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Sample records for 5d cosmological model

  1. Professor Wheeler and the crack of doom: Closed cosmologies in the 5-d Kaluza-Klein theory

    SciTech Connect

    Matzner, R.A.; Mezzacappa, A.

    1986-03-01

    We study the classical and the quantum structures of certain 5-d Kaluza-Klein cosmologies. These models were chosen because their 4-d restriction is a closed, radiation-dominated, homogeneous, isotropic cosmology in the usual sense. The extra (field) dimension is taken to be a circle. In these models the solution starts from a 5-d curvature singularity with infinite circumference for the circle and zero volume for the 3-space. It evolves in finite proper time to a solution with zero dimension for the extra field direction. In the 5-vacuum case this is not a curvature singularity, but is a singularity of the congruence describing the physics, and in particular, the solution cannot causally be extended to the future of this point. In the 5-vacuum case this event coincides with the maximum of expansion of the 5-space. In the 5-dust cases, this point is a real 5-d curvature singularity. By adjustment it can be made to occur before or after the maximum of 3-expansion. The solution stops at that instant, but the 4-cosmology reveals no pathology up to the crack of doom. The quantum behavior is identical in these respects to the classical one.

  2. 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.

  3. 2.5D Cartoon Hair Modeling and Manipulation.

    PubMed

    Yeh, Chih-Kuo; Jayaraman, Pradeep Kumar; Liu, Xiaopei; Fu, Chi-Wing; Lee, Tong-Yee

    2015-03-01

    This paper addresses a challenging single-view modeling and animation problem with cartoon images. Our goal is to model the hairs in a given cartoon image with consistent layering and occlusion, so that we can produce various visual effects from just a single image. We propose a novel 2.5D modeling approach to deal with this problem. Given an input image, we first segment the hairs of the cartoon character into regions of hair strands. Then, we apply our novel layering metric, which is derived from the Gestalt psychology, to automatically optimize the depth ordering among the hair strands. After that, we employ our hair completion method to fill the occluded part of each hair strand, and create a 2.5D model of the cartoon hair. By using this model, we can produce various visual effects, e.g., we develop a simplified fluid simulation model to produce wind blowing animations with the 2.5D hairs. To further demonstrate the applicability and versatility of our method, we compare our results with real cartoon hair animations, and also apply our model to produce a wide variety of hair manipulation effects, including hair editing and hair braiding. PMID:26357063

  4. Improved cosmological model

    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.

  5. SFT based cosmological models

    NASA Astrophysics Data System (ADS)

    Koshelev, Alexey S.

    2010-11-01

    We consider the appearance of multiple scalar fields in SFT inspired non-local models with a single scalar field at late times. In this regime all the scalar fields are free. This system minimally coupled to gravity is mainly analyzed in this note. We build one exact solution to the equations of motion. We consider an exactly solvable model which obeys a simple exact solution in the cosmological context for the Friedmann equations and that reproduces the behavior expected from SFT in the asymptotic regime.

  6. 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.

  7. Gravitational waves during inflation from a 5D large-scale repulsive gravity model

    NASA Astrophysics Data System (ADS)

    Reyes, Luz M.; Moreno, Claudia; Madriz Aguilar, José Edgar; Bellini, Mauricio

    2012-10-01

    We investigate, in the transverse traceless (TT) gauge, the generation of the relic background of gravitational waves, generated during the early inflationary stage, on the framework of a large-scale repulsive gravity model. We calculate the spectrum of the tensor metric fluctuations of an effective 4D Schwarzschild-de Sitter metric on cosmological scales. This metric is obtained after implementing a planar coordinate transformation on a 5D Ricci-flat metric solution, in the context of a non-compact Kaluza-Klein theory of gravity. We found that the spectrum is nearly scale invariant under certain conditions. One interesting aspect of this model is that it is possible to derive the dynamical field equations for the tensor metric fluctuations, valid not just at cosmological scales, but also at astrophysical scales, from the same theoretical model. The astrophysical and cosmological scales are determined by the gravity-antigravity radius, which is a natural length scale of the model, that indicates when gravity becomes repulsive in nature.

  8. 2.5-D modeling in electromagnetic methods of geophysics

    NASA Astrophysics Data System (ADS)

    Tabarovsky, L. A.; Goldman, M. M.; Rabinovich, M. B.; Strack, K.-M.

    1996-10-01

    Understanding, using, or eliminating three-dimensional (3-D) effects in electromagnetic methods of geophysics are critical requirements. Numerous achievements in 3-D modeling sometimes give the impression that they are widely available today in geophysical practice. This is not necessarily true. Existing 3-D modeling packages prove that we know how to perform 3-D modeling. However, the computer resources and costs involved make the practical application of 3-D EM modeling in geophysical applications very limited. A practical compromise, or even alternative, is represented by 2.5-D modeling characterized by the use of a 3-D source in a 2-D medium. This combination allows one to mathematically describe the related boundary value problem as a sequence of independent two-dimensional problems. The typical technique leading to such a split formulation is Fourier analysis. That is why the individual terms of a split solution are often referred to as harmonics. Although each independent problem is two-dimensional, the algorithmic implementation of finite differences or integral equations for the higher harmonics has some specific features not present in the classical 2-D cases. In this paper, a hybrid scheme consisting of a combination of the finite difference technique with the integral equation approach for transient fields is described. Evaluation of algorithm accuracy is presented and a transient logging technique application is considered. The algorithm is fast and easily implemented on a personal computer

  9. Comparison between different cosmological models

    SciTech Connect

    Panotopoulos, Grigoris

    2008-05-15

    Several cosmological models have been proposed in order to explain the current acceleration of the Universe. Recently, the normal branch of the DGP (after Dvali, Gabadadze, and Porrati) brane model with a generalized Chaplygin gas was studied as a model which can cross the phantom divide line avoiding the future singularity. In the present work, we wish to address the question of whether or not the aforementioned model has a better fit to supernovae data compared to cold dark matter with a cosmological constant, the (generalized) Chaplygin gas, and the DGP model with the self-accelerating branch without extra fluid for dark energy. We have found that the Chaplygin-DGP model has the worst fit, while the two-fluid model with Chaplygin gas and dust (baryons) has the best fit among the theoretical cosmological models considered here.

  10. Cosmology: Standard Model

    NASA Astrophysics Data System (ADS)

    Peacock, J.; Murdin, P.

    2002-07-01

    COSMOLOGY in the modern sense of quantitative study of the large-scale properties of the universe is a surprisingly recent phenomenon. The first galaxy RADIAL VELOCITY (a blueshift, as it turned out) was only measured in 1912, by Slipher. It was not until 1924 that Hubble was able to prove that the `nebulae' were indeed large systems of stars at vast distances, by which tim...

  11. Stringy Model of Cosmological Dark Energy

    SciTech Connect

    Aref'eva, Irina Ya.

    2007-11-20

    A string field theory (SFT) nonlocal model of the cosmological dark energy providing w<-1 is briefly surveyed. We summarize recent developments and open problems, as well as point out some theoretical issues related with others applications of the SFT nonlocal models in cosmology, in particular, in inflation and cosmological singularity.

  12. Higgs boson production and decay in 5D warped models

    NASA Astrophysics Data System (ADS)

    Frank, Mariana; Pourtolami, Nima; Toharia, Manuel

    2016-03-01

    We calculate the production and decay rates of the Higgs boson at the LHC in the context of general five-dimensional warped scenarios with a spacetime background modified from the usual AdS5 , with Standard Model (SM) fields propagating in the bulk. We extend previous work by considering the full flavor structure of the SM, and thus including all possible flavor effects coming from mixings with heavy fermions. We proceed in three different ways, first by only including two complete Kaluza-Klein (KK) levels (15 ×15 fermion mass matrices), then including three complete KK levels (21 ×21 fermion mass matrices) and finally we compare with the effect of including the infinite (full) KK towers. We present numerical results for the Higgs production cross section via gluon fusion and Higgs decay branching fractions in both the modified metric scenario and in the usual Randall-Sundrum metric scenario.

  13. Scalar-tensor cosmological models

    NASA Astrophysics Data System (ADS)

    Serna, A.; Alimi, J. M.

    1996-03-01

    We analyze the qualitative behavior of scalar-tensor cosmologies with an arbitrary monotonic $\\omega(\\Phi)$ function. In particular, we are interested in scalar-tensor theories distinguishable at early epochs from general relativity (GR) but leading to predictions compatible with solar-system experiments. After extending the method developed by Lorentz-Petzold and Barrow, we establish the conditions required for convergence towards GR at $t \\rightarrow \\infty$. Then, we obtain all the asymptotic analytical solutions at early times which are possible in the framework of these theories. The subsequent qualitative evolution, from these asymptotic solutions until their later convergence towards GR, is analyzed by means of numerical computations. From this analysis, we are able to establish a classification of the different qualitative behaviors of scalar-tensor cosmological models with an arbitrary monotonic $\\omega(\\Phi)$ function

  14. Nonsingular cosmological models with a variable cosmological term L

    NASA Astrophysics Data System (ADS)

    Pradhan, A.; Srivastava, K.; Ahuja, A. L.

    Exact solutions of the Einstein's field equations describing a spherically symmetric cosmological model without a big bang or any other kind of singularity recently obtained by Dadhich and Patel (2000) are revisited. The matter content of the model is a shear-free perfect fluid with isotropic pressure and a radial heat flux. Three different exact solutions are obtained both for perfect fluid and fluid with bulk viscosity. It turns out that the cosmological term L(t) is a decreasing function of time, which is consistent with recent observations of type Ia supernovae.

  15. Matrix model approach to cosmology

    NASA Astrophysics Data System (ADS)

    Chaney, A.; Lu, Lei; Stern, A.

    2016-03-01

    We perform a systematic search for rotationally invariant cosmological solutions to toy matrix models. These models correspond to the bosonic sector of Lorentzian Ishibashi, Kawai, Kitazawa and Tsuchiya (IKKT)-type matrix models in dimensions d less than ten, specifically d =3 and d =5 . After taking a continuum (or commutative) limit they yield d -1 dimensional Poisson manifolds. The manifolds have a Lorentzian induced metric which can be associated with closed, open, or static space-times. For d =3 , we obtain recursion relations from which it is possible to generate rotationally invariant matrix solutions which yield open universes in the continuum limit. Specific examples of matrix solutions have also been found which are associated with closed and static two-dimensional space-times in the continuum limit. The solutions provide for a resolution of cosmological singularities, at least within the context of the toy matrix models. The commutative limit reveals other desirable features, such as a solution describing a smooth transition from an initial inflation to a noninflationary era. Many of the d =3 solutions have analogues in higher dimensions. The case of d =5 , in particular, has the potential for yielding realistic four-dimensional cosmologies in the continuum limit. We find four-dimensional de Sitter d S4 or anti-de Sitter AdS4 solutions when a totally antisymmetric term is included in the matrix action. A nontrivial Poisson structure is attached to these manifolds which represents the lowest order effect of noncommutativity. For the case of AdS4 , we find one particular limit where the lowest order noncommutativity vanishes at the boundary, but not in the interior.

  16. Validation of a 2.5D CFD model for cylindrical gas–solids fluidized beds

    SciTech Connect

    Li, Tingwen

    2015-09-25

    The 2.5D model recently proposed by Li et al. (Li, T., Benyahia, S., Dietiker, J., Musser, J., and Sun, X., 2015. A 2.5D computational method to simulate cylindrical fluidized beds. Chemical Engineering Science. 123, 236-246.) was validated for two cylindrical gas-solids bubbling fluidized bed systems. Different types of particles tested under various flow conditions were simulated using the traditional 2D model and the 2.5D model. Detailed comparison against the experimental measurements on solid concentration and velocity were conducted. Comparing to the traditional Cartesian 2D flow simulation, the 2.5D model yielded better agreement with the experimental data especially for the solid velocity prediction in the column wall region.

  17. Validation of a 2.5D CFD model for cylindrical gas–solids fluidized beds

    DOE PAGES

    Li, Tingwen

    2015-09-25

    The 2.5D model recently proposed by Li et al. (Li, T., Benyahia, S., Dietiker, J., Musser, J., and Sun, X., 2015. A 2.5D computational method to simulate cylindrical fluidized beds. Chemical Engineering Science. 123, 236-246.) was validated for two cylindrical gas-solids bubbling fluidized bed systems. Different types of particles tested under various flow conditions were simulated using the traditional 2D model and the 2.5D model. Detailed comparison against the experimental measurements on solid concentration and velocity were conducted. Comparing to the traditional Cartesian 2D flow simulation, the 2.5D model yielded better agreement with the experimental data especially for the solidmore » velocity prediction in the column wall region.« less

  18. Top ten accelerating cosmological models

    NASA Astrophysics Data System (ADS)

    Szydłowski, Marek; Kurek, Aleksandra; Krawiec, Adam

    2006-11-01

    Recent astronomical observations indicate that the Universe is presently almost flat and undergoing a period of accelerated expansion. Basing on Einstein's general relativity all these observations can be explained by the hypothesis of a dark energy component in addition to cold dark matter (CDM). Because the nature of this dark energy is unknown, it was proposed some alternative scenario to explain the current accelerating Universe. The key point of this scenario is to modify the standard FRW equation instead of mysterious dark energy component. The standard approach to constrain model parameters, based on the likelihood method, gives a best-fit model and confidence ranges for those parameters. We always arbitrary choose the set of parameters which define a model which we compare with observational data. Because in the generic case, the introducing of new parameters improves a fit to the data set, there appears the problem of elimination of model parameters which can play an insufficient role. The Bayesian information criteria of model selection (BIC) is dedicated to promotion a set of parameters which should be incorporated to the model. We divide class of all accelerating cosmological models into two groups according to the two types of explanation acceleration of the Universe. Then the Bayesian framework of model selection is used to determine the set of parameters which gives preferred fit to the SNIa data. We find a few of flat cosmological models which can be recommend by the Bayes factor. We show that models with dark energy as a new fluid are favoured over models featuring a modified FRW equation. The work was supported by Marie Curie Host Fellowship MTKD-CT-2004-517186 (COCOS) during the staying in University of Paris 13.

  19. Supersymmetric cosmological FRW model and dark energy

    SciTech Connect

    Rosales, J. J.; Tkach, V. I.

    2010-11-15

    In this work we consider a flat cosmological model with a set of fluids in the framework of supersymmetric cosmology. The obtained supersymmetric algebra allowed us to take quantum solutions. It is shown that only in the case of a cosmological constant do we have a condition between the density of dark energy {rho}{sub {Lambda}} and density energy of matter {rho}{sub M}, {rho}{sub {Lambda}>}2{rho}{sub M}.

  20. Non-local thermodynamic equilibrium 1.5D modeling of red giant stars

    SciTech Connect

    Young, Mitchell E.; Short, C. Ian

    2014-05-20

    Spectra for two-dimensional (2D) stars in the 1.5D approximation are created from synthetic spectra of one-dimensional (1D) non-local thermodynamic equilibrium (NLTE) spherical model atmospheres produced by the PHOENIX code. The 1.5D stars have the spatially averaged Rayleigh-Jeans flux of a K3-4 III star while varying the temperature difference between the two 1D component models (ΔT {sub 1.5D}) and the relative surface area covered. Synthetic observable quantities from the 1.5D stars are fitted with quantities from NLTE and local thermodynamic equilibrium (LTE) 1D models to assess the errors in inferred T {sub eff} values from assuming horizontal homogeneity and LTE. Five different quantities are fit to determine the T {sub eff} of the 1.5D stars: UBVRI photometric colors, absolute surface flux spectral energy distributions (SEDs), relative SEDs, continuum normalized spectra, and TiO band profiles. In all cases except the TiO band profiles, the inferred T {sub eff} value increases with increasing ΔT {sub 1.5D}. In all cases, the inferred T {sub eff} value from fitting 1D LTE quantities is higher than from fitting 1D NLTE quantities and is approximately constant as a function of ΔT {sub 1.5D} within each case. The difference between LTE and NLTE for the TiO bands is caused indirectly by the NLTE temperature structure of the upper atmosphere, as the bands are computed in LTE. We conclude that the difference between T {sub eff} values derived from NLTE and LTE modeling is relatively insensitive to the degree of the horizontal inhomogeneity of the star being modeled and largely depends on the observable quantity being fit.

  1. Site-specific strong ground motion prediction using 2.5-D modelling

    NASA Astrophysics Data System (ADS)

    Narayan, J. P.

    2001-08-01

    An algorithm was developed using the 2.5-D elastodynamic wave equation, based on the displacement-stress relation. One of the most significant advantages of the 2.5-D simulation is that the 3-D radiation pattern can be generated using double-couple point shear-dislocation sources in the 2-D numerical grid. A parsimonious staggered grid scheme was adopted instead of the standard staggered grid scheme, since this is the only scheme suitable for computing the dislocation. This new 2.5-D numerical modelling avoids the extensive computational cost of 3-D modelling. The significance of this exercise is that it makes it possible to simulate the strong ground motion (SGM), taking into account the energy released, 3-D radiation pattern, path effects and local site conditions at any location around the epicentre. The slowness vector (py) was used in the supersonic region for each layer, so that all the components of the inertia coefficient are positive. The double-couple point shear-dislocation source was implemented in the numerical grid using the moment tensor components as the body-force couples. The moment per unit volume was used in both the 3-D and 2.5-D modelling. A good agreement in the 3-D and 2.5-D responses for different grid sizes was obtained when the moment per unit volume was further reduced by a factor equal to the finite-difference grid size in the case of the 2.5-D modelling. The components of the radiation pattern were computed in the xz-plane using 3-D and 2.5-D algorithms for various focal mechanisms, and the results were in good agreement. A comparative study of the amplitude behaviour of the 3-D and 2.5-D wavefronts in a layered medium reveals the spatial and temporal damped nature of the 2.5-D elastodynamic wave equation. 3-D and 2.5-D simulated responses at a site using a different strike direction reveal that strong ground motion (SGM) can be predicted just by rotating the strike of the fault counter-clockwise by the same amount as the azimuth of

  2. Simple inhomogeneous cosmological (toy) models

    NASA Astrophysics Data System (ADS)

    Chirinos Isidro, Eddy G.; Zuñiga Vargas, Cristofher; Zimdahl, Winfried

    2016-05-01

    Based on the Lemaître-Tolman-Bondi (LTB) metric we consider two flat inhomogeneous big-bang models. We aim at clarifying, as far as possible analytically, basic features of the dynamics of the simplest inhomogeneous models and to point out the potential usefulness of exact inhomogeneous solutions as generalizations of the homogeneous configurations of the cosmological standard model. We discuss explicitly partial successes but also potential pitfalls of these simplest models. Although primarily seen as toy models, the relevant free parameters are fixed by best-fit values using the Joint Light-curve Analysis (JLA)-sample data. On the basis of a likelihood analysis we find that a local hump with an extension of almost 2 Gpc provides a better description of the observations than a local void for which we obtain a best-fit scale of about 30 Mpc. Future redshift-drift measurements are discussed as a promising tool to discriminate between inhomogeneous configurations and the ΛCDM model.

  3. Will Quantum Cosmology Resurrect Chaotic Inflation Model?

    NASA Astrophysics Data System (ADS)

    Kim, Sang Pyo; Kim, Won

    2016-07-01

    The single field chaotic inflation model with a monomial power greater than one seems to be ruled out by the recent Planck and WMAP CMB data while Starobinsky model with a higher curvature term seems to be a viable model. Higher curvature terms being originated from quantum fluctuations, we revisit the quantum cosmology of the Wheeler-DeWitt equation for the chaotic inflation model. The semiclassical cosmology emerges from quantum cosmology with fluctuations of spacetimes and matter when the wave function is peaked around the semiclassical trajectory with quantum corrections a la the de Broglie-Bohm pilot theory.

  4. Homogeneous cosmological models in Yang's gravitation theory

    NASA Technical Reports Server (NTRS)

    Fennelly, A. J.; Pavelle, R.

    1979-01-01

    We present a dynamic, spatially homogeneous solution of Yang's pure space gravitational field equations which is non-Einsteinian. The predictions of this cosmological model seem to be at variance with observations.

  5. Beyond the cosmological standard model

    NASA Astrophysics Data System (ADS)

    Joyce, Austin; Jain, Bhuvnesh; Khoury, Justin; Trodden, Mark

    2015-03-01

    After a decade and a half of research motivated by the accelerating universe, theory and experiment have reached a certain level of maturity. The development of theoretical models beyond Λ or smooth dark energy, often called modified gravity, has led to broader insights into a path forward, and a host of observational and experimental tests have been developed. In this review we present the current state of the field and describe a framework for anticipating developments in the next decade. We identify the guiding principles for rigorous and consistent modifications of the standard model, and discuss the prospects for empirical tests. We begin by reviewing recent attempts to consistently modify Einstein gravity in the infrared, focusing on the notion that additional degrees of freedom introduced by the modification must "screen" themselves from local tests of gravity. We categorize screening mechanisms into three broad classes: mechanisms which become active in regions of high Newtonian potential, those in which first derivatives of the field become important, and those for which second derivatives of the field are important. Examples of the first class, such as f(R) gravity, employ the familiar chameleon or symmetron mechanisms, whereas examples of the last class are galileon and massive gravity theories, employing the Vainshtein mechanism. In each case, we describe the theories as effective theories and discuss prospects for completion in a more fundamental theory. We describe experimental tests of each class of theories, summarizing laboratory and solar system tests and describing in some detail astrophysical and cosmological tests. Finally, we discuss prospects for future tests which will be sensitive to different signatures of new physics in the gravitational sector. The review is structured so that those parts that are more relevant to theorists vs. observers/experimentalists are clearly indicated, in the hope that this will serve as a useful reference for

  6. Conformal cosmological model and SNe Ia data

    SciTech Connect

    Zakharov, A. F.; Pervushin, V. N.

    2012-11-15

    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 {Lambda} 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 {Lambda} 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 {Lambda}CDM 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 {Lambda} term (or dark energy). We confirm the claim with much larger set of observational data.

  7. Flavor-changing decays of the top quark in 5D warped models

    NASA Astrophysics Data System (ADS)

    Díaz-Furlong, Alfonso; Frank, Mariana; Pourtolami, Nima; Toharia, Manuel; Xoxocotzi, Reyna

    2016-08-01

    We study flavor-changing neutral current decays of the top quark in the context of general warped extra dimensions, where the five-dimensional (5D) metric is slightly modified from 5D anti-de Sitter (AdS5 ). These models address the Planck-electroweak hierarchies of the Standard Model and can obey all the low-energy flavor bounds and electroweak precision tests, while allowing the scale of new physics to be at the TeV level, and thus within the reach of the LHC at Run II. We perform the calculation of these exotic top decay rates for the case of a bulk Higgs, and thus include in particular the effect of the additional Kaluza-Klein (KK) Higgs modes running in the loops, along with the usual KK fermions and KK gluons.

  8. 2.5D complex resistivity modeling and inversion using unstructured grids

    NASA Astrophysics Data System (ADS)

    Xu, Kaijun; Sun, Jie

    2016-04-01

    The characteristic of complex resistivity on rock and ore has been recognized by people for a long time. Generally we have used the Cole-Cole Model(CCM) to describe complex resistivity. It has been proved that the electrical anomaly of geologic body can be quantitative estimated by CCM parameters such as direct resistivity(ρ0), chargeability(m), time constant(τ) and frequency dependence(c). Thus it is very important to obtain the complex parameters of geologic body. It is difficult to approximate complex structures and terrain using traditional rectangular grid. In order to enhance the numerical accuracy and rationality of modeling and inversion, we use an adaptive finite-element algorithm for forward modeling of the frequency-domain 2.5D complex resistivity and implement the conjugate gradient algorithm in the inversion of 2.5D complex resistivity. An adaptive finite element method is applied for solving the 2.5D complex resistivity forward modeling of horizontal electric dipole source. First of all, the CCM is introduced into the Maxwell's equations to calculate the complex resistivity electromagnetic fields. Next, the pseudo delta function is used to distribute electric dipole source. Then the electromagnetic fields can be expressed in terms of the primary fields caused by layered structure and the secondary fields caused by inhomogeneities anomalous conductivity. At last, we calculated the electromagnetic fields response of complex geoelectric structures such as anticline, syncline, fault. The modeling results show that adaptive finite-element methods can automatically improve mesh generation and simulate complex geoelectric models using unstructured grids. The 2.5D complex resistivity invertion is implemented based the conjugate gradient algorithm.The conjugate gradient algorithm doesn't need to compute the sensitivity matrix but directly computes the sensitivity matrix or its transpose multiplying vector. In addition, the inversion target zones are

  9. Coupling Landform Evolution and Soil Pedogenesis - Initial Results From the SSSPAM5D Model

    NASA Astrophysics Data System (ADS)

    Willgoose, G. R.; Welivitiya, W. D. D. P.; Hancock, G. R.; Cohen, S.

    2015-12-01

    Evolution of soil on a dynamic landform is a crucial next step in landscape evolution modelling. Some attempts have been taken such as MILESD by Vanwalleghem et al. to develop a first model which is capable of simultaneously evolving both the soil profile and the landform. In previous work we have presented physically based models for soil pedogenesis, mARM and SSSPAM. In this study we present the results of coupling a landform evolution model with our SSSPAM5D soil pedogenesis model. In previous work the SSSPAM5D soil evolution model was used to identify trends of the soil profile evolution on a static landform. Two pedogenetic processes, namely (1) armouring due to erosion, and (2) physical and chemical weathering were used in those simulations to evolve the soil profile. By incorporating elevation changes (due to erosion and deposition) we have advanced the SSSPAM5D modelling framework into the realm of landscape evolution. Simulations have been run using elevation and soil grading data of the engineered landform (spoil heap) at the Ranger Uranium Mine, Northern Territory, Australia. The results obtained for the coupled landform-soil evolution simulations predict the erosion of high slope areas, development of rudimentary channel networks in the landform and deposition of sediments in lowland areas, and qualitatively consistent with landform evolution models on their own. Examination of the soil profile characteristics revealed that hill crests are weathering dominated and tend to develop a thick soil layer. The steeper hillslopes at the edge of the landform are erosion dominated with shallow soils while the foot slopes are deposition dominated with thick soil layers. The simulation results of our coupled landform and soil evolution model provide qualitatively correct and timely characterization of the soil evolution on a dynamic landscape. Finally we will compare the characteristics of erosion and deposition predicted by the coupled landform-soil SSSPAM

  10. Warm inflationary model in loop quantum cosmology

    SciTech Connect

    Herrera, Ramon

    2010-06-15

    A warm inflationary universe model in loop quantum cosmology is studied. In general we discuss the condition of inflation in this framework. By using a chaotic potential, V({phi}){proportional_to}{phi}{sup 2}, we develop a model where the dissipation coefficient {Gamma}={Gamma}{sub 0}=constant. We use recent astronomical observations for constraining the parameters appearing in our model.

  11. The role of spin in cosmological models

    NASA Astrophysics Data System (ADS)

    Bedran, M. L.; Vasconcellos-Vaidya, E. P.

    1984-09-01

    The classical description of spin in a perfect fluid of Ray and Smalley (1982) and its energy-momentum-tensor formulation are applied to cosmological models. The Raychaudhuri equation for the evolution of a continuous matter distribution in hydrodynamic motion is analyzed, and the role of spin and torsion in the Einstein-Cartan theory of gravitation (Hehl et al., 1976) is compared to that of spin in general relativity. It is found that spin-spin interaction is significant only at extremely high densities, and that spin-vorticity interactions are of potential importance at high vorticity, as in the early moments of cosmological models.

  12. Initial insights from 2.5D hydraulic modeling of floods in Athabasca Valles, Mars

    USGS Publications Warehouse

    Keszthelyi, L.P.; Denlinger, R.P.; O'Connell, D. R. H.; Burr, D.M.

    2007-01-01

    We present the first application of a 2.5D hydraulic model to catastrophic floods on Mars. This model simulates flow over complex topography and incorporates flood dynamics that could not be modeled in the earlier 1D models. We apply this model to Athabasca Valles, the youngest outflow channel on Mars, investigating previous bank-full discharge estimates and utilizing the interpolated Mars Orbiter Laser Altimeter elevation map as input. We confirm that the bank-full assumption does not fit the observed landforms. Instead, the channel appears more deeply incised near the source. Flow modeling also identifies several areas of special interest, including a dry cataract that coincides with a region of predicted high erosion. However, artifacts in the elevation data strongly impacted estimated stages and velocities in other areas. More extensive connection between the flood hydraulics and observed landforms awaits improved topographic data.

