in terms of generalized power expansions of the scale factor in coordinate time. The strength of the found singularities is discussed following the usual definitions due to Tipler and Krolak. It is shown that while classical cosmological models are both timelike and lightlike geodesically incomplete, certain observationally allowed models which have been proposed recently are lightlike geodesically complete.
Foundations of modern cosmology
NASA Astrophysics Data System (ADS)
Hawley, John F.; Holcomb, Katherine A.
2005-07-01
Recent discoveries in astronomy, especially those made with data collected by satellites such as the Hubble Space Telescope and the Wilkinson Microwave Anisotropy Probe, have revolutionized the science of cosmology. These new observations offer the possibility that some long-standing mysteries in cosmology might be answered, including such fundamental questions as the ultimate fate of the universe. Foundations of modern cosmology provides an accessible, thorough and descriptive introduction to the physical basis for modern cosmological theory, from the big bang to a distant future dominated by dark energy. This second edition includes the latest observational results and provides the detailed background material necessary to understand their implications, with a focus on the specific model supported by these observations, the concordance model. Consistent with the book's title, emphasis is given to the scientific framework for cosmology, particularly the basics concepts of physics that underlie modern theories of relativity and cosmology; the importance of data and observations is stressed throughout. The book sketches the historical background of cosmology, and provides a review of the relevant basic physics and astronomy. After this introduction, both special and general relativity are treated, before proceeding to an in-depth discussion of the big bang theory and physics of the early universe. The book includes current research areas, including dark matter and structure formation, dark energy, the inflationary universe, and quantum cosmology. The authors' website (http://www.astro.virginia.edu/~jh8h/Foundations) offers a wealth of supplemental information, including questions and answers, references to other sources, and updates on the latest discoveries.
Cosmological phase transitions
Kolb, E.W. |
1993-10-01
If modern ideas about the role of spontaneous symmetry breaking in fundamental physics are correct, then the Universe should have undergone a series of phase transitions early in its history. The study of cosmological phase transitions has become an important aspect of early-Universe cosmology. In this lecture I review some very recent work on three aspects of phase transitions: the electroweak transition, texture, and axions.
On cosmic acceleration without dark energy
Kolb, E.W.; Matarrese, S.; Riotto, A.; /INFN, Padua
2005-06-01
We elaborate on the proposal that the observed acceleration of the Universe is the result of the backreaction of cosmological perturbations, rather than the effect of a negative-pressure dark energy fluid or a modification of general relativity. Through the effective Friedmann equations describing an inhomogeneous Universe after smoothing, we demonstrate that acceleration in our local Hubble patch is possible even if fluid elements do not individually undergo accelerated expansion. This invalidates the no-go theorem that there can be no acceleration in our local Hubble patch if the Universe only contains irrotational dust. We then study perturbatively the time behavior of general-relativistic cosmological perturbations, applying, where possible, the renormalization group to regularize the dynamics. We show that an instability occurs in the perturbative expansion involving sub-Hubble modes, which indicates that acceleration in our Hubble patch may originate from the backreaction of cosmological perturbations on observable scales.
Cosmological Models and Stability
NASA Astrophysics Data System (ADS)
Andersson, Lars
Principles in the form of heuristic guidelines or generally accepted dogma play an important role in the development of physical theories. In particular, philosophical considerations and principles figure prominently in the work of Albert Einstein. As mentioned in the talk by Jiří Bičák at this conference, Einstein formulated the equivalence principle, an essential step on the road to general relativity, during his time in Prague 1911-1912. In this talk, I would like to discuss some aspects of cosmological models. As cosmology is an area of physics where "principles" such as the "cosmological principle" or the "Copernican principle" play a prominent role in motivating the class of models which form part of the current standard model, I will start by comparing the role of the equivalence principle to that of the principles used in cosmology. I will then briefly describe the standard model of cosmology to give a perspective on some mathematical problems and conjectures on cosmological models, which are discussed in the later part of this paper.
Bag, Satadru; Sahni, Varun; Shtanov, Yuri; Unnikrishnan, Sanil E-mail: varun@iucaa.ernet.in E-mail: sanil@lnmiit.ac.in
2014-07-01
We explore the possibility of emergent cosmology using the effective potential formalism. We discover new models of emergent cosmology which satisfy the constraints posed by the cosmic microwave background (CMB). We demonstrate that, within the framework of modified gravity, the emergent scenario can arise in a universe which is spatially open/closed. By contrast, in general relativity (GR) emergent cosmology arises from a spatially closed past-eternal Einstein Static Universe (ESU). In GR the ESU is unstable, which creates fine tuning problems for emergent cosmology. However, modified gravity models including Braneworld models, Loop Quantum Cosmology (LQC) and Asymptotically Free Gravity result in a stable ESU. Consequently, in these models emergent cosmology arises from a larger class of initial conditions including those in which the universe eternally oscillates about the ESU fixed point. We demonstrate that such an oscillating universe is necessarily accompanied by graviton production. For a large region in parameter space graviton production is enhanced through a parametric resonance, casting serious doubts as to whether this emergent scenario can be past-eternal.
Building cosmological frozen stars
NASA Astrophysics Data System (ADS)
Kastor, David; Traschen, Jennie
2017-02-01
Janis-Newman-Winicour (JNW) solutions generalize Schwarzschild to include a massless scalar field. While they share the familiar infinite redshift feature of Schwarzschild, they suffer from the presence of naked singularities. Cosmological versions of JNW spacetimes were discovered some years ago, in the most general case, by Fonarev. Fonarev solutions are also plagued by naked singularities, but have the virtue, unlike e.g. Schwarzschild-deSitter, of being dynamical. Given that exact dynamical cosmological black hole solutions are scarce, Fonarev solutions merit further study. We show how Fonarev solutions can be obtained via generalized dimensional reduction from simpler static vacuum solutions. These results may lead towards constructions of actual dynamical cosmological black holes. In particular, we note that cosmological versions of extremal charged dilaton black holes are known. JNW spacetimes represent a different limiting case of the family of charged dilaton black holes, which have been important in the context of string theory, and better understanding their cosmological versions of JNW spacetimes thus provides a second data point towards finding cosmological versions of the entire family.
BOOK REVIEW: Observational Cosmology Observational Cosmology
NASA Astrophysics Data System (ADS)
Howell, Dale Andrew
2013-04-01
Observational Cosmology by Stephen Serjeant fills a niche that was underserved in the textbook market: an up-to-date, thorough cosmology textbook focused on observations, aimed at advanced undergraduates. Not everything about the book is perfect - some subjects get short shrift, in some cases jargon dominates, and there are too few exercises. Still, on the whole, the book is a welcome addition. For decades, the classic textbooks of cosmology have focused on theory. But for every Sunyaev-Zel'dovich effect there is a Butcher-Oemler effect; there are as many cosmological phenomena established by observations, and only explained later by theory, as there were predicted by theory and confirmed by observations. In fact, in the last decade, there has been an explosion of new cosmological findings driven by observations. Some are so new that you won't find them mentioned in books just a few years old. So it is not just refreshing to see a book that reflects the new realities of cosmology, it is vital, if students are to truly stay up on a field that has widened in scope considerably. Observational Cosmology is filled with full-color images, and graphs from the latest experiments. How exciting it is that we live in an era where satellites and large experiments have gathered so much data to reveal astounding details about the origin of the universe and its evolution. To have all the latest data gathered together and explained in one book will be a revelation to students. In fact, at times it was to me. I've picked up modern cosmological knowledge through a patchwork of reading papers, going to colloquia, and serving on grant and telescope allocation panels. To go back and see them explained from square one, and summarized succinctly, filled in quite a few gaps in my own knowledge and corrected a few misconceptions I'd acquired along the way. To make room for all these graphs and observational details, a few things had to be left out. For one, there are few derivations
Cosmology with cosmic shear observations: a review.
Kilbinger, Martin
2015-07-01
Cosmic shear is the distortion of images of distant galaxies due to weak gravitational lensing by the large-scale structure in the Universe. Such images are coherently deformed by the tidal field of matter inhomogeneities along the line of sight. By measuring galaxy shape correlations, we can study the properties and evolution of structure on large scales as well as the geometry of the Universe. Thus, cosmic shear has become a powerful probe into the nature of dark matter and the origin of the current accelerated expansion of the Universe. Over the last years, cosmic shear has evolved into a reliable and robust cosmological probe, providing measurements of the expansion history of the Universe and the growth of its structure. We review here the principles of weak gravitational lensing and show how cosmic shear is interpreted in a cosmological context. Then we give an overview of weak-lensing measurements, and present the main observational cosmic-shear results since it was discovered 15 years ago, as well as the implications for cosmology. We then conclude with an outlook on the various future surveys and missions, for which cosmic shear is one of the main science drivers, and discuss promising new weak cosmological lensing techniques for future observations.
The Cosmology Distinction Course in NSW
NASA Astrophysics Data System (ADS)
Hollow, Robert P.; McAdam, W. B.; O'Byrne, J.; White, Graeme L.; Holmes, R.; Webb, J. K.; Allen, L. R.; Zealey, W. J.; Hafner, R.
1994-04-01
The Cosmology Distinction Course is a new one-year course to be introduced for Year 12 candidates in the 1994 Higher School Certificate (HSC) examinations in NSW. It is one of three challenging courses of study that will enrich the HSC for talented students who accelerate and complete part of the HSC one year early. The courses will be taught through distance learning and will include residential seminars. They will be implemented on behalf of the Board of Studies by Charles Sturt University and the University of New England. The Cosmology Course is organized into nine modules of course work covering historical and social aspects of cosmology, observational techniques, key observatons and the various models developed--Newtonian, de Sitter, Friedmann, Lemaitre, steady-state, quasi-steady-state and big bang. Assessment will be through assignments, exams and a major project. As the first Distinction Course in a scientific area, the Cosmology Course represents an exciting and important educational initiative that needs the cooperation of NSW astronomers and, in return, promises to benefit the astronomical and general scientific community in Australia.
Cosmology in time asymmetric extensions of general relativity
Leon, Genly; Saridakis, Emmanuel N. E-mail: Emmanuel_Saridakis@baylor.edu
2015-11-01
We investigate the cosmological behavior in a universe governed by time asymmetric extensions of general relativity, which is a novel modified gravity based on the addition of new, time-asymmetric, terms on the Hamiltonian framework, in a way that the algebra of constraints and local physics remain unchanged. Nevertheless, at cosmological scales these new terms can have significant effects that can alter the universe evolution, both at early and late times, and the freedom in the choice of the involved modification function makes the scenario able to produce a huge class of cosmological behaviors. For basic ansatzes of modification, we perform a detailed dynamical analysis, extracting the stable late-time solutions. Amongst others, we find that the universe can result in dark-energy dominated, accelerating solutions, even in the absence of an explicit cosmological constant, in which the dark energy can be quintessence-like, phantom-like, or behave as an effective cosmological constant. Moreover, it can result to matter-domination, or to a Big Rip, or experience the sequence from matter to dark energy domination. Additionally, in the case of closed curvature, the universe may experience a cosmological bounce or turnaround, or even cyclic behavior. Finally, these scenarios can easily satisfy the observational and phenomenological requirements. Hence, time asymmetric cosmology can be a good candidate for the description of the universe.
Implications of the Cosmological Constant for Spherically Symmetric Mass Distributions
NASA Astrophysics Data System (ADS)
Zubairi, Omair; Weber, Fridolin
2013-04-01
In recent years, scientists have made the discovery that the expansion rate of the Universe is increasing rather than decreasing. This acceleration leads to an additional term in Albert Einstein's field equations which describe general relativity and is known as the cosmological constant. This work explores the aftermath of a non-vanishing cosmological constant for relativistic spherically symmetric mass distributions, which are susceptible to change against Einstein's field equations. We introduce a stellar structure equation known as the Tolman-Oppenhiemer-Volkoff (TOV) equation modified for a cosmological constant, which is derived from Einstein's modified field equations. We solve this modified TOV equation for these spherically symmetric mass distributions and obtain stellar properties such as mass and radius and investigate changes that may occur depending on the value of the cosmological constant.
The Relation between Cosmological Redshift and Scale Factor for Photons
NASA Astrophysics Data System (ADS)
Tian, Shuxun
2017-09-01
The cosmological constant problem has become one of the most important ones in modern cosmology. In this paper, we try to construct a model that can avoid the cosmological constant problem and have the potential to explain the apparent late-time accelerating expansion of the universe in both luminosity distance and angular diameter distance measurement channels. In our model, the core is to modify the relation between cosmological redshift and scale factor for photons. We point out three ways to test our hypothesis: the supernova time dilation; the gravitational waves and its electromagnetic counterparts emitted by the binary neutron star systems; and the Sandage–Loeb effect. All of this method is feasible now or in the near future.
Observational constraints on late-time {lambda}(t) cosmology
Carneiro, S.; Pigozzo, C.; Dantas, M. A.; Alcaniz, J. S.
2008-04-15
The cosmological constant {lambda}, i.e., the energy density stored in the true vacuum state of all existing fields in the Universe, is the simplest and the most natural possibility to describe the current cosmic acceleration. However, despite its observational successes, such a possibility exacerbates the well-known {lambda} problem, requiring a natural explanation for its small, but nonzero, value. In this paper we study cosmological consequences of a scenario driven by a varying cosmological term, in which the vacuum energy density decays linearly with the Hubble parameter, {lambda}{proportional_to}H. We test the viability of this scenario and study a possible way to distinguish it from the current standard cosmological model by using recent observations of type Ia supernova (Supernova Legacy Survey Collaboration), measurements of the baryonic acoustic oscillation from the Sloan Digital Sky Survey, and the position of the first peak of the cosmic microwave background angular spectrum from the three-year Wilkinson Microwave Anisotropy Probe.
Evolving Lorentzian wormholes supported by phantom matter and cosmological constant
Cataldo, Mauricio; Campo, Sergio del; Minning, Paul; Salgado, Patricio
2009-01-15
In this paper we study the possibility of sustaining an evolving wormhole via exotic matter made of phantom energy in the presence of a cosmological constant. We derive analytical evolving wormhole geometries by supposing that the radial tension of the phantom matter, which is negative to the radial pressure, and the pressure measured in the tangential directions have barotropic equations of state with constant state parameters. In this case the presence of a cosmological constant ensures accelerated expansion of the wormhole configurations. More specifically, for positive cosmological constant we have wormholes which expand forever and, for negative cosmological constant we have wormholes which expand to a maximum value and then recollapse. At spatial infinity the energy density and the pressures of the anisotropic phantom matter threading the wormholes vanish; thus these evolving wormholes are asymptotically vacuum {lambda}-Friedmann models with either open or closed or flat topologies.
Multi-scale gravity and cosmology
Calcagni, Gianluca
2013-12-01
The gravitational dynamics and cosmological implications of three classes of recently introduced multi-scale spacetimes (with, respectively, ordinary, weighted and q-derivatives) are discussed. These spacetimes are non-Riemannian: the metric structure is accompanied by an independent measure-differential structure with the characteristics of a multi-fractal, namely, different dimensionality at different scales and, at ultra-short distances, a discrete symmetry known as discrete scale invariance. Under this minimal paradigm, five general features arise: (a) the big-bang singularity can be replaced by a finite bounce, (b) the cosmological constant problem is reinterpreted, since accelerating phases can be mimicked by the change of geometry with the time scale, without invoking a slowly rolling scalar field, (c) the discreteness of geometry at Planckian scales can leave an observable imprint of logarithmic oscillations in cosmological spectra and (d) give rise to an alternative mechanism to inflation or (e) to a fully analytic model of cyclic mild inflation, where near scale invariance of the perturbation spectrum can be produced without strong acceleration. Various properties of the models and exact dynamical solutions are discussed. In particular, the multi-scale geometry with weighted derivatives is shown to be a Weyl integrable spacetime.
The Accelerator Markup Language and the Universal Accelerator Parser
Sagan, David; Forster, M.; Bates, D.; Wolski, A.; Schmidt, F.; Walker, N.J.; Larrieu, Theodore; Roblin, Yves; Pelaia, T.; Tenenbaum, P.; Woodley, M.; Reiche, S.
2006-07-01
A major obstacle to collaboration on accelerator projects has been the sharing of lattice description files between modeling codes. To address this problem, a lattice description format called Accelerator Markup Language (AML) has been created. AML is based upon the standard eXtensible Markup Language (XML) format; this provides the flexibility for AML to be easily extended to satisfy changing requirements. In conjunction with AML, a software library, called the Universal Accelerator Parser (UAP), is being developed to speed the integration of AML into any program. The UAP is structured to make it relatively straightforward (by giving appropriate specifications) to read and write lattice files in any format. This will allow programs that use the UAP code to read a variety of different file formats. Additionally this will greatly simplify conversion of files from one format to another. Currently, besides AML, the UAP supports the MAD lattice format.
The Accelerator Markup Language and the Universal Accelerator Parser
Sagan, D.; Forster, M.; Bates, D.A.; Wolski, A.; Schmidt, F.; Walker, N.J.; Larrieu, T.; Roblin, Y.; Pelaia, T.; Tenenbaum, P.; Woodley, M.; Reiche, S.; /UCLA
2006-10-06
A major obstacle to collaboration on accelerator projects has been the sharing of lattice description files between modeling codes. To address this problem, a lattice description format called Accelerator Markup Language (AML) has been created. AML is based upon the standard eXtensible Markup Language (XML) format; this provides the flexibility for AML to be easily extended to satisfy changing requirements. In conjunction with AML, a software library, called the Universal Accelerator Parser (UAP), is being developed to speed the integration of AML into any program. The UAP is structured to make it relatively straightforward (by giving appropriate specifications) to read and write lattice files in any format. This will allow programs that use the UAP code to read a variety of different file formats. Additionally, this will greatly simplify conversion of files from one format to another. Currently, besides AML, the UAP supports the MAD lattice format.
Dark energy or local acceleration?
NASA Astrophysics Data System (ADS)
Feoli, Antonio; Benedetto, Elmo
2017-07-01
We find that an observer with a suitable acceleration relative to the frame comoving whit the cosmic fluid, in the context of the FRW decelerating universe, measures the same cosmological redshift as the LambdaCDM model. The estimated value of this acceleration is beta = 1.4x10^-9m/s^2. The problem of a too high peculiar velocity can be solved assuming, for the observer, a sort of helical motion.
Inhomogeneous anisotropic cosmology
NASA Astrophysics Data System (ADS)
Kleban, Matthew; Senatore, Leonardo
2016-10-01
In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with ``flat'' (including toroidal) and ``open'' (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are ``flat'' or ``open''. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with ``flat'' or ``open'' topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.
Inhomogeneous anisotropic cosmology
Kleban, Matthew; Senatore, Leonardo
2016-10-12
In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with “flat” (including toroidal) and “open” (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are “flat” or “open”. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with “flat” or “open” topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.
Thermal tachyacoustic cosmology
NASA Astrophysics Data System (ADS)
Agarwal, Abhineet; Afshordi, Niayesh
2014-08-01
An intriguing possibility that can address pathologies in both early Universe cosmology (i.e. the horizon problem) and quantum gravity (i.e. nonrenormalizability), is that particles at very high energies and/or temperatures could propagate arbitrarily fast. A concrete realization of this possibility for the early Universe is the tachyacoustic (or speedy sound) cosmology, which could also produce a scale-invariant spectrum for scalar cosmological perturbations. Here, we study thermal tachyacoustic cosmology (TTC), i.e. this scenario with thermal initial conditions. We find that a phase transition in the early Universe, around the scale of the grand unified theory (GUT scale; T ˜1015 GeV), during which the speed of sound drops by 25 orders of magnitude within a Hubble time, can fit current CMB observations. We further discuss how production of primordial black holes constrains the cosmological acoustic history, while coupling TTC to Horava-Lifshitz gravity leads to a lower limit on the amplitude of tensor modes (r≳10-3), that are detectable by CMBpol (and might have already been seen by the BICEP-Keck Collaboration).
Inhomogeneous anisotropic cosmology
Kleban, Matthew; Senatore, Leonardo
2016-10-12
In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here in this paper, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with "flat'' (including toroidal) and "open'' (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarilymore » large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are "flat" or "open". Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with "flat'' or "open" topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.« less
Inhomogeneous anisotropic cosmology
Kleban, Matthew; Senatore, Leonardo
2016-10-12
In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here in this paper, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with "flat'' (including toroidal) and "open'' (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are "flat" or "open". Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with "flat'' or "open" topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.
Physical Foundations of Cosmology
NASA Astrophysics Data System (ADS)
Mukhanov, Viatcheslav
2005-11-01
Inflationary cosmology has been developed over the last twenty years to remedy serious shortcomings in the standard hot big bang model of the universe. Taking an original approach, this textbook explains the basis of modern cosmology and shows where the theoretical results come from. The book is divided into two parts; the first deals with the homogeneous and isotropic model of the Universe, the second part discusses how inhomogeneities can explain its structure. Established material such as the inflation and quantum cosmological perturbation are presented in great detail, however the reader is brought to the frontiers of current cosmological research by the discussion of more speculative ideas. An ideal textbook for both advanced students of physics and astrophysics, all of the necessary background material is included in every chapter and no prior knowledge of general relativity and quantum field theory is assumed. Presents detailed derivations of all basic results needed in cosmology, including robust predictions of inflation Contains an analytical treatment of nucleosynthesis, recombination and CMB fluctuations Provides elementary introductions to more advanced topics
Cosmology Solved? Quite Possibly!
NASA Astrophysics Data System (ADS)
Turner, Michael S.
1999-03-01
The discovery of the cosmic microwave background (CMB) in 1964 by Penzias and Wilson led to the establishment of the hot big bang cosmological model some 10 years later. Discoveries made in 1998 may ultimately have as profound an effect on our understanding of the origin and evolution of the universe. Taken at face value, they confirm the basic tenets of inflation + cold dark matter, a bold and expansive theory that addresses all the fundamental questions left unanswered by the hot big bang model and holds that the universe is flat, slowly moving elementary particles provide the cosmic infrastructure, and quantum fluctuations seeded all the structure seen in the universe today. Just as it took a decade to establish the hot big bang model after the discovery of the CMB, it will likely take another 10 years to establish the latest addition to the standard cosmology and make the answer to ``Cosmology solved?'' ``YES!'' Whether or not 1998 proves to be a cosmic milestone, the coming avalanche of high-quality cosmological data promises to make the next 20 years an extremely exciting period for cosmology.
Tracking the SSC test lattices
Leemann, B.T.; Douglas, D.R.; Forest, E.
1990-01-01
The dynamic aperture and its determination emerged from the SSC reference design study as the single most important accelerator physics issue pertinent to the SSC. Beside the fundamental need of a finite dynamic aperture for any accelerator, it was considered to be a useful criterion for the magnet selection. An aperture workshop organized in November 1984 at LBL served the purpose to identify the various aspects of the aperture question and to organize the aperture task force accordingly. It was recognized that numerical models had to play an important role and the qualifications of several tracking codes were investigated. None of the existing codes could meet all of the criteria for an ideal tracking code and substantial program development became unavoidable. It was therefore decided to begin tracking SSC test lattices, which were provided by the aperture task force's lattice group and are described in an other paper to this conference, with existing tracking programs. 6 refs., 5 figs., 2 tabs.
Did Cosmology Trigger the Origin of the Solar System?
NASA Technical Reports Server (NTRS)
Blome, H.-J.; Wilson, T. L.
2011-01-01
It is a matter of curious coincidence that the Solar System formed 4.6 billion years ago around the same epoch that the Friedmann-Lemaitre (FL) universe became -dominated or dark-energy-dominated, where is the cosmological constant. This observation was made in the context of known gravitational anomalies that affect spacecraft orbits during planetary flyby's and the Pioneer anomaly, both possibly having connections with cosmology. In addition, it has been known for some time that the Universe is not only expanding but accelerating as well. Hence one must add the onset of cosmological acceleration in the FL universe as having a possible influence on the origin of the Solar System. These connections will now be examined in greater detail.
Is ΛCDM an effective CCDM cosmology?
Lima, J.A.S.; Santos, R.C.; Cunha, J.V. E-mail: cliviars@gmail.com
2016-03-01
We show that a cosmology driven by gravitationally induced particle production of all non-relativistic species existing in the present Universe mimics exactly the observed flat accelerating ΛCDM cosmology with just one dynamical free parameter. This kind of scenario includes the creation cold dark matter (CCDM) model [1] as a particular case and also provides a natural reduction of the dark sector since the vacuum component is not needed to accelerate the Universe. The new cosmic scenario is equivalent to ΛCDM both at the background and perturbative levels and the associated creation process is also in agreement with the universality of the gravitational interaction and equivalence principle. Implicitly, it also suggests that the present day astronomical observations cannot be considered the ultimate proof of cosmic vacuum effects in the evolved Universe because ΛCDM may be only an effective cosmology.
New massive bigravity cosmologies with double matter coupling
Lagos, Macarena; Noller, Johannes E-mail: noller@physics.ox.ac.uk
2016-01-01
We study a previously largely unexplored branch of homogeneous and isotropic background solutions in ghost-free massive bigravity with consistent double matter coupling. For a certain family of parameters we find 'self-inflated' FLRW cosmologies, i.e. solutions with an accelerated early-time period during the radiation-dominated era. In addition, these solutions also display an accelerated late-time period closely mimicking GR with a cosmological constant. Interestingly, within this family, the particular case of β{sub 1}=β{sub 3}=0 gives bouncing cosmologies, where there is an infinite contracting past, a non-zero minimum value of the scale factor at the bounce, and an infinite expanding future.
GLAD: A Generic LAttice Debugger
Lee, M.J.
1991-11-01
Today, numerous simulation and analysis codes exist for the design, commission, and operation of accelerator beam lines. There is a need to develop a common user interface and database link to run these codes interactively. This paper will describe a proposed system, GLAD (Generic LAttice Debugger), to fulfill this need. Specifically, GLAD can be used to find errors in beam lines during commissioning, control beam parameters during operation, and design beam line optics and error correction systems for the next generation of linear accelerators and storage rings.
NASA Astrophysics Data System (ADS)
Folatelli, G.
Supernovae are very relevant astrophysical objects because they indicate the violent end of certain stars and because they alter the interstellar medium. But most importantly, they have become an extremely useful tool for measuring cosmological distances. Based on highly precise distances to type Ia supernovae it was possible to find out that the expansion of the universe is currently accelerated. This led to introducing the concept of ``dark energy'' as a dominant and yet unknown component of the cosmos. In this article we will describe the method of distance measurements that leads to the determination of cosmological parameters. We will briefly review the current status of the field with emphasis on the importance of improving our knowledge about the physical nature of supernovae. FULL TEXT IN SPANISH
A cosmological study in massive gravity theory
Pan, Supriya Chakraborty, Subenoy
2015-09-15
A detailed study of the various cosmological aspects in massive gravity theory has been presented in the present work. For the homogeneous and isotropic FLRW model, the deceleration parameter has been evaluated, and, it has been examined whether there is any transition from deceleration to acceleration in recent past, or not. With the proper choice of the free parameters, it has been shown that the massive gravity theory is equivalent to Einstein gravity with a modified Newtonian gravitational constant together with a negative cosmological constant. Also, in this context, it has been examined whether the emergent scenario is possible, or not, in massive gravity theory. Finally, we have done a cosmographic analysis in massive gravity theory.
Cosmology of a Lorentz violating Galileon theory
Haghani, Zahra; Shahidi, Shahab; Harko, Tiberiu; Sepangi, Hamid Reza E-mail: t.harko@ucl.ac.uk E-mail: s.shahidi@du.ac.ir
2015-05-01
We modify the scalar Einstein-aether theory by breaking the Lorentz invariance of a gravitational theory coupled to a Galileon type scalar field. This is done by introducing a Lagrange multiplier term into the action, thus ensuring that the gradient of the scalar field is time-like, with unit norm. The theory can also be considered as an extension to the mimetic dark matter theory, by adding some derivative self interactions to the action, which keeps the equation of motion at most second order in time derivatives. The cosmological implications of the model are discussed in detail. In particular, for pressure-less baryonic matter, we show that the universe experiences a late time acceleration. The cosmological implications of a special coupling between the scalar field and the trace of the energy-momentum tensor are also explored.
Entropic Issues in Contemporary Cosmology
NASA Astrophysics Data System (ADS)
Coule, D. H.
Penrose1 has emphasized how the initial big bang singularity requires a special low entropy state. We address how recent brane cosmological schemes address this problem and whether they offer any apparent resolution. Pushing the start time back to t = -∞, or utilizing maximally symmetric AdS spaces, simply exacerbates or transfers the problem. Since the entropy of de Sitter space is S ≤ 1/Λ, using the present acceleration of the universe as a low energy (Λ ~ 10-120) inflationary stage, as in cyclic ekpyrotic models, produces a gravitational heat death after one cycle. Only higher energy driven inflation, together with a suitable, quantum gravity holography style, restriction on ab initio degrees of freedom, gives a suitable low entropy initial state. We question the suggestion that a high energy inflationary stage could be naturally reentered by Poincaré recurrence within a finite causal region of an accelerating universe. We further give a heuristic argument that the so-called eternal inflation is not consistent with the second law of thermodynamics within a causal patch.
Crack in the cosmological paradigm
NASA Astrophysics Data System (ADS)
Di Valentino, Eleonora
2017-09-01
A time-dependent dark energy component of the Universe may be able to explain tensions between local and primordial measurements of cosmological parameters, shaking current confidence in the concept of a cosmological constant.
NASA Astrophysics Data System (ADS)
Grujic, P. V.
2008-10-01
Cosmos poses unique problems to its investigations, both from the epistemological and ontological aspects. We analyze modern cosmology as science of the totality of the material reality, with emphasis on the physical content of the principal entities involved in describing the Universe as we perceive. In particular we examine the concept of creation and anihilation and argue that these notions, if relevant, are devoid of meaningful content. If applicable, the notion of evolution refers to transition from physical field entities towards inert matter components. We discuss the meaning of the existentional quantificator and show that the cosmology is essentially a historical science. Finally, we consider an interplay between the epistemological and phenomenological aspects, arguing that in cosmology it is the former one may rely on.
General relativity and cosmology
NASA Astrophysics Data System (ADS)
Bucher, Martin; Ni, Wei-Tou
2015-10-01
This year marks the 100th anniversary of Einstein’s 1915 landmark paper “Die Feldgleichungen der Gravitation” in which the field equations of general relativity were correctly formulated for the first time, thus rendering general relativity a complete theory. Over the subsequent hundred years, physicists and astronomers have struggled with uncovering the consequences and applications of these equations. This paper, which was written as an introduction to six chapters dealing with the connection between general relativity and cosmology that will appear in the two-volume book One Hundred Years of General Relativity: From Genesis and Empirical Foundations to Gravitational Waves, Cosmology and Quantum Gravity, endeavors to provide a historical overview of the connection between general relativity and cosmology, two areas whose development has been closely intertwined.