  13. 2.5-D/3-D resistivity modelling in anisotropic media using Gaussian quadrature grids

    NASA Astrophysics Data System (ADS)

    Zhou, Bing; Greenhalgh, Mark; Greenhalgh, S. A.

    2009-01-01

    We present a new numerical scheme for 2.5-D/3-D direct current resistivity modelling in heterogeneous, anisotropic media. This method, named the `Gaussian quadrature grid' (GQG) method, cooperatively combines the solution of the Variational Principle of the partial differential equation, Gaussian quadrature abscissae and local cardinal functions so that it has the main advantages of the spectral element method. The formulation shows that the GQG method is a modification of the spectral element method but does not employ the constant elements or require the mesh generator to match the Earth's surface. This makes it much easier to deal with geological models having a 2-D/3-D complex topography than using traditional numerical methods. The GQG technique can achieve a similar convergence rate to the spectral element method. We show it transforms the 2.5-D/3-D resistivity modelling problem into a sparse and symmetric linear equation system that can be solved by an iterative or matrix inversion method. Comparison with analytic solutions for homogeneous isotropic and anisotropic models shows that the error depends on the Gaussian quadrature order (abscissa number) and the subdomain size. The higher the order or the smaller the subdomain size that is employed, the more accurate are the results obtained. Several other synthetic examples, both homogeneous and inhomogeneous, incorporating sloping, undulating and severe topography, are presented and found to yield results comparable to finite element solutions involving a dense mesh.

  14. Cosmological constraints on superconducting dark energy models

    NASA Astrophysics Data System (ADS)

    Keresztes, Zoltán; Gergely, László Á.; Harko, Tiberiu; Liang, Shi-Dong

    2015-12-01

    We consider cosmological tests of a scalar-vector-tensor gravitational model, in which the dark energy is included in the total action through a gauge-invariant, electromagnetic type contribution. The ground state of dark energy, corresponding to a constant potential V , is a Bose-Einstein type condensate with spontaneously broken U(1) symmetry. In other words, dark energy appears as a massive vector field emerging from a superposition of a massless vector and a scalar field, the latter corresponding to the Goldstone boson. Two particular cosmological models, corresponding to pure electric and pure magnetic type potentials, respectively, are confronted with type IA supernovae and Hubble parameter data. In the electric case, a good fit is obtained along a narrow inclined stripe in the Ωm-ΩV parameter plane, which includes the Λ cold dark matter limit as the best fit. The other points on this admissible region represent superconducting dark energy as a sum of a cosmological constant and a time-evolving contribution. In the magnetic case the cosmological test selects either (i) parameter ranges of the superconducting dark energy allowing for the standard baryonic sector plus dark matter or (ii) a unified superconducting dark matter and dark energy model, additionally including only the baryonic sector.

  15. Restoring unitarity in anisotropic quantum cosmological models

    NASA Astrophysics Data System (ADS)

    Pal, Sridip; Banerjee, Narayan

    2015-02-01

    The present work shows that a properly chosen ordering of operators can restore unitarity in anisotropic quantum cosmological models. Bianchi V and Bianchi IX models with a perfect fluid are worked out. A transformation of coordinates takes the Hamiltonian to that of an inverse square potential which has equal deficiency indices; thus, a self-adjoint extension is possible. Although not clearly detected before, we show here that isotropic models are also apt to violate the conservation of probability for careless operator ordering.

  16. Lensing effects in inhomogeneous cosmological models

    SciTech Connect

    Ghassemi, Sima; Khoeini-Moghaddam, Salomeh; Mansouri, Reza

    2009-05-15

    Concepts developed in the gravitational lensing techniques such as shear, convergence, tangential, and radial arcs maybe used to see how tenable inhomogeneous models proposed to explain the acceleration of the universe models are. We study the widely discussed Lemaitre-Tolman-Bondi (LTB) cosmological models. It turns out that for the observer sitting at origin of a global LTB solution the shear vanishes as in the Friedmann-Robertson-Walker models, while the value of convergence is different, which may lead to observable cosmological effects. We also consider Swiss-cheese models proposed recently based on LTB with an observer sitting in the Friedmann-Robertson-Walker part. It turns out that they have different behavior as far as the formation of radial and tangential arcs are concerned.

  17. Modeling the citation network by network cosmology.

    PubMed

    Xie, Zheng; Ouyang, Zhenzheng; Zhang, Pengyuan; Yi, Dongyun; Kong, Dexing

    2015-01-01

    Citation between papers can be treated as a causal relationship. In addition, some citation networks have a number of similarities to the causal networks in network cosmology, e.g., the similar in-and out-degree distributions. Hence, it is possible to model the citation network using network cosmology. The casual network models built on homogenous spacetimes have some restrictions when describing some phenomena in citation networks, e.g., the hot papers receive more citations than other simultaneously published papers. We propose an inhomogenous causal network model to model the citation network, the connection mechanism of which well expresses some features of citation. The node growth trend and degree distributions of the generated networks also fit those of some citation networks well.

  18. Homogeneous cosmological models and new inflation

    NASA Technical Reports Server (NTRS)

    Turner, Michael S.; Widrow, Lawrence M.

    1986-01-01

    The promise of the inflationary-universe scenario is to free the present state of the universe from extreme dependence upon initial data. Paradoxically, inflation is usually analyzed in the context of the homogeneous and isotropic Robertson-Walker cosmological models. It is shown that all but a small subset of the homogeneous models undergo inflation. Any initial anisotropy is so strongly damped that if sufficient inflation occurs to solve the flatness and horizon problems, the universe today would still be very isotropic.

  19. Cosmological perturbations in a mimetic matter model

    NASA Astrophysics Data System (ADS)

    Matsumoto, Jiro; Odintsov, Sergei D.; Sushkov, Sergey V.

    2015-03-01

    We investigate the cosmological evolution of a mimetic matter model with arbitrary scalar potential. The cosmological reconstruction—which is the method for constructing a model for an arbitrary evolution of the scale factor—is explicitly performed for different choices of potential. The cases where the mimetic matter model shows the evolution as cold dark matter (CDM), the w CDM model, dark matter and dark energy with a dynamical O m (z ) [where O m (z )≡[(H (z )/H0)2-1 ]/[(1 +z )3-1 ] ], and phantom dark energy with a phantom-nonphantom crossing are presented in detail. The cosmological perturbations for such evolutions are studied in the mimetic matter model. For instance, the evolution behavior of the matter density contrast (which is different than the usual one, i.e., δ ¨+2 H δ ˙-κ2ρ δ /2 =0 ) is investigated. The possibility of a peculiar evolution of δ in the model under consideration is shown. Special attention is paid to the behavior of the matter density contrast near the future singularity, where the decay of perturbations may occur much earlier than the singularity.

  20. A 2.5D Reactive Transport Model for Fracture Alteration Simulation.

    PubMed

    Deng, Hang; Molins, Sergi; Steefel, Carl; DePaolo, Donald; Voltolini, Marco; Yang, Li; Ajo-Franklin, Jonathan

    2016-07-19

    Understanding fracture alteration resulting from geochemical reactions is critical in predicting fluid migration in the subsurface and is relevant to multiple environmental challenges. Here, we present a novel 2.5D continuum reactive transport model that captures and predicts the spatial pattern of fracture aperture change and the development of an altered layer in the near-fracture region. The model considers permeability heterogeneity in the fracture plane and updates fracture apertures and flow fields based on local reactions. It tracks the reaction front of each mineral phase and calculates the thickness of the altered layer. Given this treatment, the model is able to account for the diffusion limitation on reaction rates associated with the altered layer. The model results are in good agreement with an experimental study in which a CO2-acidified brine was injected into a fracture in the Duperow Dolomite, causing dissolution of calcite and dolomite that result in the formation of a preferential flow channel and an altered layer. With an effective diffusion coefficient consistent with the experimentally observed porosity of the altered layer, the model captures the progressive decrease in the dissolution rate of the fast-reacting mineral in the altered layer. PMID:27357572

  1. Quantum nonthermal radiation of nonstationary rotating de Sitter cosmological model

    NASA Astrophysics Data System (ADS)

    Meitei, Irom Ablu; Singh, T. Ibungochouba; Singh, K. Yugindro

    2014-08-01

    Using the Hamilton-Jacobi method a study of quantum nonthermal radiation of nonstationary rotating de Sitter cosmological model is carried out. It is shown that there exist seas of positive and negative energy states in the vicinity of the cosmological event horizon and there also exists a forbidden energy gap between the two seas. The forbidden energy gap vanishes on the surface of the cosmological event horizon so that the positive and negative energy levels overlap. The width of the forbidden energy gap and the energy of the particle at the cosmological event horizon are found to depend on the cosmological constant, the rotation parameter, positions of the particle and the cosmological event horizon, angular momentum of the particle, evaporation rate and shape of the cosmological event horizon. The tunneling probability of the emitted particles constituting Hawking radiation is also deduced for stationary nonrotating de Sitter cosmological model and the standard Hawking temperature is recovered.

  2. Testing Cosmological Models with Clusters of Galaxies

    NASA Astrophysics Data System (ADS)

    Böhringer, Hans; Schuecker, Peter

    2003-05-01

    Galaxy clusters are ideal probes for the large-scale structure of the Universe and for the tests of cosmological models. We use, REFLEX, the currently largest and best defined cluster X-ray survey to illustrate this application of galaxy cluster studies. Based on this survey of X-ray selected clusters of galaxies we determine statistical properties of the galaxy cluster population, their spatial correlation, and the density fluctuation power spectrum of the cosmic matter distribution on large scales up to about 1 Gpc. Comparing these results with predictions of cosmological models we obtain tight constrains for the matter density parameter of the Universe, consistent with the combined results from observations of the microwave background anisotropies and distant type Ia supernovae. The only difference between the present results and the ``concordance model'' is a low value for the σ8-normalization. Exploring the parameter space of the cosmic matter density and the equation of state parameter of dark energy most favoured by the combined observations of REFLEX clusters and distant type Ia supernovae we find that the conventional cosmological constant model is best consistent with the observational data.

  3. The simplest possible bouncing quantum cosmological model

    NASA Astrophysics Data System (ADS)

    Peter, Patrick; Vitenti, Sandro D. P.

    2016-06-01

    We present and expand the simplest possible quantum cosmological bouncing model already discussed in previous works: the trajectory formulation of quantum mechanics applied to cosmology (through the Wheeler-De Witt equation) in the Friedmann-Lemaître-Robertson-Walker (FLRW) minisuperspace without spatial curvature. The initial conditions that were previously assumed were such that the wave function would not change its functional form but instead provide a dynamics to its parameters. Here, we consider a more general situation, in practice consisting of modified Gaussian wave functions, aiming at obtaining a nonsingular bounce from a contracting phase. Whereas previous works consistently obtain very symmetric bounces, we find that it is possible to produce highly non-symmetric solutions, and even cases for which multiple bounces naturally occur. We also introduce a means of treating the shear in this category of models by quantizing in the Bianchi I minisuperspace.

  4. Modelling non-dust fluids in cosmology

    SciTech Connect

    Christopherson, Adam J.; Hidalgo, Juan Carlos; Malik, Karim A. E-mail: juan.hidalgo@port.ac.uk

    2013-01-01

    Currently, most of the numerical simulations of structure formation use Newtonian gravity. When modelling pressureless dark matter, or 'dust', this approach gives the correct results for scales much smaller than the cosmological horizon, but for scenarios in which the fluid has pressure this is no longer the case. In this article, we present the correspondence of perturbations in Newtonian and cosmological perturbation theory, showing exact mathematical equivalence for pressureless matter, and giving the relativistic corrections for matter with pressure. As an example, we study the case of scalar field dark matter which features non-zero pressure perturbations. We discuss some problems which may arise when evolving the perturbations in this model with Newtonian numerical simulations and with CMB Boltzmann codes.

  5. The simplest possible bouncing quantum cosmological model

    NASA Astrophysics Data System (ADS)

    Peter, Patrick; Vitenti, Sandro D. P.

    2016-06-01

    We present and expand the simplest possible quantum cosmological bouncing model already discussed in previous works: the trajectory formulation of quantum mechanics applied to cosmology (through the Wheeler-De Witt equation) in the Friedmann-Lemaître-Robertson-Walker (FLRW) minisuperspace without spatial curvature. The initial conditions that were previously assumed were such that the wave function would not change its functional form but instead provide a dynamics to its parameters. Here, we consider a more general situation, in practice consisting of modified Gaussian wave functions, aiming at obtaining a nonsingular bounce from a contracting phase. Whereas previous works consistently obtain very symmetric bounces, we find that it is possible to produce highly non-symmetric solutions, and even cases for which multiple bounces naturally occur. We also introduce a means of treating the shear in this category of models by quantizing in the Bianchi I minisuperspace.

  6. The best-fit universe. [cosmological models

    NASA Technical Reports Server (NTRS)

    Turner, Michael S.

    1991-01-01

    Inflation provides very strong motivation for a flat Universe, Harrison-Zel'dovich (constant-curvature) perturbations, and cold dark matter. However, there are a number of cosmological observations that conflict with the predictions of the simplest such model: one with zero cosmological constant. They include the age of the Universe, dynamical determinations of Omega, galaxy-number counts, and the apparent abundance of large-scale structure in the Universe. While the discrepancies are not yet serious enough to rule out the simplest and most well motivated model, the current data point to a best-fit model with the following parameters: Omega(sub B) approximately equal to 0.03, Omega(sub CDM) approximately equal to 0.17, Omega(sub Lambda) approximately equal to 0.8, and H(sub 0) approximately equal to 70 km/(sec x Mpc) which improves significantly the concordance with observations. While there is no good reason to expect such a value for the cosmological constant, there is no physical principle that would rule out such.

  7. Neutrino masses via the Zee mechanism in the 5D split fermion model

    SciTech Connect

    Chang, We-Fu; Chen, I-Ting; Liou, Siao-Cing

    2011-01-15

    We study the original version of the Zee model, where both of the SU(2){sub L} Higgs doublets are allowed to couple to the leptons, in the framework of the split fermion model in M{sub 4}xS{sub 1}/Z{sub 2} space-time. The neutrino masses are generated through 1-loop diagrams without introducing the right-handed neutrinos. By assuming an order one anarchical complex 5D Yukawa couplings, all the effective 4D Yukawa couplings are determined by the wave function overlap between the split fermions and the bulk scalars in the fifth dimension. The predictability of the Yukawa couplings is in sharp contrast to the original Zee model in 4D where the Yukawa couplings are unknown free parameters. This setup exhibits a geometrical alternative to the lepton flavor symmetry. By giving four explicit sets of the split fermion locations, we demonstrate that it is possible to simultaneously fit the lepton masses and neutrino oscillation data by just a handful free parameters without much fine tuning. Moreover, we are able to make definite predictions for the mixing angle {theta}{sub 13}, the absolute neutrino masses, and the lepton flavor violation processes for each configuration.

  8. 5D model for accurate representation and visualization of dynamic cardiac structures

    NASA Astrophysics Data System (ADS)

    Lin, Wei-te; Robb, Richard A.

    2000-05-01

    Accurate cardiac modeling is challenging due to the intricate structure and complex contraction patterns of myocardial tissues. Fast imaging techniques can provide 4D structural information acquired as a sequence of 3D images throughout the cardiac cycle. To mode. The beating heart, we created a physics-based surface model that deforms between successive time point in the cardiac cycle. 3D images of canine hearts were acquired during one complete cardiac cycle using the DSR and the EBCT. The left ventricle of the first time point is reconstructed as a triangular mesh. A mass-spring physics-based deformable mode,, which can expand and shrink with local contraction and stretching forces distributed in an anatomically accurate simulation of cardiac motion, is applied to the initial mesh and allows the initial mesh to deform to fit the left ventricle in successive time increments of the sequence. The resulting 4D model can be interactively transformed and displayed with associated regional electrical activity mapped onto anatomic surfaces, producing a 5D model, which faithfully exhibits regional cardiac contraction and relaxation patterns over the entire heart. The model faithfully represents structural changes throughout the cardiac cycle. Such models provide the framework for minimizing the number of time points required to usefully depict regional motion of myocardium and allow quantitative assessment of regional myocardial motion. The electrical activation mapping provides spatial and temporal correlation within the cardiac cycle. In procedures which as intra-cardiac catheter ablation, visualization of the dynamic model can be used to accurately localize the foci of myocardial arrhythmias and guide positioning of catheters for optimal ablation.

  9. 5D-QSAR for spirocyclic sigma1 receptor ligands by Quasar receptor surface modeling.

    PubMed

    Oberdorf, Christoph; Schmidt, Thomas J; Wünsch, Bernhard

    2010-07-01

    Based on a contiguous and structurally as well as biologically diverse set of 87 sigma(1) ligands, a 5D-QSAR study was conducted in which a quasi-atomistic receptor surface modeling approach (program package Quasar) was applied. The superposition of the ligands was performed with the tool Pharmacophore Elucidation (MOE-package), which takes all conformations of the ligands into account. This procedure led to four pharmacophoric structural elements with aromatic, hydrophobic, cationic and H-bond acceptor properties. Using the aligned structures a 3D-model of the ligand binding site of the sigma(1) receptor was obtained, whose general features are in good agreement with previous assumptions on the receptor structure, but revealed some novel insights since it represents the receptor surface in more detail. Thus, e.g., our model indicates the presence of an H-bond acceptor moiety in the binding site as counterpart to the ligands' cationic ammonium center, rather than a negatively charged carboxylate group. The presented QSAR model is statistically valid and represents the biological data of all tested compounds, including a test set of 21 ligands not used in the modeling process, with very good to excellent accuracy [q(2) (training set, n=66; leave 1/3 out) = 0.84, p(2) (test set, n=21)=0.64]. Moreover, the binding affinities of 13 further spirocyclic sigma(1) ligands were predicted with reasonable accuracy (mean deviation in pK(i) approximately 0.8). Thus, in addition to novel insights into the requirements for binding of spirocyclic piperidines to the sigma(1) receptor, the presented model can be used successfully in the rational design of new sigma(1) ligands.

  10. Hybrid models in loop quantum cosmology

    NASA Astrophysics Data System (ADS)

    Elizaga Navascués, Beatriz; Martín-Benito, Mercedes; Mena Marugán, Guillermo A.

    2016-06-01

    In the framework of Loop Quantum Cosmology (LQC), inhomogeneous models are usually quantized by means of a hybrid approach that combines loop quantization techniques with standard quantum field theory methods. This approach is based on a splitting of the phase space in a homogeneous sector, formed by global, zero-modes and an inhomogeneous sector, formed by the remaining, infinite number of modes, that describe the local degrees of freedom. Then, the hybrid quantization is attained by adopting a loop representation for the homogeneous gravitational sector, while a Fock representation is used for the inhomogeneities. The zero-mode of the Hamiltonian constraint operator couples the homogeneous and inhomogeneous sectors. The hybrid approach, therefore, is expected to provide a suitable quantum theory in regimes where the main quantum effects of the geometry are those affecting the zero-modes, while the inhomogeneities, still being quantum, can be treated in a more conventional way. This hybrid strategy was first proposed for the simplest cosmological midisuperspaces: the Gowdy models, and it has been later applied to the case of cosmological perturbations. This paper reviews the construction and main applications of hybrid LQC.

  11. Modeling plasticity of MgO at the mesoscale using 2.5D Dislocation Dynamics.

    NASA Astrophysics Data System (ADS)

    Reali, R.; Cordier, P.; Carrez, P.; Gouriet, K.; Boioli, F.

    2015-12-01

    In the lower mantle, viscosity results from the rheological behavior of the two main constituent minerals, namely (Mg,Fe,Al)SiO3bridgmanite and (Mg,Fe)O ferropericlase. Understanding how these phases deform is thus of primary importance in geophysics. This is also a very challenging task, since the extreme conditions to which the lower mantle aggregate is subjected are not reachable in laboratory experiments. In this study, the contribution of dislocations to the deformation of periclase at the mesoscale is investigated by Dislocation Dynamics (DD) simulations, a modeling tool which considers the collective motion and interaction of dislocations. Dislocations are expected to be one of the most efficient strain producing mechanisms. To model their behavior a so-called 2.5D DD approach is employed. Within this method, dislocations are considered as straight segments perpendicular to a 2D reference plane and local rules are added to mimic 3D behavior [1]. Furthermore, both the glide and climb mechanisms can be taken into account [2]. Before simulating the deformation of MgO under P, T and strain rate conditions of the lower mantle, it is necessary to benchmark the model at ambient pressure, in order to compare the simulated behavior with experiments performed in the same conditions. At high temperatures (1500-1900 K) the strain-controlling mechanism results from the interactions between dislocations. In this regime the influence of climb may be important: to investigate the competition between glide and climb mechanisms, creep simulations in pure glide conditions were performed in a wide range of temperatures and applied stresses and compared to simulations where climb is explicitly included. Power law creep parameters are evaluated and compared with experimental data. [1] D. Ǵomez-Garćıa, B. Devincre, and L. P. Kubin, Phys. Rev. Lett. 96, 125503 (2006). [2] F. Boioli, P. Carrez, P. Cordier, B. Devincre, and , M. Marquille, accepted Phys. Rev. B (2015).

  12. Evolution of multidimensional flat anisotropic cosmological models

    SciTech Connect

    Beloborodov, A. ); Demianski, M. Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw International Center for Relativistic Astrophysics , Universita di Roma I, La Sapienza, Rome ); Ivanov, P.; Polnarev, A.G. )

    1993-07-15

    We study the dynamics of a flat multidimensional anisotropic cosmological model filled with an anisotropic fluidlike medium. By an appropriate choice of variables, the dynamical equations reduce to a two-dimensional dynamical system. We present a detailed analysis of the time evolution of this system and the conditions of the existence of spacetime singularities. We investigate the conditions under which violent, exponential, and power-law inflation is possible. We show that dimensional reduction cannot proceed by anti-inflation (rapid contraction of internal space). Our model indicates that it is very difficult to achieve dimensional reduction by classical means.

  13. Inflation in the standard cosmological model

    NASA Astrophysics Data System (ADS)

    Uzan, Jean-Philippe

    2015-12-01

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

  14. 1.5D quasilinear model and its application on beams interacting with Alfven eigenmodes in DIII-D

    SciTech Connect

    Ghantous, K.; Gorelenkov, N. N.; Berk, H. L.; Heidbrink, W. W.; Van Zeeland, M. A.

    2012-09-15

    We propose a model, denoted here by 1.5D, to study energetic particle (EP) interaction with toroidal Alfvenic eigenmodes (TAE) in the case where the local EP drive for TAE exceeds the stability limit. Based on quasilinear theory, the proposed 1.5D model assumes that the particles diffuse in phase space, flattening the pressure profile until its gradient reaches a critical value where the modes stabilize. Using local theories and NOVA-K simulations of TAE damping and growth rates, the 1.5D model calculates the critical gradient and reconstructs the relaxed EP pressure profile. Local theory is improved from previous study by including more sophisticated damping and drive mechanisms such as the numerical computation of the effect of the EP finite orbit width on the growth rate. The 1.5D model is applied on the well-diagnosed DIII-D discharges no. 142111 [M. A. Van Zeeland et al., Phys. Plasmas 18, 135001 (2011)] and no. 127112 [W. W. Heidbrink et al., Nucl. Fusion. 48, 084001 (2008)]. We achieved a very satisfactory agreement with the experimental results on the EP pressure profiles redistribution and measured losses. This agreement of the 1.5D model with experimental results allows the use of this code as a guide for ITER plasma operation where it is desired to have no more than 5% loss of fusion alpha particles as limited by the design.

  15. Cosmological model with decaying vacuum energy from quantum mechanics

    NASA Astrophysics Data System (ADS)

    Szydłowski, Marek

    2015-06-01

    We construct the cosmological model to explain the cosmological constant problem. We built the extension of the standard cosmological model Λ CDM by consideration of decaying vacuum energy represented by the running cosmological term. From the principles of quantum mechanics one can find that in the long-term behavior survival probability of unstable states is a decreasing function of the cosmological time and has the inverse powerlike form. This implies that cosmological constant ρvac=Λ (t )=Λbare+α/t2 where Λbare and α are constants. We investigate the dynamics of this model using dynamical system methods due to a link to the Λ (H ) cosmologies. We have found the exact solution for the scale factor as well as the indicators of its variability like the deceleration parameter and the jerk. From the calculation of the jerk we obtain a simple test of the decaying vacuum in the Friedman-Robertson-Walker universe. Using astronomical data [SNIa, H (z ), CMB, BAO] we have estimated the model parameters and compared this model with the Λ CDM model. Our statistical results indicate that the decaying vacuum model is a little worse than the Λ CDM model. But the decaying vacuum cosmological model explains the small value of the cosmological constant today.

  16. A Cosmological Model of Thermodynamic Open Universe

    NASA Astrophysics Data System (ADS)

    Goswami, G. K.; Trivedi, Mandwi

    2012-08-01

    In this paper we have given a generalization of the earlier work by Prigogine et al. (Gen. Relativ. Gravit. 19:1, 1989; Gen. Relativ. Gravit. 21(8):767-776, 1989) who have constructed a phenomenological model of entropy production via particle creation in the very early universe generated out of the vacuum rather than from a singularity, by including radiation also as the energy source and tried to develop an alternative cosmological model in which particle creation prevents the big bang. We developed Radiation dominated model of the universe which shows a general tendency that (i) it originates from instability of vacuum rather than from a singularity. (ii) Up to a characteristic time t c cosmological quantities like density, pressure, Hubble constant and expansion parameter vary rapidly with time. (iii) After the characteristic time these quantities settles down and the models are turned into de-Sitter type model with uniform matter, radiation, creation densities and Hubble's constant H. The de-Sitter regime survives during a decay time t d then connects continuously to a usual adiabatic matter radiation RW universe. The interesting thing in the paper is that we have related the phenomenological radiation dominated model to macroscopic model of quantum particle creation in the early universe giving rise to the present observed value of cosmic background radiation. It is also found that the dust filled model tallies exactly with that of the Prigogine's one, which justifies that our model is generalized Prigogine's model. Although the model originates from instability of vacuum rather than from a singularity, still there is a couple of unavoidable singularities in the model.

  17. 5D Modelling: An Efficient Approach for Creating Spatiotemporal Predictive 3D Maps of Large-Scale Cultural Resources

    NASA Astrophysics Data System (ADS)

    Doulamis, A.; Doulamis, N.; Ioannidis, C.; Chrysouli, C.; Grammalidis, N.; Dimitropoulos, K.; Potsiou, C.; Stathopoulou, E.-K.; Ioannides, M.

    2015-08-01

    Outdoor large-scale cultural sites are mostly sensitive to environmental, natural and human made factors, implying an imminent need for a spatio-temporal assessment to identify regions of potential cultural interest (material degradation, structuring, conservation). On the other hand, in Cultural Heritage research quite different actors are involved (archaeologists, curators, conservators, simple users) each of diverse needs. All these statements advocate that a 5D modelling (3D geometry plus time plus levels of details) is ideally required for preservation and assessment of outdoor large scale cultural sites, which is currently implemented as a simple aggregation of 3D digital models at different time and levels of details. The main bottleneck of such an approach is its complexity, making 5D modelling impossible to be validated in real life conditions. In this paper, a cost effective and affordable framework for 5D modelling is proposed based on a spatial-temporal dependent aggregation of 3D digital models, by incorporating a predictive assessment procedure to indicate which regions (surfaces) of an object should be reconstructed at higher levels of details at next time instances and which at lower ones. In this way, dynamic change history maps are created, indicating spatial probabilities of regions needed further 3D modelling at forthcoming instances. Using these maps, predictive assessment can be made, that is, to localize surfaces within the objects where a high accuracy reconstruction process needs to be activated at the forthcoming time instances. The proposed 5D Digital Cultural Heritage Model (5D-DCHM) is implemented using open interoperable standards based on the CityGML framework, which also allows the description of additional semantic metadata information. Visualization aspects are also supported to allow easy manipulation, interaction and representation of the 5D-DCHM geometry and the respective semantic information. The open source 3DCity

  18. Degeneracy and discreteness in cosmological model fitting

    NASA Astrophysics Data System (ADS)

    Teng, Huan-Yu; Huang, Yuan; Zhang, Tong-Jie

    2016-03-01

    We explore the problems of degeneracy and discreteness in the standard cosmological model (ΛCDM). We use the Observational Hubble Data (OHD) and the type Ia supernovae (SNe Ia) data to study this issue. In order to describe the discreteness in fitting of data, we define a factor G to test the influence from each single data point and analyze the goodness of G. Our results indicate that a higher absolute value of G shows a better capability of distinguishing models, which means the parameters are restricted into smaller confidence intervals with a larger figure of merit evaluation. Consequently, we claim that the factor G is an effective way of model differentiation when using different models to fit the observational data.