Elementary particles and cosmology
NASA Astrophysics Data System (ADS)
Dobrolyubov, M. I.; Ignatev, A. Yu.; Shaposhnikov, M. E.
1988-12-01
A series of lectures is devoted to actual problems which arise at the junction of elementary particle physics and cosmology. A brief review is given to the standard theory of hot universe and scenario of inflationary universe, modern state of the problem of baryon universe asymmetry and possible new mechanisms of this asymmetry formation. The possibility of construction of cosmological models on the basis of supersymmetric theories is considered: qualitative evaluation of the modern density of relic particles, cosmological restrictions for the mass of the lightest particle, astrophysical restrictions for the coupling constant of weakly interacting particles and matter are given. A perspective direction of search for light particles in light hadron decays is mentioned.
Closed inhomogeneous string cosmologies
Feinstein, A.; Lazkoz, R.; Vazquez-Mozo, M.A.
1997-10-01
We present a general algorithm which permits us to construct solutions in string cosmology for heterotic and type-IIB superstrings in four dimensions. Using a chain of transformations applied in sequence{emdash}conformal, T duality, and SL(2,{bold R}) rotations, along with the usual generating techniques associated with Geroch transformations in Einstein frame{emdash}we obtain solutions with all relevant low-energy remnants of the string theory. To exemplify our algorithm we present an inhomogeneous string cosmology with S{sup 3} topology of spatial sections, discuss some properties of the solution, and point out some subtleties involved in the concept of homogeneity and isotropy in string cosmology. {copyright} {ital 1997} {ital The American Physical Society}
f(T) teleparallel gravity and cosmology.
Cai, Yi-Fu; Capozziello, Salvatore; De Laurentis, Mariafelicia; Saridakis, Emmanuel N
2016-10-01
Over recent decades, the role of torsion in gravity has been extensively investigated along the main direction of bringing gravity closer to its gauge formulation and incorporating spin in a geometric description. Here we review various torsional constructions, from teleparallel, to Einstein-Cartan, and metric-affine gauge theories, resulting in extending torsional gravity in the paradigm of f (T) gravity, where f (T) is an arbitrary function of the torsion scalar. Based on this theory, we further review the corresponding cosmological and astrophysical applications. In particular, we study cosmological solutions arising from f (T) gravity, both at the background and perturbation levels, in different eras along the cosmic expansion. The f (T) gravity construction can provide a theoretical interpretation of the late-time universe acceleration, alternative to a cosmological constant, and it can easily accommodate with the regular thermal expanding history including the radiation and cold dark matter dominated phases. Furthermore, if one traces back to very early times, for a certain class of f (T) models, a sufficiently long period of inflation can be achieved and hence can be investigated by cosmic microwave background observations-or, alternatively, the Big Bang singularity can be avoided at even earlier moments due to the appearance of non-singular bounces. Various observational constraints, especially the bounds coming from the large-scale structure data in the case of f (T) cosmology, as well as the behavior of gravitational waves, are described in detail. Moreover, the spherically symmetric and black hole solutions of the theory are reviewed. Additionally, we discuss various extensions of the f (T) paradigm. Finally, we consider the relation with other modified gravitational theories, such as those based on curvature, like f (R) gravity, trying to illuminate the subject of which formulation, or combination of formulations, might be more suitable
f(T) teleparallel gravity and cosmology
NASA Astrophysics Data System (ADS)
Cai, Yi-Fu; Capozziello, Salvatore; De Laurentis, Mariafelicia; Saridakis, Emmanuel N.
2016-10-01
Over recent decades, the role of torsion in gravity has been extensively investigated along the main direction of bringing gravity closer to its gauge formulation and incorporating spin in a geometric description. Here we review various torsional constructions, from teleparallel, to Einstein-Cartan, and metric-affine gauge theories, resulting in extending torsional gravity in the paradigm of f (T) gravity, where f (T) is an arbitrary function of the torsion scalar. Based on this theory, we further review the corresponding cosmological and astrophysical applications. In particular, we study cosmological solutions arising from f (T) gravity, both at the background and perturbation levels, in different eras along the cosmic expansion. The f (T) gravity construction can provide a theoretical interpretation of the late-time universe acceleration, alternative to a cosmological constant, and it can easily accommodate with the regular thermal expanding history including the radiation and cold dark matter dominated phases. Furthermore, if one traces back to very early times, for a certain class of f (T) models, a sufficiently long period of inflation can be achieved and hence can be investigated by cosmic microwave background observations—or, alternatively, the Big Bang singularity can be avoided at even earlier moments due to the appearance of non-singular bounces. Various observational constraints, especially the bounds coming from the large-scale structure data in the case of f (T) cosmology, as well as the behavior of gravitational waves, are described in detail. Moreover, the spherically symmetric and black hole solutions of the theory are reviewed. Additionally, we discuss various extensions of the f (T) paradigm. Finally, we consider the relation with other modified gravitational theories, such as those based on curvature, like f (R) gravity, trying to illuminate the subject of which formulation, or combination of formulations, might be more
The kinematic component of the cosmological redshift
NASA Astrophysics Data System (ADS)
Chodorowski, Michał J.
2011-05-01
It is widely believed that the cosmological redshift is not a Doppler shift. However, Bunn & Hogg have recently pointed out that to solve this problem properly, one has to transport parallelly the velocity four-vector of a distant galaxy to the observer's position. Performing such a transport along the null geodesic of photons arriving from the galaxy, they found that the cosmological redshift is purely kinematic. Here we argue that one should rather transport the velocity four-vector along the geodesic connecting the points of intersection of the world-lines of the galaxy and the observer with the hypersurface of constant cosmic time. We find that the resulting relation between the transported velocity and the redshift of arriving photons is not given by a relativistic Doppler formula. Instead, for small redshifts it coincides with the well-known non-relativistic decomposition of the redshift into a Doppler (kinematic) component and a gravitational one. We perform such a decomposition for arbitrary large redshifts and derive a formula for the kinematic component of the cosmological redshift, valid for any Friedman-Lemaître-Robertson-Walker (FLRW) cosmology. In particular, in a universe with Ωm= 0.24 and ΩΛ= 0.76, a quasar at a redshift 6, at the time of emission of photons reaching us today had the recession velocity v= 0.997c. This can be contrasted with v= 0.96c, had the redshift been entirely kinematic. Thus, for recession velocities of such high-redshift sources, the effect of deceleration of the early Universe clearly prevails over the effect of its relatively recent acceleration. Last but not the least, we show that the so-called proper recession velocities of galaxies, commonly used in cosmology, are in fact radial components of the galaxies' four-velocity vectors. As such, they can indeed attain superluminal values, but should not be regarded as real velocities.
Cosmological simulations of DGP braneworld gravity
NASA Astrophysics Data System (ADS)
Schmidt, Fabian
2009-09-01
We perform cosmological N-body simulations of the Dvali-Gabadadze- Porrati braneworld model, by solving the full non-linear equations of motion for the scalar degree of freedom in this model, the brane bending mode. While coupling universally to matter, the brane-bending mode has self-interactions that become important as soon as the density field becomes non-linear. These self-interactions lead to a suppression of the field in high-density environments, and restore gravity to General Relativity. The code uses a multi- grid relaxation scheme to solve the non-linear field equation in the quasi- static approximation. We perform simulations of a flat self-accelerating DGP model without cosmological constant. However, the type of non-linear interactions of the brane-bending mode, which are the focus of this study, are generic to a wide class of braneworld cosmologies. The results of the DGP simulations are compared with standard gravity simulations assuming the same expansion history, and with DGP simulations using the linearized equation for the brane bending mode. This allows us to isolate the effects of the non-linear self-couplings of the field which are noticeable already on quasi-linear scales. We present results on the matter power spectrum and the halo mass function, and discuss the behavior of the brane bending mode within cosmological structure formation. We find that, independently of CMB constraints, the self-accelerating DGP model is strongly constrained by current weak lensing and cluster abundance measurements.
Newtonian and relativistic cosmologies
NASA Astrophysics Data System (ADS)
Green, Stephen R.; Wald, Robert M.
2012-03-01
Cosmological N-body simulations are now being performed using Newtonian gravity on scales larger than the Hubble radius. It is well known that a uniformly expanding, homogeneous ball of dust in Newtonian gravity satisfies the same equations as arise in relativistic Friedmann-Lemaître-Robinson-Walker cosmology, and it also is known that a correspondence between Newtonian and relativistic dust cosmologies continues to hold in linearized perturbation theory in the marginally bound/spatially flat case. Nevertheless, it is far from obvious that Newtonian gravity can provide a good global description of an inhomogeneous cosmology when there is significant nonlinear dynamical behavior at small scales. We investigate this issue in the light of a perturbative framework that we have recently developed [S. R. Green and R. M. Wald, Phys. Rev. DPRVDAQ1550-7998 83, 084020 (2011).10.1103/PhysRevD.83.084020], which allows for such nonlinearity at small scales. We propose a relatively straightforward dictionary—which is exact at the linearized level—that maps Newtonian dust cosmologies into general relativistic dust cosmologies, and we use our “ordering scheme” to determine the degree to which the resulting metric and matter distribution solve Einstein’s equation. We find that, within our ordering scheme, Einstein’s equation fails to hold at “order 1” at small scales and at “order ɛ” at large scales. We then find the additional corrections to the metric and matter distribution needed to satisfy Einstein’s equation to these orders. While these corrections are of some interest in their own right, our main purpose in calculating them is that their smallness should provide a criterion for the validity of the original dictionary (as well as simplified versions of this dictionary). We expect that, in realistic Newtonian cosmologies, these additional corrections will be very small; if so, this should provide strong justification for the use of Newtonian simulations
Nonlinear backreaction in cosmology
NASA Astrophysics Data System (ADS)
Green, Stephen Roland
This thesis, based on two papers by Green and Wald, investigates the problem of nonlinear backreaction in cosmology. We first analyze the problem in a general context by developing a new, mathematically precise framework for treating the effects of nonlinear phenomena occurring on small scales in general relativity. Our framework requires the metric to be close to a background metric (not necessarily a cosmological metric), but allows arbitrarily large stress-energy fluctuations on small scales. We prove that, within our framework, if the matter stress-energy tensor satisfies the weak energy condition (i.e., positivity of energy density in all frames), then the only effect that small-scale inhomogeneities can have on the background metric is to provide an effective stress-energy tensor that is traceless and satisfies the weak energy condition itself—corresponding to the presence of gravitational radiation. In particular, nonlinear effects produced by small-scale inhomogeneities cannot mimic the effects of dark energy. We also develop perturbation theory off of the background metric. We derive an equation for the long-wavelength part of the leading order deviation of the metric from the background metric, which contains the usual terms occurring in linearized perturbation theory plus additional contributions from the small-scale inhomogeneities. Next, we apply our framework to the cosmological context, specializing our background metric to be of the Friedmann-Lemaitre-Robertson-Walker form. We demonstrate that, in the case of dust matter, a cosmological constant, and vanishing spatial curvature (i.e., our universe today), Newtonian gravity alone provides a good
Planck 2015 Cosmological results
NASA Astrophysics Data System (ADS)
Tristram, Matthieu
2015-08-01
On behalf of the Planck collaboration, I will present the cosmological results from the 2015 release. The new release now include polarization data from both the LFI and the HFI.I will focus on the impact of the polarization on both the standard LCDM model and its basic extensions. I will compare these constraints with other cosmological probes such as BAO, gravitational lensing and redshift space distortions.LCDM is still a very good fit of the Planck CMB data. The scalar fluctuations are consistent with adiabatic modes.
Midisuperspace supersymmetric quantum cosmology
Macias, Alfredo; Camacho, Abel; Kunz, Jutta; Laemmerzahl, Claus
2008-03-15
We investigate the canonical quantization in the framework of N=1 simple supergravity for the case of a very simple gravitational midisuperspace described by Gowdy T{sup 3} cosmological models. We consider supersymmetric quantum cosmology in the mentioned midisuperspace, where a matrix representation for the gravitino covector-spinor is used. The full Lorentz constraint and its implications for the wave function of the Universe are analyzed in detail. We found that there are indeed physical states in the midisuperspace sector of the theory in contrast to the case of minisuperspace where there exist no physical states.
Information entropy in cosmology.
Hosoya, Akio; Buchert, Thomas; Morita, Masaaki
2004-04-09
The effective evolution of an inhomogeneous cosmological model may be described in terms of spatially averaged variables. We point out that in this context, quite naturally, a measure arises which is identical to a fluid model of the Kullback-Leibler relative information entropy, expressing the distinguishability of the local inhomogeneous mass density field from its spatial average on arbitrary compact domains. We discuss the time evolution of "effective information" and explore some implications. We conjecture that the information content of the Universe-measured by relative information entropy of a cosmological model containing dust matter-is increasing.
Cosmology with varying constants.
Martins, Carlos J A P
2002-12-15
The idea of possible time or space variations of the 'fundamental' constants of nature, although not new, is only now beginning to be actively considered by large numbers of researchers in the particle physics, cosmology and astrophysics communities. This revival is mostly due to the claims of possible detection of such variations, in various different contexts and by several groups. I present the current theoretical motivations and expectations for such variations, review the current observational status and discuss the impact of a possible confirmation of these results in our views of cosmology and physics as a whole.
Bimetric gravity doubly coupled to matter: theory and cosmological implications
Akrami, Yashar; Koivisto, Tomi S.; Mota, David F.; Sandstad, Marit E-mail: t.s.koivisto@astro.uio.no E-mail: marit.sandstad@astro.uio.no
2013-10-01
A ghost-free theory of gravity with two dynamical metrics both coupled to matter is shown to be consistent and viable. Its cosmological implications are studied, and the models, in particular in the context of partially massless gravity, are found to explain the cosmic acceleration without resorting to dark energy.
Laniakea in a Cosmological Context
NASA Astrophysics Data System (ADS)
Hernandez-Charpak, S. D.; Forero-Romero, J. E.
2017-07-01
Laniakea, our local supercluster, was defined by recent observationa of the local cosmic flow. In this work we present a study on large cosmological N-body simulations aimed at establishing the significance of Laniakea in a cosmological context. We find that superclusters similar in size and structure to Laniakea are relatively uncommon on a broader cosmological context.
The New Era of Precision Cosmology: Testing Gravity at Large Scales
NASA Technical Reports Server (NTRS)
Prescod-Weinstein, Chanda
2011-01-01
Cosmic acceleration may be the biggest phenomenological mystery in cosmology today. Various explanations for its cause have been proposed, including the cosmological constant, dark energy and modified gravities. Structure formation provides a strong test of any cosmic acceleration model because a successful dark energy model must not inhibit the development of observed large-scale structures. Traditional approaches to studies of structure formation in the presence of dark energy ore modified gravity implement the Press & Schechter formalism (PGF). However, does the PGF apply in all cosmologies? The search is on for a better understanding of universality in the PGF In this talk, I explore the potential for universality and talk about what dark matter haloes may be able to tell us about cosmology. I will also discuss the implications of this and new cosmological experiments for better understanding our theory of gravity.
BOOK REVIEW: The Oxford Companion to Cosmology
NASA Astrophysics Data System (ADS)
Coles, Peter
2008-10-01
compare the two books as I am clearly biased, but looking at mine again in the course of writing this review it struck me how much the landscape of cosmology has changed in the relatively short time that has elapsed between their publication dates. The past decade has seen the discovery of cosmic acceleration, detailed all-sky maps of the microwave background, the completion of huge galaxy surveys, and the synthesis of these observations into a standard 'concordance' cosmological model. If someone has the time and energy to undertake a project like this in ten years' time, I wonder if the current consensus will have survived.
Lattice quantum gravity and asymptotic safety
NASA Astrophysics Data System (ADS)
Laiho, J.; Bassler, S.; Coumbe, D.; Du, D.; Neelakanta, J. T.
2017-09-01
We study the nonperturbative formulation of quantum gravity defined via Euclidean dynamical triangulations (EDT) in an attempt to make contact with Weinberg's asymptotic safety scenario. We find that a fine-tuning is necessary in order to recover semiclassical behavior. Such a fine-tuning is generally associated with the breaking of a target symmetry by the lattice regulator; in this case we argue that the target symmetry is the general coordinate invariance of the theory. After introducing and fine-tuning a nontrivial local measure term, we find no barrier to taking a continuum limit, and we find evidence that four-dimensional, semiclassical geometries are recovered at long distance scales in the continuum limit. We also find that the spectral dimension at short distance scales is consistent with 3 /2 , a value that could resolve the tension between asymptotic safety and the holographic entropy scaling of black holes. We argue that the number of relevant couplings in the continuum theory is one, once symmetry breaking by the lattice regulator is accounted for. Such a theory is maximally predictive, with no adjustable parameters. The cosmological constant in Planck units is the only relevant parameter, which serves to set the lattice scale. The cosmological constant in Planck units is of order 1 in the ultraviolet and undergoes renormalization group running to small values in the infrared. If these findings hold up under further scrutiny, the lattice may provide a nonperturbative definition of a renormalizable quantum field theory of general relativity with no adjustable parameters and a cosmological constant that is naturally small in the infrared.
Harko, Tiberiu; Lobo, Francisco S.N.; Otalora, G.; Saridakis, Emmanuel N. E-mail: flobo@cii.fc.ul.pt
2014-12-01
We present an extension of f(T) gravity, allowing for a general coupling of the torsion scalar T with the trace of the matter energy-momentum tensor T. The resulting f(T,T) theory is a new modified gravity, since it is different from all the existing torsion or curvature based constructions. Applied to a cosmological framework, it leads to interesting phenomenology. In particular, one can obtain a unified description of the initial inflationary phase, the subsequent non-accelerating, matter-dominated expansion, and then the transition to a late-time accelerating phase. Additionally, the effective dark energy sector can be quintessence or phantom-like, or exhibit the phantom-divide crossing during the evolution. Moreover, in the far future the universe results either to a de Sitter exponential expansion, or to eternal power-law accelerated expansions. Finally, a detailed study of the scalar perturbations at the linear level reveals that f(T,T) cosmology can be free of ghosts and instabilities for a wide class of ansatzes and model parameters.
An ancient revisits cosmology.
Greenstein, J L
1993-01-01
In this after-dinner speech, a somewhat light-hearted attempt is made to view the observational side of physical cosmology as a subdiscipline of astrophysics, still in an early stage of sophistication and in need of more theoretical understanding. The theoretical side of cosmology, in contrast, has its deep base in general relativity. A major result of observational cosmology is that an expansion of the Universe arose from a singularity some 15 billion years ago. This has had an enormous impact on the public's view of both astronomy and theology. It places on cosmologists an extra responsibility for clear thinking and interpretation. Recently, gravitational physics caused another crisis from an unexpected observational result that nonbaryonic matter appears to dominate. Will obtaining information about this massive nonbaryonic component require that astronomers cease to rely on measurement of photons? But 40 years ago after radio astronomical techniques uncovered the high-energy universe, we happily introduced new subfields, with techniques from physics and engineering still tied to photon detection. Another historical example shows how a subfield of cosmology, big bang nucleosynthesis, grew in complexity from its spectroscopic astrophysics beginning 40 years ago. Determination of primordial abundances of lighter nuclei does illuminate conditions in the Big Bang, but the observational results faced and overcame many hurdles on the way. PMID:11607403
Coc, Alain
2014-05-09
There are important aspects of Cosmology, the scientific study of the large scale properties of the universe as a whole, for which nuclear physics can provide insights. Here, we will focus on Standard Big-Bang Nucleosynthesis and we refer to the previous edition of the School [1] for the aspects concerning the variations of constants in nuclear cosmo-physics.
Ekpyrotic and cyclic cosmology
NASA Astrophysics Data System (ADS)
Lehners, Jean-Luc
2008-09-01
Ekpyrotic and cyclic cosmologies provide theories of the very early and of the very late universe. In these models, the big bang is described as a collision of branes — and thus the big bang is not the beginning of time. Before the big bang, there is an ekpyrotic phase with equation of state w=Pρ≫1 (where P is the average pressure and ρ the average energy density) during which the universe slowly contracts. This phase resolves the standard cosmological puzzles and generates a nearly scale-invariant spectrum of cosmological perturbations containing a significant non-Gaussian component. At the same time it produces small-amplitude gravitational waves with a blue spectrum. The dark energy dominating the present-day cosmological evolution is reinterpreted as a small attractive force between our brane and a parallel one. This force eventually induces a new ekpyrotic phase and a new brane collision, leading to the idea of a cyclic universe. This review discusses the detailed properties of these models, their embedding in M-theory and their viability, with an emphasis on open issues and observational signatures.
An ancient revisits cosmology.
Greenstein, J L
1993-06-01
In this after-dinner speech, a somewhat light-hearted attempt is made to view the observational side of physical cosmology as a subdiscipline of astrophysics, still in an early stage of sophistication and in need of more theoretical understanding. The theoretical side of cosmology, in contrast, has its deep base in general relativity. A major result of observational cosmology is that an expansion of the Universe arose from a singularity some 15 billion years ago. This has had an enormous impact on the public's view of both astronomy and theology. It places on cosmologists an extra responsibility for clear thinking and interpretation. Recently, gravitational physics caused another crisis from an unexpected observational result that nonbaryonic matter appears to dominate. Will obtaining information about this massive nonbaryonic component require that astronomers cease to rely on measurement of photons? But 40 years ago after radio astronomical techniques uncovered the high-energy universe, we happily introduced new subfields, with techniques from physics and engineering still tied to photon detection. Another historical example shows how a subfield of cosmology, big bang nucleosynthesis, grew in complexity from its spectroscopic astrophysics beginning 40 years ago. Determination of primordial abundances of lighter nuclei does illuminate conditions in the Big Bang, but the observational results faced and overcame many hurdles on the way.
Consistency relation in cosmology
Chiba, Takeshi; Takahashi, Ryuichi
2007-05-15
We provide a consistency relation between cosmological observables in general relativity without relying on the equation of state of dark energy. The consistency relation should be satisfied if general relativity is the correct theory of gravity and dark energy clustering is negligible. As an extension, we also provide the DGP counterpart of the relation.
Sefusatti, Emiliano; Crocce, Martin; Pueblas, Sebastian; Scoccimarro, Roman; /CCPP, New York
2006-04-01
The present spatial distribution of galaxies in the Universe is non-Gaussian, with 40% skewness in 50 h{sup -1} Mpc spheres, and remarkably little is known about the information encoded in it about cosmological parameters beyond the power spectrum. In this work they present an attempt to bridge this gap by studying the bispectrum, paying particular attention to a joint analysis with the power spectrum and their combination with CMB data. They address the covariance properties of the power spectrum and bispectrum including the effects of beat coupling that lead to interesting cross-correlations, and discuss how baryon acoustic oscillations break degeneracies. They show that the bispectrum has significant information on cosmological parameters well beyond its power in constraining galaxy bias, and when combined with the power spectrum is more complementary than combining power spectra of different samples of galaxies, since non-Gaussianity provides a somewhat different direction in parameter space. In the framework of flat cosmological models they show that most of the improvement of adding bispectrum information corresponds to parameters related to the amplitude and effective spectral index of perturbations, which can be improved by almost a factor of two. Moreover, they demonstrate that the expected statistical uncertainties in {sigma}s of a few percent are robust to relaxing the dark energy beyond a cosmological constant.
Quantifying concordance in cosmology
NASA Astrophysics Data System (ADS)
Seehars, Sebastian; Grandis, Sebastian; Amara, Adam; Refregier, Alexandre
2016-05-01
Quantifying the concordance between different cosmological experiments is important for testing the validity of theoretical models and systematics in the observations. In earlier work, we thus proposed the Surprise, a concordance measure derived from the relative entropy between posterior distributions. We revisit the properties of the Surprise and describe how it provides a general, versatile, and robust measure for the agreement between data sets. We also compare it to other measures of concordance that have been proposed for cosmology. As an application, we extend our earlier analysis and use the Surprise to quantify the agreement between WMAP 9, Planck 13, and Planck 15 constraints on the Λ CDM model. Using a principle component analysis in parameter space, we find that the large Surprise between WMAP 9 and Planck 13 (S =17.6 bits, implying a deviation from consistency at 99.8% confidence) is due to a shift along a direction that is dominated by the amplitude of the power spectrum. The Planck 15 constraints deviate from the Planck 13 results (S =56.3 bits), primarily due to a shift in the same direction. The Surprise between WMAP and Planck consequently disappears when moving to Planck 15 (S =-5.1 bits). This means that, unlike Planck 13, Planck 15 is not in tension with WMAP 9. These results illustrate the advantages of the relative entropy and the Surprise for quantifying the disagreement between cosmological experiments and more generally as an information metric for cosmology.
Relativistic cosmology. Proceedings.
NASA Astrophysics Data System (ADS)
Sasaki, M.
The symposium was intended to present in-depth reviews of the problems and prospects of present-day cosmology. The topics covered were the inflationary universe, the large scale structure of the universe, gravitational lenses, black hole physics, numerical relativity, gravitational waves and related subjects.
Culture and Children's Cosmology
ERIC Educational Resources Information Center
Siegal, Michael; Butterworth, George; Newcombe, Peter A.
2004-01-01
In this investigation, we examined children's knowledge of cosmology in relation to the shape of the earth and the day-night cycle. Using explicit questioning involving a choice of alternative answers and 3D models, we carried out a comparison of children aged 4-9 years living in Australia and England. Though Australia and England have a close…
Gravitational lensing in cosmology
NASA Astrophysics Data System (ADS)
Futamase, Toshifumi
2015-02-01
Gravitational lensing is a unique and direct probe of mass in the universe. It depends only on the law of gravity and does not depend on the dynamical state nor the composition of matter. Thus, it is used to study the distribution of the dark matter in the lensing object. Combined with the traditional observations such as optical and X-ray, it gives us useful informations of the structure formation in the universe. The lensing observables depend also on the global geometry as well as large scale structure of the universe. Therefore it is possible to withdraw useful constraints on the cosmological parameters once the distribution of lensing mass is accurately known. Since the first discovery of the lensing event by a galaxy in 1979, various kinds of lensing phenomena caused by star, galaxy, cluster of galaxies and large scale structure have been observed and are used to study mass distribution in various scales and cosmology. Thus, the gravitational lensing is now regarded as an indispensable research field in the observational cosmology. In this paper, we give an instructive introduction to gravitational lensing and its applications to cosmology.
Culture and Children's Cosmology
ERIC Educational Resources Information Center
Siegal, Michael; Butterworth, George; Newcombe, Peter A.
2004-01-01
In this investigation, we examined children's knowledge of cosmology in relation to the shape of the earth and the day-night cycle. Using explicit questioning involving a choice of alternative answers and 3D models, we carried out a comparison of children aged 4-9 years living in Australia and England. Though Australia and England have a close…
Projective relativity, cosmology and gravitation
Arcidiacono, G.
1986-01-01
This book describes the latest applications of projective geometry to cosmology and gravitation. The contents of the book are; the Poincare group and Special Relativity, the thermodynamics and electromagnetism, general relativity, gravitation and cosmology, group theory and models of universe, the special projective relativity, the Fantappie group and Big-Bang cosmology, a new cosmological projective mechanics, the plasma physics and cosmology, the projective magnetohydrodynamics field, projective relativity and waves propagation, the generalizations of the gravitational field, the general projective relativity, the projective gravitational field, the De Sitter Universe and quantum physics, the conformal relativity and Newton gravitation.
Dynamical symmetries in Brans-Dicke cosmology
NASA Astrophysics Data System (ADS)
Papagiannopoulos, G.; Barrow, John D.; Basilakos, S.; Giacomini, A.; Paliathanasis, A.
2017-01-01
In the context of generalized Brans-Dicke cosmology we use the Killing tensors of the minisuperspace in order to determine the unspecified potential of a scalar-tensor gravity theory. Specifically, based on the existence of contact symmetries of the field equations, we find four types of potentials which provide exactly integrable dynamical systems. We investigate the dynamical properties of these potentials by using a critical point analysis and we find solutions which lead to cosmic acceleration and under specific conditions we can have de-Sitter points as stable late-time attractors.
Some cosmological consequences of Weyl invariance
Alvarez, Enrique; González-Martín, Sergio; Herrero-Valea, Mario E-mail: sergio.gonzalez.martin@csic.es
2015-03-01
We examine some Weyl invariant cosmological models in the framework of generalized dilaton gravity, in which the action is made of a set of N conformally coupled scalar fields. It will be shown that when the FRW ansatz for the spacetime metric is assumed, the Ward identity for conformal invariance guarantees that the gravitational equations hold whenever the scalar fields EM do so. It follows that any scale factor can solve the theory provided a non-trivial profile for a dilaton field. In particular, accelerated expansion is a natural solution to the full set of equations.
Bianchi-I cosmology from causal thermodynamics
NASA Astrophysics Data System (ADS)
Bittencourt, Eduardo; Gomes, Leandro G.; Klippert, Renato
2017-02-01
We investigate diagonal Bianchi-I spacetimes in the presence of viscous fluids by using the shear and the anisotropic pressure components as the basic variables, where the viscosity is driven by the (second-order) causal thermodynamics. A few exact solutions are presented, among which we mention the anisotropic versions of de Sitter/anti-de Sitter geometries as well as an asymptotically isotropic spacetime presenting an effectively constant cosmic acceleration without any cosmological constant. The qualitative analysis of the solutions for barotropic fluids with linear equations of state suggests that the behaviour is quite general.
Neutrino masses, neutrino oscillations, and cosmological implications
NASA Technical Reports Server (NTRS)
Stecker, F. W.
1982-01-01
Theoretical concepts and motivations for considering neutrinos having finite masses are discussed and the experimental situation on searches for neutrino masses and oscillations is summarized. The solar neutrino problem, reactor, deep mine and accelerator data, tri decay experiments and double beta-decay data are considered and cosmological implications and astrophysical data relating to neutrino masses are reviewed. The neutrino oscillation solution to the solar neutrino problem, the missing mass problem in galaxy halos and galaxy cluster galaxy formation and clustering, and radiative neutrino decay and the cosmic ultraviolet background radiation are examined.
Some cosmological consequences of Weyl invariance
Alvarez, Enrique; González-Martín, Sergio; Herrero-Valea, Mario
2015-03-19
We examine some Weyl invariant cosmological models in the framework of generalized dilaton gravity, in which the action is made of a set of N conformally coupled scalar fields. It will be shown that when the FRW ansatz for the spacetime metric is assumed, the Ward identity for conformal invariance guarantees that the gravitational equations hold whenever the scalar fields EM do so. It follows that any scale factor can solve the theory provided a non-trivial profile for a dilaton field. In particular, accelerated expansion is a natural solution to the full set of equations.
DESIGN OF THE RCMS LATTICE OPTICS.
CARDONA,J.; KEWISCH,J.; PEGGS,S.
2002-06-02
THE RAPID CYCLING MEDICAL SYNCHROTRON (RCMS) IS DESIGNED TO BE A VERY LIGHT AND INEXPENSIVE ACCELERATOR. THIS IS POSSIBLE DUE TO THE SMALL BEAM SIZE THAT HAS BEEN CHOSEN EARLY DURING THE DESIGN STAGE. THIS CHOICE HAS IMPLICATIONS IN THE DESIGN OF THE LATTICE OPTICS. IN THIS PAPER, WE PRESENT AN OVERVIEW OF THE RCMS OPTICS LATTICE, THE KIND OF MAGNETS TO BE USED AND ALSO A DESCRIPTION OF A SPECIAL OPTIC MODULE THAT MATCHES THE ROTATING GANTRY WITH THE REST OF THE FIXED ACCELERATOR. TECHNIQUESDEVELOPED TO WIN ADDITIONAL SPACE BETWEEN QUADRUPOLES WITHOUT DISTRUBING BETA FUNCTIONS ARE ALSO PRESENTED.
Holographic dark energy and late cosmic acceleration
NASA Astrophysics Data System (ADS)
Pavón, Diego
2007-06-01
It has been persuasively argued that the number of effective degrees of freedom of a macroscopic system is proportional to its area rather than to its volume. This entails interesting consequences for cosmology. Here we present a model based on this 'holographic principle' that accounts for the present stage of accelerated expansion of the Universe and significantly alleviates the coincidence problem also for non-spatially flat cosmologies. Likewise, we comment on a recently proposed late transition to a fresh decelerated phase.
The Future of Theoretical Physics and Cosmology
NASA Astrophysics Data System (ADS)
Gibbons, G. W.; Shellard, E. P. S.; Rankin, S. J.
2009-08-01
Preface; List of contributors; 1. Introduction; Part I. Popular Symposium: 2. Our complex cosmos and its future Martin J. Rees; 3. Theories of everything and Hawking's wave function of the Universe James B. Hartle; 4. The problem of space-time singularities: implications for quantum gravity? Roger Penrose; 5. Warping spacetime Kip Thorne; 6. 60 years in a nutshell Stephen W. Hawking; Part II. Spacetime Singularities: 7. Cosmological perturbations and singularities George F. R. Ellis; 8. The quantum physics of chronology protection Matt Visser; 9. Energy dominance and the Hawking-Ellis vacuum conservation theorem Brandon Carter; 10. On the instability of extra space dimensions Roger Penrose; Part III. Black Holes: 11. Black hole uniqueness and the inner horizon stability problem Werner Israel; 12. Black holes in the real universe and their prospects as probes of relativistic gravity Martin J. Rees; 13. Primordial black holes Bernard Carr; 14. Black hole pair creation Simon F. Ross; 15. Black holes as accelerators Steven Giddings; Part IV. Hawking Radiation: 16. Black holes and string theory Malcolm Perry; 17. M theory and black hole quantum mechanics Joe Polchinski; 18. Playing with black strings Gary Horowitz; 19. Twenty years of debate with Stephen Leonard Susskind; Part V. Quantum Gravity: 20. Euclidean quantum gravity: the view from 2002 Gary Gibbons; 21. Zeta functions, anomalies and stable branes Ian Moss; 22. Some reflections on the status of conventional quantum theory when applied to quantum gravity Chris Isham; 23. Quantum geometry and its ramifications Abhay Ashtekar; 24. Topology change in quantum gravity Fay Dowker; Part VI. M Theory and Beyond: 25. The past and future of string theory Edward Witten; 26. String theory David Gross; 27. A brief description of string theory Michael Green; 28. The story of M Paul Townsend; 29. Gauged supergravity and holographic field theory Nick Warner; 30. 57 varieties in a NUTshell Chris Pope; Part VII. de Sitter Space
Supernova tests of the timescape cosmology
NASA Astrophysics Data System (ADS)
Smale, Peter R.; Wiltshire, David L.
2011-05-01
The timescape cosmology has been proposed as a viable alternative to homogeneous cosmologies with dark energy. It realizes cosmic acceleration as an apparent effect that arises in calibrating average cosmological parameters in the presence of spatial curvature and gravitational energy gradients that grow large with the growth of inhomogeneities at late epochs. Recently Kwan, Francis and Lewis have claimed that the timescape model provides a relatively poor fit to the Union and Constitution supernovae compilations, as compared to the standard Λ cold dark matter (ΛCDM) model. We show this conclusion is a result of systematic issues in supernova light-curve fitting, and of failing to exclude data below the scale of statistical homogeneity, z≲ 0.033. Using all currently available supernova data sets (Gold07, Union, Constitution, MLCS17, MLCS31, SDSS-II, CSP, Union2), and making cuts at the statistical homogeneity scale, we show that data reduced by the SALT/SALT-II (Spectral Adaptive Light curve Template) fitters provide Bayesian evidence that favours the spatially flat ΛCDM model over the timescape model, whereas data reduced with MLCS2k2 fitters give Bayesian evidence which favours the timescape model over the ΛCDM model. We discuss the questions of extinction and reddening by dust, and of intrinsic colour variations in supernovae which do not correlate with the decay time, and the likely impact these systematics would have in a scenario consistent with the timescape model.
The Directedness of Time in Classical Cosmology
NASA Astrophysics Data System (ADS)
Bartels, Andreas; Wohlfarth, Daniel
2014-03-01
The aim of this paper is to show that a new understanding of fundamentality can be applied successfully in classical cosmology based on General Relativity. We are thereby able to achieve an account of cosmological time asymmetry as an intrinsic and fun-damental property of the universe. First, we consider Price's arguments against the fundamental status of time-asymmetry (Price (1996, 2002, 2011)). We show that these arguments have some force, but their force depends on understanding fundamentality as law-likeness. Second, we show that alternative approaches attempting to explain time directedness either by applying an anthropic strategy based on a multiverse approach, or by using the empirical fact of accelerated expansion of the universe, equally fail to provide a fundamental explanation of time directedness. In the third part, we present our own new concept of fundamentality based on properties of the solution space of fundamental laws. We demonstrate how this new concept of fundamentality is effective in understanding the cosmological asymmetry.
C-field cosmological models: revisited
NASA Astrophysics Data System (ADS)
Yadav, Anil Kumar; Tawfiq Ali, Ahmad; Ray, Saibal; Rahaman, Farook; Hossain Sardar, Iftikar
2016-12-01
We investigate plane symmetric spacetime filled with perfect fluid in the C-field cosmology of Hoyle and Narlikar. A new class of exact solutions has been obtained by considering the creation field C as a function of time only. To get the deterministic solution, it has been assumed that the rate of creation of matter-energy density is proportional to the strength of the existing C-field energy density. Several physical aspects and geometrical properties of the models are discussed in detail, especially showing that some of our solutions of C-field cosmology are free from singularity in contrast to the Big Bang cosmology. A comparative study has been carried out between two models, one singular and the other nonsingular, by contrasting the behaviour of the physical parameters. We note that the model in a unique way represents both the features of the accelerating as well as decelerating universe depending on the parameters and thus seems to provide glimpses of the oscillating or cyclic model of the universe without invoking any other agent or theory in allowing cyclicity.
Constraining cosmological parameter with SN Ia
NASA Astrophysics Data System (ADS)
Indra Putri, A. N.; Wulandari, H. R. Tri
2016-11-01
A type I supemovae (SN Ia) is an exploding white dwarf, whose mass exceeds Chandrasekar limit (1.44 solar mass). If a white dwarf is in a binary system, it may accrete matter from the companion, resulting in an excess mass that cannot be balanced by the pressure of degenerated electrons in the core. SNe Ia are highly luminous objects, that they are visible from very high distances. After some corrections (stretch (s), colour (c), K-corrections, etc.), the variations in the light curves of SNe Ia can be suppressed to be no more than 10%. Their high luminosity and almost uniform intrinsic brightness at the peak light, i.e. MB ∼ -19, make SNe Ia ideal standard candle. Because of their visibility from large distances, SNe Ia can be employed as a cosmological measuring tool. It was analysis of SNe Ia data that indicated for the first time, that the universe is not only expanding, but also accelerating. This work analyzed a compilation of SNe Ia data to determine several cosmological parameters (H0, Ωm, Ωa, and w). It can be concluded from the analysis, that our universe is a flat, dark energy dominated universe, and that the cosmological constant A is a suitable candidate for dark energy.
Thermodynamics and holography of tachyon cosmology
NASA Astrophysics Data System (ADS)
Farajollahi, H.; Ravanpak, A.; Abolghasemi, M.
2013-02-01
Recently, we have investigated the dynamics of the universe in tachyon cosmology with non-minimal coupling to matter (Farajollahi et al. in Mod Phys Lett A 26(15):1125-1135, 2011; Phys Lett B 711(3-4)15:225-231,2012; Phys Rev D 83:124042, 2011; JCAP 10:014, 20112011; JCAP 05:017, 2011). In particular, for the interacting holographic dark energy (IHDE), the model is studied in Farajollahi et al. (Astrophys Space Sci 336(2):461-467, 2011). In the current work, a significant observational program has been conducted to unveil the model's thermodynamic properties. Our result shows that the IHDE version of our model better fits the observational data than Λ CDM model. The first and generalized second thermodynamics laws for the universe enveloped by cosmological apparent and event horizon are revisited. From the results, both first and generalized second laws, constrained by the observational data, are satisfied on cosmological apparent horizon.In addition, the total entropy is verified with the observation only if the horizon of the universe is taken as apparent horizon. Then, due to validity of generalized second law, the current cosmic acceleration is also predicted.
Constraining Cosmological Models with Different Observations
NASA Astrophysics Data System (ADS)
Wei, J. J.
2016-07-01
With the observations of Type Ia supernovae (SNe Ia), scientists discovered that the Universe is experiencing an accelerated expansion, and then revealed the existence of dark energy in 1998. Since the amazing discovery, cosmology has became a hot topic in the physical research field. Cosmology is a subject that strongly depends on the astronomical observations. Therefore, constraining different cosmological models with all kinds of observations is one of the most important research works in the modern cosmology. The goal of this thesis is to investigate cosmology using the latest observations. The observations include SNe Ia, Type Ic Super Luminous supernovae (SLSN Ic), Gamma-ray bursts (GRBs), angular diameter distance of galaxy cluster, strong gravitational lensing, and age measurements of old passive galaxies, etc. In Chapter 1, we briefly review the research background of cosmology, and introduce some cosmological models. Then we summarize the progress on cosmology from all kinds of observations in more details. In Chapter 2, we present the results of our studies on the supernova cosmology. The main difficulty with the use of SNe Ia as standard candles is that one must optimize three or four nuisance parameters characterizing SN luminosities simultaneously with the parameters of an expansion model of the Universe. We have confirmed that one should optimize all of the parameters by carrying out the method of maximum likelihood estimation in any situation where the parameters include an unknown intrinsic dispersion. The commonly used method, which estimates the dispersion by requiring the reduced χ^{2} to equal unity, does not take into account all possible variances among the parameters. We carry out such a comparison of the standard ΛCDM cosmology and the R_{h}=ct Universe using the SN Legacy Survey sample of 252 SN events, and show that each model fits its individually reduced data very well. Moreover, it is quite evident that SLSNe Ic may be useful
Minimally coupled scalar field cosmology in anisotropic cosmological model
NASA Astrophysics Data System (ADS)
Singh, C. P.; Srivastava, Milan
2017-02-01
We study a spatially homogeneous and anisotropic cosmological model in the Einstein gravitational theory with a minimally coupled scalar field. We consider a non-interacting combination of scalar field and perfect fluid as the source of matter components which are separately conserved. The dynamics of cosmic scalar fields with a zero rest mass and an exponential potential are studied, respectively. We find that both assumptions of potential along with the average scale factor as an exponential function of scalar field lead to the logarithmic form of scalar field in each case which further gives power-law form of the average scale factor. Using these forms of the average scale factor, exact solutions of the field equations are obtained to the metric functions which represent a power-law and a hybrid expansion, respectively. We find that the zero-rest-mass model expands with decelerated rate and behaves like a stiff matter. In the case of exponential potential function, the model decelerates, accelerates or shows the transition depending on the parameters. The isotropization is observed at late-time evolution of the Universe in the exponential potential model.
Stable cosmology in ghost-free quasidilaton theory
NASA Astrophysics Data System (ADS)
Gümrükçüoǧlu, A. Emir; Koyama, Kazuya; Mukohyama, Shinji
2017-08-01
We present a novel cosmological solution in the framework of extended quasidilaton theory which underwent scrutiny recently. We only consider terms that do not generate the Boulware-Deser degree of freedom, hence the ghost-free quasidilaton theory, and show three new branches of cosmological evolution therein. One of the solutions passes the perturbative stability tests. This new solution exhibits a late time self-acceleration and all graviton polarizations acquire masses that converge to a constant in the asymptotic future. Moreover, all modes propagate at the speed of light. We propose that this solution can be used as a benchmark model for future phenomenological studies.
Nonlocal String Tachyon as a Model for Cosmological Dark Energy
Aref'eva, Irina Ya.
2006-03-29
There are many different phenomenological models describing the cosmological dark energy and accelerating Universe by choosing adjustable functions. In this paper we consider a specific model of scalar tachyon field which is derived from the NSR string field theory and study its cosmological applications. We find that in the effective field theory approximation the equation of state parameter w < -1, i.e. one has a phantom Universe. It is shown that due to nonlocal effects there is no quantum instability that the usual phantom models suffer from. Moreover due to a flip effect of the potential the Universe does not enter to a future singularity.
Integrable cosmological models from higher dimensional Einstein equations
Sano, Masakazu; Suzuki, Hisao
2007-09-15
We consider the cosmological models for the higher dimensional space-time which includes the curvatures of our space as well as the curvatures of the internal space. We find that the condition for the integrability of the cosmological equations is that the total space-time dimensions are D=10 or D=11 which is exactly the conditions for superstrings or M theory. We obtain analytic solutions with generic initial conditions in the four-dimensional Einstein frame and study the accelerating universe when both our space and the internal space have negative curvatures.
Brans-Dicke cosmology with time-dependent cosmological term
NASA Astrophysics Data System (ADS)
Berman, Marcelo Samuel
1990-12-01
Berman and Som's solution for a Brans-Dicke cosmology with time-dependent cosmological term, Robertson-Walker metric, perfect fluid, and perfect gas law of state solves the horizon, homogeneity, and isotropy problems without requiring any unnatural fine tuning in the very early universe, thus being an alternative model to inflation. The model also does not need recourse to quantum cosmology, and solves the flatness and magnetic monopole problems.
Nonlocal teleparallel cosmology.
Bahamonde, Sebastian; Capozziello, Salvatore; Faizal, Mir; Nunes, Rafael C
2017-01-01
Even though it is not possible to differentiate general relativity from teleparallel gravity using classical experiments, it could be possible to discriminate between them by quantum gravitational effects. These effects have motivated the introduction of nonlocal deformations of general relativity, and similar effects are also expected to occur in teleparallel gravity. Here, we study nonlocal deformations of teleparallel gravity along with its cosmological solutions. We observe that nonlocal teleparallel gravity (like nonlocal general relativity) is consistent with the present cosmological data obtained by SNe Ia + BAO + CC + [Formula: see text] observations. Along this track, future experiments probing nonlocal effects could be used to test whether general relativity or teleparallel gravity gives the most consistent picture of gravitational interaction.
Discrete Newtonian cosmology: perturbations
NASA Astrophysics Data System (ADS)
Ellis, George F. R.; Gibbons, Gary W.
2015-03-01
In a previous paper (Gibbons and Ellis 2014 Discrete Newtonian cosmology Class. Quantum Grav. 31 025003), we showed how a finite system of discrete particles interacting with each other via Newtonian gravitational attraction would lead to precisely the same dynamical equations for homothetic motion as in the case of the pressure-free Friedmann-Lemaître-Robertson-Walker cosmological models of general relativity theory, provided the distribution of particles obeys the central configuration equation. In this paper we show that one can obtain perturbed such Newtonian solutions that give the same linearized structure growth equations as in the general relativity case. We also obtain the Dmitriev-Zel’dovich equations for subsystems in this discrete gravitational model, and show how it leads to the conclusion that voids have an apparent negative mass.
NASA Astrophysics Data System (ADS)
Merritt, David
2017-02-01
I argue that some important elements of the current cosmological model are "conventionalist" in the sense defined by Karl Popper. These elements include dark matter and dark energy; both are auxiliary hypotheses that were invoked in response to observations that falsified the standard model as it existed at the time. The use of conventionalist stratagems in response to unexpected observations implies that the field of cosmology is in a state of 'degenerating problemshift' in the language of Imre Lakatos. I show that the 'concordance' argument, often put forward by cosmologists in support of the current paradigm, is weaker than the convergence arguments that were made in the past in support of the atomic theory of matter or the quantization of energy.
Cosmology with hypervelocity stars
Loeb, Abraham
2011-04-01
In the standard cosmological model, the merger remnant of the Milky Way and Andromeda (Milkomeda) will be the only galaxy remaining within our event horizon once the Universe has aged by another factor of ten, ∼ 10{sup 11} years after the Big Bang. After that time, the only extragalactic sources of light in the observable cosmic volume will be hypervelocity stars being ejected continuously from Milkomeda. Spectroscopic detection of the velocity-distance relation or the evolution in the Doppler shifts of these stars will allow a precise measurement of the vacuum mass density as well as the local matter distribution. Already in the near future, the next generation of large telescopes will allow photometric detection of individual stars out to the edge of the Local Group, and may target the ∼ 10{sup 5±1} hypervelocity stars that originated in it as cosmological tracers.
NASA Astrophysics Data System (ADS)
Hobson, Michael P.; Jaffe, Andrew H.; Liddle, Andrew R.; Mukherjee, Pia; Parkinson, David
2009-12-01
Preface; Part I. Methods: 1. Foundations and algorithms John Skilling; 2. Simple applications of Bayesian methods D. S. Sivia and Steve Rawlings; 3. Parameter estimation using Monte Carlo sampling Antony Lewis and Sarah Bridle; 4. Model selection and multi-model interference Andrew R. Liddle, Pia Mukherjee and David Parkinson; 5. Bayesian experimental design and model selection forecasting Roberto Trotta, Martin Kunz, Pia Mukherjee and David Parkinson; 6. Signal separation in cosmology M. P. Hobson, M. A. J. Ashdown and V. Stolyarov; Part II. Applications: 7. Bayesian source extraction M. P. Hobson, Graça Rocha and R. Savage; 8. Flux measurement Daniel Mortlock; 9. Gravitational wave astronomy Neil Cornish; 10. Bayesian analysis of cosmic microwave background data Andrew H. Jaffe; 11. Bayesian multilevel modelling of cosmological populations Thomas J. Loredo and Martin A. Hendry; 12. A Bayesian approach to galaxy evolution studies Stefano Andreon; 13. Photometric redshift estimation: methods and applications Ofer Lahav, Filipe B. Abdalla and Manda Banerji; Index.
Bojowald, Martin
2015-02-01
In quantum cosmology, one applies quantum physics to the whole universe. While no unique version and no completely well-defined theory is available yet, the framework gives rise to interesting conceptual, mathematical and physical questions. This review presents quantum cosmology in a new picture that tries to incorporate the importance of inhomogeneity. De-emphasizing the traditional minisuperspace view, the dynamics is rather formulated in terms of the interplay of many interacting 'microscopic' degrees of freedom that describe the space-time geometry. There is thus a close relationship with more-established systems in condensed-matter and particle physics even while the large set of space-time symmetries (general covariance) requires some adaptations and new developments. These extensions of standard methods are needed both at the fundamental level and at the stage of evaluating the theory by effective descriptions.
The Changing Cosmology Narrative
NASA Astrophysics Data System (ADS)
Eastman, T. E.
2009-12-01
The CBR discovery in 1965 was followed by successive triumphs for the Big Bang approach resulting in the current age of so-called "precision'' cosmology. I propose that the emerging data-rich environment is a game changer because it makes possible a major shift from a focus on theory and confirmation to observations, testing and potential falsification, and a shift from theory-driven claims of "precision'' cosmology to data-driven, multi-level testing of more limited and modest models. Greater flexibility in framing alternative hypotheses, and greater appreciation for rigorous data analysis unencumbered by preferred outcomes, may enable more critical assessments of grand theories that are at present excessively shielded from data-driven scrutiny.
Integrable cosmological potentials
NASA Astrophysics Data System (ADS)
Sokolov, V. V.; Sorin, A. S.
2017-05-01
The problem of classification of the Einstein-Friedman cosmological Hamiltonians H with a single scalar inflaton field φ, which possess an additional integral of motion polynomial in momenta on the shell of the Friedman constraint H=0 , is considered. Necessary and sufficient conditions for the existence of the first-, second- and third-degree integrals are derived. These conditions have the form of ODEs for the cosmological potential V(φ) . In the case of linear and quadratic integrals we find general solutions of the ODEs and construct the corresponding integrals explicitly. A new wide class of Hamiltonians that possess a cubic integral is derived. The corresponding potentials are represented in parametric form in terms of the associated Legendre functions. Six families of special elementary solutions are described, and sporadic superintegrable cases are discussed.
Culture and children's cosmology.
Siegal, Michael; Butterworth, George; Newcombe, Peter A
2004-06-01
In this investigation, we examined children's knowledge of cosmology in relation to the shape of the earth and the day-night cycle. Using explicit questioning involving a choice of alternative answers and 3D models, we carried out a comparison of children aged 4-9 years living in Australia and England Though Australia and England have a close cultural affinity, there are differences in children's early exposure to cosmological concepts. Australian children who have early instruction in this domain were nearly always significantly in advance of their English counterparts. In general, they most often produced responses compatible with a conception of a round earth on which people can live all over without falling off. We consider coherence and fragmentation in children's knowledge in terms of the timing of culturally transmitted information, and in relation to questioning methods used in previous research that may have underestimated children's competence.
NASA Astrophysics Data System (ADS)
Tolish, Alexander; Wald, Robert M.
2016-08-01
The "memory effect" is the permanent change in the relative separation of test particles resulting from the passage of gravitational radiation. We investigate the memory effect for a general, spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) cosmology by considering the radiation associated with emission events involving particle-like sources. We find that if the resulting perturbation is decomposed into scalar, vector, and tensor parts, only the tensor part contributes to memory. Furthermore, the tensor contribution to memory depends only on the cosmological scale factor at the source and observation events, not on the detailed expansion history of the universe. In particular, for sources at the same luminosity distance, the memory effect in a spatially flat FLRW spacetime is enhanced over the Minkowski case by a factor of (1 +z ).
NASA Astrophysics Data System (ADS)
Bouchet, François R.
2015-08-01
Sketched out in 1992, selected by ESA in 1996, launched in 2009, Planck delivered a "definitive" map of the anisotropies of the Cosmic Microwave Background (CMB) as well as information on their polarisation. The CMB anisotropies, of rms ~100 microK in temperature, reveal the imprint of the primordial fluctuations which initiate the growth of the large scale structures of the Universe, as transformed by their evolution, in particular during the first 370 000 years. This evolution is governed by the Universe content at this early epoch. I will confront what temperature and polarisation anisotropies teach us, both in terms of content of the universe and of characteristics of the primordial fluctuations. I will also discuss the extent of the agreement of Planck cosmology with lower redshift cosmological probes like BAO, Weak Lensing or redshift space distortions. Submitted on behalf of the Planck Collaboration.
NASA Astrophysics Data System (ADS)
Feldbrugge, Job; Lehners, Jean-Luc; Turok, Neil
2017-05-01
We argue that the Lorentzian path integral is a better starting point for quantum cosmology than its Euclidean counterpart. In particular, we revisit the minisuperspace calculation of the Feynman path integral for quantum gravity with a positive cosmological constant. Instead of rotating to Euclidean time, we deform the contour of integration over metrics into the complex plane, exploiting Picard-Lefschetz theory to transform the path integral from a conditionally convergent integral into an absolutely convergent one. We show that this procedure unambiguously determines which semiclassical saddle point solutions are relevant to the quantum mechanical amplitude. Imposing "no-boundary" initial conditions, i.e., restricting attention to regular, complex metrics with no initial boundary, we find that the dominant saddle contributes a semiclassical exponential factor which is precisely the inverse of the famous Hartle-Hawking result.
NASA Astrophysics Data System (ADS)
Hobson, Michael P.; Jaffe, Andrew H.; Liddle, Andrew R.; Mukherjee, Pia; Parkinson, David
2014-02-01
Preface; Part I. Methods: 1. Foundations and algorithms John Skilling; 2. Simple applications of Bayesian methods D. S. Sivia and Steve Rawlings; 3. Parameter estimation using Monte Carlo sampling Antony Lewis and Sarah Bridle; 4. Model selection and multi-model interference Andrew R. Liddle, Pia Mukherjee and David Parkinson; 5. Bayesian experimental design and model selection forecasting Roberto Trotta, Martin Kunz, Pia Mukherjee and David Parkinson; 6. Signal separation in cosmology M. P. Hobson, M. A. J. Ashdown and V. Stolyarov; Part II. Applications: 7. Bayesian source extraction M. P. Hobson, Graça Rocha and R. Savage; 8. Flux measurement Daniel Mortlock; 9. Gravitational wave astronomy Neil Cornish; 10. Bayesian analysis of cosmic microwave background data Andrew H. Jaffe; 11. Bayesian multilevel modelling of cosmological populations Thomas J. Loredo and Martin A. Hendry; 12. A Bayesian approach to galaxy evolution studies Stefano Andreon; 13. Photometric redshift estimation: methods and applications Ofer Lahav, Filipe B. Abdalla and Manda Banerji; Index.
Gravitomagnetic amplification in cosmology
Tsagas, Christos G.
2010-02-15
Magnetic fields interact with gravitational waves in various ways. We consider the coupling between the Weyl and the Maxwell fields in cosmology and study the effects of the former on the latter. The approach is fully analytical and the results are gauge invariant. We show that the nature and the outcome of the gravitomagnetic interaction depends on the electric properties of the cosmic medium. When the conductivity is high, gravitational waves reduce the standard (adiabatic) decay rate of the B field, leading to its superadiabatic amplification. In poorly conductive environments, on the other hand, Weyl-curvature distortions can result into the resonant amplification of large-scale cosmological magnetic fields. Driven by the gravitational waves, these B fields oscillate with an amplitude that is found to diverge when the wavelengths of the two sources coincide. We present technical and physical aspects of the gravitomagnetic interaction and discuss its potential implications.
Cosmological element production.
Wagoner, R V
1967-03-17
Two recent observations appear to have provided critical information about the past history of the universe. The thermal character of the microwave background radiation suggests that the universe has expanded from a state of high temperature and density, and places constraints on such a big-bang cosmology. The observations of very weak helium lines in the spectra of certain stars in the halo of our galaxy are possibly due to a low primeval abundance of this element. However, the simplest model of a big-bang cosmology leads to much higher helium abundances, such as are observed in the solar system and in many stars. The production of helium can be reduced either by altering the early expansion rate or by introducing degenerate electron neutrinos. Observations of interstellar and intergalactic deuterium and He(4), and possibly even He(3) and Li(7), are needed to test the various models.
NASA Astrophysics Data System (ADS)
Kadota, Kenji; Stewart, Ewan D.
2003-07-01
We present a modular cosmology scenario where the difficulties encountered in conventional modular cosmology are solved in a self-consistent manner, with definite predictions to be tested by observation. Notably, the difficulty of the dilaton finding its way to a precarious weak coupling minimum is made irrelevant by having eternal modular inflation at the vacuum supersymmetry breaking scale after the dilaton is stabilised. Neither this eternal inflation nor the subsequent non-slow-roll modular inflation destabilise the dilaton from its precarious minimum due to the low energy scale of the inflation and consequent small back reaction on the dilaton potential. The observed flat CMB spectrum is obtained from fluctuations in the angular component of a modulus near a symmetric point, which are hugely magnified by the roll down of the modulus to Planckian values, allowing them to dominate the final curvature perturbation. We also give precise calculations of the spectral index and its running.
Barrow, J D
1977-05-12
An anisotropic, inhomogeneous cosmological model is proposed in which the inhomogeneity is generated by shear fluctuations. This is a sufficient condition for dissipative heating by collisional neutrinos to explain the present large heat content of the universe, S(b o) approximately 10(8), together with its isotropy and comparative homogeneity on large scales when the photons were last scattered. The model does not require the chaotic motions to be arbitrarily truncated on large scales and isotropises early enough with high entropy to ensure the synthesis of light elements with the observed abundancies. A population of black holes which arises in a natural way can also provide the necessary ingredients for a theory of galaxy formation and morphology. The 10(15)-g black holes, predicted by some authors, are not necessarily expected to be a feature of chaotic cosmologies.
Integrable cosmological potentials
NASA Astrophysics Data System (ADS)
Sokolov, V. V.; Sorin, A. S.
2017-09-01
The problem of classification of the Einstein-Friedman cosmological Hamiltonians H with a single scalar inflaton field φ, which possess an additional integral of motion polynomial in momenta on the shell of the Friedman constraint H=0, is considered. Necessary and sufficient conditions for the existence of the first-, second- and third-degree integrals are derived. These conditions have the form of ODEs for the cosmological potential V(φ). In the case of linear and quadratic integrals we find general solutions of the ODEs and construct the corresponding integrals explicitly. A new wide class of Hamiltonians that possess a cubic integral is derived. The corresponding potentials are represented in parametric form in terms of the associated Legendre functions. Six families of special elementary solutions are described, and sporadic superintegrable cases are discussed.
NASA Astrophysics Data System (ADS)
Merritt, David
2017-02-01
I argue that some important elements of the current cosmological model are 'conventionalist' in the sense defined by Karl Popper. These elements include dark matter and dark energy; both are auxiliary hypotheses that were invoked in response to observations that falsified the standard model as it existed at the time. The use of conventionalist stratagems in response to unexpected observations implies that the field of cosmology is in a state of 'degenerating problemshift' in the language of Imre Lakatos. I show that the 'concordance' argument, often put forward by cosmologists in support of the current paradigm, is weaker than the convergence arguments that were made in the past in support of the atomic theory of matter or the quantization of energy.