  19. 1.5D Quasilinear Model for Alpha Particle-TAE Interaction in ARIES ACT-I

    SciTech Connect

    K. Ghantous, N.N. Gorelenkov, C. Kessel, F. Poli

    2013-01-30

    We study the TAE interaction with alpha particle fusion products in ARIES ACT-I using the 1.5D quasilinear model. 1.5D uses linear analytic expressions for growth and damping rates of TAE modes evaluated using TRANSP pro les to calculates the relaxation of pressure pro les. NOVA- K simulations are conducted to validate the analytic dependancies of the rates, and to normalize their absolute value. The low dimensionality of the model permits calculating loss diagrams in large parameter spaces.

  20. A unified dark sector cosmological model

    NASA Astrophysics Data System (ADS)

    Ruiz, A. N.; Domínguez, M. J.

    We explore the consequences of the measurements of the equation of state of dark matter, Serra & Domínguez (2009), on the homogeneuos FRW uni- verse dynamics and build an alternative cosmological scenario to the con- cordance Lambda CDM universe. The new paradigm is based on the introduction of an effective scalar field that obeys a barotropic equation of state p = omega rho with omega = -1/3, replacing the undetected components of the dark sector: dark matter (DM) and dark energy (DE or Lambda). We compute a minimal set of cosmological parameters which allow us to reproduce several observational results such as baryon abundance, constrains on the age of the universe, the astronomical scale of distances and the high redshift supernovae and gamma-ray bursts data with a high degree of precision. However it should be emphasized that the new model is not accelerating, instead expands as- symptotically towards an Einstein Static Universe. We also present a brief dynamical system analysis of this model showing his stable behaviour.

  1. Cosmological constraint on Brans-Dicke Model

    NASA Astrophysics Data System (ADS)

    Li, Ji-Xia; Wu, Feng-Quan; Li, Yi-Chao; Gong, Yan; Chen, Xue-Lei

    2015-12-01

    We combine new Cosmic Microwave Background (CMB) data from Planck with Baryon Acoustic Oscillation (BAO) data to constrain the Brans-Dicke (BD) theory, in which the gravitational constant G evolves with time. Observations of type Ia supernovae (SNeIa) provide another important set of cosmological data, as they may be regarded as standard candles after some empirical corrections. However, in theories that include modified gravity like the BD theory, there is some risk and complication when using the SNIa data because their luminosity may depend on G. In this paper, we assume a power law relation between the SNIa luminosity and G, but treat the power index as a free parameter. We then test whether the difference in distances measured with SNIa data and BAO data can be reduced in such a model. We also constrain the BD theory and cosmological parameters by making a global fit with the CMB, BAO and SNIa data set. For the CMB+BAO+SNIa data set, we find 0.08 × 10-2 < ζ < 0.33 × 10-2 at the 68% confidence level (CL) and -0.01 × 10-2 < ζ < 0.43 × 10-2 at the 95% CL, where ζ is related to the BD parameter ω by ζ = ln(1 + 1/ω).

  2. Preon model and cosmological quantum-hyperchromodynamic phase transition

    SciTech Connect

    Nishimura, H.; Hayashi, Y.

    1987-05-15

    From the cosmological viewpoint, we investigate whether or not recent preon models are compatible with the picture of the first-order phase transition from the preon phase to the composite quark-lepton phase. It is shown that the current models accepting the 't Hooft anomaly-matching condition together with quantum hyperchromodynamics are consistent with the cosmological first-order phase transition.

  3. Preon model and cosmological quantum-hyperchromodynamic phase transition

    NASA Astrophysics Data System (ADS)

    Nishimura, H.; Hayashi, Y.

    1987-05-01

    From the cosmological viewpoint, we investigate whether or not recent preon models are compatible with the picture of the first-order phase transition from the preon phase to the composite quark-lepton phase. It is shown that the current models accepting the 't Hooft anomaly-matching condition together with quantum hyperchromodynamics are consistent with the cosmological first-order phase transition.

  4. Performance and applicability of a 2.5-D ice-flow model in the vicinity of a dome

    NASA Astrophysics Data System (ADS)

    Passalacqua, Olivier; Gagliardini, Olivier; Parrenin, Frédéric; Todd, Joe; Gillet-Chaulet, Fabien; Ritz, Catherine

    2016-07-01

    Three-dimensional ice flow modelling requires a large number of computing resources and observation data, such that 2-D simulations are often preferable. However, when there is significant lateral divergence, this must be accounted for (2.5-D models), and a flow tube is considered (volume between two horizontal flowlines). In the absence of velocity observations, this flow tube can be derived assuming that the flowlines follow the steepest slope of the surface, under a few flow assumptions. This method typically consists of scanning a digital elevation model (DEM) with a moving window and computing the curvature at the centre of this window. The ability of the 2.5-D models to account properly for a 3-D state of strain and stress has not clearly been established, nor their sensitivity to the size of the scanning window and to the geometry of the ice surface, for example in the cases of sharp ridges. Here, we study the applicability of a 2.5-D ice flow model around a dome, typical of the East Antarctic plateau conditions. A twin experiment is carried out, comparing 3-D and 2.5-D computed velocities, on three dome geometries, for several scanning windows and thermal conditions. The chosen scanning window used to evaluate the ice surface curvature should be comparable to the typical radius of this curvature. For isothermal ice, the error made by the 2.5-D model is in the range 0-10 % for weakly diverging flows, but is 2 or 3 times higher for highly diverging flows and could lead to a non-physical ice surface at the dome. For non-isothermal ice, assuming a linear temperature profile, the presence of a sharp ridge makes the 2.5-D velocity field unrealistic. In such cases, the basal ice is warmer and more easily laterally strained than the upper one, the walls of the flow tube are not vertical, and the assumptions of the 2.5-D model are no longer valid.

  5. Experimentally testing the standard cosmological model

    SciTech Connect

    Schramm, D.N. Fermi National Accelerator Lab., Batavia, IL )

    1990-11-01

    The standard model of cosmology, the big bang, is now being tested and confirmed to remarkable accuracy. Recent high precision measurements relate to the microwave background; and big bang nucleosynthesis. This paper focuses on the latter since that relates more directly to high energy experiments. In particular, the recent LEP (and SLC) results on the number of neutrinos are discussed as a positive laboratory test of the standard cosmology scenario. Discussion is presented on the improved light element observational data as well as the improved neutron lifetime data. alternate nucleosynthesis scenarios of decaying matter or of quark-hadron induced inhomogeneities are discussed. It is shown that when these scenarios are made to fit the observed abundances accurately, the resulting conclusions on the baryonic density relative to the critical density, {Omega}{sub b}, remain approximately the same as in the standard homogeneous case, thus, adding to the robustness of the standard model conclusion that {Omega}{sub b} {approximately} 0.06. This latter point is the deriving force behind the need for non-baryonic dark matter (assuming {Omega}{sub total} = 1) and the need for dark baryonic matter, since {Omega}{sub visible} < {Omega}{sub b}. Recent accelerator constraints on non-baryonic matter are discussed, showing that any massive cold dark matter candidate must now have a mass M{sub x} {approx gt} 20 GeV and an interaction weaker than the Z{sup 0} coupling to a neutrino. It is also noted that recent hints regarding the solar neutrino experiments coupled with the see-saw model for {nu}-masses may imply that the {nu}{sub {tau}} is a good hot dark matter candidate. 73 refs., 5 figs.

  6. Non-standard models and the sociology of cosmology

    NASA Astrophysics Data System (ADS)

    López-Corredoira, Martín

    2014-05-01

    I review some theoretical ideas in cosmology different from the standard "Big Bang": the quasi-steady state model, the plasma cosmology model, non-cosmological redshifts, alternatives to non-baryonic dark matter and/or dark energy, and others. Cosmologists do not usually work within the framework of alternative cosmologies because they feel that these are not at present as competitive as the standard model. Certainly, they are not so developed, and they are not so developed because cosmologists do not work on them. It is a vicious circle. The fact that most cosmologists do not pay them any attention and only dedicate their research time to the standard model is to a great extent due to a sociological phenomenon (the "snowball effect" or "groupthink"). We might well wonder whether cosmology, our knowledge of the Universe as a whole, is a science like other fields of physics or a predominant ideology.

  7. Precision cosmology defeats void models for acceleration

    SciTech Connect

    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.

  8. A New Fate of a Warped 5D FLRW Model with a U(1) Scalar Gauge Field

    NASA Astrophysics Data System (ADS)

    Slagter, Reinoud Jan; Pan, Supriya

    2016-09-01

    If we live on the weak brane with zero effective cosmological constant in a warped 5D bulk spacetime, gravitational waves and brane fluctuations can be generated by a part of the 5D Weyl tensor and carries information of the gravitational field outside the brane. We consider on a cylindrical symmetric warped FLRW background a U(1) self-gravitating scalar field coupled to a gauge field without bulk matter. It turns out that brane fluctuations can be formed dynamically, due to the modified energy-momentum tensor components of the scalar-gauge field ("cosmic string"). As a result, we find that the late-time behavior could significantly deviate from the standard evolution of the universe. The effect is triggered by the time-dependent warpfactor with two branches of the form ± 1/√{τ r}√{(c_1e^{√{2τ } t}+c_2e^{-√{2τ } t})(c_3e^{√{2τ } r}+c_4e^{-√{2τ } r})} ( with τ , c_i constants) and the modified brane equations comparable with a dark energy effect. This is a brane-world mechanism, not present in standard 4D FLRW, where the large disturbances are rapidly damped as the expansion proceed. Because gravity can propagate in the bulk, the cosmic string can build up a huge angle deficit (or mass per unit length) by the warpfactor and can induce massive KK-modes felt on the brane. Disturbances in the spatial components of the stress-energy tensor cause cylindrical symmetric waves, amplified due to the presence of the bulk space and warpfactor. They could survive the natural damping due to the expansion of the universe. It turns out that one of the metric components becomes singular at the moment the warp factor develops an extremum. This behavior could have influence on the possibility of a transition from acceleration to deceleration or vice versa.

  9. A New Fate of a Warped 5D FLRW Model with a U(1) Scalar Gauge Field

    NASA Astrophysics Data System (ADS)

    Slagter, Reinoud Jan; Pan, Supriya

    2016-03-01

    If we live on the weak brane with zero effective cosmological constant in a warped 5D bulk spacetime, gravitational waves and brane fluctuations can be generated by a part of the 5D Weyl tensor and carries information of the gravitational field outside the brane. We consider on a cylindrical symmetric warped FLRW background a U(1) self-gravitating scalar field coupled to a gauge field without bulk matter. It turns out that brane fluctuations can be formed dynamically, due to the modified energy-momentum tensor components of the scalar-gauge field ("cosmic string"). As a result, we find that the late-time behavior could significantly deviate from the standard evolution of the universe. The effect is triggered by the time-dependent warpfactor with two branches of the form ± 1/√{τ r}√{(c_1e^{√{2τ } t}+c_2e^{-√{2τ } t})(c_3e^{√{2τ } r}+c_4e^{-√{2τ } r})} ( with τ c_i constants) and the modified brane equations comparable with a dark energy effect. This is a brane-world mechanism, not present in standard 4D FLRW, where the large disturbances are rapidly damped as the expansion proceed. Because gravity can propagate in the bulk, the cosmic string can build up a huge angle deficit (or mass per unit length) by the warpfactor and can induce massive KK-modes felt on the brane. Disturbances in the spatial components of the stress-energy tensor cause cylindrical symmetric waves, amplified due to the presence of the bulk space and warpfactor. They could survive the natural damping due to the expansion of the universe. It turns out that one of the metric components becomes singular at the moment the warp factor develops an extremum. This behavior could have influence on the possibility of a transition from acceleration to deceleration or vice versa.

  10. 5D respiratory motion model based image reconstruction algorithm for 4D cone-beam computed tomography

    NASA Astrophysics Data System (ADS)

    Liu, Jiulong; Zhang, Xue; Zhang, Xiaoqun; Zhao, Hongkai; Gao, Yu; Thomas, David; Low, Daniel A.; Gao, Hao

    2015-11-01

    4D cone-beam computed tomography (4DCBCT) reconstructs a temporal sequence of CBCT images for the purpose of motion management or 4D treatment in radiotherapy. However the image reconstruction often involves the binning of projection data to each temporal phase, and therefore suffers from deteriorated image quality due to inaccurate or uneven binning in phase, e.g., under the non-periodic breathing. A 5D model has been developed as an accurate model of (periodic and non-periodic) respiratory motion. That is, given the measurements of breathing amplitude and its time derivative, the 5D model parametrizes the respiratory motion by three time-independent variables, i.e., one reference image and two vector fields. In this work we aim to develop a new 4DCBCT reconstruction method based on 5D model. Instead of reconstructing a temporal sequence of images after the projection binning, the new method reconstructs time-independent reference image and vector fields with no requirement of binning. The image reconstruction is formulated as a optimization problem with total-variation regularization on both reference image and vector fields, and the problem is solved by the proximal alternating minimization algorithm, during which the split Bregman method is used to reconstruct the reference image, and the Chambolle's duality-based algorithm is used to reconstruct the vector fields. The convergence analysis of the proposed algorithm is provided for this nonconvex problem. Validated by the simulation studies, the new method has significantly improved image reconstruction accuracy due to no binning and reduced number of unknowns via the use of the 5D model.

  11. Observational constraints to a unified cosmological model

    NASA Astrophysics Data System (ADS)

    Cuzinatto, Rodrigo R.; de Morais, Eduardo M.; Medeiros, Leo G.

    2016-01-01

    We propose a phenomenological unified model (UM) for dark matter and dark energy based on an equation of state parameter w that scales with the arctan of the redshift. The free parameters of the model are three constants: Ωb0, α and β. Parameter α dictates the transition rate between the matter dominated era and the accelerated expansion period. The ratio β/α gives the redshift of the equivalence between both regimes. Cosmological parameters are fixed by observational data from primordial nucleosynthesis (PN), supernovae of the type Ia (SNIa), gamma-ray bursts (GRBs) and baryon acoustic oscillations (BAOs). The calibration of the 138 GRB events is performed using the 580 SNIa of the Union2.1 data set and a new set of 79 high-redshift GRB is obtained. The various sets of data are used in different combinations to constraint the parameters through statistical analysis. The UM is compared to the ΛCDM model and their differences are emphasized.

  12. Cosmological constraints on extended Galileon models

    SciTech Connect

    Felice, Antonio De; Tsujikawa, Shinji E-mail: shinji@rs.kagu.tus.ac.jp

    2012-03-01

    The extended Galileon models possess tracker solutions with de Sitter attractors along which the dark energy equation of state is constant during the matter-dominated epoch, i.e. w{sub DE} = −1−s, where s is a positive constant. Even with this phantom equation of state there are viable parameter spaces in which the ghosts and Laplacian instabilities are absent. Using the observational data of the supernovae type Ia, the cosmic microwave background (CMB), and baryon acoustic oscillations, we place constraints on the tracker solutions at the background level and find that the parameter s is constrained to be s = 0.034{sub −0.034}{sup +0.327} (95 % CL) in the flat Universe. In order to break the degeneracy between the models we also study the evolution of cosmological density perturbations relevant to the large-scale structure (LSS) and the Integrated-Sachs-Wolfe (ISW) effect in CMB. We show that, depending on the model parameters, the LSS and the ISW effect is either positively or negatively correlated. It is then possible to constrain viable parameter spaces further from the observational data of the ISW-LSS cross-correlation as well as from the matter power spectrum.

  13. Improving lognormal models for cosmological fields

    NASA Astrophysics Data System (ADS)

    Xavier, Henrique S.; Abdalla, Filipe B.; Joachimi, Benjamin

    2016-07-01

    It is common practice in cosmology to model large-scale structure observables as lognormal random fields, and this approach has been successfully applied in the past to the matter density and weak lensing convergence fields separately. We argue that this approach has fundamental limitations which prevent its use for jointly modelling these two fields since the lognormal distribution's shape can prevent certain correlations to be attainable. Given the need of ongoing and future large-scale structure surveys for fast joint simulations of clustering and weak lensing, we propose two ways of overcoming these limitations. The first approach slightly distorts the power spectra of the fields using one of two algorithms that minimizes either the absolute or the fractional distortions. The second one is by obtaining more accurate convergence marginal distributions, for which we provide a fitting function, by integrating the lognormal density along the line of sight. The latter approach also provides a way to determine directly from theory the skewness of the convergence distribution and, therefore, the parameters for a lognormal fit. We present the public code Full-sky Lognormal Astro-fields Simulation Kit (FLASK) which can make tomographic realizations on the sphere of an arbitrary number of correlated lognormal or Gaussian random fields by applying either of the two proposed solutions, and show that it can create joint simulations of clustering and lensing with sub-per-cent accuracy over relevant angular scales and redshift ranges.

  14. Cosmological perturbations from the Standard Model Higgs

    SciTech Connect

    Simone, Andrea De; Riotto, Antonio E-mail: antonio.riotto@unige.ch

    2013-02-01

    We propose that the Standard Model (SM) Higgs is responsible for generating the cosmological perturbations of the universe by acting as an isocurvature mode during a de Sitter inflationary stage. In view of the recent ATLAS and CMS results for the Higgs mass, this can happen if the Hubble rate during inflation is in the range (10{sup 10}−10{sup 14}) GeV (depending on the SM parameters). Implications for the detection of primordial tensor perturbations through the B-mode of CMB polarization via the PLANCK satellite are discussed. For example, if the Higgs mass value is confirmed to be m{sub h} = 125.5 GeV and m{sub t},α{sub s} are at their central values, our mechanism predicts tensor perturbations too small to be detected in the near future. On the other hand, if tensor perturbations will be detected by PLANCK through the B-mode of CMB, then there is a definite relation between the Higgs and top masses, making the mechanism predictive and falsifiable.

  15. Natural inflation from 5D SUGRA and low reheat temperature

    NASA Astrophysics Data System (ADS)

    Paccetti Correia, Filipe; Schmidt, Michael G.; Tavartkiladze, Zurab

    2015-09-01

    Motivated by recent cosmological observations of a possibly unsuppressed primordial tensor component r of inflationary perturbations, we reanalyze in detail the 5D conformal SUGRA originated natural inflation model of Ref. [1]. The model is a supersymmetric variant of 5D extranatural inflation, also based on a shift symmetry, and leads to the potential of natural inflation. Coupling the bulk fields generating the inflaton potential via a gauge coupling to the inflaton with brane SM states we necessarily obtain a very slow gauge inflaton decay rate and a very low reheating temperature Tr ≲ O (100) GeV. Analysis of the required number of e-foldings (from the CMB observations) leads to values of ns in the lower range of present Planck 2015 results. Some related theoretical issues of the construction, along with phenomenological and cosmological implications, are also discussed.

  16. Finite Element Analysis of 2.5D Woven Composites, Part I: Microstructure and 3D Finite Element Model

    NASA Astrophysics Data System (ADS)

    Song, Jian; Wen, Weidong; Cui, Haitao; Zhang, Hongjian; Xu, Ying

    2016-02-01

    A new parameterized finite element model, called the Full-cell model, has been established based on the practical microstructure of 2.5D angle-interlock woven composites. This model considering the surface layer structure can predict the mechanical properties and estimate the structural performance such as the fiber volume fraction and inclination angle. According to introducing a set of periodic boundary condition, a reasonable overall stress field and periodic deformation are obtained. Furthermore, the model investigates the relationships among the woven parameters and elastic moduli, and shows the structural variation along with the corresponding woven parameters. Comparing the results calculated by FEM with the experiments, the veracity of calculation and reasonability based on the Full-cell model are confirmed. In the meantime, the predicted results based on the Full-cell model are more closed to the test results compared to those based on the Inner-cell model.

  17. Statistics of SU(5) D-brane models on a type II orientifold

    NASA Astrophysics Data System (ADS)

    Gmeiner, Florian; Stein, Maren

    2006-06-01

    We perform a statistical analysis of models with SU(5) and flipped SU(5) gauge group in a type II orientifold setup. We investigate the distribution and correlation of properties of these models, including the number of generations and the hidden sector gauge group. Compared to the recent analysis [F. Gmeiner, R. Blumenhagen, G. Honecker, D. Lüst, and T. Weigand, J. High Energy Phys.JHEPFG1029-8479 01 (2006) 004; F. Gmeiner, Fortschr. Phys.FPYKA60015-8208 54, 391 (2006).10.1088/1126-6708/2006/01/004] of models with a standard model-like gauge group, we find very similar results.

  18. Dynamical analysis of anisotropic cosmological model with quintessence

    NASA Astrophysics Data System (ADS)

    Chaubey, R.; Raushan, Rakesh

    2016-07-01

    The present work is a phase-plane analysis of LRS Bianchi type I cosmological model with a scalar field and exponential potential. The evolution equations are reduced to an autonomous system of ordinary equations by suitable transformation of variables. We also analyse the evolution of the effective equation of state parameter for different values of curvature. The nature of critical points is analysed and stable attractors are examined from the point of view of cosmology.

  19. Cosmological model-independent Gamma-ray bursts calibration and its cosmological constraint to dark energy

    SciTech Connect

    Xu, Lixin

    2012-04-01

    As so far, the redshift of Gamma-ray bursts (GRBs) can extend to z ∼ 8 which makes it as a complementary probe of dark energy to supernova Ia (SN Ia). However, the calibration of GRBs is still a big challenge when they are used to constrain cosmological models. Though, the absolute magnitude of GRBs is still unknown, the slopes of GRBs correlations can be used as a useful constraint to dark energy in a completely cosmological model independent way. In this paper, we follow Wang's model-independent distance measurement method and calculate their values by using 109 GRBs events via the so-called Amati relation. Then, we use the obtained model-independent distances to constrain ΛCDM model as an example.

  20. Characterization of free breathing patterns with 5D lung motion model

    SciTech Connect

    Zhao Tianyu; Lu Wei; Yang Deshan; Mutic, Sasa; Noel, Camille E.; Parikh, Parag J.; Bradley, Jeffrey D.; Low, Daniel A.

    2009-11-15

    Purpose: To determine the quiet respiration breathing motion model parameters for lung cancer and nonlung cancer patients. Methods: 49 free breathing patient 4DCT image datasets (25 scans, cine mode) were collected with simultaneous quantitative spirometry. A cross-correlation registration technique was employed to track the lung tissue motion between scans. The registration results were applied to a lung motion model: X-vector=X-vector{sub 0}+{alpha}-vector{beta}-vector f, where X-vector is the position of a piece of tissue located at reference position X-vector{sub 0} during a reference breathing phase (zero tidal volume v, zero airflow f). {alpha}-vector is a parameter that characterizes the motion due to air filling (motion as a function of tidal volume v) and {beta}-vector is the parameter that accounts for the motion due to the imbalance of dynamical stress distributions during inspiration and exhalation that causes lung motion hysteresis (motion as a function of airflow f). The parameters {alpha}-vector and {beta}-vector together provide a quantitative characterization of breathing motion that inherently includes the complex hysteresis interplay. The {alpha}-vector and {beta}-vector distributions were examined for each patient to determine overall general patterns and interpatient pattern variations. Results: For 44 patients, the greatest values of |{alpha}-vector| were observed in the inferior and posterior lungs. For the rest of the patients, |{alpha}-vector| reached its maximum in the anterior lung in three patients and the lateral lung in two patients. The hysteresis motion {beta}-vector had greater variability, but for the majority of patients, |{beta}-vector| was largest in the lateral lungs. Conclusions: This is the first report of the three-dimensional breathing motion model parameters for a large cohort of patients. The model has the potential for noninvasively predicting lung motion. The majority of patients exhibited similar |{alpha}-vector| maps

  1. Building a 2.5D Digital Elevation Model from 2D Imagery

    NASA Technical Reports Server (NTRS)

    Padgett, Curtis W.; Ansar, Adnan I.; Brennan, Shane; Cheng, Yang; Clouse, Daniel S.; Almeida, Eduardo

    2013-01-01

    When projecting imagery into a georeferenced coordinate frame, one needs to have some model of the geographical region that is being projected to. This model can sometimes be a simple geometrical curve, such as an ellipse or even a plane. However, to obtain accurate projections, one needs to have a more sophisticated model that encodes the undulations in the terrain including things like mountains, valleys, and even manmade structures. The product that is often used for this purpose is a Digital Elevation Model (DEM). The technology presented here generates a high-quality DEM from a collection of 2D images taken from multiple viewpoints, plus pose data for each of the images and a camera model for the sensor. The technology assumes that the images are all of the same region of the environment. The pose data for each image is used as an initial estimate of the geometric relationship between the images, but the pose data is often noisy and not of sufficient quality to build a high-quality DEM. Therefore, the source imagery is passed through a feature-tracking algorithm and multi-plane-homography algorithm, which refine the geometric transforms between images. The images and their refined poses are then passed to a stereo algorithm, which generates dense 3D data for each image in the sequence. The 3D data from each image is then placed into a consistent coordinate frame and passed to a routine that divides the coordinate frame into a number of cells. The 3D points that fall into each cell are collected, and basic statistics are applied to determine the elevation of that cell. The result of this step is a DEM that is in an arbitrary coordinate frame. This DEM is then filtered and smoothed in order to remove small artifacts. The final step in the algorithm is to take the initial DEM and rotate and translate it to be in the world coordinate frame [such as UTM (Universal Transverse Mercator), MGRS (Military Grid Reference System), or geodetic] such that it can be saved in

  2. The scaling window of the 5D Ising model with free boundary conditions

    NASA Astrophysics Data System (ADS)

    Lundow, P. H.; Markström, K.

    2016-10-01

    The five-dimensional Ising model with free boundary conditions has recently received a renewed interest in a debate concerning the finite-size scaling of the susceptibility near the critical temperature. We provide evidence in favour of the conventional scaling picture, where the susceptibility scales as L2 inside a critical scaling window of width 1 /L2. Our results are based on Monte Carlo data gathered on system sizes up to L = 79 (ca. three billion spins) for a wide range of temperatures near the critical point. We analyse the magnetisation distribution, the susceptibility and also the scaling and distribution of the size of the Fortuin-Kasteleyn cluster containing the origin. The probability of this cluster reaching the boundary determines the correlation length, and its behaviour agrees with the mean field critical exponent δ = 3, that the scaling window has width 1 /L2.

  3. Cosmological Galaxy Formation Model with New Dust SED Model

    NASA Astrophysics Data System (ADS)

    Makiya, R.; Totani, T.; Nagashima, M.; Kobayashi, M. A. R.; Takeuchi, T. T.

    2015-12-01

    Understanding the dust emission from a galaxy is very important to obtain a full picture of galaxy formation, since it contains rich information about hidden star formation activity and physical properties of interstellar dust. Recent observations revealed that several physical quantities such as star formation rate, cold gas density, and dust surface brightness, are tightly correlated with each other (e.g., Totani et al. 2011; Sun & Hirashita 2011; Kennicutt & Evans 2012; Makiya et al. 2014). Based on those recent observational findings, we newly introduced the dust radiation process into our cosmological galaxy formation model (νGC model; Nagashima et al. 2005; Makiya et al. 2015 in prep.).

  4. 2.5D S-wave velocity model of the TESZ area in northern Poland from receiver function analysis

    NASA Astrophysics Data System (ADS)

    Wilde-Piorko, Monika; Polkowski, Marcin; Grad, Marek

    2016-04-01

    Receiver function (RF) locally provides the signature of sharp seismic discontinuities and information about the shear wave (S-wave) velocity distribution beneath the seismic station. The data recorded by "13 BB Star" broadband seismic stations (Grad et al., 2015) and by few PASSEQ broadband seismic stations (Wilde-Piórko et al., 2008) are analysed to investigate the crustal and upper mantle structure in the Trans-European Suture Zone (TESZ) in northern Poland. The TESZ is one of the most prominent suture zones in Europe separating the young Palaeozoic platform from the much older Precambrian East European craton. Compilation of over thirty deep seismic refraction and wide angle reflection profiles, vertical seismic profiling in over one hundred thousand boreholes and magnetic, gravity, magnetotelluric and thermal methods allowed for creation a high-resolution 3D P-wave velocity model down to 60 km depth in the area of Poland (Grad et al. 2016). On the other hand the receiver function methods give an opportunity for creation the S-wave velocity model. Modified ray-tracing method (Langston, 1977) are used to calculate the response of the structure with dipping interfaces to the incoming plane wave with fixed slowness and back-azimuth. 3D P-wave velocity model are interpolated to 2.5D P-wave velocity model beneath each seismic station and synthetic back-azimuthal sections of receiver function are calculated for different Vp/Vs ratio. Densities are calculated with combined formulas of Berteussen (1977) and Gardner et al. (1974). Next, the synthetic back-azimuthal sections of RF are compared with observed back-azimuthal sections of RF for "13 BB Star" and PASSEQ seismic stations to find the best 2.5D S-wave models down to 60 km depth. National Science Centre Poland provided financial support for this work by NCN grant DEC-2011/02/A/ST10/00284.

  5. Loop quantum cosmology of Bianchi type I models

    SciTech Connect

    Ashtekar, Abhay; Wilson-Ewing, Edward

    2009-04-15

    The ''improved dynamics'' of loop quantum cosmology is extended to include anisotropies of the Bianchi type I model. As in the isotropic case, a massless scalar field serves as a relational time parameter. However, the extension is nontrivial because one has to face several conceptual subtleties as well as technical difficulties. These include a better understanding of the relation between loop quantum gravity and loop quantum cosmology, handling novel features associated with the nonlocal field strength operator in presence of anisotropies, and finding dynamical variables that make the action of the Hamiltonian constraint manageable. Our analysis provides a conceptually complete description that overcomes limitations of earlier works. We again find that the big-bang singularity is resolved by quantum geometry effects but, because of the presence of Weyl curvature, Planck scale physics is now much richer than in the isotropic case. Since the Bianchi I models play a key role in the Belinskii, Khalatnikov, Lifshitz conjecture on the nature of generic spacelike singularities in general relativity, the quantum dynamics of Bianchi I cosmologies is likely to provide considerable intuition about the fate of generic spacelike singularities in quantum gravity. Finally, we show that the quantum dynamics of Bianchi I cosmologies projects down exactly to that of the Friedmann model. This opens a new avenue to relate more complicated models to simpler ones, thereby providing a new tool to relate the quantum dynamics of loop quantum gravity to that of loop quantum cosmology.

  6. Aspects of Cosmology from particle physics beyond the Standard Model

    NASA Astrophysics Data System (ADS)

    Shuhmaher, Natalia

    The interface of Cosmology and High Energy physics is a forefront area of research which is constantly undergoing development. This thesis makes various contributions to this endeavor. String-inspired cosmology is the subject of the first part of the thesis, where we propose both a new inflationary and a new alternative cosmological model. The second part of the thesis concentrates on the problems of integrating cosmology with particle physics beyond the Standard Model. Inspired by new opportunities due to stringy degrees of freedom, we propose a non-inflationary resolution of the entropy and horizon problems. In this string-inspired scenario, 'our' dimensions expand while the extra dimensions first expand and then contract, before eventually stabilizing. The equation of state of the bulk matter (which consists of branes) is negative. Hence, there is a net gain in the total energy of the universe during the pre-stabilization phase. At the end of this phase, the energy stored in the branes is converted into radiation. The result is a large and dense 3-dimensional universe. Making use of similar ideas, we propose a not-fine-tuned model of brane inflation. In this scenario the brane separation, playing the role of the inflaton, is the same as the overall volume modulus. The bulk matter provides an initial expansion phase which drives the inflaton up its potential, so that the conditions for inflation are realized. The specific choice of the inflationary potential nicely fits the cosmological observations. Another aspect of this research concentrates on the cosmological moduli problem: namely, the existence of weakly coupled particles those decay is late enough to interfere with Big Bang Nucleosynthesis. As a solution, we suggest parametric and tachyonic resonances to shorten the decay time. Even heavy moduli are dangerous for cosmology if they cause the overproduction of gravitinos. We find that tachyonic decay channels help to transfer most of the energy of these

  7. Supernovae constraints on cosmological constant and scalar field dominated cosmological models

    NASA Astrophysics Data System (ADS)

    Podariu, Silviu

    Predictions of a spatially-flat cosmological model dominated by a scalar field with potential V (φ) ~ φ-α , which behaves like a time-variable cosmological constant, are compared to recent Type Ia supernova (SN Ia) apparent magnitude versus redshift data. A large region of model parameter space is consistent with current observations. We extend tree method to include constraints from recent measurements of the Hubble constant H0 and of the age of the universe to in the constant and time- variable cosmological constant models. A non-informative prior for the non-relativistic matter density parameter is also considered. We develop median statistics that provide powerful alternatives to χ 2 likelihood methods and require fewer assumptions about the data. Applying median statistics to Huchra's compilation of nearly all estimates of H0, we find a median value H0 = 67 km/s/Mpc. The 95% range of purely statistical errors is +/-2 km/s/Mpc. The statistical precision of this result leads us to analyze the range of possible systematic errors in the median, which we estimate to be roughly +/-5 km/s/Mpc (95% limits), dominating over the statistical errors. A Bayesian median statistics treatment of high-redshift SN Ia apparent magnitude versus redshift data from Riess et al. yields a posterior probability that the cosmological constant A > 0 of 70 or 89%, depending on the prior information used. The posterior probability of an open universe is about 47%. Median statistics analyses of the SN Ia data do not rule out a time-variable A model, and may even favor it over a time-independent Λ and a Λ = 0 open model. We examine the constraints that satellite-acquired SN Ia apparent magnitude versus redshift data will place on cosmological model parameters in models with and without a constant or time-variable Λ. High-quality data which could be acquired in the near future will result in tight constraints on these parameters.

  8. Kinematic Cosmology & a new ``Steady State'' Model of Continued Creation

    NASA Astrophysics Data System (ADS)

    Wegener, Mogens

    2006-03-01

    Only a new "steady state" model justifies the observations of fully mature galaxies at ever increasing distances. The basic idea behind the world model presented here, which is a synthesis of the cosmologies of Parmenides and Herakleitos, is that the invariant structure of the infinite contents of a universe in flux may be depicted as a finite hyperbolic pseudo-sphere.

  9. Cosmological models in Weyl geometrical scalar-tensor theory

    NASA Astrophysics Data System (ADS)

    Pucheu, M. L.; Alves Junior, F. A. P.; Barreto, A. B.; Romero, C.

    2016-09-01

    We investigate cosmological models in a recently proposed geometrical theory of gravity, in which the scalar field appears as part of the spacetime geometry. We extend the previous theory to include a scalar potential in the action. We solve the vacuum field equations for different choices of the scalar potential and give a detailed analysis of the solutions. We show that, in some cases, a cosmological scenario is found that seems to suggest the appearance of a geometric phase transition. We build a toy model, in which the accelerated expansion of the early Universe is driven by pure geometry.

  10. Modeling Ranking, Time Trade-Off and Visual Analogue Scale Values for EQ-5D Health States

    PubMed Central

    Craig, Benjamin M.; Busschbach, Jan J. V.; Salomon, Joshua A.

    2009-01-01

    Background There is rising interest in eliciting health state valuations using rankings. Due to their relative simplicity, ordinal measurement methods may offer an attractive practical alternative to cardinal methods, such as time trade-off (TTO) and visual analog scale (VAS). In this paper, we explore alternative models for estimating cardinal health state values from rank responses in a unique multi-country database. We highlight an estimation challenge pertaining to health states just below perfect health (the ‘non-optimal gap’) and propose an analytic solution to ameliorate this problem. Methods Using rank, a standardized protocol developed by the EuroQol Group, TTO and VAS responses were collected for 43 health states in eight countries: Slovenia, Argentina, Denmark, Japan, Netherlands, Spain, United Kingdom, and United States, yielding a sample of 179,431 state responses from 11,483 subjects. States were described using the EQ-5D system, which allows for three different possible levels on five different dimensions of health. We estimated conditional logit and probit regression models for rank responses. The regressions included 17 health-state attribute variables reflecting specific levels on each dimension and counts of different levels across dimensions. This flexible specification accommodates previously published valuation models, such as models applied in the United Kingdom and United States. In addition to fitting standard conditional logit and probit models, which assume equal variance across health states (homoskedasticity), we examined a heteroskedastic probit model that assumes no variance for the two points anchoring the scale (“optimal health” and “dead”) and relaxes the equal-variance assumption for all other states. Rank-based predictions for the 243 unique states defined by the EQ-5D system were compared to predictions from conventional linear models fitted to TTO and VAS responses. Results By construction, the TTO and VAS models

  11. Perturbative stability of SFT-based cosmological models

    NASA Astrophysics Data System (ADS)

    Galli, Federico; Koshelev, Alexey S.

    2011-05-01

    We review the appearance of multiple scalar fields in linearized SFT based cosmological models with a single non-local scalar field. Some of these local fields are canonical real scalar fields and some are complex fields with unusual coupling. These systems only admit numerical or approximate analysis. We introduce a modified potential for multiple scalar fields that makes the system exactly solvable in the cosmological context of Friedmann equations and at the same time preserves the asymptotic behavior expected from SFT. The main part of the paper consists of the analysis of inhomogeneous cosmological perturbations in this system. We show numerically that perturbations corresponding to the new type of complex fields always vanish. As an example of application of this model we consider an explicit construction of the phantom divide crossing and prove the perturbative stability of this process at the linear order. The issue of ghosts and ways to resolve it are briefly discussed.

  12. SU-D-17A-03: 5D Respiratory Motion Model Based Iterative Reconstruction Method for 4D Cone-Beam CT

    SciTech Connect

    Gao, Y; Thomas, D; Low, D; Gao, H

    2014-06-01

    Purpose: The purpose of this work is to develop a new iterative reconstruction method for 4D cone-beam CT (CBCT) based on a published time-independent 5D respiratory motion model. The proposed method will offer a single high-resolution image at a user-selected breathing phase and the 5D motion model parameters, which could be used to generate the breathing pattern during the CT acquisition. Methods: 5D respiratory motion model was proposed for accurately modeling the motion of lung and lung tumor tissues. 4D images are then parameterized by a reference image, measured breathing amplitude, breathing rate, two time-independent vector fields that describe the 5D model parameters, and a scalar field that describes the change in HU as a function of breathing amplitude. In contrast with the traditional method of reconstructing multiple temporal image phases to reduce respiratory artifact, 5D model based method simplify the problem into the reconstruction of a single reference image and the 5D motion model parameters. The reconstruction formulation of the reference image and scalar and vector fields is a nonlinear least-square optimization problem that consists of solving the reference image and fields alternately, in which the reference image is regularized with the total variation sparsity transform and the vector fields are solved through linearizations regularized by the H1 norm. 2D lung simulations were performed in this proof-of-concept study. Results: The breathing amplitude, its rate, and the corresponding scalar and vector fields were generated from a patient case. Compared with filtered backprojection method and sparsity regularized iterative method for the phase-by-phase reconstruction, the proposed 5D motion model based method yielded improved image quality. Conclusion: Based on 5D respiratory motion model, we have developed a new iterative reconstruction method for 4D CBCT that has the potential for improving image quality while providing needed on

  13. Solving the hierarchy problem in two-brane cosmological models

    SciTech Connect

    Kanti, Panagiota; Olive, Keith A.; Pospelov, Maxim

    2000-12-15

    We analyze cosmological solutions in the class of two-brane models with arbitrary tensions which contain matter with general equations of state. We show that the mass hierarchy between the two branes is determined by the ratio of the lapse functions evaluated on the branes. This ratio can be sufficiently small without fine-tuning the brane separation, once the transverse dimension is stabilized. For suitably large interbrane separations, both brane tensions are positive. We also find that the cosmological evolution obeys the standard four-dimensional Friedmann equation up to small corrections.

  14. Emergent universe in spatially flat cosmological model

    SciTech Connect

    Zhang, Kaituo; Yu, Hongwei; Wu, Puxun E-mail: wpx0227@gmail.com

    2014-01-01

    The scenario of an emergent universe provides a promising resolution to the big bang singularity in universes with positive or negative spatial curvature. It however remains unclear whether the scenario can be successfully implemented in a spatially flat universe which seems to be favored by present cosmological observations. In this paper, we study the stability of Einstein static state solutions in a spatially flat Shtanov-Sahni braneworld scenario. With a negative dark radiation term included and assuming a scalar field as the only matter energy component, we find that the universe can stay at an Einstein static state past eternally and then evolve to an inflation phase naturally as the scalar field climbs up its potential slowly. In addition, we also propose a concrete potential of the scalar field that realizes this scenario.

  15. Comparison of cosmological models using standard rulers and candles

    NASA Astrophysics Data System (ADS)

    Li, Xiao-Lei; Cao, Shuo; Zheng, Xiao-Gang; Li, Song; Biesiada, Marek

    2016-05-01

    In this paper, we used standard rulers and standard candles (separately and jointly) to explore five popular dark energy models under the assumption of the spatial flatness of the Universe. As standard rulers, we used a data set comprised of 118 galactic scale strong lensing systems (individual standard rulers if properly calibrated for the mass density profile) combined with BAO diagnostics (statistical standard ruler). Type Ia supernovae served as standard candles. Unlike most previous statistical studies involving strong lensing systems, we relaxed the assumption of a singular isothermal sphere (SIS) in favor of its generalization: the power-law mass density profile. Therefore, along with cosmological model parameters, we fitted the power law index and its first derivative with respect to the redshift (thus allowing for mass density profile evolution). It turned out that the best fitted γ parameters are in agreement with each other, irrespective of the cosmological model considered. This demonstrates that galactic strong lensing systems may provide a complementary probe to test the properties of dark energy. The fits for cosmological model parameters which we obtained are in agreement with alternative studies performed by other researchers. Because standard rulers and standard candles have different parameter degeneracies, a combination of standard rulers and standard candles gives much more restrictive results for cosmological parameters. Finally, we attempted an analysis based on model selection using information theoretic criteria (AIC and BIC). Our results support the claim that the cosmological constant model is still best and there is no (at least statistical) reason to prefer any other more complex model.

  16. Asymptotic behaviour of the Boltzmann equation as a cosmological model

    NASA Astrophysics Data System (ADS)

    Lee, Ho

    2016-08-01

    As a Newtonian cosmological model the Vlasov-Poisson-Boltzmann system is considered, and a slightly modified Boltzmann equation, which describes the stability of an expanding universe, is derived. Asymptotic behaviour of solutions turns out to depend on the expansion of the universe, and in this paper we consider the soft potential case and will obtain asymptotic behaviour.

  17. Gauge-Invariant Perturbations in Anisotropic Homogeneous Cosmological Models

    NASA Astrophysics Data System (ADS)

    Patra, Amar Chandra; Ray, Dipankar

    1988-05-01

    In a recent paper K. Tomita and M. Den found a set of coupled differential equations for spatially flat, anisotropic homogeneous, N- dimensional cosmological models. Some particular exact solutions of those differential equations for a few specific equations of state were obtained by D. Lorentz-Petzold. In the present work we solve those differential equations completely.

  18. Integrable multidimensional gravitational and cosmological models and applications

    NASA Astrophysics Data System (ADS)

    Ivashchuk, V. D.; Melnikov, V. N.

    2016-01-01

    Two families of exact solutions in multidimensional gravity with scalar fields and fields of forms are considered: fluxbrane and black brane ones. A brief overview of main results on billiard approach for cosmological-type models with branes is also presented.

  19. Investigating inhomogeneous Szekeres models and their applications to precision cosmology

    NASA Astrophysics Data System (ADS)

    Peel, Austin Chandler

    Exact solutions of Einstein's field equations that can describe the evolution of complex structures in the universe provide complementary frameworks to standard perturbation theory in which to analyze cosmological and astrophysical phenomena. The flexibility and generality of the inhomogeneous and anisotropic Szekeres metric make it the best known exact solution to explore nonlinearities in the universe. We study applications of Szekeres models to precision cosmology, focusing on the influence of inhomogeneities in two primary contexts---the growth rate of cosmic structures and biases in distance determinations to remote sources. We first define and derive evolution equations for a Szekeres density contrast, which quantifies exact deviations from a smooth background cosmology. Solving these equations and comparing to the usual perturbative approach, we find that for models with the same matter content, the Szekeres growth rate is larger through the matter-dominated cosmic era. Including a cosmological constant, we consider exact global perturbations, as well as the evolution of a single extended structure surrounded by an almost homogeneous background. For the former, we use growth data to obtain a best fit Szekeres model and find that it can fit the data as well as the standard Lambda-Cold Dark Matter (LCDM) cosmological model but with different cosmological parameters. Next, to study effects of inhomogeneities on distance measures, we build an exact relativistic Swiss-cheese model of the universe, where a large number of non-symmetric and randomly placed Szekeres structures are embedded within a LCDM background. Solving the full relativistic propagation equations, light beams are traced through the model, where they traverse the inhomogeneous structures in a way that mimics the paths of real light beams in the universe. For beams crossing a single structure, their magnification or demagnification reflects primarily the net density encountered along the path

  20. TESTING NONSTANDARD COSMOLOGICAL MODELS WITH SNLS3 SUPERNOVA DATA AND OTHER COSMOLOGICAL PROBES

    SciTech Connect

    Li Zhengxiang; Yu Hongwei; Wu Puxun

    2012-01-10

    We investigate the implications for some nonstandard cosmological models using data from the first three years of the Supernova Legacy Survey (SNLS3), assuming a spatially flat universe. A comparison between the constraints from the SNLS3 and those from other SN Ia samples, such as the ESSENCE, Union2, SDSS-II, and Constitution samples, is given and the effects of different light-curve fitters are considered. We find that analyzing SNe Ia with SALT2 or SALT or SiFTO can give consistent results and the tensions between different data sets and different light-curve fitters are obvious for fewer-free-parameters models. At the same time, we also study the constraints from SNLS3 along with data from the cosmic microwave background and the baryonic acoustic oscillations (CMB/BAO), and the latest Hubble parameter versus redshift (H(z)). Using model selection criteria such as {chi}{sup 2}/dof, goodness of fit, Akaike information criterion, and Bayesian information criterion, we find that, among all the cosmological models considered here ({Lambda}CDM, constant w, varying w, Dvali-Gabadadze-Porrati (DGP), modified polytropic Cardassian, and the generalized Chaplygin gas), the flat DGP is favored by SNLS3 alone. However, when additional CMB/BAO or H(z) constraints are included, this is no longer the case, and the flat {Lambda}CDM becomes preferred.

  1. Confronting the concordance model of cosmology with Planck data

    SciTech Connect

    Hazra, Dhiraj Kumar; Shafieloo, Arman E-mail: arman@apctp.org

    2014-01-01

    We confront the concordance (standard) model of cosmology, the spatially flat ΛCDM Universe with power-law form of the primordial spectrum with Planck CMB angular power spectrum data searching for possible smooth deviations beyond the flexibility of the standard model. The departure from the concordance cosmology is modeled in the context of Crossing statistic and statistical significance of this deviation is used as a measure to test the consistency of the standard model to the Planck data. Derived Crossing functions suggest the presence of some broad features in angular spectrum beyond the expectations of the concordance model. Our results indicate that the concordance model of cosmology is consistent to the Planck data only at 2 to 3σ confidence level if we allow smooth deviations from the angular power spectrum given by the concordance model. This might be due to random fluctuations or may hint towards smooth features in the primordial spectrum or departure from another aspect of the standard model. Best fit Crossing functions indicate that there are lack of power in the data at both low-ℓ and high-ℓ with respect to the concordance model. This hints that we may need some modifications in the foreground modeling to resolve the significant inconsistency at high-ℓ. However, presence of some systematics at high-ℓ might be another reason for the deviation we found in our analysis.

  2. 2.5D real waveform and real noise simulation of receiver functions in 3D models

    NASA Astrophysics Data System (ADS)

    Schiffer, Christian; Jacobsen, Bo; Balling, Niels

    2014-05-01

    There are several reasons why a real-data receiver function differs from the theoretical receiver function in a 1D model representing the stratification under the seismometer. Main reasons are ambient noise, spectral deficiencies in the impinging P-waveform, and wavefield propagation in laterally varying velocity variations. We present a rapid "2.5D" modelling approach which takes these aspects into account, so that a given 3D velocity model of the crust and uppermost mantle can be tested more realistically against observed recordings from seismometer arrays. Each recorded event at each seismometer is simulated individually through the following steps: A 2D section is extracted from the 3D model along the direction towards the hypocentre. A properly slanted plane or curved impulsive wavefront is propagated through this 2D section, resulting in noise free and spectrally complete synthetic seismometer data. The real vertical component signal is taken as a proxy of the real impingent wavefield, so by convolution and subsequent addition of real ambient noise recorded just before the P-arrival we get synthetic vertical and horizontal component data which very closely match the spectral signal content and signal to noise ratio of this specific recording. When these realistic synthetic data undergo exactly the same receiver function estimation and subsequent graphical display we get a much more realistic image to compare to the real-data receiver functions. We applied this approach to the Central Fjord area in East Greenland (Schiffer et al., 2013), where a 3D velocity model of crust and uppermost mantle was adjusted to receiver functions from 2 years of seismometer recordings and wide angle crustal profiles (Schlindwein and Jokat, 1999; Voss and Jokat, 2007). Computationally this substitutes tens or hundreds of heavy 3D computations with hundreds or thousands of single-core 2D computations which parallelize very efficiently on common multicore systems. In perspective

  3. Noninflationary model with scale invariant cosmological perturbations

    SciTech Connect

    Peter, Patrick; Pinho, Emanuel J. C.; Pinto-Neto, Nelson

    2007-01-15

    We show that a contracting universe which bounces due to quantum cosmological effects and connects to the hot big-bang expansion phase, can produce an almost scale invariant spectrum of perturbations provided the perturbations are produced during an almost matter dominated era in the contraction phase. This is achieved using Bohmian solutions of the canonical Wheeler-DeWitt equation, thus treating both the background and the perturbations in a fully quantum manner. We find a very slightly blue spectrum (n{sub S}-1>0). Taking into account the spectral index constraint as well as the cosmic microwave background normalization measure yields an equation of state that should be less than {omega} < or approx. 8x10{sup -4}, implying n{sub S}-1{approx}O(10{sup -4}), and that the characteristic curvature scale of the Universe at the bounce is L{sub 0}{approx}10{sup 3}l{sub Pl}, a region where one expects that the Wheeler-DeWitt equation should be valid without being spoiled by string or loop quantum gravity effects. We have also obtained a consistency relation between the tensor-to-scalar ratio T/S and the scalar spectral index as T/S{approx}4.6x10{sup -2}{radical}(n{sub S}-1), leading to potentially measurable differences with inflationary predictions.

  4. Code interoperability and standard data formats in quantum chemistry and quantum dynamics: The Q5/D5Cost data model.

    PubMed

    Rossi, Elda; Evangelisti, Stefano; Laganà, Antonio; Monari, Antonio; Rampino, Sergio; Verdicchio, Marco; Baldridge, Kim K; Bendazzoli, Gian Luigi; Borini, Stefano; Cimiraglia, Renzo; Angeli, Celestino; Kallay, Peter; Lüthi, Hans P; Ruud, Kenneth; Sanchez-Marin, José; Scemama, Anthony; Szalay, Peter G; Tajti, Attila

    2014-03-30

    Code interoperability and the search for domain-specific standard data formats represent critical issues in many areas of computational science. The advent of novel computing infrastructures such as computational grids and clouds make these issues even more urgent. The design and implementation of a common data format for quantum chemistry (QC) and quantum dynamics (QD) computer programs is discussed with reference to the research performed in the course of two Collaboration in Science and Technology Actions. The specific data models adopted, Q5Cost and D5Cost, are shown to work for a number of interoperating codes, regardless of the type and amount of information (small or large datasets) to be exchanged. The codes are either interfaced directly, or transfer data by means of wrappers; both types of data exchange are supported by the Q5/D5Cost library. Further, the exchange of data between QC and QD codes is addressed. As a proof of concept, the H + H2 reaction is discussed. The proposed scheme is shown to provide an excellent basis for cooperative code development, even across domain boundaries. Moreover, the scheme presented is found to be useful also as a production tool in the grid distributed computing environment.

  5. The models of cosmological inflation in the context of kinetic approximation

    NASA Astrophysics Data System (ADS)

    Fomin, I.

    2016-07-01

    In this work the building of models of cosmological inflation with approximate linear dependence of the scalar field kinetic energy on the state parameter is considered. The key parameters of cosmological perturbations are also calculated.

  6. The adhesion model as a field theory for cosmological clustering

    SciTech Connect

    Rigopoulos, Gerasimos

    2015-01-01

    The adhesion model has been proposed in the past as an improvement of the Zel'dovich approximation, providing a good description of the formation of the cosmic web. We recast the model as a field theory for cosmological large scale structure, adding a stochastic force to account for power generated from very short, highly non-linear scales that is uncorrelated with the initial power spectrum. The dynamics of this Stochastic Adhesion Model (SAM) is reminiscent of the well known Kardar-Parisi-Zhang equation with the difference that the viscosity and the noise spectrum are time dependent. Choosing the viscosity proportional to the growth factor D restricts the form of noise spectrum through a 1-loop renormalization argument. For this choice, the SAM field theory is renormalizable to one loop. We comment on the suitability of this model for describing the non-linear regime of the CDM power spectrum and its utility as a relatively simple approach to cosmological clustering.

  7. Loop quantum cosmology of Bianchi type IX models

    SciTech Connect

    Wilson-Ewing, Edward

    2010-08-15

    The loop quantum cosmology 'improved dynamics' of the Bianchi type IX model are studied. The action of the Hamiltonian constraint operator is obtained via techniques developed for the Bianchi type I and type II models, no new input is required. It is shown that the big bang and big crunch singularities are resolved by quantum gravity effects. We also present effective equations which provide quantum geometry corrections to the classical equations of motion.

  8. Canonical Transformation for Stiff Matter Models in Quantum Cosmology

    NASA Astrophysics Data System (ADS)

    Neves, C.; Monerat, G. A.; Corrêa Silva, E. V.; Ferreira Filho, L. G.; Oliveira-Neto, G.

    2011-06-01

    In the present work we consider Friedmann-Robertson-Walker models in the presence of a stiff matter perfect fluid and a cosmological constant. We write the superhamiltonian of these models using the Schutz's variational formalism. We notice that the resulting superhamiltonians have terms that will lead to factor ordering ambiguities when they are written as quantum operators. In order to remove these ambiguities, we introduce appropriate coordinate transformations and prove that these transformations are canonical using the symplectic method.

  9. Hamilton-Jacobi approach to cosmology with nonlinear sigma model

    NASA Astrophysics Data System (ADS)

    Kerner, Richard; van Holten, Jan-Willem

    2016-05-01

    We start with a short introduction of the role that constraints and Lagrange multiplers play in variational calculus. After recalling briefly the properties of the nonlinear sigma model, we show how the Hamilton-Jacobi method can be applied to find its solutions. We discuss the importance of the Hamiltonian constraint in the standard cosmological model, and finally, apply the Hamilton-Jacobi method to the solution of coupled gravitational and sigma-field equations.

  10. A Dark Energy Model in Kaluza-Klein Cosmology

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Utpal; Chakraborty, Ipsita; Ray, Saibal; Usmani, A. A.

    2016-01-01

    We study a dynamic Λ model with varying gravitational constant G under the Kaluza-Klein cosmology. Physical features and the limitations of the present model have been explored and discussed. Solutions are found mostly in accordance with the observed features of the accelerating universe. Interestingly, signature flipping of the deceleration parameter is noticed and the present age of the Universe is also attainable under certain stringent conditions. We find that the time variation of gravitational constant is not permitted without vintage Λ.

  11. On a class of scaling FRW cosmological models

    SciTech Connect

    Cataldo, Mauricio; Arevalo, Fabiola; Minning, Paul E-mail: pminning@udec.cl

    2010-02-01

    We study Friedmann-Robertson-Walker cosmological models with matter content composed of two perfect fluids ρ{sub 1} and ρ{sub 2}, with barotropic pressure densities p{sub 1}/ρ{sub 1} = ω{sub 1} = const and p{sub 2}/ρ{sub 2} = ω{sub 2} = const, where one of the energy densities is given by ρ{sub 1} = C{sub 1}a{sup α}+C{sub 2}a{sup β}, with C{sub 1}, C{sub 2}, α and β taking constant values. We solve the field equations by using the conservation equation without breaking it into two interacting parts with the help of a coupling interacting term Q. Nevertheless, with the found solution may be associated an interacting term Q, and then a number of cosmological interacting models studied in the literature correspond to particular cases of our cosmological model. Specifically those models having constant coupling parameters α-tilde , β-tilde and interacting terms given by Q = α-tilde Hρ{sub D{sub M}}, Q = α-tilde Hρ{sub D{sub E}}, Q = α-tilde H(ρ{sub D{sub M}}+ρ{sub D{sub E}}) and Q = α-tilde Hρ{sub D{sub M}}+β-tilde Hρ{sub D{sub E}}, where ρ{sub D{sub M}} and ρ{sub D{sub E}} are the energy densities of dark matter and dark energy respectively. The studied set of solutions contains a class of cosmological models presenting a scaling behavior at early and at late times. On the other hand the two-fluid cosmological models considered in this paper also permit a three fluid interpretation which is also discussed. In this reinterpretation, for flat Friedmann-Robertson-Walker cosmologies, the requirement of positivity of energy densities of the dark matter and dark energy components allows the state parameter of dark energy to be in the range −1.37∼<ω{sub D{sub E}} < −1/3.