Cosmology, Clusters and Calorimeters
NASA Technical Reports Server (NTRS)
Figueroa-Feliciano, Enectali
2005-01-01
I will review the current state of Cosmology with Clusters and discuss the application of microcalorimeter arrays to this field. With the launch of Astro-E2 this summer and a slew of new missions being developed, microcalorimeters are the next big thing in x-ray astronomy. I will cover the basics and not-so-basic concepts of microcalorimeter designs and look at the future to see where this technology will go.
Topics in inflationary cosmologies
Mahajan, S.
1986-04-01
Several aspects of inflationary cosmologies are discussed. An introduction to the standard hot big bang cosmological model is reviewed, and some of the problems associated with it are presented. A short review of the proposals for solving the cosmological conundrums of the big bang model is presented. Old and the new inflationary scenarios are discussed and shown to be unacceptable. Some alternative scenarios especially those using supersymmetry are reviewed briefly. A study is given of inflationary models where the same set of fields that breaks supersymmetry is also responsible for inflation. In these models, the scale of supersymmetry breaking is related to the slope of the potential near the origin and can thus be kept low. It is found that a supersymmetry breaking scale of the order of the weak breaking scale. The cosmology obtained from the simplest of such models is discussed in detail and it is shown that there are no particular problems except a low reheating temperature and a violation of the thermal constraint. A possible solution to the thermal constraint problem is given by introducing a second field, and the role played by this second field in the scenario is discussed. An alternative mechanism for the generation of baryon number within the framework of supergravity inflationary models is studied using the gravitational couplings of the heavy fields with the hidden sector (the sector which breaks supersymmetry). This mechanism is applied to two specific models - one with and one without supersymmetry breaking. The baryon to entropy ratio is found to be dependent on parameters which are model dependent. Finally, the effect of direct coupling between the two sectors on results is related, 88 refs., 6 figs.
NASA Astrophysics Data System (ADS)
Jones, Alexander
The structure, composition, and long-term history of the cosmos were prominent topics in many ancient Greek philosophical systems. Philosophers and philosophically informed astronomers differed over whether the cosmos was finite or infinite, eternal or transient, and composed of discrete particles or continuous, homogeneous elements. The Aristotelian cosmology preferred by astronomers following Ptolemy assumed a finite, spherical shell of eternally unalterable matter enclosing a terrestrial globe composed of earth, water, air, and fire.
Cosmology, Clusters and Calorimeters
NASA Technical Reports Server (NTRS)
Figueroa-Feliciano, Enectali
2005-01-01
I will review the current state of Cosmology with Clusters and discuss the application of microcalorimeter arrays to this field. With the launch of Astro-E2 this summer and a slew of new missions being developed, microcalorimeters are the next big thing in x-ray astronomy. I will cover the basics and not-so-basic concepts of microcalorimeter designs and look at the future to see where this technology will go.
Statistical Methods in Cosmology
NASA Astrophysics Data System (ADS)
Verde, L.
2010-03-01
The advent of large data-set in cosmology has meant that in the past 10 or 20 years our knowledge and understanding of the Universe has changed not only quantitatively but also, and most importantly, qualitatively. Cosmologists rely on data where a host of useful information is enclosed, but is encoded in a non-trivial way. The challenges in extracting this information must be overcome to make the most of a large experimental effort. Even after having converged to a standard cosmological model (the LCDM model) we should keep in mind that this model is described by 10 or more physical parameters and if we want to study deviations from it, the number of parameters is even larger. Dealing with such a high dimensional parameter space and finding parameters constraints is a challenge on itself. Cosmologists want to be able to compare and combine different data sets both for testing for possible disagreements (which could indicate new physics) and for improving parameter determinations. Finally, cosmologists in many cases want to find out, before actually doing the experiment, how much one would be able to learn from it. For all these reasons, sophisiticated statistical techniques are being employed in cosmology, and it has become crucial to know some statistical background to understand recent literature in the field. I will introduce some statistical tools that any cosmologist should know about in order to be able to understand recently published results from the analysis of cosmological data sets. I will not present a complete and rigorous introduction to statistics as there are several good books which are reported in the references. The reader should refer to those.
NASA Astrophysics Data System (ADS)
Ryden, Barbara
2016-11-01
Preface to second edition; Preface to first edition; 1. Introduction; 2. Fundamental observations; 3. Newton versus Einstein; 4. Cosmic dynamics; 5. Model universes; 6. Measuring cosmological parameters; 7. Dark matter; 8. The cosmic microwave background; 9. Nucleosynthesis and the early Universe; 10. Inflation and the very early Universe; 11. Structure formation: gravitational instability; 12. Structure formation: baryons and photons; Epilogue; Bibliography; Table of useful constants; Index.
Cosmology with galaxy cluster phase spaces
NASA Astrophysics Data System (ADS)
Stark, Alejo; Miller, Christopher J.; Huterer, Dragan
2017-07-01
We present a novel approach to constrain accelerating cosmologies with galaxy cluster phase spaces. With the Fisher matrix formalism we forecast constraints on the cosmological parameters that describe the cosmological expansion history. We find that our probe has the potential of providing constraints comparable to, or even stronger than, those from other cosmological probes. More specifically, with 1000 (100) clusters uniformly distributed in the redshift range 0 ≤z ≤0.8 , after applying a conservative 80% mass scatter prior on each cluster and marginalizing over all other parameters, we forecast 1 σ constraints on the dark energy equation of state w and matter density parameter ΩM of σw=0.138 (0.431 ) and σΩM=0.007(0.025 ) in a flat universe. Assuming 40% mass scatter and adding a prior on the Hubble constant we can achieve a constraint on the Chevallier-Polarski-Linder parametrization of the dark energy equation of state parameters w0 and wa with 100 clusters in the same redshift range: σw 0=0.191 and σwa=2.712. Dropping the assumption of flatness and assuming w =-1 we also attain competitive constraints on the matter and dark energy density parameters: σΩ M=0.101 and σΩ Λ=0.197 for 100 clusters uniformly distributed in the range 0 ≤z ≤0.8 after applying a prior on the Hubble constant. We also discuss various observational strategies for tightening constraints in both the near and far future.
Quantum Vacuum Structure and Cosmology
Rafelski, Johann; Labun, Lance; Hadad, Yaron; Chen, Pisin; /Taiwan, Natl. Taiwan U. /KIPAC, Menlo Park /SLAC
2011-12-05
Contemporary physics faces three great riddles that lie at the intersection of quantum theory, particle physics and cosmology. They are: (1) The expansion of the universe is accelerating - an extra factor of two appears in the size; (2) Zero-point fluctuations do not gravitate - a matter of 120 orders of magnitude; and (3) The 'True' quantum vacuum state does not gravitate. The latter two are explicitly problems related to the interpretation and the physical role and relation of the quantum vacuum with and in general relativity. Their resolution may require a major advance in our formulation and understanding of a common unified approach to quantum physics and gravity. To achieve this goal we must develop an experimental basis and much of the discussion we present is devoted to this task. In the following, we examine the observations and the theory contributing to the current framework comprising these riddles. We consider an interpretation of the first riddle within the context of the universe's quantum vacuum state, and propose an experimental concept to probe the vacuum state of the universe.
Cosmology in generalized Proca theories
NASA Astrophysics Data System (ADS)
De Felice, Antonio; Heisenberg, Lavinia; Kase, Ryotaro; Mukohyama, Shinji; Tsujikawa, Shinji; Zhang, Ying-li
2016-06-01
We consider a massive vector field with derivative interactions that propagates only the 3 desired polarizations (besides two tensor polarizations from gravity) with second-order equations of motion in curved space-time. The cosmological implications of such generalized Proca theories are investigated for both the background and the linear perturbation by taking into account the Lagrangian up to quintic order. In the presence of a matter fluid with a temporal component of the vector field, we derive the background equations of motion and show the existence of de Sitter solutions relevant to the late-time cosmic acceleration. We also obtain conditions for the absence of ghosts and Laplacian instabilities of tensor, vector, and scalar perturbations in the small-scale limit. Our results are applied to concrete examples of the general functions in the theory, which encompass vector Galileons as a specific case. In such examples, we show that the de Sitter fixed point is always a stable attractor and study viable parameter spaces in which the no-ghost and stability conditions are satisfied during the cosmic expansion history.
Cosmological perturbations in antigravity
NASA Astrophysics Data System (ADS)
Oltean, Marius; Brandenberger, Robert
2014-10-01
We compute the evolution of cosmological perturbations in a recently proposed Weyl-symmetric theory of two scalar fields with oppositely signed conformal couplings to Einstein gravity. It is motivated from the minimal conformal extension of the standard model, such that one of these scalar fields is the Higgs while the other is a new particle, the dilaton, introduced to make the Higgs mass conformally symmetric. At the background level, the theory admits novel geodesically complete cyclic cosmological solutions characterized by a brief period of repulsive gravity, or "antigravity," during each successive transition from a big crunch to a big bang. For simplicity, we consider scalar perturbations in the absence of anisotropies, with potential set to zero and without any radiation. We show that despite the necessarily wrong-signed kinetic term of the dilaton in the full action, these perturbations are neither ghostlike nor tachyonic in the limit of strongly repulsive gravity. On this basis, we argue—pending a future analysis of vector and tensor perturbations—that, with respect to perturbative stability, the cosmological solutions of this theory are viable.
Ekpyrotic loop quantum cosmology
Wilson-Ewing, Edward
2013-08-01
We consider the ekpyrotic paradigm in the context of loop quantum cosmology. In loop quantum cosmology the classical big-bang singularity is resolved due to quantum gravity effects, and so the contracting ekpyrotic branch of the universe and its later expanding phase are connected by a smooth bounce. Thus, it is possible to explicitly determine the evolution of scalar perturbations, from the contracting ekpyrotic phase through the bounce and to the post-bounce expanding epoch. The possibilities of having either one or two scalar fields have been suggested for the ekpyrotic universe, and both cases will be considered here. In the case of a single scalar field, the constant mode of the curvature perturbations after the bounce is found to have a blue spectrum. On the other hand, for the two scalar field ekpyrotic model where scale-invariant entropy perturbations source additional terms in the curvature perturbations, the power spectrum in the post-bounce expanding cosmology is shown to be nearly scale-invariant and so agrees with observations.
NASA Astrophysics Data System (ADS)
Hoyle, Fred
The worrying situation at that time in cosmology, as it seemed, turned out to be a relatively minor matter, namely the choice of suitable coordinates. Even the best-known cosmologists - de Sitter, Eddington and Lemaitre - had chosen coordinates appropriate to localities in the universe rather than the whole. This produced a sense of mystery that was more apparent than real as to what happened at the boundary of a locality. It is one of the features of Einstein's general relativity that when you choose coordinate systems with special properties you can mistakenly come to think of the properties as physical instead of as mathematical artefacts. Early workers on gravitational waves thought they were investigating physical waves when in fact the waves were in their coordinate system, and a similar situation existed in cosmology. It was also in 1935-36 that this situation was put right, by H.P. Robertson in the United States and A.E. Walker in Britain and the resulting choice of coordinates later became known as the Robertson-Walker line element. Then in 1937 Robertson published an important article on cosmology in the Reviews of Modern Physics, which unfortunately I didn't read at that time because my research interests were in quantum mechanics and nuclear physics.
NASA Astrophysics Data System (ADS)
Magueijo, João; Zlosnik, T. G.; Kibble, T. W. B.
2013-03-01
Using the chiral representation for spinors we present a particularly transparent way to generate the most general spinor dynamics in a theory where gravity is ruled by the Einstein-Cartan-Holst action. In such theories torsion need not vanish, but it can be reinterpreted as a four-fermion self-interaction within a torsion-free theory. The self-interaction may or may not break parity invariance, and may contribute positively or negatively to the energy density, depending on the couplings considered. We then examine cosmological models ruled by a spinorial field within this theory. We find that while there are cases for which no significant cosmological novelties emerge, the self-interaction can also turn a mass potential into an upside-down Mexican hat potential. Then, as a general rule, the model leads to cosmologies with a bounce, for which there is a maximal energy density, and where the cosmic singularity has been removed. These solutions are stable, and range from the very simple to the very complex.
Backreaction mechanism in multifluid and extended cosmologies
Jiménez, Jose Beltrán; Cruz-Dombriz, Álvaro de la; Dunsby, Peter K.S.; Sáez-Gómez, Diego E-mail: dombriz@fis.ucm.es E-mail: diego.saezgomez@uct.ac.za
2014-05-01
One possible explanation for the present observed acceleration of the Universe is the breakdown of homogeneity and isotropy due to the formation of non-linear structures. How inhomogeneities affect the averaged cosmological expansion rate and lead to late-time acceleration is generally considered to be due to some backreaction mechanism. In the recent literature most averaging calculations have focused their attention on General Relativity together with pressure-free matter. In this communication we focus our attention on more general scenarios, including imperfect fluids as well as alternative theories of gravity, and apply an averaging procedure to them in order to determine possible backreaction effects. For illustrative purposes, we present our results for dark energy models, quintessence and Brans-Dicke theories. We also provide a discussion about the limitations of frame choices in the averaging procedure.
NASA Astrophysics Data System (ADS)
Benoit-Lévy, Aurélien; Chardin, Gabriel
2014-05-01
We study an unconventional cosmology, in which we investigate the consequences that antigravity would pose to cosmology. We present the main characteristics of the Dirac-Milne Universe, a cosmological model where antimatter has a negative active gravitational mass. In this non-standard Universe, separate domains of matter and antimatter coexist at our epoch without annihilation, separated by a gravitationally induced depletion zone. We show that this cosmology does not require a priori the Dark Matter and Dark Energy components of the standard model of cosmology. Additionally, inflation becomes an unnecessary ingredient. Investigating this model, we show that the classical cosmological tests such as primordial nucleosynthesis, Type Ia supernovæ and Cosmic Microwave Background are surprisingly concordant.
NASA Astrophysics Data System (ADS)
Sidorin, Anatoly
2010-01-01
In linear accelerators the particles are accelerated by either electrostatic fields or oscillating Radio Frequency (RF) fields. Accordingly the linear accelerators are divided in three large groups: electrostatic, induction and RF accelerators. Overview of the different types of accelerators is given. Stability of longitudinal and transverse motion in the RF linear accelerators is briefly discussed. The methods of beam focusing in linacs are described.
Sidorin, Anatoly
2010-01-05
In linear accelerators the particles are accelerated by either electrostatic fields or oscillating Radio Frequency (RF) fields. Accordingly the linear accelerators are divided in three large groups: electrostatic, induction and RF accelerators. Overview of the different types of accelerators is given. Stability of longitudinal and transverse motion in the RF linear accelerators is briefly discussed. The methods of beam focusing in linacs are described.
Cosmology for high energy physicists
Albrecht, A.
1987-11-01
The standard big bang model of cosmology is presented. Although not perfect, its many successes make it a good starting point for most discussions of cosmology. Places are indicated where well understood laboratory physics is incorporated into the big bang, leading to successful predictions. Much less established aspects of high energy physics and some of the new ideas they have introduced into the field of cosmology are discussed, such as string theory, inflation and monopoles. 49 refs., 5 figs.
String cosmology and the landscape
NASA Astrophysics Data System (ADS)
Bena, Iosif; Graña, Mariana
2017-03-01
String Theory is believed to have a landscape of 10500 vacua with properties that resemble those of our Universe. The existence of these vacua can be combined with anthropic reasoning to explain some of the hardest problems in cosmology and high-energy physics: the cosmological constant problem, the hierarchy problem, and the un-natural almost-flatness of the inflationary potential. We will explain the construction of these vacua, focusing on the challenges of obtaining vacua with a positive cosmological constant.
A review on the lattice design of large hadron colliders
Lee, S.Y.
1987-01-01
The conceptual evolution of the accelerator lattice design is discussed. Indicated are aspects of IR design. We emphasize the cancellation of stop-band width in the cluster design. The case of symmetric vs antisymmetric design is also discussed. The SSC lattice is used as an example. 9 refs.
Cosmological relativity: A special relativity for cosmology
NASA Astrophysics Data System (ADS)
Carmeli, M.
1995-07-01
Under the assumption that Hubble's constant H0 is constant in cosmic time, there is an analogy between the equation of propagation of light and that of expansion of the universe. Using this analogy, and assuming that the laws of physics are the same at all cosmic times, a new special relativity, a cosmological relativity, is developed. As a result, a transformation is obtained that relates physical quantities at different cosmic times. In a one-dimensional motion, the new transformation is given by 10701_2005_Article_BF02059524_TeX2GIFE1.gif x' = {x - Tv}/{(1 - T^2 /T_0^2 )^{{1 / 2}}v' = {v - xT/T_0^2 }/{(1 - T^2 /T_0^2 )^{{1 /2 }} where x and v are the coordinate and velocity, T is the cosmic time measured backward with respect to our present time T=0, tand T0 is Hubble's time. Some consequences of this transformation are given, and its applicability limitation is pointed out.
A transitionless lattice for the Fermilab Main Injector
Ng, K.Y.; Trbojevic, D. ); Lee, S.Y. . Dept. of Physics)
1991-05-01
Medium energy (1 to 30 GeV) accelerators are often confronted with transition crossing during acceleration. A lattice without transition is presented, which is a design for the Fermilab Main Injector. The main properties of this lattice are that the {gamma}{sub t} is an imaginary number, the maxima of the dispersion function are small, and two long-straight section with zero dispersion. 7 refs., 5 figs.
Inflation from supersymmetric quantum cosmology
Socorro, J.; D'Oleire, Marco
2010-08-15
We derive a special scalar field potential using the anisotropic Bianchi type I cosmological model from canonical quantum cosmology under determined conditions in the evolution to anisotropic variables {beta}{sub {+-}}. In the process, we obtain a family of potentials that has been introduced by hand in the literature to explain cosmological data. Considering supersymmetric quantum cosmology, this family is scanned, fixing the exponential potential as more viable in the inflation scenario V({phi})=V{sub 0}e{sup -{radical}(3){phi}}.
Philosophical aspects of modern cosmology
NASA Astrophysics Data System (ADS)
Zinkernagel, Henrik
2014-05-01
Cosmology is the attempt to understand in scientific terms the structure and evolution of the universe as a whole. This ambition has been with us since the ancient Greeks, even if the developments in modern cosmology have provided a picture of the universe dramatically different from that of Pythagoras, Plato and Aristotle. The cosmological thinking of these figures, e.g. the belief in uniform circular motion of the heavens, was closely related to their philosophical ideas, and it shaped the field of cosmology at least up to the times of Copernicus and Kepler.
Dynamics of anisotropic power-law f( R) cosmology
NASA Astrophysics Data System (ADS)
Shamir, M. F.
2016-12-01
Modified theories of gravity have attracted much attention of the researchers in the recent years. In particular, the f( R) theory has been investigated extensively due to important f( R) gravity models in cosmological contexts. This paper is devoted to exploring an anisotropic universe in metric f( R) gravity. A locally rotationally symmetric Bianchi type I cosmological model is considered for this purpose. Exact solutions of modified field equations are obtained for a well-known f( R) gravity model. The energy conditions are also discussed for the model under consideration. The viability of the model is investigated via graphical analysis using the present-day values of cosmological parameters. The model satisfies null energy, weak energy, and dominant energy conditions for a particular range of the anisotropy parameter while the strong energy condition is violated, which shows that the anisotropic universe in f( R) gravity supports the crucial issue of accelerated expansion of the universe.
Dynamics of anisotropic power-law f(R) cosmology
Shamir, M. F.
2016-12-15
Modified theories of gravity have attracted much attention of the researchers in the recent years. In particular, the f(R) theory has been investigated extensively due to important f(R) gravity models in cosmological contexts. This paper is devoted to exploring an anisotropic universe in metric f(R) gravity. A locally rotationally symmetric Bianchi type I cosmological model is considered for this purpose. Exact solutions of modified field equations are obtained for a well-known f(R) gravity model. The energy conditions are also discussed for the model under consideration. The viability of the model is investigated via graphical analysis using the present-day values of cosmological parameters. The model satisfies null energy, weak energy, and dominant energy conditions for a particular range of the anisotropy parameter while the strong energy condition is violated, which shows that the anisotropic universe in f(R) gravity supports the crucial issue of accelerated expansion of the universe.
Singular cosmological evolution using canonical and ghost scalar fields
Nojiri, Shin'ichi; Odintsov, S.D.; Oikonomou, V.K.; Saridakis, Emmanuel N. E-mail: odintsov@ieec.uab.es E-mail: Emmanuel_Saridakis@baylor.edu
2015-09-01
We demonstrate that finite time singularities of Type IV can be consistently incorporated in the Universe's cosmological evolution, either appearing in the inflationary era, or in the late-time regime. While using only one scalar field instabilities can in principle occur at the time of the phantom-divide crossing, when two fields are involved we are able to avoid such instabilities. Additionally, the two-field scalar-tensor theories prove to be able to offer a plethora of possible viable cosmological scenarios, at which various types of cosmological singularities can be realized. Amongst others, it is possible to describe inflation with the appearance of a Type IV singularity, and phantom late-time acceleration which ends in a Big Rip. Finally, for completeness, we also present the Type IV realization in the context of suitably reconstructed F(R) gravity.
A nonlocal approach to the cosmological constant problem
NASA Astrophysics Data System (ADS)
Carroll, Sean M.; Remmen, Grant N.
2017-06-01
We construct a model in which the cosmological constant is canceled from the gravitational equations of motion. Our model relies on two key ingredients: a nonlocal constraint on the action, which forces the spacetime average of the Lagrangian density to vanish, and a dynamical way for this condition to be satisfied classically with arbitrary matter content. We implement the former condition with a spatially constant Lagrange multiplier associated with the volume form and the latter by including a free four-form gauge field strength in the action. These two features are enough to remove the cosmological constant from the Einstein equation. The model is consistent with all cosmological and experimental bounds on modification of gravity and allows for both cosmic inflation and the present epoch of acceleration.
Cosmological and astrophysical constraints on tachyon dark energy models
NASA Astrophysics Data System (ADS)
Martins, C. J. A. P.; Moucherek, F. M. O.
2016-06-01
Rolling tachyon field models are among the candidates suggested as explanations for the recent acceleration of the Universe. In these models the field is expected to interact with gauge fields and lead to variations of the fine-structure constant α . Here we take advantage of recent observational progress and use a combination of background cosmological observations of type Ia supernovas and astrophysical and local measurements of α to improve constraints on this class of models. We show that the constraints on α imply that the field dynamics must be extremely slow, leading to a constraint of the present-day dark energy equation of state (1 +w0)<2.4 ×10-7 at the 99.7% confidence level. Therefore current and forthcoming standard background cosmology observational probes cannot distinguish this class of models from a cosmological constant, while detections of α variations could possibly do so since they would have a characteristic redshift dependence.
Gravitation and modern cosmology - The cosmological constant problem
NASA Astrophysics Data System (ADS)
Zichichi, Antonino; de Sabbata, Venzo; Sanchez, Norma
An updated version of different approaches to the cosmological constant problem discussed at a symposium in honor of Peter Gabriel Bergmann's 75th birthday, that took place in Erice on 17-20 September 1990, is presented. Topics addressed include an effective action model for the cosmological constant revisited; torsion, quantum effects, and the problem of cosmological constant; variations of constants and exact solutions in multidimensional gravity; null surface canonical formalism; qualitative cosmology; and the gravitational field of an arbitrary axisymmetric mass with a magnetic dipole moment. Attention is also given to a simple model of the universe without singularities; string theory and quantization of gravity; and velocity of propagation of gravitational radiation, mass of the gravitation, range of the gravitational force, and the cosmological constant.
Precision cosmological parameter estimation
NASA Astrophysics Data System (ADS)
Fendt, William Ashton, Jr.
2009-09-01
Experimental efforts of the last few decades have brought. a golden age to mankind's endeavor to understand tine physical properties of the Universe throughout its history. Recent measurements of the cosmic microwave background (CMB) provide strong confirmation of the standard big bang paradigm, as well as introducing new mysteries, to unexplained by current physical models. In the following decades. even more ambitious scientific endeavours will begin to shed light on the new physics by looking at the detailed structure of the Universe both at very early and recent times. Modern data has allowed us to begins to test inflationary models of the early Universe, and the near future will bring higher precision data and much stronger tests. Cracking the codes hidden in these cosmological observables is a difficult and computationally intensive problem. The challenges will continue to increase as future experiments bring larger and more precise data sets. Because of the complexity of the problem, we are forced to use approximate techniques and make simplifying assumptions to ease the computational workload. While this has been reasonably sufficient until now, hints of the limitations of our techniques have begun to come to light. For example, the likelihood approximation used for analysis of CMB data from the Wilkinson Microwave Anistropy Probe (WMAP) satellite was shown to have short falls, leading to pre-emptive conclusions drawn about current cosmological theories. Also it can he shown that an approximate method used by all current analysis codes to describe the recombination history of the Universe will not be sufficiently accurate for future experiments. With a new CMB satellite scheduled for launch in the coming months, it is vital that we develop techniques to improve the analysis of cosmological data. This work develops a novel technique of both avoiding the use of approximate computational codes as well as allowing the application of new, more precise analysis
Nonlinear field space cosmology
NASA Astrophysics Data System (ADS)
Mielczarek, Jakub; Trześniewski, Tomasz
2017-08-01
We consider the FRW cosmological model in which the matter content of the Universe (playing the role of an inflaton or quintessence) is given by a novel generalization of the massive scalar field. The latter is a scalar version of the recently introduced nonlinear field space theory, where the physical phase space of a given field is assumed to be compactified at large energies. For our analysis, we choose the simple case of a field with the spherical phase space and endow it with the generalized Hamiltonian analogous to the XXZ Heisenberg model, normally describing a system of spins in condensed matter physics. Subsequently, we study both the homogenous cosmological sector and linear perturbations of such a test field. In the homogenous sector, we find that nonlinearity of the field phase space is becoming relevant for large volumes of the Universe and can lead to a recollapse, and possibly also at very high energies, leading to the phase of a bounce. Quantization of the field is performed in the limit where the nontrivial nature of its phase space can be neglected, while there is a nonvanishing contribution from the Lorentz symmetry breaking term of the Hamiltonian. As a result, in the leading order of the XXZ anisotropy parameter, we find that the inflationary spectral index remains unmodified with respect to the standard case but the total amplitude of perturbations is subject to a correction. The Bunch-Davies vacuum state also becomes appropriately corrected. The proposed new approach is bringing cosmology and condensed matter physics closer together, which may turn out to be beneficial for both disciplines.
Bojowald, Martin
2005-01-01
Quantum gravity is expected to be necessary in order to understand situations where classical general relativity breaks down. In particular in cosmology one has to deal with initial singularities, i.e., the fact that the backward evolution of a classical space-time inevitably comes to an end after a finite amount of proper time. This presents a breakdown of the classical picture and requires an extended theory for a meaningful description. Since small length scales and high curvatures are involved, quantum effects must play a role. Not only the singularity itself but also the surrounding space-time is then modified. One particular realization is loop quantum cosmology, an application of loop quantum gravity to homogeneous systems, which removes classical singularities. Its implications can be studied at different levels. Main effects are introduced into effective classical equations which allow to avoid interpretational problems of quantum theory. They give rise to new kinds of early universe phenomenology with applications to inflation and cyclic models. To resolve classical singularities and to understand the structure of geometry around them, the quantum description is necessary. Classical evolution is then replaced by a difference equation for a wave function which allows to extend space-time beyond classical singularities. One main question is how these homogeneous scenarios are related to full loop quantum gravity, which can be dealt with at the level of distributional symmetric states. Finally, the new structure of space-time arising in loop quantum gravity and its application to cosmology sheds new light on more general issues such as time.
Bojowald, Martin
2008-01-01
Quantum gravity is expected to be necessary in order to understand situations in which classical general relativity breaks down. In particular in cosmology one has to deal with initial singularities, i.e., the fact that the backward evolution of a classical spacetime inevitably comes to an end after a finite amount of proper time. This presents a breakdown of the classical picture and requires an extended theory for a meaningful description. Since small length scales and high curvatures are involved, quantum effects must play a role. Not only the singularity itself but also the surrounding spacetime is then modified. One particular theory is loop quantum cosmology, an application of loop quantum gravity to homogeneous systems, which removes classical singularities. Its implications can be studied at different levels. The main effects are introduced into effective classical equations, which allow one to avoid the interpretational problems of quantum theory. They give rise to new kinds of early-universe phenomenology with applications to inflation and cyclic models. To resolve classical singularities and to understand the structure of geometry around them, the quantum description is necessary. Classical evolution is then replaced by a difference equation for a wave function, which allows an extension of quantum spacetime beyond classical singularities. One main question is how these homogeneous scenarios are related to full loop quantum gravity, which can be dealt with at the level of distributional symmetric states. Finally, the new structure of spacetime arising in loop quantum gravity and its application to cosmology sheds light on more general issues, such as the nature of time.
Cosmology with the WFIRST High Latitude Survey
NASA Astrophysics Data System (ADS)
Dore, Olivier
Cosmic acceleration is the most surprising cosmological discovery in many decades. Testing and distinguishing among possible explanations requires cosmological measurements of extremely high precision that probe the full history of cosmic expansion and structure growth. The WFIRST-AFTA mission, as described in the Science Definition Team (SDT) reports (Spergel 2013, 2015), has the ability to improve these measurements by 1-2 orders of magnitude compared to the current state of the art, while simultaneously extending their redshift grasp, greatly improving control of systematic effects, and taking a unified approach to multiple probes that provide complementary physical information and cross-checks of cosmological results. We have assembled a team with the expertise and commitment needed to address the stringent challenges of the WFIRST dark energy program through the Project's formulation phase. After careful consideration, we have elected to address investigations A (Galaxy Redshift Survey) and C (Weak Lensing and Cluster Growth) of the WFIRST SIT NRA with a unified team, because the two investigations are tightly linked at both the technical level and the theoretical modeling level. The imaging and spectroscopic elements of the High Latitude Survey (HLS) will be realized as an integrated observing program, and they jointly impose requirements on instrument and telescope performance, operations, and data transfer. The methods for simulating and interpreting weak lensing and galaxy clustering observations largely overlap, and many members of our team have expertise in both areas. The team PI, Olivier Dore, is a cosmologist with a broad expertise in cosmic microwave background and large scale structures. Yun Wang and Chris Hirata will serve as Lead Co-Investigators for topics A and C, respectively. Many members of our team have been involved with the design and requirements of a dark energy space mission for a decade or more, including the Co-Chair and three
Cosmology with a stiff matter era
NASA Astrophysics Data System (ADS)
Chavanis, Pierre-Henri
2015-11-01
bouncing like in loop quantum cosmology. At t =0 , the scale factor is finite and the energy density is equal to zero. The universe first has a phantom behavior where the energy density increases with the scale factor, then a normal behavior where the energy density decreases with the scale factor. For the sake of generality, we consider a cosmological constant of arbitrary sign. When the cosmological constant is positive, the Universe asymptotically reaches a de Sitter regime where the scale factor increases exponentially rapidly with time. This can account for the accelerating expansion of the Universe that we observe at present. When the cosmological constant is negative (anti-de Sitter), the evolution of the Universe is cyclic. Therefore, depending on the sign of the internal energy of the dark fluid and on the sign of the cosmological constant, we obtain analytical solutions of the Friedmann equations describing singular and nonsingular expanding, bouncing, or cyclic universes.