  12. Cosmological Signatures of a UV-Conformal Standard Model

    NASA Astrophysics Data System (ADS)

    Dorsch, Glauber C.; Huber, Stephan J.; No, Jose Miguel

    2014-09-01

    Quantum scale invariance in the UV has been recently advocated as an attractive way of solving the gauge hierarchy problem arising in the standard model. We explore the cosmological signatures at the electroweak scale when the breaking of scale invariance originates from a hidden sector and is mediated to the standard model by gauge interactions (gauge mediation). These scenarios, while being hard to distinguish from the standard model at LHC, can give rise to a strong electroweak phase transition leading to the generation of a large stochastic gravitational wave signal in possible reach of future space-based detectors such as eLISA and BBO. This relic would be the cosmological imprint of the breaking of scale invariance in nature.

  13. 1.5D quasilinear model and its application on beams interacting with Alfvén eigenmodes in DIII-D

    NASA Astrophysics Data System (ADS)

    Ghantous, K.; Gorelenkov, N. N.; Berk, H. L.; Heidbrink, W. W.; Van Zeeland, M. A.

    2012-09-01

    We propose a model, denoted here by 1.5D, to study energetic particle (EP) interaction with toroidal Alfvenic eigenmodes (TAE) in the case where the local EP drive for TAE exceeds the stability limit. Based on quasilinear theory, the proposed 1.5D model assumes that the particles diffuse in phase space, flattening the pressure profile until its gradient reaches a critical value where the modes stabilize. Using local theories and NOVA-K simulations of TAE damping and growth rates, the 1.5D model calculates the critical gradient and reconstructs the relaxed EP pressure profile. Local theory is improved from previous study by including more sophisticated damping and drive mechanisms such as the numerical computation of the effect of the EP finite orbit width on the growth rate. The 1.5D model is applied on the well-diagnosed DIII-D discharges #142111 [M. A. Van Zeeland et al., Phys. Plasmas 18, 135001 (2011)] and #127112 [W. W. Heidbrink et al., Nucl. Fusion. 48, 084001 (2008)]. We achieved a very satisfactory agreement with the experimental results on the EP pressure profiles redistribution and measured losses. This agreement of the 1.5D model with experimental results allows the use of this code as a guide for ITER plasma operation where it is desired to have no more than 5% loss of fusion alpha particles as limited by the design.

  14. Effective equations of cosmological models in (loop) quantum gravity

    NASA Astrophysics Data System (ADS)

    Simpson, David

    This dissertation focuses on the properties of several differing models within quantum cosmology. Specifically, by using the method of effective equations, we explore: a linear discrete Schrodinger model, a non-linear discrete Schrodinger model, factor ordering ambiguities in the Hamiltonian constraint (with a focus on large-volume behavior), and the use of the electric vector potential as deparameterized time. In the linear and non-linear Schrodinger models, we arrive at a new possibility for studying inhomogeneous quantum cosmology (where the non-linearities are interpreted as non-local deviations from the spatial average) that allows for a variety of dynamics and raises a number of questions for future research. We then turn our focus to the general effects of factor ordering ambiguities and their possible role in large-volume collapse of a k = 0 isotropic quantum cosmology with a free, massless scalar field. With the additional inclusion of holonomy and inverse-triad corrections, the choice in factor ordering of the Hamiltonian constraint is quite relevant; however, with our assumptions, we do not see any significant departure from classical large-volume behavior. The final model discussed is formulated with the electric vector potential as the global internal time in a Wheeler-DeWitt setting sourced by radiation. While further analysis is required to make a definitive statement on the impact that the choice of deparameterization makes, we find that the specific form of quantum state can affect early-universe dynamics and even lead to new possibilities.

  15. Spherical collapse model in time varying vacuum cosmologies

    SciTech Connect

    Basilakos, Spyros; Plionis, Manolis; Sola, Joan

    2010-10-15

    We investigate the virialization of cosmic structures in the framework of flat Friedmann-Lemaitre-Robertson-Walker cosmological models, in which the vacuum energy density evolves with time. In particular, our analysis focuses on the study of spherical matter perturbations, as they decouple from the background expansion, 'turn around', and finally collapse. We generalize the spherical collapse model in the case when the vacuum energy is a running function of the Hubble rate, {Lambda}={Lambda}(H). A particularly well-motivated model of this type is the so-called quantum field vacuum, in which {Lambda}(H) is a quadratic function, {Lambda}(H)=n{sub 0}+n{sub 2}H{sup 2}, with n{sub 0{ne}}0. This model was previously studied by our team using the latest high quality cosmological data to constrain its free parameters, as well as the predicted cluster formation rate. It turns out that the corresponding Hubble expansion history resembles that of the traditional {Lambda}CDM cosmology. We use this {Lambda}(t)CDM framework to illustrate the fact that the properties of the spherical collapse model (virial density, collapse factor, etc.) depend on the choice of the considered vacuum energy (homogeneous or clustered). In particular, if the distribution of the vacuum energy is clustered, then, under specific conditions, we can produce more concentrated structures with respect to the homogeneous vacuum energy case.

  16. Approximate Bayesian computation for forward modeling in cosmology

    NASA Astrophysics Data System (ADS)

    Akeret, Joël; Refregier, Alexandre; Amara, Adam; Seehars, Sebastian; Hasner, Caspar

    2015-08-01

    Bayesian inference is often used in cosmology and astrophysics to derive constraints on model parameters from observations. This approach relies on the ability to compute the likelihood of the data given a choice of model parameters. In many practical situations, the likelihood function may however be unavailable or intractable due to non-gaussian errors, non-linear measurements processes, or complex data formats such as catalogs and maps. In these cases, the simulation of mock data sets can often be made through forward modeling. We discuss how Approximate Bayesian Computation (ABC) can be used in these cases to derive an approximation to the posterior constraints using simulated data sets. This technique relies on the sampling of the parameter set, a distance metric to quantify the difference between the observation and the simulations and summary statistics to compress the information in the data. We first review the principles of ABC and discuss its implementation using a Population Monte-Carlo (PMC) algorithm and the Mahalanobis distance metric. We test the performance of the implementation using a Gaussian toy model. We then apply the ABC technique to the practical case of the calibration of image simulations for wide field cosmological surveys. We find that the ABC analysis is able to provide reliable parameter constraints for this problem and is therefore a promising technique for other applications in cosmology and astrophysics. Our implementation of the ABC PMC method is made available via a public code release.

  17. Searching for a cosmological preferred axis in complicated class of cosmological models: case study f ( R, T ) model

    NASA Astrophysics Data System (ADS)

    Salehi, A.; Aftabi, S.

    2016-09-01

    Recent astronomical observations show that the universe may be anisotropic on large scales. The Union2 SnIa data hint that the universe has a preferred direction. If such a cosmological privileged axis indeed exists, one has to consider an anisotropic expanding Universe instead of the isotropic cosmological model. In this paper, we present a detailed analysis of the dark energy dipole in f ( R, T ) = f 1( R) + f 2( T ) Cosmological Model using three types of dipole fit (DF) method which are (I) dipole + monopole fitting for distance modulus (DMFDM), (II) dipole + monopole fitting for luminosity distance (DMFLD) and (III) general dipole fitting for luminosity distance (GDFLD). We have found the maximum anisotropic deviation direction for (DMFDM) method as ( l, b) = (315 - 25 + 25 , - 23 - 15 + 14 ), for (DMFLD) as ( l, b) = ( l, b) = (315 - 37 + 35 , - 23 - 18 + 18 ), and for (GDFLD) method as ( l, b) = (317 - 32 + 32 , - 23 - 18 + 18 ) which are located very close to each other. We compare our model with the CPL, ΛCDM and ωCDM models. Constraints on ( l, b) in f ( R, T ) model are not much different from the cases of the CPL, ΛCDM and ωCDM models. Moreover, the results are consistent with other studies.

  18. Addition of vasopressin synthetic analogue [V(4)Q(5)]dDAVP to standard chemotherapy enhances tumour growth inhibition and impairs metastatic spread in aggressive breast tumour models.

    PubMed

    Garona, Juan; Pifano, Marina; Pastrian, Maria B; Gomez, Daniel E; Ripoll, Giselle V; Alonso, Daniel F

    2016-08-01

    [V(4)Q(5)]dDAVP is a novel 2nd generation vasopressin analogue with robust antitumour activity against metastatic breast cancer. We recently reported that, by acting on vasopressin V2r membrane receptor present in tumour cells and microvascular endothelium, [V(4)Q(5)]dDAVP inhibits angiogenesis and metastatic progression of the disease without overt toxicity. Despite chemotherapy remaining as a primary therapeutic option for aggressive breast cancer, its use is limited by low selectivity and associated adverse effects. In this regard, we evaluated potential combinational benefits by adding [V(4)Q(5)]dDAVP to standard-of-care chemotherapy. In vitro, combination of [V(4)Q(5)]dDAVP with sub-IC50 concentrations of paclitaxel or carmustine resulted in a cooperative inhibition of breast cancer cell growth in comparison to single-agent therapy. In vivo antitumour efficacy of [V(4)Q(5)]dDAVP addition to chemotherapy was first evaluated using the triple-negative MDA-MB-231 breast cancer xenograft model. Tumour-bearing mice were treated with i.v. injections of [V(4)Q(5)]dDAVP (0.3 μg/kg, thrice weekly) in combination with weekly cycles of paclitaxel (10 mg/kg i.p.). After 6 weeks of treatment, combination regimen resulted in greater tumour growth inhibition compared to monotherapy. [V(4)Q(5)]dDAVP addition was also associated with reduction of local aggressiveness, and impairment of tumour invasion and infiltration of the skin. Benefits of combined therapy were confirmed in the hormone-independent and metastatic F3II breast cancer model by combining [V(4)Q(5)]dDAVP with carmustine (25 mg/kg i.p.). Interestingly, [V(4)Q(5)]dDAVP plus cytotoxic agents severely impaired colony forming ability of tumour cells and inhibited breast cancer metastasis to lung. The present study shows that [V(4)Q(5)]dDAVP may complement conventional chemotherapy by modulating metastatic progression and early stages of microtumour establishment, and thus supports further preclinical testing of

  19. Addition of vasopressin synthetic analogue [V(4)Q(5)]dDAVP to standard chemotherapy enhances tumour growth inhibition and impairs metastatic spread in aggressive breast tumour models.

    PubMed

    Garona, Juan; Pifano, Marina; Pastrian, Maria B; Gomez, Daniel E; Ripoll, Giselle V; Alonso, Daniel F

    2016-08-01

    [V(4)Q(5)]dDAVP is a novel 2nd generation vasopressin analogue with robust antitumour activity against metastatic breast cancer. We recently reported that, by acting on vasopressin V2r membrane receptor present in tumour cells and microvascular endothelium, [V(4)Q(5)]dDAVP inhibits angiogenesis and metastatic progression of the disease without overt toxicity. Despite chemotherapy remaining as a primary therapeutic option for aggressive breast cancer, its use is limited by low selectivity and associated adverse effects. In this regard, we evaluated potential combinational benefits by adding [V(4)Q(5)]dDAVP to standard-of-care chemotherapy. In vitro, combination of [V(4)Q(5)]dDAVP with sub-IC50 concentrations of paclitaxel or carmustine resulted in a cooperative inhibition of breast cancer cell growth in comparison to single-agent therapy. In vivo antitumour efficacy of [V(4)Q(5)]dDAVP addition to chemotherapy was first evaluated using the triple-negative MDA-MB-231 breast cancer xenograft model. Tumour-bearing mice were treated with i.v. injections of [V(4)Q(5)]dDAVP (0.3 μg/kg, thrice weekly) in combination with weekly cycles of paclitaxel (10 mg/kg i.p.). After 6 weeks of treatment, combination regimen resulted in greater tumour growth inhibition compared to monotherapy. [V(4)Q(5)]dDAVP addition was also associated with reduction of local aggressiveness, and impairment of tumour invasion and infiltration of the skin. Benefits of combined therapy were confirmed in the hormone-independent and metastatic F3II breast cancer model by combining [V(4)Q(5)]dDAVP with carmustine (25 mg/kg i.p.). Interestingly, [V(4)Q(5)]dDAVP plus cytotoxic agents severely impaired colony forming ability of tumour cells and inhibited breast cancer metastasis to lung. The present study shows that [V(4)Q(5)]dDAVP may complement conventional chemotherapy by modulating metastatic progression and early stages of microtumour establishment, and thus supports further preclinical testing of

  20. Cosmology of generalized modified gravity models

    NASA Astrophysics Data System (ADS)

    Carroll, Sean M.; de Felice, Antonio; Duvvuri, Vikram; Easson, Damien A.; Trodden, Mark; Turner, Michael S.

    2005-03-01

    We consider general curvature-invariant modifications of the Einstein-Hilbert action that become important only in regions of extremely low space-time curvature. We investigate the far future evolution of the Universe in such models, examining the possibilities for cosmic acceleration and other ultimate destinies. The models generically possess de Sitter space as an unstable solution and exhibit an interesting set of attractor solutions which, in some cases, provide alternatives to dark energy models.

  1. The halo model in a massive neutrino cosmology

    SciTech Connect

    Massara, Elena; Villaescusa-Navarro, Francisco; Viel, Matteo E-mail: villaescusa@oats.inaf.it

    2014-12-01

    We provide a quantitative analysis of the halo model in the context of massive neutrino cosmologies. We discuss all the ingredients necessary to model the non-linear matter and cold dark matter power spectra and compare with the results of N-body simulations that incorporate massive neutrinos. Our neutrino halo model is able to capture the non-linear behavior of matter clustering with a ∼20% accuracy up to very non-linear scales of k = 10 h/Mpc (which would be affected by baryon physics). The largest discrepancies arise in the range k = 0.5 – 1 h/Mpc where the 1-halo and 2-halo terms are comparable and are present also in a massless neutrino cosmology. However, at scales k < 0.2 h/Mpc our neutrino halo model agrees with the results of N-body simulations at the level of 8% for total neutrino masses of < 0.3 eV. We also model the neutrino non-linear density field as a sum of a linear and clustered component and predict the neutrino power spectrum and the cold dark matter-neutrino cross-power spectrum up to k = 1 h/Mpc with ∼30% accuracy. For masses below 0.15 eV the neutrino halo model captures the neutrino induced suppression, casted in terms of matter power ratios between massive and massless scenarios, with a 2% agreement with the results of N-body/neutrino simulations. Finally, we provide a simple application of the halo model: the computation of the clustering of galaxies, in massless and massive neutrinos cosmologies, using a simple Halo Occupation Distribution scheme and our halo model extension.

  2. The Hypergeometrical Universe: Cosmology and Standard Model

    NASA Astrophysics Data System (ADS)

    Pereira, Marco A.

    2010-12-01

    This paper presents a simple and purely geometrical Grand Unification Theory. Quantum Gravity, Electrostatic and Magnetic interactions are shown in a unified framework. Newton's, Gauss' and Biot-Savart's Laws are derived from first principles. Unification symmetry is defined for all the existing forces. This alternative model does not require Strong and Electroweak forces. A 4D Shock -Wave Hyperspherical topology is proposed for the Universe which together with a Quantum Lagrangian Principle and a Dilator based model for matter result in a quantized stepwise expansion for the whole Universe along a radial direction within a 4D spatial manifold. The Hypergeometrical Standard Model for matter, Universe Topology and a new Law of Gravitation are presented.

  3. The Hypergeometrical Universe: Cosmology and Standard Model

    SciTech Connect

    Pereira, Marco A.

    2010-12-22

    This paper presents a simple and purely geometrical Grand Unification Theory. Quantum Gravity, Electrostatic and Magnetic interactions are shown in a unified framework. Newton's, Gauss' and Biot-Savart's Laws are derived from first principles. Unification symmetry is defined for all the existing forces. This alternative model does not require Strong and Electroweak forces. A 4D Shock -Wave Hyperspherical topology is proposed for the Universe which together with a Quantum Lagrangian Principle and a Dilator based model for matter result in a quantized stepwise expansion for the whole Universe along a radial direction within a 4D spatial manifold. The Hypergeometrical Standard Model for matter, Universe Topology and a new Law of Gravitation are presented.

  4. Viscous dissipative Chaplygin gas dominated homogenous and isotropic cosmological models

    SciTech Connect

    Pun, C. S. J.; Mak, M. K.; Harko, T.; Gergely, L. A.; Kovacs, Z.; Szabo, G. M.

    2008-03-15

    The generalized Chaplygin gas, which interpolates between a high density relativistic era and a nonrelativistic matter phase, is a popular dark energy candidate. We consider a generalization of the Chaplygin gas model, by assuming the presence of a bulk viscous type dissipative term in the effective thermodynamic pressure of the gas. The dissipative effects are described by using the truncated Israel-Stewart model, with the bulk viscosity coefficient and the relaxation time functions of the energy density only. The corresponding cosmological dynamics of the bulk viscous Chaplygin gas dominated universe is considered in detail for a flat homogeneous isotropic Friedmann-Robertson-Walker geometry. For different values of the model parameters we consider the evolution of the cosmological parameters (scale factor, energy density, Hubble function, deceleration parameter, and luminosity distance, respectively), by using both analytical and numerical methods. In the large time limit the model describes an accelerating universe, with the effective negative pressure induced by the Chaplygin gas and the bulk viscous pressure driving the acceleration. The theoretical predictions of the luminosity distance of our model are compared with the observations of the type Ia supernovae. The model fits well the recent supernova data. From the fitting we determine both the equation of state of the Chaplygin gas, and the parameters characterizing the bulk viscosity. The evolution of the scalar field associated to the viscous Chaplygin fluid is also considered, and the corresponding potential is obtained. Hence the viscous Chaplygin gas model offers an effective dynamical possibility for replacing the cosmological constant, and for explaining the recent acceleration of the universe.

  5. Model-independent cosmological constraints from the CMB

    SciTech Connect

    Vonlanthen, Marc; Räsänen, Syksy; Durrer, Ruth E-mail: syksy.rasanen@iki.fi

    2010-08-01

    We analyse CMB data in a manner which is as independent as possible of the model of late-time cosmology. We encode the effects of late-time cosmology into a single parameter which determines the distance to the last scattering surface. We exclude low multipoles l < 40 from the analysis. We consider the WMAP5 and ACBAR data. We obtain the cosmological parameters 100ω{sub b} = 2.13±0.05, ω{sub c} = 0.124±0.007, n{sub s} = 0.93±0.02 and θ{sub A} = 0.593°±0.001° (68% C.L.). The last number is the angular scale subtended by the sound horizon at decoupling. There is a systematic shift in the parameters as more low l data are omitted, towards smaller values of ω{sub b} and n{sub s} and larger values of ω{sub c}. The scale θ{sub A} remains stable and very well determined.

  6. Electroweak scale invariant models with small cosmological constant

    NASA Astrophysics Data System (ADS)

    Foot, Robert; Kobakhidze, Archil

    2015-07-01

    We consider scale invariant models where the classical scale invariance is broken perturbatively by radiative corrections at the electroweak scale. These models potentially offer an elegant and simple solution to the hierarchy problem. If we further require the cosmological constant to be small then such models are also highly predictive. Indeed, the minimal such model, comprizing a Higgs doublet and a real singlet, has the same number of parameters as the standard model. Although this minimal model is disfavored by recent LHC data, we show that two specific extensions incorporating neutrino masses and dark matter are fully realistic. That is, consistent with all experiments and observations. These models predict a light pseudo-Goldstone boson, h, with mass around 10 GeV or less. A fermionic-bosonic mass relation is also predicted. The specific models considered, as well as more generic scale invariant models, can be probed at the LHC.

  7. Anisotropic cosmological models in f(G) gravity

    NASA Astrophysics Data System (ADS)

    Farasat Shamir, M.

    2016-04-01

    The main objective of this manuscript is to study the anisotropic universe in f(G) Gravity. For this purpose, locally rotationally symmetric Bianchi type I spacetime is considered. A viable f(G) model is used to explore the exact solutions of modified field equations. In particular, two families involving power law and exponential type solutions have been discussed. Some important cosmological parameters are calculated for the obtained solutions. Moreover, energy density and pressure of the universe is analyzed for the model under consideration.

  8. Constraining interacting dark energy models with latest cosmological observations

    NASA Astrophysics Data System (ADS)

    Xia, Dong-Mei; Wang, Sai

    2016-11-01

    The local measurement of H0 is in tension with the prediction of Λ cold dark matter model based on the Planck data. This tension may imply that dark energy is strengthened in the late-time Universe. We employ the latest cosmological observations on cosmic microwave background, the baryon acoustic oscillation, large-scale structure, supernovae, H(z) and H0 to constrain several interacting dark energy models. Our results show no significant indications for the interaction between dark energy and dark matter. The H0 tension can be moderately alleviated, but not totally released.

  9. Constraining interacting dark energy models with latest cosmological observations

    NASA Astrophysics Data System (ADS)

    Xia, Dong-Mei; Wang, Sai

    2016-08-01

    The local measurement of H0 is in tension with the prediction of ΛCDM model based on the Planck data. This tension may imply that dark energy is strengthened in the late-time Universe. We employ the latest cosmological observations on CMB, BAO, LSS, SNe, H(z) and H0 to constrain several interacting dark energy models. Our results show no significant indications for the interaction between dark energy and dark matter. The H0 tension can be moderately alleviated, but not totally released.

  10. On hyperbolicity violations in cosmological models with vector fields

    SciTech Connect

    Golovnev, Alexey; Klementev, Aleksandr E-mail: sas5292@yandex.ru

    2014-02-01

    Cosmological models with vector fields received much attention in recent years. Unfortunately, most of them are plagued with severe instabilities or other problems. In particular, it was noted in ref. [1] that the models with a non-linear function of the Maxwellian kinetic term do always imply violations of hyperbolicity somewhere in the phase space. In this work we make this statement more precise in several respects and show that those violations may not be present around spatially homogeneous configurations of the vector field.

  11. Anisotropic, nonsingular early universe model leading to a realistic cosmology

    SciTech Connect

    Dechant, Pierre-Philippe; Lasenby, Anthony N.; Hobson, Michael P.

    2009-02-15

    We present a novel cosmological model in which scalar field matter in a biaxial Bianchi IX geometry leads to a nonsingular 'pancaking' solution: the hypersurface volume goes to zero instantaneously at the 'big bang', but all physical quantities, such as curvature invariants and the matter energy density remain finite, and continue smoothly through the big bang. We demonstrate that there exist geodesics extending through the big bang, but that there are also incomplete geodesics that spiral infinitely around a topologically closed spatial dimension at the big bang, rendering it, at worst, a quasiregular singularity. The model is thus reminiscent of the Taub-NUT vacuum solution in that it has biaxial Bianchi IX geometry and its evolution exhibits a dimensionality reduction at a quasiregular singularity; the two models are, however, rather different, as we will show in a future work. Here we concentrate on the cosmological implications of our model and show how the scalar field drives both isotropization and inflation, thus raising the question of whether structure on the largest scales was laid down at a time when the universe was still oblate (as also suggested by [T. S. Pereira, C. Pitrou, and J.-P. Uzan, J. Cosmol. Astropart. Phys. 9 (2007) 6.][C. Pitrou, T. S. Pereira, and J.-P. Uzan, J. Cosmol. Astropart. Phys. 4 (2008) 4.][A. Guemruekcueoglu, C. Contaldi, and M. Peloso, J. Cosmol. Astropart. Phys. 11 (2007) 005.]). We also discuss the stability of our model to small perturbations around biaxiality and draw an analogy with cosmological perturbations. We conclude by presenting a separate, bouncing solution, which generalizes the known bouncing solution in closed FRW universes.

  12. A 2.5D boundary element formulation for modeling damped waves in arbitrary cross-section waveguides and cavities

    SciTech Connect

    Mazzotti, M.; Bartoli, I.; Marzani, A.; Viola, E.

    2013-09-01

    Highlights: •Dispersive properties of viscoelastic waveguides and cavities are computed using a regularized 2.5D BEM. •Linear viscoelasticity is introduced at the constitutive level by means of frequency dependent complex moduli. •A contour integral algorithm is used to solve the nonlinear eigenvalue problem. •The Sommerfeld radiation condition is used to select the permissible Riemann sheets. •Attenuation of surface waves in cavities approaches the attenuation of Rayleigh waves. -- Abstract: A regularized 2.5D boundary element method (BEM) is proposed to predict the dispersion properties of damped stress guided waves in waveguides and cavities of arbitrary cross-section. The wave attenuation, induced by material damping, is introduced using linear viscoelastic constitutive relations and described in a spatial manner by the imaginary component of the axial wavenumber. The discretized dispersive wave equation results in a nonlinear eigenvalue problem, which is solved obtaining complex axial wavenumbers for a fixed frequency using a contour integral algorithm. Due to the singular characteristics and the multivalued feature of the wave equation, the requirement of holomorphicity inside the contour region over the complex wavenumber plane is fulfilled by the introduction of the Sommerfeld branch cuts and by the choice of the permissible Riemann sheets. A post processing analysis is developed for the extraction of the energy velocity of propagative guided waves. The reliability of the method is demonstrated by comparing the results obtained for a rail and a bar with square cross-section with those obtained from a 2.5D Finite Element formulation also known in literature as Semi Analytical Finite Element (SAFE) method. Next, to show the potential of the proposed numerical framework, dispersion properties are predicted for surface waves propagating along cylindrical cavities of arbitrary cross-section. It is demonstrated that the attenuation of surface waves

  13. Cosmological constraints on the modified entropic force model

    NASA Astrophysics Data System (ADS)

    Wei, Hao

    2010-08-01

    Very recently, Verlinde considered a theory in which space is emergent through a holographic scenario, and proposed that gravity can be explained as an entropic force caused by changes in the information associated with the positions of material bodies. Then, motivated by the Debye model in thermodynamics which is very successful in very low temperatures, Gao modified the entropic force scenario. The modified entropic force (MEF) model is in fact a modified gravity model, and the universe can be accelerated without dark energy. In the present work, we consider the cosmological constraints on the MEF model, and successfully constrain the model parameters to a narrow range. We also discuss many other issues of the MEF model. In particular, we clearly reveal the implicit root to accelerate the universe in the MEF model.

  14. A comparison of cosmological models using time delay lenses

    SciTech Connect

    Wei, Jun-Jie; Wu, Xue-Feng; Melia, Fulvio E-mail: xfwu@pmo.ac.cn

    2014-06-20

    The use of time-delay gravitational lenses to examine the cosmological expansion introduces a new standard ruler with which to test theoretical models. The sample suitable for this kind of work now includes 12 lens systems, which have thus far been used solely for optimizing the parameters of ΛCDM. In this paper, we broaden the base of support for this new, important cosmic probe by using these observations to carry out a one-on-one comparison between competing models. The currently available sample indicates a likelihood of ∼70%-80% that the R {sub h} = ct universe is the correct cosmology versus ∼20%-30% for the standard model. This possibly interesting result reinforces the need to greatly expand the sample of time-delay lenses, e.g., with the successful implementation of the Dark Energy Survey, the VST ATLAS survey, and the Large Synoptic Survey Telescope. In anticipation of a greatly expanded catalog of time-delay lenses identified with these surveys, we have produced synthetic samples to estimate how large they would have to be in order to rule out either model at a ∼99.7% confidence level. We find that if the real cosmology is ΛCDM, a sample of ∼150 time-delay lenses would be sufficient to rule out R {sub h} = ct at this level of accuracy, while ∼1000 time-delay lenses would be required to rule out ΛCDM if the real universe is instead R {sub h} = ct. This difference in required sample size reflects the greater number of free parameters available to fit the data with ΛCDM.