Cosmology of hybrid metric-Palatini f(X)-gravity
Capozziello, Salvatore; Harko, Tiberiu; Koivisto, Tomi S.; Lobo, Francisco S.N.; Olmo, Gonzalo J. E-mail: t.harko@ucl.ac.uk E-mail: flobo@cii.fc.ul.pt
2013-04-01
A new class of modified theories of gravity, consisting of the superposition of the metric Einstein-Hilbert Lagrangian with an f(R) term constructed à la Palatini was proposed recently. The dynamically equivalent scalar-tensor representation of the model was also formulated, and it was shown that even if the scalar field is very light, the theory passes the Solar System observational constraints. Therefore the model predicts the existence of a long-range scalar field, modifying the cosmological and galactic dynamics. An explicit model that passes the local tests and leads to cosmic acceleration was also obtained. In the present work, it is shown that the theory can be also formulated in terms of the quantity X≡κ{sup 2}T+R, where T and R are the traces of the stress-energy and Ricci tensors, respectively. The variable X represents the deviation with respect to the field equation trace of general relativity. The cosmological applications of this hybrid metric-Palatini gravitational theory are also explored, and cosmological solutions coming from the scalar-tensor representation of f(X)-gravity are presented. Criteria to obtain cosmic acceleration are discussed and the field equations are analyzed as a dynamical system. Several classes of dynamical cosmological solutions, depending on the functional form of the effective scalar field potential, describing both accelerating and decelerating Universes are explicitly obtained. Furthermore, the cosmological perturbation equations are derived and applied to uncover the nature of the propagating scalar degree of freedom and the signatures these models predict in the large-scale structure.
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.
Galileons on cosmological backgrounds
Goon, Garrett; Hinterbichler, Kurt; Trodden, Mark E-mail: kurthi@physics.upenn.edu
2011-12-01
We construct four-dimensional effective field theories of a generalized DBI galileon field, the dynamics of which naturally take place on a Friedmann-Robertson-Walker spacetime. The theories are invariant under non-linear symmetry transformations, which can be thought of as being inherited from five-dimensional bulk Killing symmetries via the probe brane technique through which they are constructed. The resulting model provides a framework in which to explore the cosmological role that galileons may play as the universe evolves.
Stochastic processes in cosmology
NASA Astrophysics Data System (ADS)
Cáceres, Manuel O.; Diaz, Mario C.; Pullin, Jorge A.
1987-08-01
The behavior of a radiation filled de Sitter universe in which the equation of state is perturbed by a stochastic term is studied. The corresponding two-dimensional Fokker-Planck equation is solved. The finiteness of the cosmological constant appears to be a necessary condition for the stability of the model which undergoes an exponentially expanding state. Present address: Facultad de Matemática Astronomía y Física, Universidad Nacional de Córdoba, Laprida 854, 5000 Códoba, Argentina.
DOE R&D Accomplishments Database
Wilczek, Frank; Turner, Michael S.
1990-09-01
If Peccei-Quinn (PQ) symmetry is broken after inflation, the initial axion angle is a random variable on cosmological scales; based on this fact, estimates of the relic-axion mass density give too large a value if the axion mass is less than about 10-6 eV. This bound can be evaded if the Universe underwent inflation after PQ symmetry breaking and if the observable Universe happens to be a region where the initial axion angle was atypically small, .1 . (ma/10-6eV)0.59. We show consideration of fluctuations induced during inflation severely constrains the latter alternative.
Chamseddine, Ali H.; Mukhanov, Viatcheslav; Vikman, Alexander E-mail: viatcheslav.Mukhanov@lmu.de
2014-06-01
We consider minimal extensions of the recently proposed Mimetic Dark Matter and show that by introducing a potential for the mimetic non-dynamical scalar field we can mimic nearly any gravitational properties of the normal matter. In particular, the mimetic matter can provide us with inflaton, quintessence and even can lead to a bouncing nonsingular universe. We also investigate the behaviour of cosmological perturbations due to a mimetic matter. We demonstrate that simple mimetic inflation can produce red-tilted scalar perturbations which are largely enhanced over gravity waves.
NASA Astrophysics Data System (ADS)
Krishnan, Chethan; Raju, Avinash; Roy, Shubho; Thakur, Somyadip
2014-02-01
We construct cosmological solutions of higher spin gravity in 2+1 dimensional de Sitter space. We show that a consistent thermodynamics can be obtained for their horizons by demanding appropriate holonomy conditions. This is equivalent to demanding the integrability of the Euclidean boundary conformal field theory partition function, and it reduces to Gibbons-Hawking thermodynamics in the spin-2 case. By using the prescription of Maldacena, we relate the thermodynamics of these solutions to those of higher spin black holes in AdS3.
McFadden, Paul; Skenderis, Kostas
2010-01-15
We propose a holographic description of four-dimensional single-scalar inflationary universes, and show how cosmological observables, such as the primordial power spectrum, are encoded in the correlation functions of a three-dimensional quantum field theory (QFT). The holographic description correctly reproduces standard inflationary predictions in the regime where a perturbative quantization of fluctuations is justified. In the opposite regime, wherein gravity is strongly coupled at early times, we propose a holographic description in terms of perturbative large N QFT. Initiating a holographic phenomenological approach, we show that models containing only two parameters, N and a dimensionful coupling constant, are capable of satisfying the current observational constraints.
NASA Technical Reports Server (NTRS)
Turner, Michael S.; Wilczek, Frank
1991-01-01
If Peccei-Quinn (PQ) symmetry is broken after inflation, the initial axion angle is a random variable on cosmological scales; based on this fact, estimates of the relic-axion mass density give too large a value if the axion mass is less than about 10 to the -6th eV. This bound can be evaded if the universe underwent inflation after PQ-symmetry breaking and if the observable universe happens to be a region where the initial axion angle was atypically small. Consideration of fluctuations induced during inflation severely constrains the latter alternative is shown.
Supersymmetric quantum cosmology
Macias, Alfredo; Camacho, Abel
2009-05-01
We address the canonical quantization in the framework of N = 1 simple supergravity for the case of Gowdy T{sup 3} cosmological models. It will be proved that there exist physical states in the minisuperspace sector of the theory. Our result will be confronted against the so-called no-physical states conjecture and in this way it will be proved that this conjecture is based upon an assumption involving the constraint equations and initial-value hypersurface which, in general, is not valid.
Cosmology of bifundamental fields
Vachaspati, Tanmay
2009-01-15
If a field theory contains gauged, non-Abelian, bifundamental fields, i.e. fields that are charged under two separate non-Abelian gauge groups, the transition from a deconfined phase to a hadronic phase may be frustrated. Similar frustration may occur in non-Abelian gauge models containing matter only in higher dimensional representations, e.g. models with pure glue, or if ordinary quarks are confined by two flux tubes, as implied in the triangular configuration of baryons within QCD. In a cosmological setting, such models can lead to the formation of a web of confining electric flux tubes that can potentially have observational signatures.
Anisotropic spinfoam cosmology
NASA Astrophysics Data System (ADS)
Rennert, Julian; Sloan, David
2014-01-01
The dynamics of a homogeneous, anisotropic universe are investigated within the context of spinfoam cosmology. Transition amplitudes are calculated for a graph consisting of a single node and three links—the ‘Daisy graph’—probing the behaviour a classical Bianchi I spacetime. It is shown further how the use of such single node graphs gives rise to a simplification of states such that all orders in the spin expansion can be calculated, indicating that it is the vertex expansion that contains information about quantum dynamics.
Cosmological special relativity
NASA Astrophysics Data System (ADS)
Carmeli, M.
1996-03-01
Recently we presented a new special relativity theory for cosmology in which it was assumed that gravitation can be neglected and thus the bubble constant can be taken as a constant. The theory was presented in a six-dimensional hvperspace. three for the ordinary space and three for the velocities. In this paper we reduce our hyperspace to four dimensions by assuming that the three-dimensional space expands only radially, thus one is left with the three dimensions of ordinary space and one dimension of the radial velocity.
NASA Astrophysics Data System (ADS)
Gill, Stuart P. D.; Knebe, Alexander; Gibson, Brad K.; Flynn, Chris; Ibata, Rodrigo A.; Lewis, Geraint F.
2003-04-01
An adaptive multi grid approach to simulating the formation of structure from collisionless dark matter is described. MLAPM (Multi-Level Adaptive Particle Mesh) is one of the most efficient serial codes available on the cosmological "market" today. As part of Swinburne University's role in the development of the Square Kilometer Array, we are implementing hydrodynamics, feedback, and radiative transfer within the MLAPM adaptive mesh, in order to simulate baryonic processes relevant to the interstellar and intergalactic media at high redshift. We will outline our progress to date in applying the existing MLAPM to a study of the decay of satellite galaxies within massive host potentials.
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.
Republication of: Relativistic cosmology
NASA Astrophysics Data System (ADS)
Robertson, H. P.
2012-08-01
This is a reprinting of the paper by Howard Percy Robertson, first published in 1933 in Rev. Mod. Phys., that is a very authoritative summary of relativistic cosmology at the stage at which it was up to 1933. The paper has been selected by the Editors of General Relativity and Gravitation for re-publication in the Golden Oldies series of the journal. This republication is accompanied by an editorial note written by George Ellis, and by Robertson's biography, compiled by Andrzej Krasinski from printed sources.
NASA Astrophysics Data System (ADS)
Rasanen, Syksy
The thesis consists of three research papers and an introduction which provides background and also contains some new observations not included in the papers. In the thesis I consider certain questions in the new field of brane cosmology. The basic idea of brane cosmology is that the visible universe is a four- dimensional slice in higher-dimensional spacetime. I give a self-contained introduction to the field, starting from the Randall-Sundrum model and proceeding to the general case of brane gravity and cosmology in the case of one extra dimension. I emphasise the main result of studies of brane gravity: it is possible to obtain approximately four-dimensional gravity independent of the size of the extra dimension, in contrast to set-ups where the observers are not localised in the extra dimension. I proceed to examine a new and promising brave cosmology set-up, the ekpyrotic scenario, in detail. The ekpyrotic scenario aims to be a comprehensive model of the primordial universe and has been presented as an alternative to the prominent scenarios, inflation and pre-big bang. I give an overview of these three scenarios of the primordial universe. I then present the starting point of the ekpyrotic scenario and the construction of the four-dimensional effective theory. After briefly discussing the internal problems of the four-dimensional effective theory, I proceed to the far more serious problems of the four- dimensional construction itself. I conclude that the four-dimensional effective theory does not give a correct description even at a qualitative level. I then discuss some problems faced by the five-dimensional approach, and comment on the spin-off known as the “cyclic model of the universe”. I conclude that the ekpyrotic scenario is a welcome new idea but that most work done thus far is not solid. Careful analysis in the five-dimensional setting is needed to promote the scenario from an interesting concept to a working model with testable predictions.
Non-minimal derivative coupling gravity in cosmology
NASA Astrophysics Data System (ADS)
Gumjudpai, Burin; Rangdee, Phongsaphat
2015-11-01
We give a brief review of the non-minimal derivative coupling (NMDC) scalar field theory in which there is non-minimal coupling between the scalar field derivative term and the Einstein tensor. We assume that the expansion is of power-law type or super-acceleration type for small redshift. The Lagrangian includes the NMDC term, a free kinetic term, a cosmological constant term and a barotropic matter term. For a value of the coupling constant that is compatible with inflation, we use the combined WMAP9 (WMAP9 + eCMB + BAO + H_0) dataset, the PLANCK + WP dataset, and the PLANCK TT, TE, EE + lowP + Lensing + ext datasets to find the value of the cosmological constant in the model. Modeling the expansion with power-law gives a negative cosmological constants while the phantom power-law (super-acceleration) expansion gives positive cosmological constant with large error bar. The value obtained is of the same order as in the Λ CDM model, since at late times the NMDC effect is tiny due to small curvature.
Dark flows and the cosmological axis
NASA Astrophysics Data System (ADS)
Tsagas, Christos G.
2012-10-01
Recent surveys indicate coherent large-scale peculiar motions, commonly referred to as 'dark flows', considerably stronger than expected. At the same time, an increasing number of reports suggest the presence of a weak dipolar anisotropy in the supernova data. The Universe seems to accelerate slightly faster in one direction and equally slower in the opposite. Also, this 'cosmological axis' lies fairly close to the cosmic microwave background dipole. Since apparent, dipole-like, anisotropies are the trademark signature of peculiar motions, we consider the possibility that these, seemingly unconnected, observations are actually related. In the process, we find that observers living inside a dark flow could experience locally accelerated expansion in a globally decelerating Universe. Moreover, to these observers, the acceleration should appear slightly faster in one direction and equally slower in the opposite, as if there is a preferred axis in the universe. When combined, these results open, in principle at least, the theoretical possibility of addressing the supernova data and the cosmic acceleration by appealing to dark flows rather than dark energy.
Cosmology: Recent and future developments
Joshua A. Frieman
2003-01-15
The precision with which the cosmological parameters have been determined has made dramatic progress in just the last two years. The author reviews this recent observational progress, highlights some of the key questions facing cosmology in the new millennium, and briefly discusses some of the projects now being mounted or contemplated to address them.
Rolling Tachyon in Nonlocal Cosmology
Joukovskaya, L.
2007-11-20
Nonlocal cosmological models derived from String Field Theory are considered. A new method for constructing rolling tachyon solutions in the FRW metric in two field configuration is proposed and solutions of the Friedman equations with nonlocal operator are presented. The cosmological properties of these solutions are discussed.
Turner, Michael S.
1997-03-01
The Hubble constant sets the size and age of the Universe, and, together with independent determinations of the age, provides a consistency check of the standard cosmology. The Hubble constant also provides an important test of our most attractive paradigm for extending the standard cosmology, inflation and cold dark matter.
Can Accelerators Accelerate Learning?
NASA Astrophysics Data System (ADS)
Santos, A. C. F.; Fonseca, P.; Coelho, L. F. S.
2009-03-01
The 'Young Talented' education program developed by the Brazilian State Funding Agency (FAPERJ) [1] makes it possible for high-schools students from public high schools to perform activities in scientific laboratories. In the Atomic and Molecular Physics Laboratory at Federal University of Rio de Janeiro (UFRJ), the students are confronted with modern research tools like the 1.7 MV ion accelerator. Being a user-friendly machine, the accelerator is easily manageable by the students, who can perform simple hands-on activities, stimulating interest in physics, and getting the students close to modern laboratory techniques.
Can Accelerators Accelerate Learning?
Santos, A. C. F.; Fonseca, P.; Coelho, L. F. S.
2009-03-10
The 'Young Talented' education program developed by the Brazilian State Funding Agency (FAPERJ)[1] makes it possible for high-schools students from public high schools to perform activities in scientific laboratories. In the Atomic and Molecular Physics Laboratory at Federal University of Rio de Janeiro (UFRJ), the students are confronted with modern research tools like the 1.7 MV ion accelerator. Being a user-friendly machine, the accelerator is easily manageable by the students, who can perform simple hands-on activities, stimulating interest in physics, and getting the students close to modern laboratory techniques.
Cosmology with a dark refraction index
NASA Astrophysics Data System (ADS)
Chen, Bin
2009-09-01
In this dissertation we review Gordon's optical metric theory, generalize it, and apply it to modern cosmology. In Chapter 1, we build the notation, define important quantities (luminosity distance, angular diameter distance, etc.), derive a few key equations (reciprocity relation, transport equations of optical scalars, etc.), and develop some basic techniques which will be useful later on. In Chapter 2 we apply Gordon's optical metric theory to Friedman-Lemaître- Robertson-Walker cosmologies. We associate a refraction index with the cosmic fluid and derive the refraction-corrected distance redshift relations. We then fit the Hubble curve of current supernova observations with a non-accelerating cosmological model. We also show that some observational effects caused by inhomogeneities, e.g., the Sachs-Wolfe effect, can be interpreted as being caused by an effective index of refraction, and hence this theory could extend to other speed of light communications such as gravitational radiation and neutrino fluxes. In Chapter 3 we show that Gordon's optical metric on a curved spacetime can be generalized to include absorption by allowing the metric to become complex. We distinguish two different cases, i.e., strong and weak absorption, and demonstrate the use of the complex optical metric theory by giving three examples. We use one of these examples to compute corrected distance-redshift relations for Friedman-Lemaître-Robertson-Walker models in which the cosmic fluid possesses a complex index of refraction that represents grey extinction. We then fit this corrected Hubble curve to the same supernovae data used in Chapter 2 by assuming pure absorption. In Chapter 4 we equate the physical intensity reduction of a light wave caused by weak absorption with a geometrical reduction in intensity caused by a "transverse" conformal transformation of the spacetime metric in which the wave travels. We then modify Gordon's optical metric to include absorption via a totally
Teng, L.C.
1960-01-19
ABS>A combination of two accelerators, a cyclotron and a ring-shaped accelerator which has a portion disposed tangentially to the cyclotron, is described. Means are provided to transfer particles from the cyclotron to the ring accelerator including a magnetic deflector within the cyclotron, a magnetic shield between the ring accelerator and the cyclotron, and a magnetic inflector within the ring accelerator.
Is cosmology a historical science?
NASA Astrophysics Data System (ADS)
Grignon, Claude
2012-06-01
To explain the formation and the evolution of the Universe, cosmology settles universal laws. In this respect, cosmology belongs to the category of the nomothetic sciences, which write and think in mathematics. But cosmology is also akin to the historical sciences; like archaeology, geology or the biology of evolution, cosmology infers history from the vestiges of the past; moreover, it is not an experimental but an observational science. Due to this ambivalence, cosmology confronts divergent epistemological options. Nomothetic and historical sciences use indeed different, even opposite conceptions of such fundamental notions as time, causality and chance. Is it possible to make the history of the Universe intelligible without referring to the narrative conception of history congruent with the course of the historical world?.
Higher dimensional loop quantum cosmology
NASA Astrophysics Data System (ADS)
Zhang, Xiangdong
2016-07-01
Loop quantum cosmology (LQC) is the symmetric sector of loop quantum gravity. In this paper, we generalize the structure of loop quantum cosmology to the theories with arbitrary spacetime dimensions. The isotropic and homogeneous cosmological model in n+1 dimensions is quantized by the loop quantization method. Interestingly, we find that the underlying quantum theories are divided into two qualitatively different sectors according to spacetime dimensions. The effective Hamiltonian and modified dynamical equations of n+1 dimensional LQC are obtained. Moreover, our results indicate that the classical big bang singularity is resolved in arbitrary spacetime dimensions by a quantum bounce. We also briefly discuss the similarities and differences between the n+1 dimensional model and the 3+1 dimensional one. Our model serves as a first example of higher dimensional loop quantum cosmology and offers the possibility to investigate quantum gravity effects in higher dimensional cosmology.
More problems for Newtonian cosmology
NASA Astrophysics Data System (ADS)
Wallace, David
2017-02-01
I point out a radical indeterminism in potential-based formulations of Newtonian gravity once we drop the condition that the potential vanishes at infinity (as is necessary, and indeed celebrated, in cosmological applications). This indeterminism, which is well known in theoretical cosmology but has received little attention in foundational discussions, can be removed only by specifying boundary conditions at all instants of time, which undermines the theory's claim to be fully cosmological, i.e., to apply to the Universe as a whole. A recent alternative formulation of Newtonian gravity due to Saunders (Philosophy of Science 80 (2013) pp. 22-48) provides a conceptually satisfactory cosmology but fails to reproduce the Newtonian limit of general relativity in homogenous but anisotropic universes. I conclude that Newtonian gravity lacks a fully satisfactory cosmological formulation.
Palmer, R.B.
1987-05-01
This paper looks at, and compares three types of damping ring lattices: conventional, wiggler lattice with finite ..cap alpha.., wiggler lattice with ..cap alpha.. = 0, and observes the attainable equilibrium emittances for the three cases assuming a constraint on the attainable longitudinal impedance of 0.2 ohms. The emittance obtained are roughly in the ratio 4:2:1 for these cases.
Tracking the SSC test lattices
Leemann, B.T.; Douglas, D.R.; Forest, E.
1985-10-01
The dynamic aperture and its determination emerged from the SSC reference design study as the single most important accelerator physics issue pertinent to the SSC. Beside the fundamental need of a finite dynamic aperture for any accelerator, it was considered to be a useful criterion for the magnet selection. An aperture workshop organized in November 1984 at LBL served the purpose to identify the various aspects of the aperture question and to organize the aperture task force accordingly. It was recognized that numerical models had to play an important role and the qualifications of several tracking codes were investigated. None of the existing codes could meet all of the criteria for an ideal tracking code and substantial program development became unavoidable. It was therefore decided to begin tracking SSC test lattices.
FFAG lattice without opposite bends
NASA Astrophysics Data System (ADS)
Trbojevic, Dejan; Courant, Ernest D.; Garren, Al
2000-08-01
A future "neutrino factory" or Muon Collider requires fast muon acceleration before the storage ring. Several alternatives for fast muon acceleration have previously been considered. One of them is the FFAG (Fixed Field Alternating Gradient) synchrotron. The FFAG concept was developed in 1952 by K. R. Symon (ref. 1). The advantages of this design are the fixed magnetic field, large range of particle energy, simple RF; power supplies are simple, and there is no transition energy. But a drawback is that reverse bending magnets are included in the configuration; this increases the size and cost of the ring. Recently some modified FFAG lattice designs have been described where the amount of opposite bending was significantly reduced (ref. 2, ref. 3).
Dark Energy and Dark Matter as Components of Cosmological Term Stand for Vorticity and Shear
NASA Astrophysics Data System (ADS)
Nurgaliev, Ildus S.
2015-01-01
This report brings attention to the ignored components of the kinetic energy related to vorticity and shear in the standard cosmological dynamics. It is concluded that averaged term of squared vorticity is term attributed as an accelerated expansion caused by negative energy of an enigmatic repulsive factor. Cosmological singularity has been a consequence of the unrealistically excessive cosmological principle (too detailed symmetry of flow) such as "Hubble law". Appropriate realistic one is suggested, which is also linear function of space coordinates (because of homogeneity principle) but has tensor character. Cosmological principle is applied to irregularities - they are homogeneous and isotropic in average to some extend within the corresponding Megagalactic scales. The "Big Bang" is nothing but the local bounce of the Meta-galaxy which is typical among myriads others. Exact solutions are presented (dynamic, steady and static) of the cosmologic dynamics. "Negative radiation" equation of state p =∈/3 with p≤0, ∈≤0 is generated by vorticity which is dynamic carrier of the dark energy. This fact dismisses the need in any other artificial cosmologic term, the need in any other modifications of the gravity theory or in an exotic matter as a cause for cosmological accelerated expansion. New conception of material point established. Social and educational aspects of the findings touched slightly.
Cosmological evolution of quintessence and phantom with a new type of interaction in dark sector
NASA Astrophysics Data System (ADS)
Wei, Hao
2011-04-01
In the present work, motivated by the work of Cai and Su [Phys. Rev. D 81 (2010) 103514], we propose a new type of interaction in dark sector, which can change its sign when our universe changes from deceleration to acceleration. We consider the cosmological evolution of quintessence and phantom with this type of interaction, and find that there are some scaling attractors which can help to alleviate the cosmological coincidence problem. Our results also show that this new type of interaction can bring new features to cosmology.
Particle physics and cosmology
Kolb, E.W.
1986-10-01
This series of lectures is about the role of particle physics in physical processes that occurred in the very early stages of the bug gang. Of particular interest is the role of particle physics in determining the evolution of the early Universe, and the effect of particle physics on the present structure of the Universe. The use of the big bang as a laboratory for placing limits on new particle physics theories will also be discussed. Section 1 reviews the standard cosmology, including primordial nucleosynthesis. Section 2 reviews the decoupling of weakly interacting particles in the early Universe, and discusses neutrino cosmology and the resulting limits that may be placed on the mass and lifetime of massive neutrinos. Section 3 discusses the evolution of the vacuum through phase transitions in the early Universe and the formation of topological defects in the transitions. Section 4 covers recent work on the generation of the baryon asymmetry by baryon-number violating reactions in Grand Unified Theories, and mentions some recent work on baryon number violation effects at the electroweak transition. Section 5 is devoted to theories of cosmic inflation. Finally, Section 6 is a discussion of the role of extra spatial dimensions in the evolution of the early Universe. 78 refs., 32 figs., 6 tabs.
The standard cosmological model
NASA Astrophysics Data System (ADS)
Scott, D.
2006-06-01
The Standard Model of Particle Physics (SMPP) is an enormously successful description of high-energy physics, driving ever more precise measurements to find "physics beyond the standard model", as well as providing motivation for developing more fundamental ideas that might explain the values of its parameters. Simultaneously, a description of the entire three-dimensional structure of the present-day Universe is being built up painstakingly. Most of the structure is stochastic in nature, being merely the result of the particular realization of the "initial conditions" within our observable Universe patch. However, governing this structure is the Standard Model of Cosmology (SMC), which appears to require only about a dozen parameters. Cosmologists are now determining the values of these quantities with increasing precision to search for "physics beyond the standard model", as well as trying to develop an understanding of the more fundamental ideas that might explain the values of its parameters. Although it is natural to see analogies between the two Standard Models, some intrinsic differences also exist, which are discussed here. Nevertheless, a truly fundamental theory will have to explain both the SMPP and SMC, and this must include an appreciation of which elements are deterministic and which are accidental. Considering different levels of stochasticity within cosmology may make it easier to accept that physical parameters in general might have a nondeterministic aspect.
Investigations in theoretical cosmology
NASA Astrophysics Data System (ADS)
Barnard, Michael James
This report is a compilation of research I have done in the field of cosmology while at the University of California, Davis. The topics are all closely linked to the physics of scalar fields in General Relativity. This thesis contains the text of two papers, both of which deal with the goals and motivations of future projects in observational cosmology. The first is an evaluation of the effect of future observations on constraints on the parameter space of the Albrecht- Skordis model of dark energy. These future data sets were found to be able of constraining the scalar field model parameters in ways consistent with the constraints on the phenomenological equation of state parameters used by the Dark Energy Task Force. The second paper used principle component analysis of the equation of state parameter on simulated future data sets to construct parameter spaces. Distributions of dark energy quintessence models were then projected into these parameter spaces; it was found that there is structure in the separation of these models that is marginally detectable by so called "Stage 4" experiments. Also included are a review of the derivation of the scale invariant primordial power spectrum and an evaluation of a model of open inflation as the cause of the low CMB quadrupole.
Peculiar cosmological velocities
Lewis, C.M.
1990-01-01
In the first section a gauge-invariant, variations formalism for investigating vector perturbations is set up, suitable for showing that there is no natural way that the usual scalar inflation field could give rise to vorticities. In the last two sections, a vector field A{sub {mu}} is coupled to the Einstein equations with a linearly perturbed Friedmann-Robertson-Walker (FRW) metric, constructed to generate first order vector perturbations. A working classical chaotic vector inflation is demonstrated and then quantum fluctuations of the field are used to constrain the cosmological perturbations. In particular, the vector momentum flux, T{sub 0i}, is tracked to the epoch where a radiation-dominated matter exists. Matching conditions using observational constraints of the cosmic microwave background radiation (CMBR) gives rise to a peculiar cosmological velocity of the order of 10{sup {minus}100}c. Amplification of this number, e.g., by breaking the conformal invariance of the field, could be used to generate cosmic magnetic fields using a dynamo mechanism.
NASA Astrophysics Data System (ADS)
Perkins, D. K.
2006-08-01
Microbes swarming on a sand grain planet or integral complex organisms evolving consciousness at the forefront of cosmic evolution? How is our new cosmology contributing to redefining who we see ourselves to be at the edge of the 21^st century, as globalization and capitalism speed forward? How is the evolution of stardust and the universe offering new paradigms of process and identity regarding the role, function and emergence of life in space-time? What are the cultural and philosophical questions that are arising and how might astronomy be contributing to the creation of new visions for cooperation and community at a global scale? What is the significance of including astronomy in K-12 education and what can it offer youth regarding values in light of the present world situation? Exploring our new cosmological concepts and the emergence of life at astronomical scales may offer much of valuable orientation toward reframing the human role in global evolution. Considering new insight from astrobiology each diverse species has a definitive role to play in the facilitation and functioning of the biosphere. Thus the question may arise: Is there any sort of ethic implied by natural science and offered by our rapidly expanding cosmic frontier?
Aspects of cosmological relativity.
NASA Astrophysics Data System (ADS)
Carmeli, M.
1999-07-01
The author reviews cosmological relativity, a new special theory of relativity that was recently developed for cosmology, and discusses in detail some of its aspects. He recalls that in this theory it is assumed that gravitation is negligible. Under this assumption, the receding velocities of galaxies and the distances between them in the Hubble expansion are united into a four-dimensional pseudo-Euclidean manifold, similarly to space and time in ordinary special relativity. The Hubble law is assumed and is written in an invariant way that enables one to derive a four-dimensional transformation which is similar to the Lorentz transformation. The parameter in the new transformation is the ratio between the cosmic time to the Hubble time. Accordingly, the new transformation relates physical quantities at different cosmic times in the limit of weak or negligible gravitation. The transformation is then applied to the problem of the expansion of the universe at the very early stage when gravity was negligible and thus the transformation is applicable. New applications of the theory are presented. The author shows that there is no need to assume the existence of galaxy dark matter; the Tully-Fisher law is derived from the theory. A completely new picture of the expanding universe is thus obtained and compared to the FRW one.
Cosmology with matter diffusion
Calogero, Simone; Velten, Hermano E-mail: velten@cce.ufes.br
2013-11-01
We construct a viable cosmological model based on velocity diffusion of matter particles. In order to ensure the conservation of the total energy-momentum tensor in the presence of diffusion, we include a cosmological scalar field φ which we identify with the dark energy component of the universe. The model is characterized by only one new degree of freedom, the diffusion parameter σ. The standard ΛCDM model can be recovered by setting σ = 0. If diffusion takes place (σ > 0) the dynamics of the matter and of the dark energy fields are coupled. We argue that the existence of a diffusion mechanism in the universe may serve as a theoretical motivation for interacting models. We constrain the background dynamics of the diffusion model with Supernovae, H(z) and BAO data. We also perform a perturbative analysis of this model in order to understand structure formation in the universe. We calculate the impact of diffusion both on the CMB spectrum, with particular attention to the integrated Sachs-Wolfe signal, and on the matter power spectrum P(k). The latter analysis places strong constraints on the magnitude of the diffusion mechanism but does not rule out the model.
NASA Astrophysics Data System (ADS)
Mahootian, F.
2009-12-01
The rapid convergence of advancing sensor technology, computational power, and knowledge discovery techniques over the past decade has brought unprecedented volumes of astronomical data together with unprecedented capabilities of data assimilation and analysis. A key result is that a new, data-driven "observational-inductive'' framework for scientific inquiry is taking shape and proving viable. The anticipated rise in data flow and processing power will have profound effects, e.g., confirmations and disconfirmations of existing theoretical claims both for and against the big bang model. But beyond enabling new discoveries can new data-driven frameworks of scientific inquiry reshape the epistemic ideals of science? The history of physics offers a comparison. The Bohr-Einstein debate over the "completeness'' of quantum mechanics centered on a question of ideals: what counts as science? We briefly examine lessons from that episode and pose questions about their applicability to cosmology. If the history of 20th century physics is any indication, the abandonment of absolutes (e.g., space, time, simultaneity, continuity, determinacy) can produce fundamental changes in understanding. The classical ideal of science, operative in both physics and cosmology, descends from the European Enlightenment. This ideal has for over 200 years guided science to seek the ultimate order of nature, to pursue the absolute theory, the "theory of everything.'' But now that we have new models of scientific inquiry powered by new technologies and driven more by data than by theory, it is time, finally, to relinquish dreams of a "final'' theory.
NASA Astrophysics Data System (ADS)
Sadeghnezhad, Naser; Nozari, Kourosh
2017-06-01
We extend the idea of mimetic gravity to a Randall-Sundrum II braneworld model. As for the 4-dimensional mimetic gravity, we isolate the conformal degree of freedom of 5-dimensional gravity in a covariant manner. We assume the bulk metric to be made up of a non-dynamical scalar field Φ and an auxiliary metric G˜AB so that GAB =G˜CDΦ,CΦ,DG˜AB where A , B , . . . are the bulk spacetime indices. Then we show that the induced conformal degree of freedom on the brane as an induced scalar field, plays the role of a mimetic field on the brane. In fact, we suppose that the scalar degree of freedom which mimics the dark sectors on the brane has its origin on the bulk scalar field, Φ. By adopting some suitable mimetic potentials on the brane, we show that this brane mimetic field explains the late time cosmic expansion in the favor of observational data: the equation of state parameter of this field crosses the cosmological constant line in near past from quintessence to phantom phase in a redshift well in the range of observation. We show also that this induced mimetic scalar field has the capability to explain initial time cosmological inflation. We study parameter space of the models numerically in order to constraint the models with Planck2015 data set.
Dynamical systems approach and generic properties of f (T ) cosmology
NASA Astrophysics Data System (ADS)
Hohmann, Manuel; Järv, Laur; Ualikhanova, Ulbossyn
2017-08-01
We present a systematic analysis of the dynamics of flat Friedmann-Lemaître-Robertson-Walker cosmological models with radiation and dust matter in generalized teleparallel f (T ) gravity. We show that the cosmological dynamics of this model are fully described by a function W (H ) of the Hubble parameter, which is constructed from the function f (T ) . After reducing the phase space to two dimensions, we derive the conditions on W (H ) for the occurrence of de Sitter fixed points, accelerated expansion, crossing the phantom divide, and finite time singularities. Depending on the model parameters, it is possible to have a bounce (from contraction to expansion) or a turnaround (from expansion to contraction), but cyclic or oscillating scenarios are prohibited. As an illustration of the formalism we consider power law f (T )=T +α (-T )n models, and show that these allow only one period of acceleration and no phantom divide crossing.
Initial lattice studies for the Berkeley Femtosecond X-ray Light Source
NASA Astrophysics Data System (ADS)
Zholents, A.; Reichel, I.; Robin, D.; Tanabe, J.; Wan, W.
2002-05-01
We present lattice studies for a proposed femtosecond synchrotron radiation X-ray source based on a recirculating accelerator. After a general description, we cover specific aspects of the lattice that are relevant to this type of machine and show preliminary results of particle tracking and briefly describe a new code developed for a comprehensive particle tracking in recirculating accelerators.
Numerical Studies of Localized Vibrating Structures in Nonlinear Lattices
1991-03-01
lattice, from Denardo [19901. 11 strings which supported adjacent elements , and was assumed to be approximately linear. For our purposes, we will assume a...City, State, and ZIP Code) 10 SOURCE OF FUNDING NUMBERS PROGRAM PROJECT TASK WORK UNIT ELEMENT NO NO NO ACCESSION NO 11 TITLE (Include Security...art in cosmology , particle physics, condensed matter physics, and hydrodynamics, to name but a few. Most of the soliton work performed to date has
Cosmological Physics Ground Rules and How to Evaluate Cosmologies
NASA Astrophysics Data System (ADS)
Dilworth, D. J.
2009-12-01
This paper is a simple reminder for cosmology enthusiasts of the bright line separating the laws of physics from science fiction. It provides some tools: rules, guidelines and a definition of space useful for examining cosmology science claims and concepts. It explains the stringent thresholds for an idea before it can accurately be called a scientific theory or hypothesis; and who bears the burden of proof for a theory. These simple tools provide solid ground so you may more easily examine cosmology claims to help make up your own mind which side of the science/science fiction line a specific claim belongs on.
NASA Astrophysics Data System (ADS)
Chaubey, R.; Shukla, A. K.; Raushan, Rakesh
2017-04-01
The general class of Bianchi cosmological models with dark energy in the form of modified Chaplygin gas with variable Λ and G and bulk viscosity have been considered. We discuss three types of average scale factor by using a special law for deceleration parameter which is linear in time with negative slope. The exact solutions to the corresponding field equations are obtained. We obtain the solution of bulk viscosity ( ξ), cosmological constant (Λ), gravitational parameter ( G) and deceleration parameter ( q) for different equations of state. The model describes an accelerating Universe for large value of time t, wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.
The accelerating universe and dark energy
NASA Astrophysics Data System (ADS)
Baltay, Charles
2014-05-01
The recent discovery by Riess et al.1 and Perlmutter et al.2 that the expansion of the universe is accelerating is one of the most significant discoveries in cosmology in the last few decades. To explain this acceleration a mysterious new component of the universe, dark energy, was hypothesized. Using general relativity (GR), the measured rate of acceleration translates to the present understanding that the baryonic matter, of which the familiar world is made of, is a mere 4% of the total mass-energy of the universe, with nonbaryonic dark matter making up 24% and dark energy making up the majority 72%. Dark matter, by definition, has attractive gravity, and even though we presently do not know what it is, it could be made of the next heavy particles discovered by particle physicists. Dark energy, however, is much more mysterious, in that even though we do not know what it is, it must have some kind of repulsive gravity and negative pressure, very unusual properties that are not part of the present understanding of physics. Investigating the nature of dark energy is therefore one of the most important areas of cosmology. In this review, the cosmology of an expanding universe, based on GR, is discussed. The methods of studying the acceleration of the universe, and the nature of dark energy, are presented. A large amount of experimentation on this topic has taken place in the decade since the discovery of the acceleration. These are discussed and the present state of knowledge of the cosmological parameters is summarized in Table 7 below. A vigorous program to further these studies is under way. These are presented and the expected results are summarized in Table 10 below. The hope is that at the end of this program, it would be possible to tell whether dark energy is due to Einstein's cosmological constant or is some other new constituent of the universe, or alternately the apparent acceleration is due to some modification of GR.
Report of the workshop on realistic SSC lattices
1985-10-01
A workshop was held at the SSC Central Design Group from May 29 to June 4, 1985, on topics relating to the lattice of the SSC. The workshop marked a shift of emphasis from the investigation of simplified test lattices to the development of a realistic lattice suitable for the conceptual design report. The first day of the workshop was taken up by reviews of accelerator system requirements, of the reference design solutions for these requirements, of lattice work following the reference design, and of plans for the workshop. The work was divided among four working groups. The first, chaired by David Douglas, concerned the arcs of regular cells. The second group, which studied the utility insertions, was chaired by Beat Leemann. The third group, under David E. Johnson, concerned itself with the experimental insertions, dispersion suppressors, and phase trombones. The fourth group, responsible for global lattice considerations and the design of a new realistic lattice example, was led by Ernest Courant. The papers resulting from this workshop are roughly divided into three sets: those relating to specific lattice components, to complete lattices, and to other topics. Among the salient accomplishments of the workshop were additions to and optimization of lattice components, especially those relating to lattices using 1-in-1 magnets, either horizontally or vertically separated, and the design of complete lattice examples. Selected papers are indexed separately for inclusion in the Energy Science and Technology Database.
Lee, Y.Y.; Barton, D.S.; Claus, J.; Cottingham, J.G.; Courant, E.D.; Danby, G.T.; Dell, G.F.; Forsyth, E.B.; Gupta, R.C.; Kats, J.
1987-01-01
The AGS Booster has three objectives. They are to increase the space charge limit of the AGS, to increase the intensity of the polarized proton beam by accumulating many linac pulses (since the intensity is limited by the polarized ion source), and to reaccelerate heavy ions from the BNL Tandem Van de Graaff before injection into the AGS. The machine is capable of accelerating protons at 7.5 Hertz from 200 MeV to 1.5 GeV or to lower final energies at faster repetition rates. The machine will also be able to accelerate heavy ions from as low as 1 MeV/nucleon to a magnetic rigidity as high as 17.6 Tesla-meters with a one second repetition rate. As an accumulator for polarized protons, the Booster should be able to store the protons at 200 MeV for several seconds. We expect that the Booster will increase the AGS proton intensity by a factor of four, polarized proton intensity by a factor of twenty to thirty, and will also enable the AGS to accelerate all species of heavy ions (at present the AGS heavy ion program is limited to the elements lighter than sulfur because it can only accelerate fully stripped ions). The construction project started in FY 1985 and is expected to be completed in 1989. The purpose of this paper is to provide a future reference for the AGS Booster lattice.
An Introduction to Galaxies and Cosmology
NASA Astrophysics Data System (ADS)
Jones, Mark H.; Lambourne, Robert J. A.
2004-06-01
Introduction; 1. The Milky Way - our galaxy; 2. Normal galaxies; 3. Active galaxies; 4. The spatial distribution of galaxies; 5. Introducing cosmology - the science of the Universe; 6. Big Bang cosmology - the Evolving Universe; 7. Observational cosmology - measuring the Universe; 8. Questioning cosmology - outstanding problems about the Universe; Answers and comments; Appendix. Useful quantities and units; Glossary; Acknowledgements; Index.
Anisotropic cosmological solutions in massive vector theories
NASA Astrophysics Data System (ADS)
Heisenberg, Lavinia; Kase, Ryotaro; Tsujikawa, Shinji
2016-11-01
In beyond-generalized Proca theories including the extension to theories higher than second order, we study the role of a spatial component v of a massive vector field on the anisotropic cosmological background. We show that, as in the case of the isotropic cosmological background, there is no additional ghostly degrees of freedom associated with the Ostrogradski instability. In second-order generalized Proca theories we find the existence of anisotropic solutions on which the ratio between the anisotropic expansion rate Σ and the isotropic expansion rate H remains nearly constant in the radiation-dominated epoch. In the regime where Σ/H is constant, the spatial vector component v works as a dark radiation with the equation of state close to 1/3. During the matter era, the ratio Σ/H decreases with the decrease of v. As long as the conditions |Σ| ll H and v2 ll phi2 are satisfied around the onset of late-time cosmic acceleration, where phi is the temporal vector component, we find that the solutions approach the isotropic de Sitter fixed point (Σ = 0 = v) in accordance with the cosmic no-hair conjecture. In the presence of v and Σ the early evolution of the dark energy equation of state wDE in the radiation era is different from that in the isotropic case, but the approach to the isotropic value wDE(iso) typically occurs at redshifts z much larger than 1. Thus, apart from the existence of dark radiation, the anisotropic cosmological dynamics at low redshifts is similar to that in isotropic generalized Proca theories. In beyond-generalized Proca theories the only consistent solution to avoid the divergence of a determinant of the dynamical system corresponds to v = 0, so Σ always decreases in time.
A New Cosmological Model: Black Hole Universe
NASA Astrophysics Data System (ADS)
Zhang, Tianxi
2007-12-01
An alternative cosmological model called by Black Hole Universe is newly developed. According to this model, the universe originated from a hot star-like black hole with several solar masses, and gradually grew up through a supermassive black hole with million to billion solar masses to the present state with trillion-trillion solar masses due to continuously inhaling matter from its outside - the mother universe. The structure and evolution of the black hole universe are spatially hierarchical and temporally iterative. In each of iterations, the matter reconfigures and the universe is renewed rather than a simple repeat. A universe passes through birth, growth, and death. The entire life of a universe roughly divides into three periods with different rates of expansion. In the early period, the universe was a child, which did not eat much and thus grew slowly. In the middle period, the universe is an adult, which expands quickly with a speed up to the speed of light. And in the final period, the universe will become elder and slow down the expansion till a complete stop when the outside matter is all swallowed. The black hole universe model is consistent with the Mach principle, the observations of the universe, and the Einstein general theory of relativity and can be understood with the well-developed physics. This new model does not need a dark energy for acceleration and has a great impact on the traditional big bang cosmology. In this presentation, we will show the origin, evolution, and expansion of the black hole universe, explain the cosmic microwave background radiation, describe the energy mechanism of quasars, illustrate the black hole nucleosynthesis of elements, analyze the mechanisms of redshifts, and compare the black hole universe model with the big bang cosmology.
Quantum Cosmology of f( R, T) gravity
NASA Astrophysics Data System (ADS)
Xu, Min-Xing; Harko, Tiberiu; Liang, Shi-Dong
2016-08-01
Modified gravity theories have the potential of explaining the recent acceleration of the Universe without resorting to the mysterious concept of dark energy. In particular, it has been pointed out that matter-geometry coupling may be responsible for the recent cosmological dynamics of the Universe, and matter itself may play a more fundamental role in the description of the gravitational processes that usually assumed. In the present paper we study the quantum cosmology of the f( R, T) theory of gravity, in which the effective Lagrangian of the gravitational field is given by an arbitrary function of the Ricci scalar, and the trace of the matter energy-momentum tensor, respectively. For the background geometry we adopt the Friedmann-Robertson-Walker metric, and we assume that matter content of the Universe consists of a perfect fluid. In this framework we obtain the general form of the gravitational Hamiltonian, of the quantum potential, and of the canonical momenta, respectively. This allows us to formulate the full Wheeler-de Witt equation describing the quantum properties of this modified gravity model. As a specific application we consider in detail the quantum cosmology of the f(R,T)=F^0(R)+θ RT model, in which F^0(R) is an arbitrary function of the Ricci scalar, and θ is a function of the scale factor only. The Hamiltonian form of the equations of motion, and the Wheeler-de Witt equations are obtained, and a time parameter for the corresponding dynamical system is identified, which allows one to formulate the Schrödinger-Wheeler-de Witt equation for the quantum-mechanical description of the model under consideration. A perturbative approach for the study of this equation is developed, and the energy levels of the Universe are obtained by using a twofold degenerate perturbation approach. A second quantization approach for the description of quantum time is also proposed and briefly discussed.
Experience with split transition lattices at RHIC
Montag, C.; Tepikian, S.; Blaskiewicz, M.; Brennan, J.M.
2010-05-23
During the acceleration process, heavy ion beams in RHIC cross the transition energy. When RHIC was colliding deuterons and gold ions during Run-8, lattices with different integer tunes were used for the two rings. This resulted in the two rings crossing transition at different times, which proved beneficial for the 'Yellow' ring, the RF system of which is slaved to the 'Blue' ring. For the symmetric gold-gold run in FY2010, lattices with different transition energies but equal tunes were implemented. We report the optics design concept as well as operational experience with this configuration.
Splotch: visualizing cosmological simulations
NASA Astrophysics Data System (ADS)
Dolag, K.; Reinecke, M.; Gheller, C.; Imboden, S.
2008-12-01
We present a light and fast, publicly available, ray-tracer Splotch software tool which supports the effective visualization of cosmological simulations data. We describe the algorithm it relies on, which is designed in order to deal with point-like data, optimizing the ray-tracing calculation by ordering the particles as a function of their 'depth', defined as a function of one of the coordinates or other associated parameters. Realistic three-dimensional impressions are reached through a composition of the final colour in each pixel properly calculating emission and absorption of individual volume elements. We describe several scientific as well as public applications realized with Splotch. We emphasize how different datasets and configurations lead to remarkably different results in terms of the images and animations. A few of these results are available online.
A presocratic cosmological proposal
NASA Astrophysics Data System (ADS)
Danezis, E.; Theodossiou, E.; Stathopoulou, M.; Grammenos, Th.
1999-12-01
Alcman is known as one of the greatest lyric poets of the ancient world. However, the publication of the Oxyrhynchus papyrus No. 2390 in 1957 caused a great deal of excitement. This papyrus, from the second century AD, contains parts of a comment written in prose, which implies that in one of his poems Alcman deals with a kind of a god-created cosmogony. That cosmogonical view, formulated by Alcman in the middle of the seventh century BC, describes much older considerations that resemble certain modern cosmological conjectures. In terms of the latter, the observable universe emerged out of a point singularity interior to a white hole which, due to the time symmetry of Einstein's field equations, can be considered as a time-reversed black hole.
Supersymmetric classical cosmology
Escamilla-Rivera, Celia; Obregón, Octavio; Ureña-López, L. Arturo E-mail: octavio@fisica.ugto.mx
2010-12-01
In this work a supersymmetric cosmological model is analyzed in which we consider a general superfield action of a homogeneous scalar field supermultiplet interacting with the scale factor in a supersymmetric FRW model. There appear fermionic superpartners associated with both the scale factor and the scalar field, and classical equations of motion are obtained from the super-Wheeler-DeWitt equation through the usual WKB method. The resulting supersymmetric Einstein-Klein-Gordon equations contain extra radiation and stiff matter terms, and we study their solutions in flat space for different scalar field potentials. The solutions are compared to the standard case, in particular those corresponding to the exponential potential, and their implications for the dynamics of the early Universe are discussed in turn.
Cosmological disformal invariance
Domènech, Guillem; Sasaki, Misao; Naruko, Atsushi E-mail: naruko@th.phys.titech.ac.jp
2015-10-01
The invariance of physical observables under disformal transformations is considered. It is known that conformal transformations leave physical observables invariant. However, whether it is true for disformal transformations is still an open question. In this paper, it is shown that a pure disformal transformation without any conformal factor is equivalent to rescaling the time coordinate. Since this rescaling applies equally to all the physical quantities, physics must be invariant under a disformal transformation, that is, neither causal structure, propagation speed nor any other property of the fields are affected by a disformal transformation itself. This fact is presented at the action level for gravitational and matter fields and it is illustrated with some examples of observable quantities. We also find the physical invariance for cosmological perturbations at linear and high orders in perturbation, extending previous studies. Finally, a comparison with Horndeski and beyond Horndeski theories under a disformal transformation is made.
Cosmological structure formation
NASA Technical Reports Server (NTRS)
Schramm, David N.
1991-01-01
A summary of the current forefront problem of physical cosmology, the formation of structures (galaxies, clusters, great walls, etc.) in the universe is presented. Solutions require two key ingredients: (1) matter; and (2) seeds. Regarding the matter, it now seems clear that both baryonic and non-baryonic matter are required. Whether the non-baryonic matter is hot or cold depends on the choice of seeds. Regarding the seeds, both density fluctuations and topological defects are discussed. The combination of isotropy of the microwave background and the recent observations indicating more power on large scales have severly constrained, if not eliminated, Gaussian fluctuations with equal power on all scales, regardless of the eventual resolution of both the matter and seed questions. It is important to note that all current structure formation ideas require new physics beyond SU(3) x SU(2) x U(1).
NASA Astrophysics Data System (ADS)
Bianchi, Eugenio; Rovelli, Carlo; Vidotto, Francesca
2010-10-01
We compute the transition amplitude between coherent quantum states of geometry peaked on homogeneous-isotropic metrics. We work in the context of pure gravity without matter, we use the holomorphic representations of loop quantum gravity and the Kaminski-Kisielowski-Lewandowski generalization of the new vertex, and work at first order in the vertex expansion, second order in the graph (multipole) expansion, and first order in volume-1. We show that the resulting amplitude is in the kernel of a differential operator whose classical limit is the canonical Hamiltonian of a Friedmann-Robertson-Walker cosmology. This result is an indication that the dynamics of loop quantum gravity defined by the new vertex reproduces the gravity part of the Friedmann equation in the appropriate limit.
Bianchi, Eugenio; Rovelli, Carlo; Vidotto, Francesca
2010-10-15
We compute the transition amplitude between coherent quantum states of geometry peaked on homogeneous-isotropic metrics. We work in the context of pure gravity without matter, we use the holomorphic representations of loop quantum gravity and the Kaminski-Kisielowski-Lewandowski generalization of the new vertex, and work at first order in the vertex expansion, second order in the graph (multipole) expansion, and first order in volume{sup -1}. We show that the resulting amplitude is in the kernel of a differential operator whose classical limit is the canonical Hamiltonian of a Friedmann-Robertson-Walker cosmology. This result is an indication that the dynamics of loop quantum gravity defined by the new vertex reproduces the gravity part of the Friedmann equation in the appropriate limit.
NASA Astrophysics Data System (ADS)
Davydov, E. A.
2012-06-01
Vector fields can arise in the cosmological context in different ways, and we discuss both abelian and nonabelian sector. In the abelian sector vector fields of the geometrical origin (from dimensional reduction and Einstein-Eddington modification of gravity) can provide a very non-trivial dynamics, which can be expressed in terms of the effective dilaton-scalar gravity with the specific potential. In the non-abelian sector we investigate the Yang-Mills SU(2) theory which admits isotropic and homogeneous configuration. Provided the non-linear dependence of the lagrangian on the invariant FμνF~μν, one can obtain the inflationary regime with the exponential growth of the scale factor. The effective amplitudes of the `electric' and `magnetic' components behave like slowly varying scalars at this regime, what allows the consideration of some realistic models with non-linear terms in the Yang-Mills lagrangian.
Cosmological disformal invariance
NASA Astrophysics Data System (ADS)
Domènech, Guillem; Naruko, Atsushi; Sasaki, Misao
2015-10-01
The invariance of physical observables under disformal transformations is considered. It is known that conformal transformations leave physical observables invariant. However, whether it is true for disformal transformations is still an open question. In this paper, it is shown that a pure disformal transformation without any conformal factor is equivalent to rescaling the time coordinate. Since this rescaling applies equally to all the physical quantities, physics must be invariant under a disformal transformation, that is, neither causal structure, propagation speed nor any other property of the fields are affected by a disformal transformation itself. This fact is presented at the action level for gravitational and matter fields and it is illustrated with some examples of observable quantities. We also find the physical invariance for cosmological perturbations at linear and high orders in perturbation, extending previous studies. Finally, a comparison with Horndeski and beyond Horndeski theories under a disformal transformation is made.
NASA Astrophysics Data System (ADS)
Kunze, Kerstin E.
2013-12-01
Magnetic fields are observed on nearly all scales in the Universe, from stars and galaxies up to galaxy clusters and even beyond. The origin of cosmic magnetic fields is still an open question, however a large class of models puts its origin in the very early Universe. A magnetic dynamo amplifying an initial seed magnetic field could explain the present day strength of the galactic magnetic field. However, it is still an open problem how and when this initial magnetic field was created. Observations of the cosmic microwave background (CMB) provide a window to the early Universe and might therefore be able to tell us whether cosmic magnetic fields are of a primordial cosmological origin and at the same time constrain its parameters. We will give an overview of the observational evidence of large-scale magnetic fields, describe generation mechanisms of primordial magnetic fields and possible imprints in the CMB.
NASA Astrophysics Data System (ADS)
Calcagni, Gianluca; Montobbio, Michele; Nardelli, Giuseppe
2007-12-01
An analytic approach to phenomenological models inspired by cubic string field theory is introduced and applied to some examples. We study a class of actions for a minimally coupled, homogeneous scalar field whose energy density contains infinitely many time derivatives. These nonlocal systems are systematically localized and an algorithm to find cosmological solutions of the dynamical equations is provided. Our formalism is able to define the nonlocal field in regions of the parameter space which are inaccessible by standard methods. Also, problems related to nonlocality are reinterpreted under a novel perspective and naturally overcome. We consider phenomenological models living on a Friedmann-Robertson-Walker background with power-law scale factor, both in four dimensions and on a high-energy braneworld. The quest for solutions unravels general features of nonlocal dynamics indicating several future directions of investigation.
Cosmology and the weak interaction
Schramm, D.N. ):)
1989-12-01
The weak interaction plays a critical role in modern Big Bang cosmology. This review will emphasize two of its most publicized cosmological connections: Big Bang nucleosynthesis and Dark Matter. The first of these is connected to the cosmological prediction of Neutrino Flavours, N{sub {nu}} {approximately} 3 which is now being confirmed at SLC and LEP. The second is interrelated to the whole problem of galaxy and structure formation in the universe. This review will demonstrate the role of the weak interaction both for dark matter candidates and for the problem of generating seeds to form structure. 87 refs., 3 figs., 5 tabs.
Initial conditions and quantum cosmology
NASA Technical Reports Server (NTRS)
Hartle, James B.
1987-01-01
A theory of initial conditions is necessary for a complete explanation of the presently observed large scale structural features of the universe, and a quantum theory of cosmology is probably needed for its formulation. The kinematics of quantum cosmology are reviewed, and some candidates for a law of initial conditions are discussed. The proposal that the quantum state of a closed universe is the natural analog of the ground state for closed cosmologies and is specified by a Euclidean sum over histories is sketched. When implemented in simple models, this proposal is consistent with the most important large-scale observations.
Cosmological perturbations in massive bigravity
Lagos, Macarena; Ferreira, Pedro G. E-mail: p.ferreira1@physics.ox.ac.uk
2014-12-01
We present a comprehensive analysis of classical scalar, vector and tensor cosmological perturbations in ghost-free massive bigravity. In particular, we find the full evolution equations and analytical solutions in a wide range of regimes. We show that there are viable cosmological backgrounds but, as has been found in the literature, these models generally have exponential instabilities in linear perturbation theory. However, it is possible to find stable scalar cosmological perturbations for a very particular choice of parameters. For this stable subclass of models we find that vector and tensor perturbations have growing solutions. We argue that special initial conditions are needed for tensor modes in order to have a viable model.
Time-varying cosmological term
NASA Astrophysics Data System (ADS)
Socorro, J.; D'oleire, M.; Pimentel, Luis O.
2015-11-01
We present the case of time-varying cosmological term using the Lagrangian formalism characterized by a scalar field ϕ with standard kinetic energy and arbitrary potential V(ϕ). This model is applied to Friedmann-Robertson-Walker (FRW)cosmology. Exact solutions of the field equations are obtained by a special ansats to solve the Einstein-Klein-Gordon equation and a particular potential for the scalar field and barotropic perfect fluid. We present the evolution on this cosmological term with different scenarios.
Initial conditions and quantum cosmology
NASA Technical Reports Server (NTRS)
Hartle, James B.
1987-01-01
A theory of initial conditions is necessary for a complete explanation of the presently observed large scale structural features of the universe, and a quantum theory of cosmology is probably needed for its formulation. The kinematics of quantum cosmology are reviewed, and some candidates for a law of initial conditions are discussed. The proposal that the quantum state of a closed universe is the natural analog of the ground state for closed cosmologies and is specified by a Euclidean sum over histories is sketched. When implemented in simple models, this proposal is consistent with the most important large-scale observations.
Ψ-epistemic quantum cosmology?
NASA Astrophysics Data System (ADS)
Evans, Peter W.; Gryb, Sean; Thébault, Karim P. Y.
2016-11-01
This paper provides a prospectus for a new way of thinking about the wavefunction of the universe: a Ψ-epistemic quantum cosmology. We present a proposal that, if successfully implemented, would resolve the cosmological measurement problem and simultaneously allow us to think sensibly about probability and evolution in quantum cosmology. Our analysis draws upon recent work on the problem of time in quantum gravity and causally symmetric local hidden variable theories. Our conclusion weighs the strengths and weaknesses of the approach and points towards paths for future development.
Quantum cosmology near two dimensions
NASA Astrophysics Data System (ADS)
Bautista, Teresa; Dabholkar, Atish
2016-08-01
We consider a Weyl-invariant formulation of gravity with a cosmological constant in d -dimensional spacetime and show that near two dimensions the classical action reduces to the timelike Liouville action. We show that the renormalized cosmological term leads to a nonlocal quantum momentum tensor which satisfies the Ward identities in a nontrivial way. The resulting evolution equations for an isotropic, homogeneous universe lead to slowly decaying vacuum energy and power-law expansion. We outline the implications for the cosmological constant problem, inflation, and dark energy.
Bianchi Type V Cosmological Models with Varying Cosmological Term
NASA Astrophysics Data System (ADS)
Tiwari, R. K.; Singh, Rameshwar
2015-05-01
We have analyzed a new class of spatially homogeneous and anisotropic Bianchi type-V cosmological models with perfect fluid distribution in presence of time varying cosmological and gravitational constants in the framework of general relativity. Exact solutions of Einstein's field equations are obtained for two types of cosmologies viz. m ≠ 3 and m = 3 respectively. We propose an alternate variation law in which the anisotropy ( σ/ 𝜃) per unit expansion scalar ( 𝜃) is proportional to a function of scale factor R i.e. (where σ is a shear scalar) Tiwari (The African Review of Physics, 8, 437-447 2013). Physical properties of the models are discussed in detail. The models isotropize at late times. Some cosmological distance parameters for both the models have also been presented. We also discussed state finder parameters and observe that our solutions favor Λ C D M model.