  15. A Comparison of Cosmological Models Using Strong Gravitational Lensing Galaxies

    NASA Astrophysics Data System (ADS)

    Melia, Fulvio; Wei, Jun-Jie; Wu, Xue-Feng

    2015-01-01

    Strongly gravitationally lensed quasar-galaxy systems allow us to compare competing cosmologies as long as one can be reasonably sure of the mass distribution within the intervening lens. In this paper, we assemble a catalog of 69 such systems from the Sloan Lens ACS and Lens Structure and Dynamics surveys suitable for this analysis, and carry out a one-on-one comparison between the standard model, ΛCDM, and the {{R}h}=ct universe, which has thus far been favored by the application of model selection tools to other kinds of data. We find that both models account for the lens observations quite well, though the precision of these measurements does not appear to be good enough to favor one model over the other. Part of the reason is the so-called bulge-halo conspiracy that, on average, results in a baryonic velocity dispersion within a fraction of the optical effective radius virtually identical to that expected for the whole luminous-dark matter distribution modeled as a singular isothermal ellipsoid, though with some scatter among individual sources. Future work can greatly improve the precision of these measurements by focusing on lensing systems with galaxies as close as possible to the background sources. Given the limitations of doing precision cosmological testing using the current sample, we also carry out Monte Carlo simulations based on the current lens measurements to estimate how large the source catalog would have to be in order to rule out either model at a ˜ 99.7% confidence level. We find that if the real cosmology is ΛCDM, a sample of ˜ 200 strong gravitational lenses would be sufficient to rule out {{R}h}=ct at this level of accuracy, while ˜ 300 strong gravitational lenses would be required to rule out ΛCDM if the real universe were instead {{R}h}=ct. The difference in required sample size reflects the greater number of free parameters available to fit the data with ΛCDM. We point out that, should the {{R}h}=ct universe eventually emerge as

  16. A comparison of cosmological models using strong gravitational lensing galaxies

    SciTech Connect

    Melia, Fulvio; Wei, Jun-Jie; Wu, Xue-Feng E-mail: jjwei@pmo.ac.cn E-mail: fmelia@email.arizona.edu E-mail: xfwu@pmo.ac.cn

    2015-01-01

    Strongly gravitationally lensed quasar-galaxy systems allow us to compare competing cosmologies as long as one can be reasonably sure of the mass distribution within the intervening lens. In this paper, we assemble a catalog of 69 such systems from the Sloan Lens ACS and Lens Structure and Dynamics surveys suitable for this analysis, and carry out a one-on-one comparison between the standard model, ΛCDM, and the R{sub h}=ct universe, which has thus far been favored by the application of model selection tools to other kinds of data. We find that both models account for the lens observations quite well, though the precision of these measurements does not appear to be good enough to favor one model over the other. Part of the reason is the so-called bulge-halo conspiracy that, on average, results in a baryonic velocity dispersion within a fraction of the optical effective radius virtually identical to that expected for the whole luminous-dark matter distribution modeled as a singular isothermal ellipsoid, though with some scatter among individual sources. Future work can greatly improve the precision of these measurements by focusing on lensing systems with galaxies as close as possible to the background sources. Given the limitations of doing precision cosmological testing using the current sample, we also carry out Monte Carlo simulations based on the current lens measurements to estimate how large the source catalog would have to be in order to rule out either model at a ∼99.7% confidence level. We find that if the real cosmology is ΛCDM, a sample of ∼200 strong gravitational lenses would be sufficient to rule out R{sub h}=ct at this level of accuracy, while ∼300 strong gravitational lenses would be required to rule out ΛCDM if the real universe were instead R{sub h}=ct. The difference in required sample size reflects the greater number of free parameters available to fit the data with ΛCDM. We point out that, should the R{sub h}=ct universe eventually

  17. The novel desmopressin analogue [V4Q5]dDAVP inhibits angiogenesis, tumour growth and metastases in vasopressin type 2 receptor-expressing breast cancer models

    PubMed Central

    GARONA, JUAN; PIFANO, MARINA; ORLANDO, ULISES D.; PASTRIAN, MARIA B.; IANNUCCI, NANCY B.; ORTEGA, HUGO H.; PODESTA, ERNESTO J.; GOMEZ, DANIEL E.; RIPOLL, GISELLE V.; ALONSO, DANIEL F.

    2015-01-01

    Desmopressin (dDAVP) is a safe haemostatic agent with previously reported antitumour activity. It acts as a selective agonist for the V2 vasopressin membrane receptor (V2r) present on tumour cells and microvasculature. The purpose of this study was to evaluate the novel peptide derivative [V4Q5]dDAVP in V2r-expressing preclinical mouse models of breast cancer. We assessed antitumour effects of [V4Q5]dDAVP using human MCF-7 and MDA-MB-231 breast carcinoma cells, as well as the highly metastatic mouse F3II cell line. Effect on in vitro cancer cell growth was evaluated by cell proliferation and clonogenic assays. Cell cycle distribution was analysed by flow cytometry. In order to study the effect of intravenously administered [V4Q5]dDAVP on tumour growth and angiogenesis, breast cancer xenografts were generated in athymic mice. F3II cells were injected into syngeneic mice to evaluate the effect of [V4Q5]dDAVP on spontaneous and experimental metastatic spread. In vitro cytostatic effects of [V4Q5]dDAVP against breast cancer cells were greater than those of dDAVP, and associated with V2r-activated signal transduction and partial cell cycle arrest. In MDA-MB-231 xenografts, [V4Q5]dDAVP (0.3 μg/kg, thrice a week) reduced tumour growth and angiogenesis. Treatment of F3II mammary tumour-bearing immunocompetent mice resulted in complete inhibition of metastatic progression. [V4Q5]dDAVP also displayed greater antimetastatic efficacy than dDAVP on experimental lung colonisation by F3II cells. The novel analogue was well tolerated in preliminary acute toxicology studies, at doses ≥300-fold above that required for anti-angiogenic/antimetastatic effects. Our data establish the preclinical activity of [V4Q5]dDAVP in aggressive breast cancer, providing the rationale for further clinical trials. PMID:25846632

  18. The fractal bubble model with a cosmological constant

    NASA Astrophysics Data System (ADS)

    Viaggiu, Stefano

    2012-02-01

    We generalize the fractal bubble (FB) model, recently proposed in the literature as an alternative to the standard ΛCDM cosmology, to include a non-zero cosmological constant. We retain the same volume partition of voids and walls as the original FB model, and the same matching conditions for null geodesics, but do not include effects associated with a nonuniform time flow arising from differences of quasilocal gravitational energy that may arise in the coarse-graining process. The Buchert equations are written and partially integrated and the asymptotic behavior of the solutions is given. For a universe with Λ = 0, as is the case in the FB model, an initial void fraction with hyperbolic curvature evolves in such a way that it asymptotically fills completely our particle horizon. Conversely, in the presence of a nonvanishing Λ, we show that this does not happen and the voids fill a finite fraction f_{v_{\\infty }}<1, where the value of (1-f_{v_{\\infty }}) is expected to depend on Λ and the initial fraction fvi and also to be small. For its determination, a numerical integration of the equations is necessary. Finally, an interesting prediction of our model is a formula giving a minimum allowed value of present day dark energy as a function of the age of the universe and of the matter and curvature density parameters at our time. To my mother Cristina Pergolini

  19. Towards viable cosmological models of disformal theories of gravity

    NASA Astrophysics Data System (ADS)

    Sakstein, Jeremy

    2015-01-01

    The late-time cosmological dynamics of disformal gravity are investigated using dynamical systems methods. It is shown that in the general case there are no stable attractors that screen fifth forces locally and simultaneously describe a dark energy dominated universe. Viable scenarios have late-time properties that are independent of the disformal parameters and are identical to the equivalent conformal quintessence model. Our analysis reveals that configurations where the Jordan frame metric becomes singular are only reached in the infinite future, thus explaining the natural pathology resistance observed numerically by several previous works. The viability of models where this can happen is discussed in terms of both the cosmological dynamics and local phenomena. We identify a special parameter tuning such that there is a new fixed point that can match the presently observed dark energy density and equation of state. This model is unviable when the scalar couples to the visible sector but may provide a good candidate model for theories where only dark matter is disformally coupled.

  20. Troubles with Quantum Anisotropic Cosmological Models: Loss of Unitarity

    NASA Astrophysics Data System (ADS)

    Alvarenga, F. G.; Batista, A. B.; Fabris, J. C.; Gonçalves, S. V. B.

    2003-09-01

    The anisotropic Bianchi I cosmological model coupled with perfect fluid is quantized in the minisuperspace. The perfect fluid is described by using the Schutz formalism which allows to attribute dynamical degrees of freedom to matter. A Schrödinger-type equation is obtained where the matter variables play the role of time. However, the signature of the kinetic term is hyperbolic. This Schrödinger-like equation is solved and a wave packet is constructed. The norm of the resulting wave function comes out to be time dependent, indicating the loss of unitarity in this model. The loss of unitarity is due to the fact that the effective Hamiltonian is hermitian but not self-adjoint. The expectation value and the bohmian trajectories are evaluated leading to different cosmological scenarios, what is a consequence of the absence of a unitary quantum structure. The consistency of this quantum model is discussed as well as the generality of the absence of unitarity in anisotropic quantum models.

  1. Formation of a ''child'' universe in an inflationary cosmological model

    SciTech Connect

    Holcomb, K.A.; Park, S.J.; Vishniac, E.T.

    1989-02-15

    The evolution of a flat, spherically symmetric cosmological model, containing radiation and an inhomogeneous scalar field, is simulated numerically to determine whether the inhomogeneity could cause a ''child'' universe, connected by a wormhole to the external universe, to form. The gravitational and field quantities were computed self-consistently by means of the techniques of numerical relativity. Although we were unable to follow the process to its completion, preliminary indications are that the ''budding'' phenomenon could occur under very general initial conditions, as long as the scalar field is sufficiently inhomogeneous that the wormhole forms before the inflation is damped by the expansion of the background spacetime.

  2. Constraints on cosmological models from strong gravitational lensing systems

    SciTech Connect

    Cao, Shuo; Pan, Yu; Zhu, Zong-Hong; Biesiada, Marek; Godlowski, Wlodzimierz E-mail: panyu@cqupt.edu.cn E-mail: godlowski@uni.opole.pl

    2012-03-01

    Strong lensing has developed into an important astrophysical tool for probing both cosmology and galaxies (their structure, formation, and evolution). Using the gravitational lensing theory and cluster mass distribution model, we try to collect a relatively complete observational data concerning the Hubble constant independent ratio between two angular diameter distances D{sub ds}/D{sub s} from various large systematic gravitational lens surveys and lensing by galaxy clusters combined with X-ray observations, and check the possibility to use it in the future as complementary to other cosmological probes. On one hand, strongly gravitationally lensed quasar-galaxy systems create such a new opportunity by combining stellar kinematics (central velocity dispersion measurements) with lensing geometry (Einstein radius determination from position of images). We apply such a method to a combined gravitational lens data set including 70 data points from Sloan Lens ACS (SLACS) and Lens Structure and Dynamics survey (LSD). On the other hand, a new sample of 10 lensing galaxy clusters with redshifts ranging from 0.1 to 0.6 carefully selected from strong gravitational lensing systems with both X-ray satellite observations and optical giant luminous arcs, is also used to constrain three dark energy models (ΛCDM, constant w and CPL) under a flat universe assumption. For the full sample (n = 80) and the restricted sample (n = 46) including 36 two-image lenses and 10 strong lensing arcs, we obtain relatively good fitting values of basic cosmological parameters, which generally agree with the results already known in the literature. This results encourages further development of this method and its use on larger samples obtained in the future.

  3. Dynamics and phenomenology of higher order gravity cosmological models

    NASA Astrophysics Data System (ADS)

    Moldenhauer, Jacob Andrew

    2010-10-01

    I present here some new results about a systematic approach to higher-order gravity (HOG) cosmological models. The HOG models are derived from curvature invariants that are more general than the Einstein-Hilbert action. Some of the models exhibit late-time cosmic acceleration without the need for dark energy and fit some current observations. The open question is that there are an infinite number of invariants that one could select, and many of the published papers have stressed the need to find a systematic approach that will allow one to study methodically the various possibilities. We explore a new connection that we made between theorems from the theory of invariants in general relativity and these cosmological models. In summary, the theorems demonstrate that curvature invariants are not all independent from each other and that for a given Ricci Segre type and Petrov type (symmetry classification) of the space-time, there exists a complete minimal set of independent invariants (a basis) in terms of which all the other invariants can be expressed. As an immediate consequence of the proposed approach, the number of invariants to consider is dramatically reduced from infinity to four invariants in the worst case and to only two invariants in the cases of interest, including all Friedmann-Lemaitre-Robertson-Walker metrics. We derive models that pass stability and physical acceptability conditions. We derive dynamical equations and phase portrait analyses that show the promise of the systematic approach. We consider observational constraints from magnitude-redshift Supernovae Type Ia data, distance to the last scattering surface of the Cosmic Microwave Background radiation, and Baryon Acoustic Oscillations. We put observational constraints on general HOG models. We constrain different forms of the Gauss-Bonnet, f(G), modified gravity models with these observations. We show some of these models pass solar system tests. We seek to find models that pass physical and

  4. Loop quantum cosmology of k=1 FRW models

    SciTech Connect

    Ashtekar, Abhay; Pawlowski, Tomasz; Singh, Parampreet; Vandersloot, Kevin

    2007-01-15

    The closed, k=1, FRW model coupled to a massless scalar field is investigated in the framework of loop quantum cosmology using analytical and numerical methods. As in the k=0 case, the scalar field can be again used as emergent time to construct the physical Hilbert space and introduce Dirac observables. The resulting framework is then used to address a major challenge of quantum cosmology: resolving the big-bang singularity while retaining agreement with general relativity at large scales. It is shown that the framework fulfills this task. In particular, for states which are semiclassical at some late time, the big bang is replaced by a quantum bounce and a recollapse occurs at the value of the scale factor predicted by classical general relativity. Thus, the 'difficulties' pointed out by Green and Unruh in the k=1 case do not arise in a more systematic treatment. As in k=0 models, quantum dynamics is deterministic across the deep Planck regime. However, because it also retains the classical recollapse, in contrast to the k=0 case one is now led to a cyclic model. Finally, we clarify some issues raised by Laguna's recent work addressed to computational physicists.

  5. Nonsingular ekpyrotic/cyclic model in loop quantum cosmology

    SciTech Connect

    Cailleteau, Thomas; Singh, Parampreet; Vandersloot, Kevin

    2009-12-15

    We study the role of nonperturbative quantum gravity effects in the ekpyrotic/cyclic model using the effective framework of loop quantum cosmology in the presence of anisotropies. We show that quantum geometric modifications to the dynamical equations near the Planck scale as understood in the quantization of Bianchi-I spacetime in loop quantum cosmology lead to the resolution of classical singularity and result in a nonsingular transition of the Universe from the contracting to the expanding branch. In the Planck regime, the Universe undergoes multiple small bounces and the anisotropic shear remains bounded throughout the evolution. A novel feature, which is absent for isotropic models, is a natural turn-around of the moduli field from the negative region of the potential leading to a cyclic phenomena as envisioned in the original paradigm. Our work suggests that incorporation of quantum gravitational effects in the ekpyrotic/cyclic model may lead to a viable scenario without any violation of the null energy condition.

  6. Cosmological constant from the ghost: A toy model

    SciTech Connect

    Urban, Federico R.; Zhitnitsky, Ariel R.

    2009-09-15

    We suggest that the solution to the cosmological vacuum energy puzzle is linked to the infrared sector of the effective theory of gravity interacting with standard model fields. We propose a specific solvable two dimensional model where our proposal can be explicitly tested. We analyze the 2d Schwinger model on a 2-torus and in curved 2d space, mostly exploiting the properties of its topological susceptibility, its links with the nontrivial topology or deviations from spacetime flatness, and its relations to the real 4d world. The Kogut-Susskind ghost (which is a direct analogue of the Veneziano ghost in 4d) on a 2-torus and in curved 2d space plays a crucial role in the computation of the vacuum energy. The departure from Minkowski flatness, which is defined as the cosmological constant in our framework, is found to scale as 1/L, where L is the linear size of the torus. Therefore, in spite of the fact that the physical sector of 2d QED is represented by a single massive scalar particle, the deviation from Minkowski space is linear in L rather than exponentially suppressed as one could naievely expect.

  7. Cosmological constant from the ghost: A toy model

    NASA Astrophysics Data System (ADS)

    Urban, Federico R.; Zhitnitsky, Ariel R.

    2009-09-01

    We suggest that the solution to the cosmological vacuum energy puzzle is linked to the infrared sector of the effective theory of gravity interacting with standard model fields. We propose a specific solvable two dimensional model where our proposal can be explicitly tested. We analyze the 2d Schwinger model on a 2-torus and in curved 2d space, mostly exploiting the properties of its topological susceptibility, its links with the nontrivial topology or deviations from spacetime flatness, and its relations to the real 4d world. The Kogut-Susskind ghost (which is a direct analogue of the Veneziano ghost in 4d) on a 2-torus and in curved 2d space plays a crucial role in the computation of the vacuum energy. The departure from Minkowski flatness, which is defined as the cosmological constant in our framework, is found to scale as 1/L, where L is the linear size of the torus. Therefore, in spite of the fact that the physical sector of 2d QED is represented by a single massive scalar particle, the deviation from Minkowski space is linear in L rather than exponentially suppressed as one could naïvely expect.

  8. New model of axion monodromy inflation and its cosmological implications

    NASA Astrophysics Data System (ADS)

    Cai, Yi-Fu; Chen, Fang; Ferreira, Elisa G. M.; Quintin, Jerome

    2016-06-01

    We propose a new realization of axion monodromy inflation in which axion monodromy arises from torsional cycles in a type IIB compactification. A class of monomial potentials is obtained with specific values for the power index. Moreover, the inflaton mass changes profile due to the couplings between various fields after compactification. Consequently, the potential obtains a step-like profile at some critical scale. We study the cosmological implications of one concrete realization of this model. At the background level, it realizes a sufficiently long inflationary stage, which allows for the violation of the slow-roll conditions for a short period of time when the inflaton is close to the critical scale. Accordingly, the Hubble horizon is perturbed and affects the dynamics of primordial cosmological perturbations. In particular, we analyze the angular power spectrum of B-mode polarization and find a boost on very large scales. We also find that the amplitude of scalar perturbations is suppressed near the critical scale. Thus our model provides an interpretation for the low-l suppression of temperature anisotropies in the CMB power spectrum. We examine these effects and confront the model to observations.

  9. Loop quantum cosmology in Bianchi type I models: Analytical investigation

    SciTech Connect

    Chiou, D.-W.

    2007-01-15

    The comprehensive formulation for loop quantum cosmology in the spatially flat, isotropic model was recently constructed. In this paper, the methods are extended to the anisotropic Bianchi I cosmology. Both the precursor and the improved strategies are applied and the expected results are established: (i) the scalar field again serves as an internal clock and is treated as emergent time; (ii) the total Hamiltonian constraint is derived by imposing the fundamental discreteness and gives the evolution as a difference equation; and (iii) the physical Hilbert space, Dirac observables, and semiclassical states are constructed rigorously. It is also shown that the state in the kinematical Hilbert space associated with the classical singularity is decoupled in the difference evolution equation, indicating that the big bounce may take place when any of the area scales undergoes the vanishing behavior. The investigation affirms the robustness of the framework used in the isotropic model by enlarging its domain of validity and provides foundations to conduct the detailed numerical analysis.

  10. Shear-free anisotropic cosmological models in {f (R)} gravity

    NASA Astrophysics Data System (ADS)

    Abebe, Amare; Momeni, Davood; Myrzakulov, Ratbay

    2016-04-01

    We study a class of shear-free, homogeneous but anisotropic cosmological models with imperfect matter sources in the context of f( R) gravity. We show that the anisotropic stresses are related to the electric part of the Weyl tensor in such a way that they balance each other. We also show that within the class of orthogonal f( R) models, small perturbations of shear are damped, and that the electric part of the Weyl tensor and the anisotropic stress tensor decay with the expansion as well as the heat flux of the curvature fluid. Specializing in locally rotationally symmetric spacetimes in orthonormal frames, we examine the late-time behaviour of the de Sitter universe in f( R) gravity. For the Starobinsky model of f( R), we study the evolutionary behavior of the Universe by numerically integrating the Friedmann equation, where the initial conditions for the expansion, acceleration and jerk parameters are taken from observational data.

  11. Quintessence models and the cosmological evolution of {alpha}

    SciTech Connect

    Lee, Seokcheon; Olive, Keith A.; Pospelov, Maxim

    2004-10-15

    The cosmological evolution of a quintessencelike scalar field {phi} coupled to matter and gauge fields leads to effective modifications of the coupling constants and particle masses over time. We analyze a class of models where the scalar field potential V({phi}) and the couplings to matter B({phi}) admit common extremum in {phi}, as in the Damour-Polyakov ansatz. We find that even for the simplest choices of potentials and B({phi}), the observational constraints on {delta}{alpha}/{alpha} coming from quasar absorption spectra, the Oklo phenomenon and Big Bang nucleosynthesis provide complementary constraints on the parameters of the model. We show the evolutionary history of these models in some detail and describe the effects of a varying mass for dark matter.

  12. Quintessence models and the cosmological evolution of α

    NASA Astrophysics Data System (ADS)

    Lee, Seokcheon; Olive, Keith A.; Pospelov, Maxim

    2004-10-01

    The cosmological evolution of a quintessencelike scalar field ϕ coupled to matter and gauge fields leads to effective modifications of the coupling constants and particle masses over time. We analyze a class of models where the scalar field potential V(ϕ) and the couplings to matter B(ϕ) admit common extremum in ϕ, as in the Damour-Polyakov ansatz. We find that even for the simplest choices of potentials and B(ϕ), the observational constraints on Δα/α coming from quasar absorption spectra, the Oklo phenomenon and Big Bang nucleosynthesis provide complementary constraints on the parameters of the model. We show the evolutionary history of these models in some detail and describe the effects of a varying mass for dark matter.

  13. Investigating cosmological distances as a function of the red-shift in the Szekeres inhomogeneous cosmological models

    NASA Astrophysics Data System (ADS)

    Nwankwo, Anthony Chukwuemeka

    2011-09-01

    The interpretation of cosmological observations depends on the choice of a cosmological model. One must choose a cosmological model, calculate the observables in the chosen cosmological model and then confront the results of the calculations with the data. Cosmological observations are made on the past null cone, which involve observation of luminosities and red-shifts of astrophysical objects like distant supernovae in the universe. The physical characteristics of these observed objects such as the red-shift and the magnitudes are dependent on the space-time in which they travelled through to reach the observer, and thus choosing the correct model of the universe is of crucial importance in the interpretation of cosmological observations. The universe has been observed to be inhomogeneous on scales that can affect observed quantities such as area distance, luminosity distance and red-shift. Because of this, it is necessary to use cosmological models that can take into account the observed inhomogeneities to study the universe such as the Szekeres inhomogeneous models and computing observable quantities in the Szekeres model is a non-trivial problem, more specifically computing the area distance in general requires one to compute the partial derivatives of the null vector components. The goal of this dissertation is to derive observables in the Szekeres models in all generality. For the general space-time, an analytical expression for the null vector components is not known and thus computing the partial derivatives of the null vector components is not straight-forward. In this dissertation, we will show a new method to compute these partial derivatives in the Szekeres inhomogeneous models and use them to derive and calculate cosmological distances. Using the computed partial derivatives of the null vector components, we will then compute for the first time in the history of the Szekeres inhomogeneous models, the area distance for the case where the Szekeres model

  14. Cylindrically symmetric inhomogeneous cosmological models with viscous fluid and varying Λ

    NASA Astrophysics Data System (ADS)

    Pradhan, Anirudh; Singh, Prashant Kumar; Jotania, R. Kanti

    2006-06-01

    Cylindrically symmetric non-static cosmological models representing a bulk viscous fluid distribution have been obtained which are inhomogeneous and anisotropic. Without assuming any adhoc law, we obtain a cosmological constant as a decreasing function of time. Various physical and geometrical features of the models are also discussed.

  15. Adiabatic density perturbations in a cosmological model with massive neutrinos

    NASA Astrophysics Data System (ADS)

    Jaroszynski, M.

    Lifshitz (1946) has investigated the gravitational instability of a Friedmann Universe model. He treated the matter content of the universe as a single perfect fluid. In other studies, a two fluid approach was used to represent neutrinos and other kinds of matter separately. A distribution function was used by Peebles and Yu (1970), and also by Silk and Wilson (1980) to describe photons of the black-body background during and after the recombination of the primeval plasma. The approach used in the present investigation is similar, except for two differences. No collisional term is used in the kinetic equation, and massive particles are considered. A detailed description is provided of the method used to investigate the gravitational instability of a cosmological model with massive neutrinos. It is pointed out that the obtained results are preliminary. The final spectrum of perturbations is similar to those of Peebles and Yu (1970), and Wilson and Silk (1981).

  16. Model of cosmology and particle physics at an intermediate scale

    SciTech Connect

    Bastero-Gil, M.; Di Clemente, V.; King, S. F.

    2005-05-15

    We propose a model of cosmology and particle physics in which all relevant scales arise in a natural way from an intermediate string scale. We are led to assign the string scale to the intermediate scale M{sub *}{approx}10{sup 13} GeV by four independent pieces of physics: electroweak symmetry breaking; the {mu} parameter; the axion scale; and the neutrino mass scale. The model involves hybrid inflation with the waterfall field N being responsible for generating the {mu} term, the right-handed neutrino mass scale, and the Peccei-Quinn symmetry breaking scale. The large scale structure of the Universe is generated by the lightest right-handed sneutrino playing the role of a coupled curvaton. We show that the correct curvature perturbations may be successfully generated providing the lightest right-handed neutrino is weakly coupled in the seesaw mechanism, consistent with sequential dominance.

  17. nIFTy cosmology: comparison of galaxy formation models

    NASA Astrophysics Data System (ADS)

    Knebe, Alexander; Pearce, Frazer R.; Thomas, Peter A.; Benson, Andrew; Blaizot, Jeremy; Bower, Richard; Carretero, Jorge; Castander, Francisco J.; Cattaneo, Andrea; Cora, Sofia A.; Croton, Darren J.; Cui, Weiguang; Cunnama, Daniel; De Lucia, Gabriella; Devriendt, Julien E.; Elahi, Pascal J.; Font, Andreea; Fontanot, Fabio; Garcia-Bellido, Juan; Gargiulo, Ignacio D.; Gonzalez-Perez, Violeta; Helly, John; Henriques, Bruno; Hirschmann, Michaela; Lee, Jaehyun; Mamon, Gary A.; Monaco, Pierluigi; Onions, Julian; Padilla, Nelson D.; Power, Chris; Pujol, Arnau; Skibba, Ramin A.; Somerville, Rachel S.; Srisawat, Chaichalit; Vega-Martínez, Cristian A.; Yi, Sukyoung K.

    2015-08-01

    We present a comparison of 14 galaxy formation models: 12 different semi-analytical models and 2 halo occupation distribution models for galaxy formation based upon the same cosmological simulation and merger tree information derived from it. The participating codes have proven to be very successful in their own right but they have all been calibrated independently using various observational data sets, stellar models, and merger trees. In this paper, we apply them without recalibration and this leads to a wide variety of predictions for the stellar mass function, specific star formation rates, stellar-to-halo mass ratios, and the abundance of orphan galaxies. The scatter is much larger than seen in previous comparison studies primarily because the codes have been used outside of their native environment within which they are well tested and calibrated. The purpose of the `nIFTy comparison of galaxy formation models' is to bring together as many different galaxy formation modellers as possible and to investigate a common approach to model calibration. This paper provides a unified description for all participating models and presents the initial, uncalibrated comparison as a baseline for our future studies where we will develop a common calibration framework and address the extent to which that reduces the scatter in the model predictions seen here.

  18. Gravitational radiation in Bianchi Type V cosmological models

    SciTech Connect

    Hogan, P.A.

    1988-01-01

    This paper is concerned with the development of the theory of embedding gravitational radiation fields in expanding universes pioneered by Hawking. The problem of embedding such fields in the expanding Friedmann-Lemaitre-Robertson-Walker dust-filled universe, considered by Hawking, is reexamined in a new formalism which permits an easy analysis, in particular, of the relationship between the boundary conditions and the satisfaction, by the Weyl tensor, of the conventional peeling-off behavior. Since gravity wave detectors are expected to pick up plane-fronted gravitational waves, the main thrust of this paper concerns the development of a formulation of Bianchi Type V cosmological models which enables the embedding of such plane-fronted waves to be carried out. This is worked out explicitly in the case of a perfect fluid, with pressure proportional to energy density, and with the histories of the fluid particles orthogonal to the surfaces of homogeneity. 18 references.