Cosmological and supernova neutrinos
NASA Astrophysics Data System (ADS)
Kajino, T.; Aoki, W.; Balantekin, A. B.; Cheoun, M.-K.; Hayakawa, T.; Hidaka, J.; Hirai, Y.; Kusakabe, M.; Mathews, G. J.; Nakamura, K.; Pehlivan, Y.; Shibagaki, S.; Suzuki, T.
2014-06-01
The Big Bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) anisotropies are the pillars of modern cosmology. It has recently been suggested that axion which is a dark matter candidate in the framework of the standard model could condensate in the early universe and induce photon cooling before the epoch of the photon last scattering. Although this may render a solution to the overproduction problem of primordial 7Li abundance, there arises another serious difficulty of overproducing D abundance. We propose a hybrid dark matter model with both axions and relic supersymmetric (SUSY) particles to solve both overproduction problems of the primordial D and 7Li abundances simultaneously. The BBN also serves to constrain the nature of neutrinos. Considering non-thermal photons produced in the decay of the heavy sterile neutrinos due to the magnetic moment, we explore the cosmological constraint on the strength of neutrino magnetic moment consistent with the observed light element abundances. Core-collapse supernovae eject huge flux of energetic neutrinos which affect explosive nucleosynthesis of rare isotopes like 7Li, 11B, 92Nb, 138La and 180Ta and r-process elements. Several isotopes depend strongly on the neutrino flavor oscillation due to the Mikheyev-Smirnov-Wolfenstein (MSW) effect. Combining the recent experimental constraints on θ13 with predicted and observed supernova-produced abundance ratio 11B/7Li encapsulated in the presolar grains from the Murchison meteorite, we show a marginal preference for an inverted neutrino mass hierarchy. We also discuss supernova relic neutrinos (SRN) that may indicate the softness of the equation of state (EoS) of nuclear matter and adiabatic conditions of the neutrino oscillation.
Cosmological and supernova neutrinos
Kajino, T.; Aoki, W.; Balantekin, A. B.; Cheoun, M.-K.; Hayakawa, T.; Hidaka, J.; Hirai, Y.; Shibagaki, S.; Kusakabe, M.; Mathews, G. J.; Nakamura, K.; Pehlivan, Y.; Suzuki, T.
2014-06-24
The Big Bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) anisotropies are the pillars of modern cosmology. It has recently been suggested that axion which is a dark matter candidate in the framework of the standard model could condensate in the early universe and induce photon cooling before the epoch of the photon last scattering. Although this may render a solution to the overproduction problem of primordial {sup 7}Li abundance, there arises another serious difficulty of overproducing D abundance. We propose a hybrid dark matter model with both axions and relic supersymmetric (SUSY) particles to solve both overproduction problems of the primordial D and {sup 7}Li abundances simultaneously. The BBN also serves to constrain the nature of neutrinos. Considering non-thermal photons produced in the decay of the heavy sterile neutrinos due to the magnetic moment, we explore the cosmological constraint on the strength of neutrino magnetic moment consistent with the observed light element abundances. Core-collapse supernovae eject huge flux of energetic neutrinos which affect explosive nucleosynthesis of rare isotopes like {sup 7}Li, {sup 11}B, {sup 92}Nb, {sup 138}La and {sup 180}Ta and r-process elements. Several isotopes depend strongly on the neutrino flavor oscillation due to the Mikheyev-Smirnov-Wolfenstein (MSW) effect. Combining the recent experimental constraints on θ{sub 13} with predicted and observed supernova-produced abundance ratio {sup 11}B/{sup 7}Li encapsulated in the presolar grains from the Murchison meteorite, we show a marginal preference for an inverted neutrino mass hierarchy. We also discuss supernova relic neutrinos (SRN) that may indicate the softness of the equation of state (EoS) of nuclear matter and adiabatic conditions of the neutrino oscillation.
Cosmology in beyond-generalized Proca theories
NASA Astrophysics Data System (ADS)
Nakamura, Shintaro; Kase, Ryotaro; Tsujikawa, Shinji
2017-05-01
The beyond-generalized Proca theories are the extension of second-order massive vector-tensor theories (dubbed generalized Proca theories) with two transverse vector modes and one longitudinal scalar besides two tensor polarizations. Even with this extension, the propagating degrees of freedom remain unchanged on the isotropic cosmological background without an Ostrogradski instability. We study the cosmology in beyond-generalized Proca theories by paying particular attention to the dynamics of late-time cosmic acceleration and resulting observational consequences. We derive conditions for avoiding ghosts and instabilities of tensor, vector, and scalar perturbations and discuss viable parameter spaces in concrete models allowing the dark energy equation of state smaller than -1 . The propagation speeds of those perturbations are subject to modifications beyond the domain of generalized Proca theories. There is a mixing between scalar and matter sound speeds, but such a mixing is suppressed during most of the cosmic expansion history without causing a new instability. On the other hand, we find that derivative interactions arising in beyond-generalized Proca theories give rise to important modifications to the cosmic growth history. The growth rate of matter perturbations can be compatible with the redshift-space distortion data due to the realization of gravitational interaction weaker than that in generalized Proca theories. Thus, it is possible to distinguish the dark energy model in beyond-generalized Proca theories from the counterpart in generalized Proca theories as well as from the Λ CDM model.
Scale factor duality for conformal cyclic cosmologies
NASA Astrophysics Data System (ADS)
Camara da Silva, U.; Alves Lima, A. L.; Sotkov, G. M.
2016-11-01
The scale factor duality is a symmetry of dilaton gravity which is known to lead to pre-big-bang cosmologies. A conformal time version of the scale factor duality (SFD) was recently implemented as a UV/IR symmetry between decelerated and accelerated phases of the post-big-bang evolution within Einstein gravity coupled to a scalar field. The problem investigated in the present paper concerns the employment of the conformal time SFD methods to the construction of pre-big-bang and cyclic extensions of these models. We demonstrate that each big-bang model gives rise to two qualitatively different pre-big-bang evolutions: a contraction/expansion SFD model and Penrose's Conformal Cyclic Cosmology (CCC). A few examples of SFD symmetric cyclic universes involving certain gauged Kähler sigma models minimally coupled to Einstein gravity are studied. We also describe the specific SFD features of the thermodynamics and the conditions for validity of the generalized second law in the case of Gauss-Bonnet (GB) extension of these selected CCC models.
Cosmological evolution of a D-brane
Li Huiquan
2011-03-15
We study the cosmological evolution of a single BPS D-brane coupled to gravity in the absence of potential. When such a D-brane moves in the bulk with nonvanishing velocity, it tends to slow down to zero velocity via mechanisms like gravitational wave leakage to the bulk, losing its kinetic energy to fuel the expansion of the Universe on the D-brane. If the initial velocity of the D-brane is high enough, the Universe on the D-brane undergoes a dustlike stage at early times and an acceleration stage at late times, realizing the original Chaplygin gas model. When the D-brane velocity is initially zero, the D-brane will always remain fixed at some position in the bulk, with the brane tension over the Plank mass squared as a cosmological constant. It is further shown that this kind of fixed brane universe can arise as defects from tachyon inflation on a non-Bogomol'nyi-Prasad-Sommerfeld D-brane with one dimension higher.
High Energy Astrophysics and Cosmology from Space
NASA Astrophysics Data System (ADS)
Hornschemeier, Ann
2014-03-01
While much can be learned from physics experiments on and astronomical observations from the ground, certain questions require space-based investigations. Sometimes the scale of the measurement, such as the baseline of approximately 106 km necessary for the observation of gravitational waves in the frequency range expected for high-redshift supermassive black hole mergers, causes us to leave behind the limitations of the earth. From space we measure the X-ray emission from the final stages of accretion onto black holes and critical energy ranges of cosmic rays and gamma ray photons resulting from particle acceleration in e.g., star forming environments, that otherwise we could not measure due to the atmosphere. Space-borne experiments may also measure all of the cosmological information available in the polarization of the cosmic microwave background to probe the physical conditions that caused the process of inflation in the early universe, moments after the big bang. This presentation will cover the NASA high energy astrophysics and cosmology science portfolio, embodied in its Physics of the Cosmos program, including updates on technology development and programmatic matters.
A Large number of fast cosmological simulations
NASA Astrophysics Data System (ADS)
Koda, Jun; Kazin, E.; Blake, C.
2014-01-01
Mock galaxy catalogs are essential tools to analyze large-scale structure data. Many independent realizations of mock catalogs are necessary to evaluate the uncertainties in the measurements. We perform 3600 cosmological simulations for the WiggleZ Dark Energy Survey to obtain the new improved Baron Acoustic Oscillation (BAO) cosmic distance measurements using the density field "reconstruction" technique. We use 1296^3 particles in a periodic box of 600/h Mpc on a side, which is the minimum requirement from the survey volume and observed galaxies. In order to perform such large number of simulations, we developed a parallel code using the COmoving Lagrangian Acceleration (COLA) method, which can simulate cosmological large-scale structure reasonably well with only 10 time steps. Our simulation is more than 100 times faster than conventional N-body simulations; one COLA simulation takes only 15 minutes with 216 computing cores. We have completed the 3600 simulations with a reasonable computation time of 200k core hours. We also present the results of the revised WiggleZ BAO distance measurement, which are significantly improved by the reconstruction technique.
Cosmological constraints on Lorentz violating dark energy
Audren, B.; Lesgourgues, J.; Sibiryakov, S. E-mail: Diego.Blas@cern.ch E-mail: Sergey.Sibiryakov@cern.ch
2013-08-01
The role of Lorentz invariance as a fundamental symmetry of nature has been lately reconsidered in different approaches to quantum gravity. It is thus natural to study whether other puzzles of physics may be solved within these proposals. This may be the case for the cosmological constant problem. Indeed, it has been shown that breaking Lorentz invariance provides Lagrangians that can drive the current acceleration of the universe without experiencing large corrections from ultraviolet physics. In this work, we focus on the simplest model of this type, called ΘCDM, and study its cosmological implications in detail. At the background level, this model cannot be distinguished from ΛCDM. The differences appear at the level of perturbations. We show that in ΘCDM, the spectrum of CMB anisotropies and matter fluctuations may be affected by a rescaling of the gravitational constant in the Poisson equation, by the presence of extra contributions to the anisotropic stress, and finally by the existence of extra clustering degrees of freedom. To explore these modifications accurately, we modify the Boltzmann code class. We then use the parameter inference code Monte Python to confront ΘCDM with data from WMAP-7, SPT and WiggleZ. We obtain strong bounds on the parameters accounting for deviations from ΛCDM. In particular, we find that the discrepancy between the gravitational constants appearing in the Poisson and Friedmann equations is constrained at the level of 1.8%.
NASA Astrophysics Data System (ADS)
Pradhan, A.; Saha, B.; Rikhvitsky, V.
2015-05-01
The Einstein's field equations with variable gravitational and cosmological "constants" for a spatially homogeneous and anisotropic Bianchi type-I space-time are obtained in present study. To study the transit behaviour of Universe, we consider a law of variation of scale factor a(t) = ( tk et) ^{1/n}, which yields a time dependent deceleration parameter q = -1 + nk/(k + t)2, comprising a class of models that depicts a transition of the universe from the early decelerated phase to the recent accelerating phase. We find that the time dependent deceleration parameter is reasonable for the present day Universe and gives an appropriate description of the evolution of the universe. For n = 0.27k, we obtain q0 = -0.73, which is similar to observed value of deceleration parameter at present epoch. It is also observed that for n ≥ 2 and k = 1, we obtain a class of transit models of the universe from early decelerating to present accelerating phase. For k = 0, the universe has non-singular origin. In these models, we arrive at the decision that, from the structure of the field equations, the behaviour of cosmological and gravitational constants and are related. Taking into consideration the observational data, we conclude that the cosmological constant behaves as a positive decreasing function of time, whereas gravitational constant is increasing and tends to a constant value at late time. H(z)/(1+z) data (32 points) and model prediction as a function of redshift for different k and n are successfully presented by using recent data. Some physical and geometric properties of the models are also discussed.
Cosmology. The science of the universe.
NASA Astrophysics Data System (ADS)
Harrison, E. R.
This book is a broad and elementary introduction to the science of modern cosmology, with emphasis on its historical origins. This second edition of "Cosmology" updates and extends the first edition, published in 1981 (see Abstr. 30.003.070). The additional chapters discuss early scientific cosmology, Cartesian and Newtonian world systems, cosmology after Newton and before Einstein, observational cosmology, inflation, and creation of the universe.
Weightless bubble lattices: A case of froth wicking
NASA Technical Reports Server (NTRS)
Noever, David A.; Cronise, Raymond J.
1994-01-01
In the absence of gravity drainage, froth wicking draws excess fluid onto a bubble lattice. Capillary forces only cause fluid transport; a moving front moves stably and without fluid fingering along a constant velocity bubble-fluid contact line. This percolation of fluid crawling up the lattice shows fluid coverage on lattice borders varies linearly with available surface area (proportional to lattice perimeter) and fluid accelerates through regions or nests of high bubble density (number of bubbles/sq cm). The development of nearly two-dimensional bubble lattices in variable gravity (step function between 0.01 and 1.8 times earthly gravity) are examined experimentally and a zeroth-order model for froth wetting is presented, which captures many of the principal observations. Possible applications for bubble lattices include adhesion casting of metals and separation of biological cells, bacteria, and particles.
Fundamental Approach to the Cosmological Constant Issue
NASA Astrophysics Data System (ADS)
Carmeli, Moshe
We use a Riemannian four-dimensional presentation for gravitation in which the coordinates are distances and velocity rather than the traditional space and time. We solve the field equations and show that there are three possibilities for the Universe to expand. The theory describes the Universe as having a three-phase evolution with a decelerating expansion, followed by a constant and an accelerating expansion, and it predicts that the Universe is now in the latter phase. It is shown, assuming Ωm = 0.245, that the time at which the Universe goes over from a decelerating to an accelerating expansion, occurs at 8.5 Gyr ago, at which time the cosmic radiation temperature was 146K. Recent observations show that the Universe's growth is accelerating. Our theory confirms these recent experimental results. The theory predicts also that now there is a positive pressure in the Universe. Although the theory has no cosmological constant, we extract from it its equivalence and show that Λ = 1.934 × 10-35 s-2. This value of Λ is in excellent agreement with measurements. It is also shown that the three-dimensional space of the Universe is Euclidean, as the Boomerang experiment shows.
Cylindrical wormholes with positive cosmological constant
NASA Astrophysics Data System (ADS)
Richarte, Martín G.
2013-07-01
We construct cylindrical, traversable wormholes with finite radii by taking into account the cut-and-paste procedure for the case of cosmic string manifolds with a positive cosmological constant. Under reasonable assumptions about the equation of state of the matter located at the shell, we find that the wormhole throat undergoes a monotonous evolution provided it moves at a constant velocity. In order to explore the dynamical nonlinear behavior of the wormhole throat, we consider that the matter of the shell is supported by anisotropic Chaplygin gas, anti-Chaplygin gas, or a mixture of Chaplygin and anti-Chaplygin gases, implying that wormholes could suffer an accelerated expansion or contraction, but that oscillatory behavior seems to be forbidden.
Probing quintessence potential with future cosmological surveys
Takeuchi, Yoshitaka; Ichiki, Kiyotomo; Takahashi, Tomo; Yamaguchi, Masahide E-mail: ichiki@a.phys.nagoya-u.ac.jp E-mail: gucci@phys.titech.ac.jp
2014-03-01
Quintessence, a scalar field model, has been proposed to account for the acceleration of the Universe at present. We discuss how accurately quintessence models are discriminated by future cosmological surveys, which include experiments of CMB, galaxy clustering, weak lensing, and the type Ia SNe surveys, by making use of the conventional parameterized dark energy models. We can see clear differences between the thawing and the freezing quintessence models at more than 1σ (2σ) confidence level as long as the present equation of state for quintessence is away from -1 as w{sub X}∼>−0.95(−0.90). However, it is found to be difficult to probe the effective mass squared for the potential in thawing models, whose signs are different between the quadratic and the cosine-type potentials. This fact may require us to invent a new estimator to distinguish quintessence models beyond the thawing and the freezing ones.
Precision cosmology and the landscape
Bousso, Raphael; Bousso, Raphael
2006-10-01
After reviewing the cosmological constant problem -- why is Lambda not huge? -- I outline the two basic approaches that had emerged by the late 1980s, and note that each made a clear prediction. Precision cosmological experiments now indicate that the cosmological constant is nonzero. This result strongly favors the environmental approach, in which vacuum energy can vary discretely among widely separated regions in the universe. The need to explain this variation from first principles constitutes an observational constraint on fundamental theory. I review arguments that string theory satisfies this constraint, as it contains a dense discretuum of metastable vacua. The enormous landscape of vacua calls for novel, statistical methods of deriving predictions, and it prompts us to reexamine our description of spacetime on the largest scales. I discuss the effects of cosmological dynamics, and I speculate that weighting vacua by their entropy production may allow for prior-free predictions that do not resort to explicitly anthropic arguments.
Introduction. Cosmology meets condensed matter.
Kibble, T W B; Pickett, G R
2008-08-28
At first sight, low-temperature condensed-matter physics and early Universe cosmology seem worlds apart. Yet, in the last few years a remarkable synergy has developed between the two. It has emerged that, in terms of their mathematical description, there are surprisingly close parallels between them. This interplay has been the subject of a very successful European Science Foundation (ESF) programme entitled COSLAB ('Cosmology in the Laboratory') that ran from 2001 to 2006, itself built on an earlier ESF network called TOPDEF ('Topological Defects: Non-equilibrium Field Theory in Particle Physics, Condensed Matter and Cosmology'). The articles presented in this issue of Philosophical Transactions A are based on talks given at the Royal Society Discussion Meeting 'Cosmology meets condensed matter', held on 28 and 29 January 2008. Many of the speakers had participated earlier in the COSLAB programme, but the strength of the field is illustrated by the presence also of quite a few new participants.
Why Should People Learn Cosmology?
NASA Astrophysics Data System (ADS)
Coble, K.; Duncan, T.
2002-12-01
There are many valid answers to the question, "Why should everyone know something about cosmology?" In any educational context (college liberal arts course, museum exhibit, popular book, public lecture, or even a press release or informal conversation), it is important to clearly articulate the answer you have in mind, because your answer determines the selection and organization of topics you teach. This poster will describe one perspective on this question: that knowledge of cosmology is important for all students because it can have a profound impact on the personal mental map by which they each view their relationship to the world. This map guides their everyday choices and actions through the perspective it gives on their individual role as part of the Universe. We will make the case for the importance of cosmology for all students on this basis and discuss the selection and organization of topics from cosmology in a course motivated by this point of view.
Physical and Relativistic Numerical Cosmology.
Anninos, Peter
1998-01-01
In order to account for the observable Universe, any comprehensive theory or model of cosmology must draw from many disciplines of physics, including gauge theories of strong and weak interactions, the hydrodynamics and microphysics of baryonic matter, electromagnetic fields, and spacetime curvature, for example. Although it is difficult to incorporate all these physical elements into a single complete model of our Universe, advances in computing methods and technologies have contributed significantly towards our understanding of cosmological models, the Universe, and astrophysical processes within them. A sample of numerical calculations addressing specific issues in cosmology are reviewed in this article: from the Big Bang singularity dynamics to the fundamental interactions of gravitational waves; from the quark-hadron phase transition to the large scale structure of the Universe. The emphasis, although not exclusively, is on those calculations designed to test different models of cosmology against the observed Universe.
Evolution in bouncing quantum cosmology
NASA Astrophysics Data System (ADS)
Mielczarek, Jakub; Piechocki, Włodzimierz
2012-03-01
We present the method of describing an evolution in quantum cosmology in the framework of the reduced phase space quantization of loop cosmology. We apply our method to the flat Friedmann-Robertson-Walker model coupled to a massless scalar field. We identify the physical quantum Hamiltonian that is positive-definite and generates globally a unitary evolution of the considered quantum system. We examine the properties of expectation values of physical observables in the process of the quantum big bounce transition. The dispersion of evolved observables is studied for the Gaussian state. Calculated relative fluctuations enable an examination of the semi-classicality conditions and possible occurrence of the cosmic forgetfulness. Preliminary estimations based on the cosmological data suggest that there was no cosmic amnesia. Presented results are analytical, and numerical computations are only used for the visualization purposes. Our method may be generalized to sophisticated cosmological models including the Bianchi-type universes.
Cosmological calculations on the GPU
NASA Astrophysics Data System (ADS)
Bard, D.; Bellis, M.; Allen, M. T.; Yepremyan, H.; Kratochvil, J. M.
2013-02-01
Cosmological measurements require the calculation of nontrivial quantities over large datasets. The next generation of survey telescopes will yield measurements of billions of galaxies. The scale of these datasets, and the nature of the calculations involved, make cosmological calculations ideal models for implementation on graphics processing units (GPUs). We consider two cosmological calculations, the two-point angular correlation function and the aperture mass statistic, and aim to improve the calculation time by constructing code for calculating them on the GPU. Using CUDA, we implement the two algorithms on the GPU and compare the calculation speeds to comparable code run on the CPU. We obtain a code speed-up of between 10 and 180× faster, compared to performing the same calculation on the CPU. The code has been made publicly available. GPUs are a useful tool for cosmological calculations, even for datasets the size of current surveys, allowing calculations to be made one or two orders of magnitude faster.
Newtonian cosmology Newton would understand
Lemons, D.S.
1988-06-01
Isaac Newton envisioned a static, infinite, and initially uniform, zero field universe that was gravitationally unstable to local condensations of matter. By postulating the existence of such a universe and using it as a boundary condition on Newtonian gravity, a new field equation for gravity is derived, which differs from the classical one by a time-dependent cosmological term proportional to the average mass density of the universe. The new field equation not only makes Jeans' analysis of the gravitational instability of a Newtonian universe consistent, but also gives rise to a family of Newtonian evolutionary cosmologies parametrized by a time-invariant expansion velocity. This Newtonian cosmology contrasts with both 19th-century ones and with post general relativity Newtonian cosmology.
Semiclassical cosmology with polymer matter
NASA Astrophysics Data System (ADS)
Moeez Hassan, Syed; Husain, Viqar
2017-04-01
In loop quantum cosmology, polymer quantization is applied to gravity and Schrödinger quantization to matter. This approach misses interesting cosmological dynamics coming from the polymer quantization of matter. We demonstrate this in semiclassical cosmology with a scalar field and pressureless dust: gravity is kept classical, dust is used to fix the time gauge, and polymer quantization effects are isolated in the scalar field. The resulting dynamics shows a period of inflation, both with and without a scalar potential, and the emergence of a classical universe at late times. Since gravity is not quantized, the cosmological singularity is not resolved, but our results suggest that polymer quantization of both gravity and matter are important for a complete picture.
Heavy ion collisions and cosmology
NASA Astrophysics Data System (ADS)
Floerchinger, Stefan
2016-12-01
There are interesting parallels between the physics of heavy ion collisions and cosmology. Both systems are out-of-equilibrium and relativistic fluid dynamics plays an important role for their theoretical description. From a comparison one can draw interesting conclusions for both sides. For heavy ion physics it could be rewarding to attempt a theoretical description of fluid perturbations similar to cosmological perturbation theory. In the context of late time cosmology, it could be interesting to study dissipative properties such as shear and bulk viscosity and corresponding relaxation times in more detail. Knowledge and experience from heavy ion physics could help to constrain the microscopic properties of dark matter from observational knowledge of the cosmological fluid properties.
One model of modified gravity with dynamical torsion and its cosmological consequences
NASA Astrophysics Data System (ADS)
Nikiforova, Vasilisa
2016-10-01
We consider a model belonging to the class of Poincarè gauge gravities. The model is free of ghosts, tachyons and gradient instabilities about Minkowski and torsionless Einstein backgrounds of sufficiently small curvature. At zero cosmological constant, the model admits a self-accelerating solution with non-Riemannian connection. We study scalar perturbations about the self-accelerating solution and find that the number of scalar modes is the same as in Minkow ski background; moreover, in the limit of small effective cosmological constant and below the UV cutoff of the low energy effective theory, the scalar sector does not have pathologies like ghosts or rapid gradient instabilities.
Janse Van Rensburg, E.J.
1996-12-31
The geometry of polygonal knots in the cubic lattice may be used to define some knot invariants. One such invariant is the minimal edge number, which is the minimum number of edges necessary (and sufficient) to construct a lattice knot of given type. In addition, one may also define the minimal (unfolded) surface number, and the minimal (unfolded) boundary number; these are the minimum number of 2-cells necessary to construct an unfolded lattice Seifert surface of a given knot type in the lattice, and the minimum number of edges necessary in a lattice knot to guarantee the existence of an unfolded lattice Seifert surface. In addition, I derive some relations amongst these invariants. 8 refs., 5 figs., 2 tabs.
Cosmological stability of quantum compactification
Gleiser, M.
1987-02-01
We discuss the cosmological stability of higher dimensional models that feature internal manifolds given by the product of two spheres. In particular, we consider the case when the total number of dimensions is even. After we obtain the vacuum energy coming from one-loop fluctuations of scalars and spin-1/2 fermions, we show how a realistic cosmological scenario can arise by balancing the quantum energy with monopole-like contributions. 10 refs., 1 fig.
Neutrinos in astrophysics and cosmology
Balantekin, A. B.
2016-06-21
Neutrinos play a crucial role in many aspects of astrophysics and cosmology. Since they control the electron fraction, or equivalently neutron-to-proton ratio, neutrino properties impact yields of r-process nucleosynthesis. Similarly the weak decoupling temperature in the Big Bang Nucleosynthesis epoch is exponentially dependent on the neutron-to-proton ratio. In these conference proceedings, I briefly summarize some of the recent work exploring the role of neutrinos in astrophysics and cosmology.
Noncommutativity and scalar field cosmology
Guzman, W.; Sabido, M.; Socorro, J.
2007-10-15
In this work we extend and apply a previous proposal to study noncommutative cosmology to the Friedmann-Robertson-Walker cosmological background coupled to a scalar field. This is done in classical and quantum scenarios. In both cases noncommutativity is introduced in the gravitational field as well as in the scalar field through a deformation of minisuperspace, and we are able to find exact solutions. Finally, the effects of noncommutativity on the classical evolution are analyzed.
The topological susceptibility in finite temperature QCD and axion cosmology
Petreczky, Peter; Schadler, Hans-Peter; Sharma, Sayantan
2016-10-06
We study the topological susceptibility in 2+1 flavor QCD above the chiral crossover transition temperature using Highly Improved Staggered Quark action and several lattice spacings corresponding to temporal extent of the lattice, Nτ=6,8,10 and 12. We observe very distinct temperature dependences of the topological susceptibility in the ranges above and below 250MeV. While for temperatures above 250MeV, the dependence is found to be consistent with dilute instanton gas approximation, at lower temperatures the fall-off of topological susceptibility is milder. We discuss the consequence of our results for cosmology wherein we estimate the bounds on the axion decay constant and themore » oscillation temperature if indeed the QCD axion is a possible dark matter candidate.« less
The topological susceptibility in finite temperature QCD and axion cosmology
NASA Astrophysics Data System (ADS)
Petreczky, Peter; Schadler, Hans-Peter; Sharma, Sayantan
2016-11-01
We study the topological susceptibility in 2 + 1 flavor QCD above the chiral crossover transition temperature using Highly Improved Staggered Quark action and several lattice spacings corresponding to temporal extent of the lattice, Nτ = 6 , 8 , 10 and 12. We observe very distinct temperature dependences of the topological susceptibility in the ranges above and below 250 MeV. While for temperatures above 250 MeV, the dependence is found to be consistent with dilute instanton gas approximation, at lower temperatures the fall-off of topological susceptibility is milder. We discuss the consequence of our results for cosmology wherein we estimate the bounds on the axion decay constant and the oscillation temperature if indeed the QCD axion is a possible dark matter candidate.
Loop quantum cosmology gravitational baryogenesis
NASA Astrophysics Data System (ADS)
Odintsov, S. D.; Oikonomou, V. K.
2016-11-01
Loop quantum cosmology is an appealing quantum completion of classical cosmology, which brings along various theoretical features which in many cases offer a remedy for or modify various classical cosmology aspects. In this paper we address the gravitational baryogenesis mechanism in the context of loop quantum cosmology. As we demonstrate, when loop quantum cosmology effects are taken into account in the resulting Friedmann equations for a flat Friedmann-Robertson-Walker Universe, then even for a radiation-dominated Universe, the predicted baryon-to-entropy ratio from the gravitational baryogenesis mechanism is non-zero, in contrast to the Einstein-Hilbert case, in which case the baryon-to-entropy ratio is zero. We also discuss various other cases apart from the radiation domination case, and we discuss how the baryon-to-entropy ratio is affected from the parameters of the quantum theory. In addition, we use illustrative exact solutions of loop quantum cosmology and we investigate under which circumstances the baryon-to-entropy ratio can be compatible with the observational constraints.
Parameterized post-Newtonian cosmology
NASA Astrophysics Data System (ADS)
Sanghai, Viraj A. A.; Clifton, Timothy
2017-03-01
Einstein’s theory of gravity has been extensively tested on solar system scales, and for isolated astrophysical systems, using the perturbative framework known as the parameterized post-Newtonian (PPN) formalism. This framework is designed for use in the weak-field and slow-motion limit of gravity, and can be used to constrain a large class of metric theories of gravity with data collected from the aforementioned systems. Given the potential of future surveys to probe cosmological scales to high precision, it is a topic of much contemporary interest to construct a similar framework to link Einstein’s theory of gravity and its alternatives to observations on cosmological scales. Our approach to this problem is to adapt and extend the existing PPN formalism for use in cosmology. We derive a set of equations that use the same parameters to consistently model both weak fields and cosmology. This allows us to parameterize a large class of modified theories of gravity and dark energy models on cosmological scales, using just four functions of time. These four functions can be directly linked to the background expansion of the universe, first-order cosmological perturbations, and the weak-field limit of the theory. They also reduce to the standard PPN parameters on solar system scales. We illustrate how dark energy models and scalar-tensor and vector-tensor theories of gravity fit into this framework, which we refer to as ‘parameterized post-Newtonian cosmology’ (PPNC).
NASA Astrophysics Data System (ADS)
Roberts, Alex
2016-08-01
Recently, a new framework for describing the multiverse has been proposed which is based on the principles of quantum mechanics. The framework allows for well-defined predictions, both regarding global properties of the universe and outcomes of particular experiments, according to a single probability formula. This provides complete unification of the eternally inflating multiverse and many worlds in quantum mechanics. We elucidate how cosmological parameters can be calculated in this framework, and study the probability distribution for the value of the cosmological constant. We consider both positive and negative values, and find that the observed value is consistent with the calculated distribution at an order of magnitude level. In particular, in contrast to the case of earlier measure proposals, our framework prefers a positive cosmological constant over a negative one. These results depend only moderately on how we model galaxy formation and life evolution therein. We explore supersymmetric theories in which the Higgs mass is boosted by the non-decoupling D-terms of an extended U(1) X gauge symmetry, defined here to be a general linear combination of hypercharge, baryon number, and lepton number. Crucially, the gauge coupling, gX, is bounded from below to accommodate the Higgs mass, while the quarks and leptons are required by gauge invariance to carry non-zero charge under U(1)X. This induces an irreducible rate, sigmaBR, for pp → X → ll relevant to existing and future resonance searches, and gives rise to higher dimension operators that are stringently constrained by precision electroweak measurements. Combined, these bounds define a maximally allowed region in the space of observables, (sigmaBR, mX), outside of which is excluded by naturalness and experimental limits. If natural supersymmetry utilizes non-decoupling D-terms, then the associated X boson can only be observed within this window, providing a model independent 'litmus test' for this broad
To theory of asymptotically stable accelerating Universe in Riemann-Cartan spacetime
Garkun, A.S.; Kudin, V.I.; Minkevich, A.V. E-mail: kudzin_w@tut.by
2014-12-01
Homogeneous isotropic cosmological models built in the framework of the Poincar'e gauge theory of gravity based on general expression of gravitational Lagrangian with indefinite parameters are analyzed. Special points of cosmological solutions for flat cosmological models at asymptotics and conditions of their stability in dependence of indefinite parameters are found. Procedure of numerical integration of the system of gravitational equations at asymptotics is considered. Numerical solution for accelerating Universe without dark energy is obtained.
Shafi, Qaisar; Barr, Steven; Gaisser, Thomas; Stanev, Todor
2015-03-31
1. Executive Summary (April 1, 2012 - March 31, 2015) Title: Particle Theory, Particle Astrophysics and Cosmology Qaisar Shafi University of Delaware (Principal Investigator) Stephen M. Barr, University of Delaware (Co-Principal Investigator) Thomas K. Gaisser, University of Delaware (Co-Principal Investigator) Todor Stanev, University of Delaware (Co-Principal Investigator) The proposed research was carried out at the Bartol Research included Professors Qaisar Shafi Stephen Barr, Thomas K. Gaisser, and Todor Stanev, two postdoctoral fellows (Ilia Gogoladze and Liucheng Wang), and several graduate students. Five students of Qaisar Shafi completed their PhD during the period August 2011 - August 2014. Measures of the group’s high caliber performance during the 2012-2015 funding cycle included pub- lications in excellent refereed journals, contributions to working groups as well as white papers, and conference activities, which together provide an exceptional record of both individual performance as well as overall strength. Another important indicator of success is the outstanding quality of the past and current cohort of graduate students. The PhD students under our supervision regularly win the top departmental and university awards, and their publications records show excellence both in terms of quality and quantity. The topics covered under this grant cover the frontline research areas in today’s High Energy Theory & Phenomenology. For Professors Shafi and Barr they include LHC related topics including supersymmetry, collider physics, fl vor physics, dark matter physics, Higgs boson and seesaw physics, grand unifi and neutrino physics. The LHC two years ago discovered the Standard Model Higgs boson, thereby at least partially unlocking the secrets behind electroweak symmetry breaking. We remain optimistic that new and exciting physics will be found at LHC 14, which explain our focus on physics beyond the Standard Model. Professors Shafi continued his
Axion cold dark matter in nonstandard cosmologies
Visinelli, Luca; Gondolo, Paolo
2010-03-15
We study the parameter space of cold dark matter axions in two cosmological scenarios with nonstandard thermal histories before big bang nucleosynthesis: the low-temperature reheating (LTR) cosmology and the kination cosmology. If the Peccei-Quinn symmetry breaks during inflation, we find more allowed parameter space in the LTR cosmology than in the standard cosmology and less in the kination cosmology. On the contrary, if the Peccei-Quinn symmetry breaks after inflation, the Peccei-Quinn scale is orders of magnitude higher than standard in the LTR cosmology and lower in the kination cosmology. We show that the axion velocity dispersion may be used to distinguish some of these nonstandard cosmologies. Thus, axion cold dark matter may be a good probe of the history of the Universe before big bang nucleosynthesis.
Born-Infeld cosmology with scalar Born-Infeld matter
NASA Astrophysics Data System (ADS)
Jana, Soumya; Kar, Sayan
2016-09-01
Cosmology in Eddington-inspired Born-Infeld gravity is investigated using a scalar Born-Infeld field (e.g. tachyon condensate) as matter. In this way, both in the gravity and matter sectors we have Born-Infeld-like structures characterized by their actions and via two separate constants, κ and αT2 , respectively. With a particular choice of the form of ϕ ˙ (the time derivative of the Born-Infeld scalar), analytical cosmological solutions are found. Thereafter, we explore some of the unique features of the corresponding cosmological spacetimes. For κ >0 , our solution has a de Sitter-like expansion both at early and late times, with an intermediate deceleration sandwiched between the accelerating phases. On the other hand, when κ <0 , the initial de Sitter phase is replaced by a bounce. Our solutions, at late time, fit well with available supernova data—a fact we demonstrate explicitly. The estimated properties of the Universe obtained from the fitting of the κ >0 solution are as good as in Λ CDM cosmology. However, the κ <0 solution has to be discarded due to the occurrence of a bounce at an unacceptably low redshift.
Geometry and symmetries in lattice spinor gravity
Wetterich, C.
2012-09-15
Lattice spinor gravity is a proposal for regularized quantum gravity based on fermionic degrees of freedom. In our lattice model the local Lorentz symmetry is generalized to complex transformation parameters. The difference between space and time is not put in a priori, and the euclidean and the Minkowski quantum field theory are unified in one functional integral. The metric and its signature arise as a result of the dynamics, corresponding to a given ground state or cosmological solution. Geometrical objects as the vierbein, spin connection or the metric are expectation values of collective fields built from an even number of fermions. The quantum effective action for the metric is invariant under general coordinate transformations in the continuum limit. The action of our model is found to be also invariant under gauge transformations. We observe a 'geometrical entanglement' of gauge- and Lorentz-transformations due to geometrical objects transforming non-trivially under both types of symmetry transformations. - Highlights: Black-Right-Pointing-Pointer We formulate the geometrical aspects of a proposal for a lattice regularized model of quantum gravity. Black-Right-Pointing-Pointer The vierbein shows an entanglement between Lorentz symmetry and gauge symmetry. Black-Right-Pointing-Pointer Euclidean and Minkowski signatures of the collective metric and the vierbein are described within the same functional integral.
Turner, M.S. |
1999-03-01
One hundred years ago we did not know how stars generate energy, the age of the Universe was thought to be only millions of years, and our Milky Way galaxy was the only galaxy known. Today, we know that we live in an evolving and expanding universe comprising billions of galaxies, all held together by dark matter. With the hot big-bang model we can trace the evolution of the Universe from the hot soup of quarks and leptons that existed a fraction of a second after the beginning, to the formation of galaxies a few billion years later, and finally to the Universe we see today 13 billion years after the big bang, with its clusters of galaxies, superclusters, voids, and great walls. The attractive force of gravity acting on tiny primeval inhomogeneities in the distribution of matter gave rise to all the structure seen today. A paradigm based upon deep connections between cosmology and elementary particle physics{emdash}inflation+cold dark matter{emdash}holds the promise of extending our understanding to an even more fundamental level and much earlier times, as well as shedding light on the unification of the forces and particles of Nature. As we enter the 21st century, a flood of observations is testing this paradigm. {copyright} {ital 1999} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Ferrara, S.; Kehagias, A.; Sagnotti, A.
2016-09-01
Abdus Salam was a true master of 20th Century Theoretical Physics. Not only was he a pioneer of the Standard Model (for which he shared the Nobel Prize with S. Glashow and S. Weinberg), but he also (co)authored many other outstanding contributions to the field of Fundamental Interactions and their unification. In particular, he was a major contributor to the development of supersymmetric theories, where he also coined the word “Supersymmetry” (replacing the earlier “Supergauges” drawn from String Theory). He also introduced the basic concept of “Superspace” and the notion of “Goldstone Fermion” (Goldstino). These concepts proved instrumental for the exploration of the ultraviolet properties and for the study of spontaneously broken phases of super Yang-Mills theories and Supergravity. They continue to play a key role in current developments in Early-Universe Cosmology. In this contribution we review models of inflation based on Supergravity with spontaneously broken local supersymmetry, with emphasis on the role of nilpotent superfields to describe a de Sitter phase of our Universe.
Not Available
1990-01-01
The overall objective of the research supported by this contract is to further our understanding of the basic building blocks of matter as well as the role fundamental interactions play in cosmology and astrophysics. Astrophysical data, such as from high energy cosmic rays and large scale structure of the universe, are employed to constrain particle physics theories. Particle collisions at Tevatron and higher (SSC) energies are also under investigation. During the past year a systematic reanalysis of the correlation between solar activity and the solar neutrino flux was undertaken. The conclusion seems to be that the Homestake experimental data show a correlation at a significant level, supporting the hypothesis that the neutrino possesses a magnetic moment. A separate, but related, theoretical investigation of electromagnetic properties of elementary particles has led to the discovery of a class of models in which the neutrino is endowed with an appreciable magnetic moment while its remains small. Altogether members of the group have been co-authors of 28 papers during the grant year on topics ranging from fermion masses to the role of ultra-high energy hadronic interactions in cosmic ray physics.
Buchbinder, Evgeny I.; Khoury, Justin; Ovrut, Burt A.
2007-12-15
In this paper, we present a new scenario of the early universe that contains a pre-big bang ekpyrotic phase. By combining this with a ghost condensate, the theory explicitly violates the null energy condition without developing any ghostlike instabilities. Thus the contracting universe goes through a nonsingular bounce and evolves smoothly into the expanding post-big bang phase. The curvature perturbation acquires a scale-invariant spectrum well before the bounce in this scenario. It is sourced by the scale-invariant entropy perturbation engendered by two ekpyrotic scalar fields, a mechanism recently proposed by Lehners et al. Since the background geometry is nonsingular at all times, the curvature perturbation remains nearly constant on superhorizon scales. It emerges from the bounce unscathed and imprints a scale-invariant spectrum of density fluctuations in the matter-radiation fluid at the onset of the hot big bang phase. The ekpyrotic potential can be chosen so that the spectrum has a red tilt, in accordance with the recent data from WMAP. As in the original ekpyrotic scenario, the model predicts a negligible gravity wave signal on all observable scales. As such ''new ekpyrotic cosmology'' provides a consistent and distinguishable alternative to inflation to account for the origin of the seeds of large-scale structure.
NASA Technical Reports Server (NTRS)
Schramm, David N.
1989-01-01
Nuclear physics has provided one of two critical observational tests of all Big Bang cosmology, namely Big Bang Nucleosynthesis. Furthermore, this same nuclear physics input enables a prediction to be made about one of the most fundamental physics questions of all, the number of elementary particle families. The standard Big Bang Nucleosynthesis arguments are reviewed. The primordial He abundance is inferred from He-C and He-N and He-O correlations. The strengthened Li constraint as well as D-2 plus He-3 are used to limit the baryon density. This limit is the key argument behind the need for non-baryonic dark matter. The allowed number of neutrino families, N(nu), is delineated using the new neutron lifetime value of tau(n) = 890 + or - 4s (tau(1/2) = 10.3 min). The formal statistical result is N(nu) = 2.6 + or - 0.3 (1 sigma), providing a reasonable fit (1.3 sigma) to three families but making a fourth light (m(nu) less than or equal to 10 MeV) neutrino family exceedly unlikely (approx. greater than 4.7 sigma). It is also shown that uncertainties induced by postulating a first-order quark-baryon phase transition do not seriously affect the conclusions.
Multiverses and physical cosmology
NASA Astrophysics Data System (ADS)
Ellis, G. F. R.; Kirchner, U.; Stoeger, W. R.
2004-01-01
The idea of a multiverse - an ensemble of universes - has received increasing attention in cosmology, both as the outcome of the originating process that generated our own Universe, and as an explanation for why our Universe appears to be fine-tuned for life and consciousness. Here we carefully consider how multiverses should be defined, stressing the distinction between the collection of all possible universes, and ensembles of really existing universes that are essential for an anthropic argument. We show that such realized multiverses are by no means unique. A proper measure on the space of all really existing universes or universe domains is needed, so that probabilities can be calculated, and major problems arise in terms of realized infinities. As an illustration we examine these issues in the case of the set of Friedmann-Lemaître-Robertson-Walker universes. Then we briefly summarize scenarios such as chaotic inflation, which suggest how ensembles of universe domains may be generated, and we point out that the regularities which must underlie any systematic description of truly disjoint multiverses must imply some kind of common generating mechanism. Finally, we discuss the issue of testability, which underlies the question of whether multiverse proposals are really scientific propositions.
NASA Astrophysics Data System (ADS)
Ferrara, S.; Kehagias, A.; Sagnotti, A.
Abdus Salam was a true master of 20th Century Theoretical Physics. Not only was he a pioneer of the Standard Model (for which he shared the Nobel Prize with S. Glashow and S. Weinberg), but he also (co)authored many other outstanding contributions to the field of Fundamental Interactions and their unification. In particular, he was a major contributor to the development of supersymmetric theories, where he also coined the word "Supersymmetry" (replacing the earlier "Supergauges" drawn from String Theory). He also introduced the basic concept of "Superspace" and the notion of "Goldstone Fermion"(Goldstino). These concepts proved instrumental for the exploration of the ultraviolet properties and for the study of spontaneously broken phases of super Yang- Mills theories and Supergravity. They continue to play a key role in current developments in Early-Universe Cosmology. In this contribution we review models of inflation based on Supergravity with spontaneously broken local supersymmetry, with emphasis on the role of nilpotent superfields to describe a de Sitter phase of our Universe.
Entropy, matter, and cosmology
Prigogine, I.; Géhéniau, J.
1986-01-01
The role of irreversible processes corresponding to creation of matter in general relativity is investigated. The use of Landau-Lifshitz pseudotensors together with conformal (Minkowski) coordinates suggests that this creation took place in the early universe at the stage of the variation of the conformal factor. The entropy production in this creation process is calculated. It is shown that these dissipative processes lead to the possibility of cosmological models that start from empty conditions and gradually build up matter and entropy. Gravitational entropy takes a simple meaning as associated to the entropy that is necessary to produce matter. This leads to an extension of the third law of thermodynamics, as now the zero point of entropy becomes the space-time structure out of which matter is generated. The theory can be put into a convenient form using a supplementary “C” field in Einstein's field equations. The role of the C field is to express the coupling between gravitation and matter leading to irreversible entropy production. PMID:16593747
NASA Astrophysics Data System (ADS)
Bennett, C. L.
A prodigious burst of high-energy radiation was generated during the Big Bang. Today, this radiation is seen as a nearly uniform faint glow across the sky, now as low-energy microwaves due to the expansion of the universe over billions of years. Tiny temperature variations of the radiation across the sky were first discovered by NASA's Cosmic Background Explorer (COBE) space mission in 1992. The Wilkinson Microwave Anisotropy Probe (WMAP) space mission, launched in 2001, has now mapped the temperature variations (anisotropy) of the cosmic microwave background radiation over the full sky with unprecedented accuracy and precision. The WMAP observations provide definitive answers to cosmological questions and open the door to new investigations. For example, the WMAP has determined that the content of the universe, dominated by dark matter and dark energy. The large-scale geometry of the universe is flat, in that the sum of the interior angles of a triangle adds up to 180 degrees even over vast distances. New limits are set on the mass of neutrinos and the nature (equation of state) of the dark energy. The WMAP results also place new limits on the physics of the very early universe, usually described in terms of Inflation theory: a rapid exponential expansion of the universe within a fraction of a second. Observations are on-going and will improve our understanding of the physics of the universe.
Varying constants quantum cosmology
Leszczyńska, Katarzyna; Balcerzak, Adam; Dabrowski, Mariusz P. E-mail: abalcerz@wmf.univ.szczecin.pl
2015-02-01
We discuss minisuperspace models within the framework of varying physical constants theories including Λ-term. In particular, we consider the varying speed of light (VSL) theory and varying gravitational constant theory (VG) using the specific ansätze for the variability of constants: c(a) = c{sub 0} a{sup n} and G(a)=G{sub 0} a{sup q}. We find that most of the varying c and G minisuperspace potentials are of the tunneling type which allows to use WKB approximation of quantum mechanics. Using this method we show that the probability of tunneling of the universe ''from nothing'' (a=0) to a Friedmann geometry with the scale factor a{sub t} is large for growing c models and is strongly suppressed for diminishing c models. As for G varying, the probability of tunneling is large for G diminishing, while it is small for G increasing. In general, both varying c and G change the probability of tunneling in comparison to the standard matter content (cosmological term, dust, radiation) universe models.
NASA Technical Reports Server (NTRS)
Canuto, V. M.
1978-01-01
A review of big-bang cosmology is presented, emphasizing the big-bang model, hypotheses on the origin of galaxies, observational tests of the big-bang model that may be possible with the Large Space Telescope, and the scale-covariant theory of gravitation. Detailed attention is given to the equations of general relativity, the redshift-distance relation for extragalactic objects, expansion of the universe, the initial singularity, the discovery of the 3-K blackbody radiation, and measurements of the amount of deuterium in the universe. The curvature of the expanding universe is examined along with the magnitude-redshift relation for quasars and galaxies. Several models for the origin of galaxies are evaluated, and it is suggested that a model of galaxy formation via the formation of black holes is consistent with the model of an expanding universe. Scale covariance is discussed, a scale-covariant theory is developed which contains invariance under scale transformation, and it is shown that Dirac's (1937) large-numbers hypothesis finds a natural role in this theory by relating the atomic and Einstein units.
Cosmological perturbations without inflation
NASA Astrophysics Data System (ADS)
Melia, Fulvio
2017-01-01
A particularly attractive feature of inflation is that quantum fluctuations in the inflaton field may have seeded inhomogeneities in the cosmic microwave background (CMB) and the formation of large-scale structure. In this paper, we demonstrate that a scalar field with zero active mass, i.e. with an equation of state ρ +3p=0 , where ρ and p are its energy density and pressure, respectively, could also have produced an essentially scale-free fluctuation spectrum, though without inflation. This alternative mechanism is based on the Hollands–Wald concept of a minimum wavelength for the emergence of quantum fluctuations into the semi-classical universe. A cosmology with zero active mass does not have a horizon problem, so it does not need inflation to solve this particular (non) issue. In this picture, the {{1}\\circ}{ {--}}{{10}\\circ} fluctuations in the CMB correspond almost exactly to the Planck length at the Planck time, firmly supporting the view that CMB observations may already be probing trans-Planckian physics.
NASA Astrophysics Data System (ADS)
Gao, Xiang; Yang, Jian-Cheng; Xia, Jia-Wen; Chai, Wei-Ping; Shi, Jian; Shen, Guo-Dong
2014-04-01
The Super Heavy Experimental Ring (SHER), which is one of the rings of the next accelerator complex High Intensity Heavy Ion Accelerator Facility (HIAF) at IMP, has to be optimized for e-cooling. Its lattice is designed for two modes: the first is the isochronous mode, which is a time-of-flight mass spectrometer for short-lived secondary nuclei, the second is the storage ring mode, which is used for collecting and cooling the secondary rare isotope beams from the transport line. In order to fulfil its purpose, the ion optics can be set to different ion optical modes.
Lattice Design for the LHEC Recirculating Linac
Sun, Yipeng; Eide, Anders; Zimmermann, Frank; Adolphsen, Chris; /SLAC
2011-05-20
In this paper, we present a lattice design for the Large Hadron Electron Collider (LHeC) recirculating linac. The recirculating linac consists of one roughly 3-km long linac hosting superconducting RF (SRF) accelerating cavities, two arcs and one transfer line for the recirculation. In two passes through a pulsed SRF linac the electron beam can get a maximum energy of 140 GeV. Alternatively, in the Energy Recovery Linac (ERL) option the beam passes through a CW linac four times (two passes for acceleration and two for deceleration) for a maximum energy of 60 GeV.
Probing gravitation, dark energy, and acceleration
Linder, Eric V.
2004-02-20
The acceleration of the expansion of the universe arises from unknown physical processes involving either new fields in high energy physics or modifications of gravitation theory. It is crucial for our understanding to characterize the properties of the dark energy or gravity through cosmological observations and compare and distinguish between them. In fact, close consistencies exist between a dark energy equation of state function w(z) and changes to the framework of the Friedmann cosmological equations as well as direct spacetime geometry quantities involving the acceleration, such as ''geometric dark energy'' from the Ricci scalar. We investigate these interrelationships, including for the case of super acceleration or phantom energy where the fate of the universe may be more gentle than the Big Rip.
Calculating Buckling And Vibrations Of Lattice Structures
NASA Technical Reports Server (NTRS)
Anderson, M. S.; Durling, B. J.; Herstrom, C. L.; Williams, F. W.; Banerjee, J. R.; Kennedy, D.; Warnaar, D. B.
1989-01-01
BUNVIS-RG computer program designed to calculate vibration frequencies or buckling loads of prestressed lattice structures used in outer space. For buckling and vibration problems, BUNVIS-RG calculates deadload axial forces caused in members by any combination of externally-applied static point forces and moments at nodes, axial preload or prestrain in members, and such acceleration loads as those due to gravity. BUNVIS-RG is FORTRAN 77 computer program implemented on CDC CYBER and VAX computer.
Cosmic acceleration and the helicity-0 graviton
Rham, Claudia de; Heisenberg, Lavinia; Gabadadze, Gregory; Pirtskhalava, David
2011-05-15
We explore cosmology in the decoupling limit of a nonlinear covariant extension of Fierz-Pauli massive gravity obtained recently in arXiv:1007.0443. In this limit the theory is a scalar-tensor model of a unique form defined by symmetries. We find that it admits a self-accelerated solution, with the Hubble parameter set by the graviton mass. The negative pressure causing the acceleration is due to a condensate of the helicity-0 component of the massive graviton, and the background evolution, in the approximation used, is indistinguishable from the {Lambda}CDM model. Fluctuations about the self-accelerated background are stable for a certain range of parameters involved. Most surprisingly, the fluctuation of the helicity-0 field above its background decouples from an arbitrary source in the linearized theory. We also show how massive gravity can remarkably screen an arbitrarily large cosmological constant in the decoupling limit, while evading issues with ghosts. The obtained static solution is stable against small perturbations, suggesting that the degravitation of the vacuum energy is possible in the full theory. Interestingly, however, this mechanism postpones the Vainshtein effect to shorter distance scales. Hence, fifth force measurements severely constrain the value of the cosmological constant that can be neutralized, making this scheme phenomenologically not viable for solving the old cosmological constant problem. We briefly speculate on a possible way out of this issue.
Nonstandard Lagrangian cosmology
NASA Astrophysics Data System (ADS)
El-Nabulsi, Rami Ahmad
2013-11-01
We show that many independent scenarios as the `accelerated expansion of the universe', `eternal inflation', `eternally oscillating universe', `nonsingular oscillating universe', and `collapse of an oscillating universe' may occur without modifying the gravity theory or introducing scalar fields of any type. This is achieved by replacing the standard Lagrangian in the Friedmann-Robertson-Walker spacetime model by an exponentially nonstandard Lagrangian which modify the Euler-Lagrange equation although the standard variational approach is used.
Dissipative photonic lattice solitons.
Ultanir, Erdem A; Stegeman, George I; Christodoulides, Demetrios N
2004-04-15
We show that discrete dissipative optical lattice solitons are possible in waveguide array configurations that involve periodically patterned semiconductor optical amplifiers and saturable absorbers. The characteristics of these low-power soliton states are investigated, and their propagation constant eigenvalues are mapped on Floquet-Bloch band diagrams. The prospect of observing such low-power dissipative lattice solitons is discussed in detail.
Theory Challenges of the Accelerating Universe
Linder, Eric V.
2007-03-05
The accelerating expansion of the universe presents an exciting, fundamental challenge to the standard models of particle physics and cosmology. I highlight some of the outstanding challenges in both developing theoretical models and interpreting without bias the observational results from precision cosmology experiments in the next decade that will return data to help reveal the nature of the new physics. Examples given focus on distinguishing a new component of energy from a new law of gravity, and the effect of early dark energy on baryon acoustic oscillations.
Cosmological model from the holographic equipartition law with a modified Rényi entropy
NASA Astrophysics Data System (ADS)
Komatsu, Nobuyoshi
2017-04-01
Cosmological equations were recently derived by Padmanabhan from the expansion of cosmic space due to the difference between the degrees of freedom on the surface and in the bulk in a region of space. In this study, a modified Rényi entropy is applied to Padmanabhan's `holographic equipartition law', by regarding the Bekenstein-Hawking entropy as a nonextensive Tsallis entropy and using a logarithmic formula of the original Rényi entropy. Consequently, the acceleration equation including an extra driving term (such as a time-varying cosmological term) can be derived in a homogeneous, isotropic, and spatially flat universe. When a specific condition is mathematically satisfied, the extra driving term is found to be constant-like as if it is a cosmological constant. Interestingly, the order of the constant-like term is naturally consistent with the order of the cosmological constant measured by observations, because the specific condition constrains the value of the constant-like term.
Dark energy cosmology from higher-order, string-inspired gravity, and its reconstruction
Nojiri, Shin'ichi; Odintsov, Sergei D.; Sami, M.
2006-08-15
In this paper we investigate the cosmological effects of modified gravity with string curvature corrections added to the Einstein-Hilbert action in the presence of a dynamically evolving scalar field coupled to Riemann invariants. The scenario exhibits several features of cosmological interest for the late universe. We show that higher-order stringy corrections can lead to a class of dark energy models consistent with recent observations. The models can give rise to quintessence without recourse to a scalar field potential. The detailed treatment of the reconstruction program for general scalar-Gauss-Bonnet gravity is presented for any given cosmology. The explicit examples of reconstructed scalar potentials are given for an accelerated (quintessence, cosmological constant, or phantom) universe. Finally, the relation with modified F(G) gravity is established at the classical level and is extended to include third order terms on the curvature.
The bouncing cosmology with F(R) gravity and its reconstructing
NASA Astrophysics Data System (ADS)
Amani, Ali R.
2016-04-01
In this paper, we study F(R) gravity by Hu-Sawicki model in Friedmann-Lemaître-Robertson-Walker (FLRW) background. The Friedmann equations are calculated by modified gravity action, and then the obtained Friedmann equations are written in terms of standard Friedmann equations. Next, the behavior of bouncing cosmology is investigated in the modified gravity model, i.e. this behavior can solve the problem of nonsingularity in standard big bang cosmology. We plot the cosmological parameters in terms of cosmic time and then the bouncing condition is investigated. In what follows, we reconstruct the modified gravity by redshift parameter, and also graphs of cosmological parameters are plotted in terms of redshift, in which the figures show us an accelerated expansion of universe. Finally, the stability of the scenario is investigated by a function as sound speed, and the graph of sound speed versus redshift shows us that there is the stability in late-time.
Cosmological stability bound in massive gravity and bigravity
Fasiello, Matteo; Tolley, Andrew J. E-mail: andrew.j.tolley@case.edu
2013-12-01
We give a simple derivation of a cosmological bound on the graviton mass for spatially flat FRW solutions in massive gravity with an FRW reference metric and for bigravity theories. This bound comes from the requirement that the kinetic term of the helicity zero mode of the graviton is positive definite. The bound is dependent only on the parameters in the massive gravity potential and the Hubble expansion rate for the two metrics. We derive the decoupling limit of bigravity and FRW massive gravity, and use this to give an independent derivation of the cosmological bound. We recover our previous results that the tension between satisfying the Friedmann equation and the cosmological bound is sufficient to rule out all observationally relevant FRW solutions for massive gravity with an FRW reference metric. In contrast, in bigravity this tension is resolved due to different nature of the Vainshtein mechanism. We find that in bigravity theories there exists an FRW solution with late-time self-acceleration for which the kinetic terms for the helicity-2, helicity-1 and helicity-0 are generically nonzero and positive making this a compelling candidate for a model of cosmic acceleration. We confirm that the generalized bound is saturated for the candidate partially massless (bi)gravity theories but the existence of helicity-1/helicity-0 interactions implies the absence of the conjectured partially massless symmetry for both massive gravity and bigravity.
Milgrom's revision of Newton's laws - Dynamical and cosmological consequences
NASA Technical Reports Server (NTRS)
Felten, J. E.
1984-01-01
Milgrom's (1983) recent revision of Newtonian dynamics was introduced to eliminate the inference that large quantities of invisible mass exist in galaxies. It is shown by simple examples that a Milgrom acceleration, in the form presented so far, implies other far-reaching changes in dynamics. The momentum of an isolated system is not conserved, and the usual theorem for center-of-mass motion of any system does not hold. Naive applications require extreme caution. The model fails to provide a complete description of particle dynamics and should be thought of as a revision of Kepler's laws rather than Newton's. The Milgrom acceleration also implies fundamental changes in cosmology. A quasi-Newtonian calculation adapted from Newtonian cosmology suggests that a 'Milgrom universe' will recollapse even if the classical closure parameter Omega is much less than unity. The solution, however, fails to satisfy the cosmological principle. Reasons for the breakdown of this calculation are examined. A new theory of gravitation will be needed before the behavior of a Milgrom universe can be predicted.
Resource Letter DEAU-1: Dark energy and the accelerating universe
NASA Astrophysics Data System (ADS)
Linder, Eric V.
2008-03-01
This Resource Letter provides a guide to the literature on dark energy and the accelerating universe. It is intended to be of use to researchers, teachers, and students at several levels. Journal articles, books, and websites are cited for the following topics: Einstein's cosmological constant, quintessence or dynamical scalar fields, modified cosmic gravity, relations to high-energy physics, cosmological probes and observations, terrestrial probes, calculational tools and parameter estimation, teaching strategies and educational resources, and the fate of the universe.