  19. Cosmological Baryogenesis in Superstring Models with Stable Protons

    NASA Astrophysics Data System (ADS)

    Campbell, B. A.; Ellis, J.; Nanopoulos, D. V.; Olive, K. A.

    We discuss cosmological baryogenesis in phenomenological low-energy models inspired by the superstring which have an unobservably long baryon lifetime. The Affleck-Dine mechanism of baryogenesis in a cold (≲104 GeV) universe is shown to be feasible, with a large baryon density being produced by the decays of large expectation values for squark and slepton fields after inflation. We catalogue the gauge-invariant quartic scalar operators in the low-energy effective action which could appear once supersymmetry is broken, show that the D-terms in the potential can vanish, and discuss the possibility that the F-terms have flat directions allowing large values for these scalar fields.

  20. A no hair theorem and the problem of initial conditions. [in cosmological model

    NASA Technical Reports Server (NTRS)

    Jensen, Lars Gerhard; Stein-Schabes, Jaime A.

    1987-01-01

    It is shown that under very general conditions, any inhomogeneous cosmological model with a positive cosmological constant that can be described in a synchronous reference system will tend asymptotically in time towards the de Sitter solution. This renders the problem of initial conditions less severe.

  1. Some Cosmological Models for Poincare Gauge Gravity and Accelerated Expansion of the Universe

    SciTech Connect

    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.

  2. Halo model and halo properties in Galileon gravity cosmologies

    SciTech Connect

    Barreira, Alexandre; Li, Baojiu; Hellwing, Wojciech A.; Baugh, Carlton M.; Lombriser, Lucas; Pascoli, Silvia E-mail: baojiu.li@durham.ac.uk E-mail: llo@roe.ac.uk E-mail: silvia.pascoli@durham.ac.uk

    2014-04-01

    We investigate the performance of semi-analytical modelling of large-scale structure in Galileon gravity cosmologies using results from N-body simulations. We focus on the Cubic and Quartic Galileon models that provide a reasonable fit to CMB, SNIa and BAO data. We demonstrate that the Sheth-Tormen mass function and linear halo bias can be calibrated to provide a very good fit to our simulation results. We also find that the halo concentration-mass relation is well fitted by a power law. The nonlinear matter power spectrum computed in the halo model approach is found to be inaccurate in the mildly nonlinear regime, but captures reasonably well the effects of the Vainshtein screening mechanism on small scales. In the Cubic model, the screening mechanism hides essentially all of the effects of the fifth force inside haloes. In the case of the Quartic model, the screening mechanism leaves behind residual modifications to gravity, which make the effective gravitational strength time-varying and smaller than the standard value. Compared to normal gravity, this causes a deficiency of massive haloes and leads to a weaker matter clustering on small scales. For both models, we show that there are realistic halo occupation distributions of Luminous Red Galaxies that can match both the observed large-scale clustering amplitude and the number density of these galaxies.

  3. Bianchi Type VI0 Inflationary Cosmological Model in General Relativity

    NASA Astrophysics Data System (ADS)

    Bali, Raj; Poonia, Laxmi

    Bianchi Type VI0 inflationary cosmological model with flat potential in General Relativity, is investigated. To get the deterministic solution in terms of cosmic time t, we assume that σ (shear) is proportional to expansion (θ) where σ = {1 / {√ 3 }}t( {{{{A}{4} } / {A}} - {{{B}{4} } / {B}}}), θ = {{{A}{4} } / {A}} + {{{2B}{4} } / {B}}. Thus {{σ / θ } = constant}, leads to A = Bn where A and B are metric potentials and n is a constant. We find that spatial volume increases with time. Hence inflationary scenario exists in the model. Since {σ / θ } != 0 in general. Thus the model represents anisotropic universe throughout. However, if l = {1 / {{4k}}} then the model isotropizes. This result matches with astronomical observations. The model represents decelerating and late time acceleration which matches with recent astronomical observations Riess et al. [29], Perlmutter et al. [30]. The model has Point Type singularity at τ = {1 / α }{sin}{ - 1} ({{1 / {{2k}}}} ) (MacCallum [31]). The rate of Higg’s field (φ) decreases with time.

  4. Short Wavelength Electromagnetic Perturbations Excited Near the Solar Probe Plus Spacecraft in the Inner Heliosphere: 2.5D Hybrid Modeling

    NASA Technical Reports Server (NTRS)

    Lipatov, Alexander S.; Sittler, Edward C.; Hartle, Richard E.; Cooper, John F.

    2011-01-01

    A 2.5D numerical plasma model of the interaction of the solar wind (SW) with the Solar Probe Plus spacecraft (SPPSC) is presented. These results should be interpreted as a basic plasma model derived from the SW-interaction with the spacecraft (SC), which could have consequences for both plasma wave and electron plasma measurements on board the SC in the inner heliosphere. Compression waves and electric field jumps with amplitudes of about 1.5 V/m and (12-18) V/m were also observed. A strong polarization electric field was also observed in the wing of the plasma wake. However, 2.5D hybrid modeling did not show excitation of whistler/Alfven waves in the upstream connected with the bidirectional current closure that was observed in short-time 3D modeling SPPSC and near a tether in the ionosphere. The observed strong electromagnetic perturbations may be a crucial point in the electromagnetic measurements planned for the future Solar Probe Plus (SPP) mission. The results of modeling electromagnetic field perturbations in the SW due to shot noise in absence of SPPSC are also discussed.

  5. Two-fluid 2.5D MHD model of the fast solar wind and the effective proton temperature

    NASA Astrophysics Data System (ADS)

    Ofman, L.; Davila, J. M.

    1999-06-01

    Recent SOHO/UVCS observations indicate that the perpendicular proton and ion temperatures are much larger than electron temperatures (Kohl et al. 1997). In the present study we simulate numerically the solar wind flow in a coronal hole with the two-fluid approach. For simplicity, we neglect electron inertia. We investigate the effects of electron and proton temperatures on the solar wind acceleration by nonlinear waves. In the model the nonlinear waves are generated by Alfvén waves with frequencies in the 10-3 Hz range, driven at the base of the coronal hole. The resulting electron and proton flow profile exhibits density and velocity fluctuations. The fluctuations may steepen into shocks as they propagate away from the sun. We construct the proton velocity distribution and a synthetic Ly-α line profile by including the combined effects of temperature and velocity fluctuations in the model, and compare them to the UVCS observations.

  6. Spectral action models of gravity on packed swiss cheese cosmology

    NASA Astrophysics Data System (ADS)

    Ball, Adam; Marcolli, Matilde

    2016-06-01

    We present a model of (modified) gravity on spacetimes with fractal structure based on packing of spheres, which are (Euclidean) variants of the packed swiss cheese cosmology models. As the action functional for gravity we consider the spectral action of noncommutative geometry, and we compute its expansion on a space obtained as an Apollonian packing of three-dimensional spheres inside a four-dimensional ball. Using information from the zeta function of the Dirac operator of the spectral triple, we compute the leading terms in the asymptotic expansion of the spectral action. They consist of a zeta regularization of the divergent sum of the leading terms of the spectral actions of the individual spheres in the packing. This accounts for the contribution of points 1 and 3 in the dimension spectrum (as in the case of a 3-sphere). There is an additional term coming from the residue at the additional point in the real dimension spectrum that corresponds to the packing constant, as well as a series of fluctuations coming from log-periodic oscillations, created by the points of the dimension spectrum that are off the real line. These terms detect the fractality of the residue set of the sphere packing. We show that the presence of fractality influences the shape of the slow-roll potential for inflation, obtained from the spectral action. We also discuss the effect of truncating the fractal structure at a certain scale related to the energy scale in the spectral action.

  7. 2.5D global-disk oscillation models of the Be shell star ζ Tauri. I. Spectroscopic and polarimetric analysis

    NASA Astrophysics Data System (ADS)

    Escolano, C.; Carciofi, A. C.; Okazaki, A. T.; Rivinius, T.; Baade, D.; Štefl, S.

    2015-04-01

    Context. A large number of Be stars exhibit intensity variations of their violet and red emission peaks in their H i lines observed in emission. This is the so-called V/R phenomenon, usually explained by the precession of a one-armed spiral density perturbation in the circumstellar disk. That global-disk oscillation scenario was confirmed, both observationally and theoretically, in the previous series of two papers analyzing the Be shell star ζ Tauri. The vertically averaged (2D) global-disk oscillation model used at the time was able to reproduce the V/R variations observed in Hα, as well as the spatially resolved interferometric data from AMBER/VLTI. Unfortunately, that model failed to reproduce the V/R phase of Br15 and the amplitude of the polarization variation, suggesting that the inner disk structure predicted by the model was incorrect. Aims: The first aim of the present paper is to quantify the temporal variations of the shell-line characteristics of ζ Tauri. The second aim is to better understand the physics underlying the V/R phenomenon by modeling the shell-line variations together with the V/R and polarimetric variations. The third aim is to test a new 2.5D disk oscillation model, which solves the set of equations that describe the 3D perturbed disk structure but keeps only the equatorial (i.e., 2D) component of the solution. This approximation was adopted to allow comparisons with the previous 2D model, and as a first step toward a future 3D model. Methods: We carried out an extensive analysis of ζ Tauri's spectroscopic variations by measuring various quantities characterizing its Balmer line profiles: red and violet emission peak intensities (for Hα, Hβ, and Br15), depth and asymmetry of the shell absorption (for Hβ, Hγ, and Hδ), and the respective position (i.e., radial velocity) of each component. We attempted to model the observed variations by implementing in the radiative transfer code HDUST the perturbed disk structure computed with a

  8. High cell density culture with S. cerevisiae CEN.PK113-5D for IL-1β production: optimization, modeling, and physiological aspects.

    PubMed

    Landi, Carmine; Paciello, Lucia; de Alteriis, Elisabetta; Brambilla, Luca; Parascandola, Palma

    2015-02-01

    Saccharomyces cerevisiae CEN.PK113-5D, a strain auxotrophic for uracil belonging to the CEN.PK family of the yeast S. cerevisiae, was cultured in aerated fed-batch reactor as such and once transformed to express human interleukin-1β (IL-1β), aiming at obtaining high cell densities and optimizing IL-1β production. Three different exponentially increasing glucose feeding profiles were tested, all of them "in theory" promoting respiratory metabolism to obtain high biomass/product yield. A non-structured non-segregated model was developed to describe the performance of S. cerevisiae CEN.PK113-5D during the fed-batch process and, in particular, its capability to metabolize simultaneously glucose and ethanol which derived from the precedent batch growth. Our study showed that the proliferative capacity of the yeast population declined along the fed-batch run, as shown by the exponentially decreasing specific growth rates on glucose. Further, a shift towards fermentative metabolism occurred. This shift took place earlier the higher was the feed rate and was more pronounced in the case of the recombinant strain. Determination of some physiological markers (acetate production, intracellular ROS accumulation, catalase activity and cell viability) showed that neither poor oxygenation nor oxidative stress was responsible for the decreased specific growth rate, nor for the shift to fermentative metabolism.

  9. High cell density culture with S. cerevisiae CEN.PK113-5D for IL-1β production: optimization, modeling, and physiological aspects.

    PubMed

    Landi, Carmine; Paciello, Lucia; de Alteriis, Elisabetta; Brambilla, Luca; Parascandola, Palma

    2015-02-01

    Saccharomyces cerevisiae CEN.PK113-5D, a strain auxotrophic for uracil belonging to the CEN.PK family of the yeast S. cerevisiae, was cultured in aerated fed-batch reactor as such and once transformed to express human interleukin-1β (IL-1β), aiming at obtaining high cell densities and optimizing IL-1β production. Three different exponentially increasing glucose feeding profiles were tested, all of them "in theory" promoting respiratory metabolism to obtain high biomass/product yield. A non-structured non-segregated model was developed to describe the performance of S. cerevisiae CEN.PK113-5D during the fed-batch process and, in particular, its capability to metabolize simultaneously glucose and ethanol which derived from the precedent batch growth. Our study showed that the proliferative capacity of the yeast population declined along the fed-batch run, as shown by the exponentially decreasing specific growth rates on glucose. Further, a shift towards fermentative metabolism occurred. This shift took place earlier the higher was the feed rate and was more pronounced in the case of the recombinant strain. Determination of some physiological markers (acetate production, intracellular ROS accumulation, catalase activity and cell viability) showed that neither poor oxygenation nor oxidative stress was responsible for the decreased specific growth rate, nor for the shift to fermentative metabolism. PMID:25106469

  10. Cosmological perturbations in coherent oscillating scalar field models

    NASA Astrophysics Data System (ADS)

    Cembranos, J. A. R.; Maroto, A. L.; Jareño, S. J. Núñez

    2016-03-01

    The fact that fast oscillating homogeneous scalar fields behave as perfect fluids in average and their intrinsic isotropy have made these models very fruitful in cosmology. In this work we will analyse the perturbations dynamics in these theories assuming general power law potentials V( ϕ) = λ| ϕ| n /n. At leading order in the wavenumber expansion, a simple expression for the effective sound speed of perturbations is obtained c eff 2 = ω = ( n - 2)/( n + 2) with ω the effective equation of state. We also obtain the first order correction in k 2/ ω eff 2 , when the wavenumber k of the perturbations is much smaller than the background oscillation frequency, ω eff. For the standard massive case we have also analysed general anharmonic contributions to the effective sound speed. These results are reached through a perturbed version of the generalized virial theorem and also studying the exact system both in the super-Hubble limit, deriving the natural ansatz for δϕ; and for sub-Hubble modes, exploiting Floquet's theorem.

  11. Electromagnetic quantum effects in higher-dimensional cosmological models

    NASA Astrophysics Data System (ADS)

    Kotanjyan, Anna; Sargsyan, Hayk; Simonyan, David; Saharian, Aram

    2016-07-01

    Among the most interesting directions in quantum field theory on curved spacetimes is the investigation of the influence of the gravitational field on the properties of the quantum vacuum. The corresponding problems are exactly solvable for highly symmetric background geometries only. In particular, the investigations of quantum effects in de Sitter (dS) and anti-de Sitter (AdS) spacetimes have attracted a great deal of attention. We consider electromagnetic quantum effects in higher-dimensional cosmological models. The two-point functions of the vector potential and of the field tensor for the electromagnetic field in background of dS and AdS spacetime are evaluated in arbitrary number of spatial dimensions. First we consider the two-point functions in the boundary-free geometry and then generalize the results in the presence of a reflecting boundary, for AdS spacetimes parallel to the AdS horizon. By using the expressions for the two-point functions of the field tensor, we investigate the vacuum expectation values of the electric field squared and of the energy-momentum tensor. Simple asymptotic expressions are provided for both cases, in particular for AdS geometry near the AdS boundary and horizon.

  12. Five dimensional FRW cosmological models in a scalar-tensor theory of gravitation

    NASA Astrophysics Data System (ADS)

    Rao, V. U. M.; PapaRao, D. C.; Reddy, D. R. K.

    2015-06-01

    A five dimensional FRW cosmological space-time is considered in the scalar-tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 2003) in the presence of a perfect fluid source. Cosmological models corresponding to stiff fluid, disordered radiation, dust and false vacuum are obtained. Some physical and kinematical properties of each of the models are also studied.

  13. Baryon isocurvature scenario in inflationary cosmology - A particle physics model and its astrophysical implications

    NASA Technical Reports Server (NTRS)

    Yokoyama, Jun'ichi; Suto, Yasushi

    1991-01-01

    A phenomenological model to produce isocurvature baryon-number fluctuations is proposed in the framework of inflationary cosmology. The resulting spectrum of density fluctuation is very different from the conventional Harrison-Zel'dovich shape. The model, with the parameters satisfying several requirements from particle physics and cosmology, provides an appropriate initial condition for the minimal baryon isocurvature scenario of galaxy formation discussed by Peebles.

  14. Simple inflationary models in Gauss-Bonnet brane-world cosmology

    NASA Astrophysics Data System (ADS)

    Okada, Nobuchika; Okada, Satomi

    2016-06-01

    In light of the recent Planck 2015 results for the measurement of the cosmic microwave background (CMB) anisotropy, we study simple inflationary models in the context of the Gauss-Bonnet (GB) brane-world cosmology. The brane-world cosmological effect modifies the power spectra of scalar and tensor perturbations generated by inflation and causes a dramatic change for the inflationary predictions of the spectral index (n s) and the tensor-to-scalar ratio (r) from those obtained in the standard cosmology. In particular, the predicted r values in the inflationary models favored by the Planck 2015 results are suppressed due to the GB brane-world cosmological effect, which is in sharp contrast with inflationary scenario in the Randall-Sundrum brane-world cosmology, where the r values are enhanced. Hence, these two brane-world cosmological scenarios are distinguishable. With the dramatic change of the inflationary predictions, the inflationary scenario in the GB brane-world cosmology can be tested by more precise measurements of n s and future observations of the CMB B-mode polarization.

  15. 2.5D Quantitative Millimeter Wave Imaging of a Hidden Object on a Simplified Human Body Model Using Value Picking Regularization

    NASA Astrophysics Data System (ADS)

    van den Bulcke, Sara; Franchois, Ann; de Zutter, Daniel

    2010-12-01

    In this contribution, the authors provide a proof of principle for quantitative imaging of concealed objects on the human body using millimeter waves. A two-and-a-half-dimensional (2.5D) quantitative millimeter wave imaging algorithm is applied to reconstruct a hidden dielectric object on a clothed simplified human body model. At millimeter wave frequencies, the incident field is typically a fully three-dimensional (3D) Gaussian beam, illuminating only a limited spot on the body. Due to the large dimensions of the human body in terms of wavelengths, a 3D discretization is hardly feasible. Therefore, it is assumed that the electromagnetic properties of the body do not significantly change within the illuminated spot, along the longitudinal direction of a person. Hence, only the cross-section of a human body model is discretized. This 2.5D assumption however is still not sufficient to reduce the forward problem to a feasible size. Therefore, a priori knowledge on the illumination and on the scattering properties of the clothed human body is used to deduce a simplified model to describe the cross-section of the clothed human abdomen. The complex permittivity profile of a small dielectric object, hidden underneath clothing and representing some type of explosive, is reconstructed. The complex permittivity profiles of all other scatterers are assumed to be known. The presented quantitative inverse scattering algorithm is based on a Newton-type optimization, combined with an approximate line search and regularized by applying Stepwise Relaxed Value Picking regularization. The input data of the quantitative inverse scattering problem are synthetic scattering data since the authors are not aware of any amplitude and phase measurement data for concealed weapon detection yet made available to the inversion community at these high frequencies.

  16. MO-E-17A-02: Incorporation of Contrast Medium Dynamics in Anthropomorphic Phantoms: The Advent of 5D XCAT Models

    SciTech Connect

    Sahbaee, P; Samei, E; Segars, W

    2014-06-15

    Purpose: To develop a unique method to incorporate the dynamics of contrast-medium propagation into the anthropomorphic phantom, to generate a five-dimensional (5D) patient model for multimodality imaging studies. Methods: A compartmental model of blood circulation network within the body was embodied into an extended cardiac-torso (4D-XCAT) patient model. To do so, a computational physiologic model of the human cardiovascular system was developed which includes a series of compartments representing heart, vessels, and organs. Patient-specific cardiac output and blood volume were used as inputs influenced by the weight, height, age, and gender of the patient's model. For a given injection protocol and given XCAT model, the contrast-medium transmission within the body was described by a series of mass balance differential equations, the solutions to which provided the contrast enhancement-time curves for each organ; thereby defining the tissue materials including the contrastmedium within the XCAT model. A library of time-dependent organ materials was then defined. Each organ in each voxelized 4D-XCAT phantom was assigned to a corresponding time-varying material to create the 5D-XCAT phantom in which the fifth dimension is blood/contrast-medium within the temporal domain. Results: The model effectively predicts the time-varying concentration behavior of various contrast-medium administration in each organ for different patient models as function of patient size (weight/height) and different injection protocol factors (injection rate and pattern, iodine concentration or volume). The contrast enhanced XCAT patient models was developed based on the concentration of iodine as a function of time after injection. Conclusion: Majority of medical imaging systems take advantage of contrast-medium administration in terms of better image quality, the effect of which was ignored in previous optimization studies. The study enables a comprehensive optimization of contrast

  17. THE COYOTE UNIVERSE. II. COSMOLOGICAL MODELS AND PRECISION EMULATION OF THE NONLINEAR MATTER POWER SPECTRUM

    SciTech Connect

    Heitmann, Katrin; Higdon, David; Williams, Brian J.; Lawrence, Earl; White, Martin; Habib, Salman; Wagner, Christian

    2009-11-01

    The power spectrum of density fluctuations is a foundational source of cosmological information. Precision cosmological probes targeted primarily at investigations of dark energy require accurate theoretical determinations of the power spectrum in the nonlinear regime. To exploit the observational power of future cosmological surveys, accuracy demands on the theory are at the 1% level or better. Numerical simulations are currently the only way to produce sufficiently error-controlled predictions for the power spectrum. The very high computational cost of (precision) N-body simulations is a major obstacle to obtaining predictions in the nonlinear regime, while scanning over cosmological parameters. Near-future observations, however, are likely to provide a meaningful constraint only on constant dark energy equation of state, 'wCDM', cosmologies. In this paper, we demonstrate that a limited set of only 37 cosmological models-the 'Coyote Universe' suite-can be used to predict the nonlinear matter power spectrum to 1% over a prior parameter range set by current cosmic microwave background observations. This paper is the second in a series of three, with the final aim to provide a high-accuracy prediction scheme for the nonlinear matter power spectrum for wCDM cosmologies.

  18. The Coyote Universe II: Cosmological Models and Precision Emulation of the Nonlinear Matter Power Spectrum

    SciTech Connect

    Heitmann, Katrin; Habib, Salman; Higdon, David; Williams, Brian J; White, Martin; Wagner, Christian

    2008-01-01

    The power spectrum of density fluctuations is a foundational source of cosmological information. Precision cosmological probes targeted primarily at investigations of dark energy require accurate theoretical determinations of the power spectrum in the nonlinear regime. To exploit the observational power of future cosmological surveys, accuracy demands on the theory are at the one percent level or better. Numerical simulations are currently the only way to produce sufficiently error-controlled predictions for the power spectrum. The very high computational cost of (precision) N-body simulations is a major obstacle to obtaining predictions in the nonlinear regime, while scanning over cosmological parameters. Near-future observations, however, are likely to provide a meaningful constraint only on constant dark energy equation of state 'wCDM' cosmologies. In this paper we demonstrate that a limited set of only 37 cosmological models -- the 'Coyote Universe' suite -- can be used to predict the nonlinear matter power spectrum at the required accuracy over a prior parameter range set by cosmic microwave background observations. This paper is the second in a series of three, with the final aim to provide a high-accuracy prediction scheme for the nonlinear matter power spectrum for wCDM cosmologies.

  19. Observing the inflation potential. [in models of cosmological inflation

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    We show how observations of the density perturbation (scalar) spectrum and the gravitational wave (tensor) spectrum allow a reconstruction of the potential responsible for cosmological inflation. A complete functional reconstruction or a perturbative approximation about a single scale are possible; the suitability of each approach depends on the data available. Consistency equations between the scalar and tensor spectra are derived, which provide a powerful signal of inflation.

  20. COSMOG: Cosmology Oriented Sub-mm Modeling of Galactic Foregrounds

    NASA Technical Reports Server (NTRS)

    Kashlinsky, A.; Leisawitz, D.

    2004-01-01

    With upcoming missions in mid- and far-Infrared there is a need for software packages to reliably simulate the planned observations. This would help in both planning the observation and scanning strategy and in developing the concepts of the far-off missions. As this workshop demonstrated, many of the new missions are to be in the far-IR range of the electromagnetic spectrum and at the same time will map the sky with a sub-arcsec angular resolution. We present here a computer package for simulating foreground maps for the planned sub-mm and far-IR missions. such as SPECS. The package allows to study confusion limits and simulate cosmological observations for specified sky location interactively and in real time. Most of the emission at wavelengths long-ward of approximately 50 microns is dominated by Galactic cirrus and Zodiacal dust emission. Stellar emission at these wavelengths is weak and is for now neglected. Cosmological sources (distant and not-so-distant) galaxies for specified cosmologies will be added. Briefly, the steps that the algorithm goes through is described.

  1. Bianchi VI cosmological models representing perfect fluid and radiation with electric-type free gravitational fields

    NASA Astrophysics Data System (ADS)

    Roy, S. R.; Banerjee, S. K.

    1992-11-01

    A homogeneous Bianchi type VIh cosmological model filled with perfect fluid, null electromagnetic field and streaming neutrinos is obtained for which the free gravitational field is of the electric type. The barotropic equation of statep = (γ-1)ɛ is imposed in the particular case of Bianchi VI0 string models. Various physical and kinematical properties of the models are discussed.

  2. V cosmological models in f (R, T) modified gravity with Λ (T) by using generation technique

    NASA Astrophysics Data System (ADS)

    Ahmed, Nasr; Pradhan, Anirudh; Fekry, M.; Alamri, Sultan Z.

    2016-06-01

    A new class of cosmological models in f (R, T) modified theories of gravity proposed by Harko et al. (2011), where the gravitational Lagrangian is given by an arbitrary function of Ricci scalar R and the trace of the stress-energy tensor T, has been investigated for a specific choice of f (R, T) =f1 (R) +f2 (T) by generation of new solutions. Motivated by recent work of Pradhan et al. (2015) we have revisited the recent work of Ahmed and Pradhan (2014) by using a generation technique, it is shown that f (R, T) modified field equations are solvable for any arbitrary cosmic scale function. A class of new solutions for particular forms of cosmic scale functions have been investigated. In the present study we consider the cosmological constant Λ as a function of the trace of the stress energy-momentum-tensor, and dub such a model " Λ (T) gravity" where we specified a certain form of Λ (T) . Such models may exhibit better equability with the cosmological observations. The cosmological constant Λ is found to be a positive decreasing function of time which is supported by results from recent supernovae Ia observations. Expressions for Hubble's parameter in terms of redshift, luminosity distance redshift, distance modulus redshift and jerk parameter are derived and their significances are described in detail. The physical and geometric properties of the cosmological models are also discussed.

  3. Classical and quantum Big Brake cosmology for scalar field and tachyonic models

    SciTech Connect

    Kamenshchik, A. Yu.; Manti, S.

    2013-02-21

    We study a relation between the cosmological singularities in classical and quantum theory, comparing the classical and quantum dynamics in some models possessing the Big Brake singularity - the model based on a scalar field and two models based on a tachyon-pseudo-tachyon field . It is shown that the effect of quantum avoidance is absent for the soft singularities of the Big Brake type while it is present for the Big Bang and Big Crunch singularities. Thus, there is some kind of a classical - quantum correspondence, because soft singularities are traversable in classical cosmology, while the strong Big Bang and Big Crunch singularities are not traversable.

  4. Improved cosmological model fitting of Planck data with a dark energy spike

    NASA Astrophysics Data System (ADS)

    Park, Chan-Gyung

    2015-06-01

    The Λ cold dark matter (Λ CDM ) model is currently known as the simplest cosmology model that best describes observations with a minimal number of parameters. Here we introduce a cosmology model that is preferred over the conventional Λ CDM one by constructing dark energy as the sum of the cosmological constant Λ and an additional fluid that is designed to have an extremely short transient spike in energy density during the radiation-matter equality era and an early scaling behavior with radiation and matter densities. The density parameter of the additional fluid is defined as a Gaussian function plus a constant in logarithmic scale-factor space. Searching for the best-fit cosmological parameters in the presence of such a dark energy spike gives a far smaller chi-square value by about 5 times the number of additional parameters introduced and narrower constraints on the matter density and Hubble constant compared with the best-fit Λ CDM model. The significant improvement in reducing the chi square mainly comes from the better fitting of the Planck temperature power spectrum around the third (ℓ≈800 ) and sixth (ℓ≈1800 ) acoustic peaks. The likelihood ratio test and the Akaike information criterion suggest that the model of a dark energy spike is strongly favored by the current cosmological observations over the conventional Λ CDM model. However, based on the Bayesian information criterion which penalizes models with more parameters, the strong evidence supporting the presence of a dark energy spike disappears. Our result emphasizes that the alternative cosmological parameter estimation with even better fitting of the same observational data is allowed in Einstein's gravity.

  5. Bianchi type-I magnetized cosmological models for the Einstein-Boltzmann equation with the cosmological constant

    NASA Astrophysics Data System (ADS)

    Ayissi, Raoul Domingo; Noutchegueme, Norbert

    2015-01-01

    Global solutions regular for the Einstein-Boltzmann equation on a magnetized Bianchi type-I cosmological model with the cosmological constant are investigated. We suppose that the metric is locally rotationally symmetric. The Einstein-Boltzmann equation has been already considered by some authors. But, in general Bancel and Choquet-Bruhat [Ann. Henri Poincaré XVIII(3), 263 (1973); Commun. Math. Phys. 33, 83 (1973)], they proved only the local existence, and in the case of the nonrelativistic Boltzmann equation. Mucha [Global existence of solutions of the Einstein-Boltzmann equation in the spatially homogeneous case. Evolution equation, existence, regularity and singularities (Banach Center Publications, Institute of Mathematics, Polish Academy of Science, 2000), Vol. 52] obtained a global existence result, for the relativistic Boltzmann equation coupled with the Einstein equations and using the Yosida operator, but confusing unfortunately with the nonrelativistic case. Noutchegueme and Dongho [Classical Quantum Gravity 23, 2979 (2006)] and Noutchegueme, Dongho, and Takou [Gen. Relativ. Gravitation 37, 2047 (2005)], have obtained a global solution in time, but still using the Yosida operator and considering only the uncharged case. Noutchegueme and Ayissi [Adv. Stud. Theor. Phys. 4, 855 (2010)] also proved a global existence of solutions to the Maxwell-Boltzmann system using the characteristic method. In this paper, we obtain using a method totally different from those used in the works of Noutchegueme and Dongho [Classical Quantum Gravity 23, 2979 (2006)], Noutchegueme, Dongho, and Takou [Gen. Relativ. Gravitation 37, 2047 (2005)], Noutchegueme and Ayissi [Adv. Stud. Theor. Phys. 4, 855 (2010)], and Mucha [Global existence of solutions of the Einstein-Boltzmann equation in the spatially homogeneous case. Evolution equation, existence, regularity and singularities (Banach Center Publications, Institute of Mathematics, Polish Academy of Science, 2000), Vol. 52] the

  6. Bianchi type-I magnetized cosmological models for the Einstein-Boltzmann equation with the cosmological constant

    SciTech Connect

    Ayissi, Raoul Domingo Noutchegueme, Norbert

    2015-01-15

    Global solutions regular for the Einstein-Boltzmann equation on a magnetized Bianchi type-I cosmological model with the cosmological constant are investigated. We suppose that the metric is locally rotationally symmetric. The Einstein-Boltzmann equation has been already considered by some authors. But, in general Bancel and Choquet-Bruhat [Ann. Henri Poincaré XVIII(3), 263 (1973); Commun. Math. Phys. 33, 83 (1973)], they proved only the local existence, and in the case of the nonrelativistic Boltzmann equation. Mucha [Global existence of solutions of the Einstein-Boltzmann equation in the spatially homogeneous case. Evolution equation, existence, regularity and singularities (Banach Center Publications, Institute of Mathematics, Polish Academy of Science, 2000), Vol. 52] obtained a global existence result, for the relativistic Boltzmann equation coupled with the Einstein equations and using the Yosida operator, but confusing unfortunately with the nonrelativistic case. Noutchegueme and Dongho [Classical Quantum Gravity 23, 2979 (2006)] and Noutchegueme, Dongho, and Takou [Gen. Relativ. Gravitation 37, 2047 (2005)], have obtained a global solution in time, but still using the Yosida operator and considering only the uncharged case. Noutchegueme and Ayissi [Adv. Stud. Theor. Phys. 4, 855 (2010)] also proved a global existence of solutions to the Maxwell-Boltzmann system using the characteristic method. In this paper, we obtain using a method totally different from those used in the works of Noutchegueme and Dongho [Classical Quantum Gravity 23, 2979 (2006)], Noutchegueme, Dongho, and Takou [Gen. Relativ. Gravitation 37, 2047 (2005)], Noutchegueme and Ayissi [Adv. Stud. Theor. Phys. 4, 855 (2010)], and Mucha [Global existence of solutions of the Einstein-Boltzmann equation in the spatially homogeneous case. Evolution equation, existence, regularity and singularities (Banach Center Publications, Institute of Mathematics, Polish Academy of Science, 2000), Vol. 52] the

  7. A 1.5-D anisotropic sigma-coordinate thermal stress model of landlocked sea ice in the Canadian Arctic Archipelago

    NASA Astrophysics Data System (ADS)

    Hata, Y.; Tremblay, L. B.

    2015-12-01

    We present a 1.5-D thermal stress model that takes into account the effect of land confinement, which causes anisotropy in thermal stresses. To this end, we fix the total strain in the direction perpendicular to the coastline to its value at landlocked ice onset. This prevents thermal expansion in the direction perpendicular to the coastline and therefore induces larger thermal stresses in this direction. The simulated stresses best match the observations, when a Young's Modulus of 0.5 GPa and a relaxation time constant of 8 days are used. This simulation gives root-mean-square errors of 13.0 and 13.1 kPa (˜15%) in the major and minor principal stresses, respectively. The simulated anisotropic component of thermal stress also generally agrees with observations. The optimal Young's Modulus is in the low range of reported values in the literature, and the optimal relaxation time constant (8 days) is larger than the largest relaxation time constant reported in the literature (5 days). A series of experiments are done to examine the model sensitivity to vertical resolution, snow cover, and the parameterizations of Young's Modulus and viscous creep. Results show that a minimum of one and three layers in the snow and ice, respectively, is required to simulate the thermal stresses within 15% error of the value assessed with the higher-resolution control simulation. This highlights the importance of resolving the internal snow and ice vertical temperature profile in order to properly model the thermal stresses of sea ice.

  8. Toward cosmological-model-independent calibrations for the luminosity relations of Gamma-Ray Bursts

    NASA Astrophysics Data System (ADS)

    Ding, Xuheng; Li, Zhengxiang; Zhu, Zong-Hong

    2015-05-01

    Gamma-ray bursts (GRBs), have been widely used as distance indicators to measure the cosmic expansion and explore the nature of dark energy. A popular method adopted in previous works is to calibrate the luminosity relations which are responsible for distance estimation of GRBs with more primary (low redshift) cosmic distance ladder objects, type Ia supernovae (SNe Ia). Since distances of SNe Ia in all SN Ia samples used to calibrate GRB luminosity relations were usually derived from the global fit in a specific cosmological model, the distance of GRB at a given redshift calibrated with matching SNe Ia was still cosmological-model-dependent. In this paper, we first directly determine the distances of SNe Ia with the Angular Diameter Distances (ADDs) of galaxy clusters without any assumption for the background of the universe, and then calibrate GRB luminosity relations with our cosmology-independent distances of SNe Ia. The results suggest that, compared to the previous original manner where distances of SNe Ia used as calibrators are determined from the global fit in a particular cosmological model, our treatments proposed here yield almost the same calibrations of GRB luminosity relations and the cosmological implications of them do not suffer any circularity.

  9. Cosmological and solar system consequences of f(R ,T) gravity models

    NASA Astrophysics Data System (ADS)

    Shabani, Hamid; Farhoudi, Mehrdad

    2014-08-01

    To find more deliberate f(R ,T) cosmological solutions, we take our previous paper further by studying some new aspects of the considered models via investigation of some new cosmological parameters/quantities to attain the most acceptable cosmological results. Our investigations are performed by applying the dynamical system approach. We obtain the cosmological parameters/quantities in terms of some defined dimensionless parameters that are used in constructing the dynamical equations of motion. The investigated parameters/quantities are the evolution of the Hubble parameter and its inverse, the "weight function"; the ratio of the matter density to the dark energy density and its time variation; the deceleration; the jerk and the snap parameters; and the equation-of-state parameter of the dark energy. We numerically examine these quantities for two general models R +αR-n+√-T and Rlog[αR]q+√-T . All considered models have some inconsistent quantities (with respect to the available observational data), except the model with n =-0.9, which has more consistent quantities than the other ones. By considering the ratio of the matter density to the dark energy density, we find that the coincidence problem does not refer to a unique cosmological event; rather, this coincidence also occurred in the early Universe. We also present the cosmological solutions for an interesting model R +c1√-T in the nonflat Friedmann-Lemaître-Robertson-Walker metric. We show that this model has an attractor solution for the late times, though with w(DE)=-1/2. This model indicates that the spatial curvature density parameter gets negligible values until the present era, in which it acquires the values of the order 10-4 or 10-3. As the second part of this work, we consider the weak-field limit of f(R ,T) gravity models outside a spherical mass immersed in the cosmological fluid. We have found that the corresponding field equations depend on the both background values of the Ricci scalar

  10. Five dimensional cosmological models in Lyra geometry with time dependent displacement field

    NASA Astrophysics Data System (ADS)

    Mohanty, G.; Mahanta, K. L.; Bishi, B. K.

    2007-08-01

    In this paper exact solutions of the five-dimensional vacuum cosmological field equations based on Lyra geometry are obtained. Further it is shown that neither dust distribution nor perfect fluid distributions survive for the model. Some properties of the vacuum model are also discussed.

  11. Bianchi type-I magnetized radiating cosmological model in self creation theory of gravitation

    NASA Astrophysics Data System (ADS)

    Jain, Vimal Chand; Jain, Nikhil

    2015-06-01

    We have investigated Bianchi type-I cosmological model in the presence of magnetized field with disordered radiation in Barber's second self-creation theory of gravitation. To obtain exact solution we assume that the component of shear tensor is proportional to expansion ( θ). Some geometrical and physical properties of the model have also been discussed.

  12. Cosmological perturbations in SFT inspired non-local scalar field models

    NASA Astrophysics Data System (ADS)

    Koshelev, Alexey S.; Vernov, Sergey Yu.

    2012-10-01

    We study cosmological perturbations in models with a single non-local scalar field originating from the string field theory description of the rolling tachyon dynamics. We construct the equation for the energy density perturbations of the non-local scalar field and explicitly prove that for the free field it is identical to a system of local cosmological perturbation equations in a particular model with multiple (maybe infinitely many) local free scalar fields. We also show that vector and tensor perturbations are absent in this set-up.

  13. Beyond Standard Model Physics: At the Frontiers of Cosmology and Particle Physics

    NASA Astrophysics Data System (ADS)

    Lopez-Suarez, Alejandro O.

    I begin to write this thesis at a time of great excitement in the field of cosmology and particle physics. The aim of this thesis is to study and search for beyond the standard model (BSM) physics in the cosmological and high energy particle fields. There are two main questions, which this thesis aims to address: 1) what can we learn about the inflationary epoch utilizing the pioneer gravitational wave detector Adv. LIGO?, and 2) what are the dark matter particle properties and interactions with the standard model particles?. This thesis will focus on advances in answering both questions.

  14. Unitary evolution for anisotropic quantum cosmologies: models with variable spatial curvature

    NASA Astrophysics Data System (ADS)

    Pandey, Sachin; Banerjee, Narayan

    2016-11-01

    Contrary to the general belief, there has recently been quite a few examples of unitary evolution of quantum cosmological models. The present work gives more examples, namely Bianchi type VI and type II. These examples are important as they involve varying spatial curvature unlike the most talked about homogeneous but anisotropic cosmological models like Bianchi I, V and IX. We exhibit either an explicit example of the unitary solutions of the Wheeler–DeWitt equation, or at least show that a self-adjoint extension is possible.

  15. 3.5-D model of sediment age and grain size for the Northern Gulf of Aqaba-Elat (Red Sea) using submarine cores

    NASA Astrophysics Data System (ADS)

    Kanari, Mor; Ben-Avraham, Zvi; Tibor, Gideon; Goodman Tchernov, Beverly N.; Bookman, Revital; Taha, Nimer; Marco, Shmuel

    2016-04-01

    The Northern Gulf of Aqaba-Elat (NGAE) is the northeast extension of the Red Sea, located at the southernmost part of the Dead Sea Fault, at the transition zone between the deep en-echelon submarine basins of the Red Sea and the shallow continental basins of the Arava Valley (Israel and Jordan). We aim to characterize the top sedimentary cover across the NGAE in order to check the effect of tectonics on the sedimentary column, using high resolution grain size data and radiocarbon dating of core sediments. We analyzed 11 piston cores and 9 short cores: high resolution grain-size and radiocarbon age determinations were used to compile a 3.5-D (3.5 dimensional) model of age-depth-grain size for the top 3-5 meters of the NGAE. Two general trends of the grain size spatial distribution are observed: grains are coarsest at the NE corner of the NGAE (Aqaba coastline) and grow finer with the distance to the west on the shelf and with the distance from shore to the south. Long- and short-term accumulation rates were compiled for the entire NGAE, demonstrating a distinct E-W trend on the shelf and a NNE-SSW trend in the deep basin. The 3.5-D age-depth-grain size model conforms to- and validates the tectonic structure of the shelf detailed by previous authors. We suggest that the impact of tectonic structure of the shelf is highly significant in terms of spatial variations across the shelf, both in age of the sediment and its grain size characteristics. The temporal-spatial distribution of the grain size in the deep basin of the NGAE reveals a correlation between sediment age, dominant grain size and active tectonics: fine-grain, old sediment in the margins (Late Pleistocene, as old as >40 ka on the west margin; Early Holocene, as old as 7.5 ka, on the east margin), and Late Pleistocene sediment farther south from the dominant active diagonal fault which underlies the Elat Canyon. Young coarse sediment is present in the middle of the basin, where most of the active sediment

  16. Are cosmological data sets consistent with each other within the Λ cold dark matter model?

    NASA Astrophysics Data System (ADS)

    Raveri, Marco

    2016-02-01

    We use a complete and rigorous statistical indicator to measure the level of concordance between cosmological data sets, without relying on the inspection of the marginal posterior distribution of some selected parameters. We apply this test to state of the art cosmological data sets, to assess their agreement within the Λ cold dark matter model. We find that there is a good level of concordance between all the experiments with one noticeable exception. There is substantial evidence of tension between the cosmic microwave background temperature and polarization measurements of the Planck satellite and the data from the CFHTLenS weak lensing survey even when applying ultraconservative cuts. These results robustly point toward the possibility of having unaccounted systematic effects in the data, an incomplete modeling of the cosmological predictions or hints toward new physical phenomena.

  17. Probing cosmology with weak lensing selected clusters. II. Dark energy and f(R) gravity models

    NASA Astrophysics Data System (ADS)

    Shirasaki, Masato; Hamana, Takashi; Yoshida, Naoki

    2016-02-01

    Ongoing and future wide-field galaxy surveys can be used to locate a number of clusters of galaxies with cosmic shear measurement alone. We study constraints on cosmological models using statistics of weak lensing selected galaxy clusters. We extend our previous theoretical framework to model the statistical properties of clusters in variants of cosmological models as well as in the standard ΛCDM model. Weak lensing selection of clusters does not rely on conventional assumptions such as the relation between luminosity and mass and/or hydrostatic equilibrium, but a number of observational effects compromise robust identification. We use a large set of realistic mock weak lensing catalogs as well as analytic models to perform a Fisher analysis and make a forecast for constraining two competing cosmological models, the wCDM model and f(R) model proposed by Hu and Sawicki (2007, Phys. Rev. D, 76, 064004), with our lensing statistics. We show that weak lensing selected clusters are excellent probes of cosmology when combined with cosmic shear power spectrum even in the presence of galaxy shape noise and masked regions. With the information from weak lensing selected clusters, the precision of cosmological parameter estimates can be improved by a factor of ˜1.6 and ˜8 for the wCDM model and f(R) model, respectively. The Hyper Suprime-Cam survey with sky coverage of 1250 degrees squared can constrain the equation of state of dark energy w0 with a level of Δw0 ˜ 0.1. It can also constrain the additional scalar degree of freedom in the f(R) model with a level of |fR0| ˜ 5 × 10-6, when constraints from cosmic microwave background measurements are incorporated. Future weak lensing surveys with sky coverage of 20000 degrees squared will place tighter constraints on w0 and |fR0| even without cosmic microwave background measurements.

  18. Regional-scale geometry of the central Skellefte district, northern Sweden—results from 2.5D potential field modeling along three previously acquired seismic profiles

    NASA Astrophysics Data System (ADS)

    Tavakoli, Saman; Bauer, Tobias E.; Elming, Sten-Åke; Thunehed, Hans; Weihed, Pär

    2012-10-01

    The Skellefte district in northern Sweden is one of the most important mining districts in Europe hosting approximately 80 volcanic massive sulfide (VMS) deposits. Due to its economical importance, geological and geophysical studies were carried out in order to create an image of the geometry of the upper crustal structure and integral geological elements and to evaluate their relationship to mineral deposits. Consequently, seismic reflection data along three sub-parallel profiles were acquired during 2009-2010 to map the spatial relationships between the geological structures down to a depth of ~ 4.5 km. Although these seismic studies helped researchers understand the regional relationship between geologic units in the central Skellefte district (CSD), the seismic reflection data did not succeed entirely in mapping the lithological contacts in the area. In this study, the model derived from the seismic reflection data was examined by using 2.5D modeling of potential field data (down to a 5 km depth) constrained by physical properties of the rocks and surface geology. Moreover, we modeled gravity and magnetic data along the non-reflective or poorly reflective parts of the seismic profiles to identify major lithological contacts and shear zones in the CSD, which could not be modeled on the basis of the seismic reflection data. Gravity and magnetic data helped reveal the spatial relationship between the Skellefte volcanic rocks, Vargfors group meta-sedimentary rocks and two meta­intrusive complexes. Results suggest a maximum depth extent of 2.1 km for the tectonic contact at the southern border of the Jörn granitoid. Furthermore, this north-dipping Skellefte-Jörn contact coincides closely with magnetic lows and gravity highs, which implies that the Jörn intrusive rocks have a greater thickness than the underlying basalt. Further to the NW, gravity and magnetic data suggest a depth extent of 2 km for the Gallejaur complex, which coincides with a set of gently

  19. 2.5D modelling of a horizontal electric dipole using Finite Difference method with non-uniform grids and preconditioned sparse matrices

    NASA Astrophysics Data System (ADS)

    Miranda, D. D.; Howard, A. Q.

    2012-12-01

    Computational modelling of geophysical data is an important step in the process of hydrocarbon exploration. It consists in simulating the exploratory procedure and realistic geological environments. It allows a preliminary evaluation of the exploration feasibility of a particular terrain or geological model, indicating the best conditions for geophysical surveys. In this paper, we assess the Finite Difference frequency domain method for modelling the electromagnetic response of a horizontal electric dipole in 1D and 2.5D geometries. The non-uniform grid is refined in regions where the electromagnetic fields vary rapidly, namely the regions where we have variation in conductivity distribution and near the source dipole. We chose the horizontal electromagnetic dipole because it is the source normally used in the marine controlled-source electromagnetic surveys (mCSEM), which is the next step in our research. The mCSEM, also known as Sea Bed Logging, is a method for detection and characterization of thin resistive structures, like hydrocarbon reservoirs, often located in regions of deep water. It consists of a mobile electric dipole or a magnetic loop as a source, positioned near the sea floor where an array of electric and magnetic receivers are deployed. The source transmitter uses a low frequency signal on the order of 1Hz, that diffuses both in the ocean and in the sediments beneath it and is captured by the receivers . Amplitude and phase of this signal depend on the electrical conductivity of the seabed environment. The complexity of the environments and the large dimensions of the geological domains that we want to investigate make the modelling procedure extremely demanding, since the Finite Difference method requires a total discretization of the studied domain, resulting in large systems of linear equations, which can make the procedure long and expensive. Non-uniform grids and exploitation of the sparse property of the Finite Difference matrices are example

  20. Equivalent off-diagonal cosmological models and ekpyrotic scenarios in -modified, massive, and einstein gravity

    NASA Astrophysics Data System (ADS)

    Vacaru, Sergiu I.

    2015-04-01

    We reinvestigate how generic off-diagonal cosmological solutions depending, in general, on all spacetime coordinates can be constructed in massive and -modified gravity using the anholonomic frame deformation method. New classes of locally anisotropic and (in-) homogeneous cosmological metrics are constructed with open and closed spatial geometries. By resorting to such solutions, we show that they describe the late time acceleration due to effective cosmological terms induced by nonlinear off-diagonal interactions, possible modifications of the gravitational action and graviton mass. The cosmological metrics and related Stückelberg fields are constructed in explicit form up to nonholonomic frame transforms of the Friedmann-Lamaître-Robertson-Walker (FLRW) coordinates. The solutions include matter, graviton mass, and other effective sources modeling nonlinear gravitational and matter field interactions with polarization of physical constants and deformations of metrics, which may explain dark energy and dark matter effects. However, we argue that it is not always necessary to modify gravity if we consider the effective generalized Einstein equations with nontrivial vacuum and/or non-minimal coupling with matter. Indeed, we state certain conditions when such configurations mimic interesting solutions in general relativity and modifications, for instance, when we can extract the general Painlevé-Gullstrand and FLRW metrics. In a more general context, we elaborate on a reconstruction procedure for off-diagonal cosmological solutions which describe cyclic and ekpyrotic universes. Finally, open issues and further perspectives are discussed.

  1. Cosmological dynamics of spatially flat Einstein-Gauss-Bonnet models in various dimensions: Vacuum case

    NASA Astrophysics Data System (ADS)

    Pavluchenko, Sergey A.

    2016-07-01

    In this paper we perform a systematic study of vacuum spatially flat anisotropic [(3 +D )+1 ]-dimensional Einstein-Gauss-Bonnet cosmological models. We consider models that topologically are the product of two flat isotropic submanifolds with different scale factors. One of these submanifolds is three dimensional and represents our 3D space and the other is D dimensional and represents extra dimensions. We consider no Ansatz on the scale factors, which makes our results quite general. With both Einstein-Hilbert and Gauss-Bonnet contributions in play and with the symmetry involved, the cases with D =1 , D =2 , D =3 , and D ≥4 have different dynamics due to the different structures of the equations of motion. We analytically analyze equations of motion in all cases and describe all possible regimes. It appears that the only regimes with nonsingular future asymptotes are the Kasner regime in general relativity and exponential regimes. As of the past asymptotes, for a smooth transition only the Kasner regime in Gauss-Bonnet is an option. With this at hand, we are down to only two viable regimes: the "pure" Kasner regime [transition from a high-energy (Gauss-Bonnet) to a low-energy (general relativity) Kasner regime] and a transition from a high-energy Kasner regime to an anisotropic exponential solution. It appears that these regimes take place for different signs of the Gauss-Bonnet coupling α : the "pure" Kasner regime occurs for α >0 at low D and α <0 for high D ; the anisotropic exponential regime is reached only for α >0 . So if we restrain ourselves with α >0 solutions (which would be the case, say, if we identify α with inverse string tension in heterotic string theory), the only late-time regimes are Kasner for D =1 , 2 and anisotropic exponential for D ≥2 . Also, low-energy Kasner regimes [a (t )∝tp] have expansion rates for (3 +1 )-dimensional subspace ("our Universe") ranging from p =0.5 (D =1 ) to p =1 /√{3 }≈0.577 (D →∞ ), which

  2. Classical and quantum cosmology of Born-Infeld type models

    NASA Astrophysics Data System (ADS)

    Kamenshchik, Alexander; Kiefer, Claus; Kwidzinski, Nick

    2016-04-01

    We discuss Born-Infeld type fields (tachyon fields) in classical and quantum cosmology. We first partly review and partly extend the discussion of the classical solutions and focus in particular on the occurrence of singularities. For quantization, we employ geometrodynamics. In the case of constant potential, we discuss both Wheeler-DeWitt quantization and reduced quantization. We are able to give various solutions and discuss their asymptotics. For the case of general potential, we transform the Wheeler-DeWitt equation to a form where it leads to a difference equation. Such a difference equation was previously found in the quantization of black holes. We give explicit results for the cases of constant potential and inverse squared potential and point out special features possessed by solutions of the difference equation.

  3. Loop Quantum Cosmology: holonomy corrections to inflationary models

    SciTech Connect

    Artymowski, Michal; Lalak, Zygmunt; Szulc, Lukasz

    2009-01-15

    In the recent years the quantization methods of Loop Quantum Gravity have been successfully applied to the homogeneous and isotropic Friedmann-Robertson-Walker space-times. The resulting theory, called Loop Quantum Cosmology (LQC), resolves the Big Bang singularity by replacing it with the Big Bounce. We argue that the LQC holonomy corrections generate also certain corrections to field theoretical inflationary scenarios. These corrections imply that in the LQC the effective sonic horizon becomes infinite at some point after the bounce and that the scale of the inflationary potential implied by the COBE normalisation increases. The evolution of scalar fields immediately after the Bounce becomes modified in an interesting way. We point out that one can use COBE normalisation to establish an upper bound on the quantum of length of LQG. LQC corrections other than the holonomy one are assumed to be subdominant.

  4. Non-linear structure formation in the `Running FLRW' cosmological model

    NASA Astrophysics Data System (ADS)

    Bibiano, Antonio; Croton, Darren J.

    2016-07-01

    We present a suite of cosmological N-body simulations describing the `Running Friedmann-Lemaïtre-Robertson-Walker' (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends Lambda cold dark matter (ΛCDM) with a time-evolving vacuum density, Λ(z), and time-evolving gravitational Newton's coupling, G(z). In this paper, we review the model and introduce the necessary analytical treatment needed to adapt a reference N-body code. Our resulting simulations represent the first realization of the full growth history of structure in the R-FLRW cosmology into the non-linear regime, and our normalization choice makes them fully consistent with the latest cosmic microwave background data. The post-processing data products also allow, for the first time, an analysis of the properties of the halo and sub-halo populations. We explore the degeneracies of many statistical observables and discuss the steps needed to break them. Furthermore, we provide a quantitative description of the deviations of R-FLRW from ΛCDM, which could be readily exploited by future cosmological observations to test and further constrain the model.

  5. ΛXCDM: a cosmon model solution to the cosmological coincidence problem?

    NASA Astrophysics Data System (ADS)

    Grande, Javier; Solà, Joan; Stefancic, Hrvoje

    2006-08-01

    We consider the possibility that the total dark energy (DE) of the Universe is made out of two dynamical components of different nature: a variable cosmological term, Λ, and a dynamical 'cosmon', X, possibly interacting with Λ but not with matter—which remains conserved. We call this scenario the ΛXCDM model. One possibility for X would be a scalar field χ, but it is not the only one. The overall equation of state (EOS) of the ΛXCDM model can effectively appear as quintessence or phantom energy depending on the mixture of the two components. Both the dynamics of Λ and that of X could be linked to high energy effects near the Planck scale. In the case of Λ it may be related to the running of this parameter under quantum effects, whereas X might be identified with some fundamental field (say, a dilaton) left over as a low energy 'relic' by e.g. string theory. We find that the dynamics of the ΛXCDM model can trigger a future stopping of the Universe expansion and can keep the ratio ρD/ρm (DE density to matter radiation density) bounded and of order 1. Therefore, the model could explain the so-called 'cosmological coincidence problem'. This is in part related to the possibility that the present value of the cosmological term can be Λ0 < 0 in this framework (the current total DE density nevertheless being positive). However, a cosmic halt could occur even if Λ0 > 0 because of the peculiar behaviour of X as 'phantom matter'. We describe various cosmological scenarios made possible by the composite and dynamical nature of ΛXCDM, and discuss in detail their impact on the cosmological coincidence problem.

  6. Dimensionless cosmology

    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.

  7. A fully cosmological model of a Monoceros-like ring

    NASA Astrophysics Data System (ADS)

    Gómez, Facundo A.; White, Simon D. M.; Marinacci, Federico; Slater, Colin T.; Grand, Robert J. J.; Springel, Volker; Pakmor, Rüdiger

    2016-03-01

    We study the vertical structure of a stellar disc obtained from a fully cosmological high-resolution hydrodynamical simulation of the formation of a Milky Way-like galaxy. At the present day, the disc's mean vertical height shows a well defined and strong pattern, with amplitudes as large as 3 kpc in its outer regions. This pattern is the result of a satellite- host halo-disc interaction and reproduces, qualitatively, many of the observable properties of the Monoceros Ring. In particular we find disc material at the distance of Monoceros (R ˜ 12-16 kpc, galactocentric) extending far above the mid plane (30°, ˜ 1-2 kpc) in both hemispheres, as well as well-defined arcs of disc material at heliocentric distances ≳5 kpc. The pattern was first excited ≈3 Gyr ago as an m = 1 mode that later winds up into a leading spiral pattern. Interestingly, the main driver behind this perturbation is a low-mass low-velocity fly-by encounter. The satellite has total mass, pericentre distance and pericentric velocity of ˜5 per cent of the host, ˜80 kpc and 215 km s-1, respectively. The satellite is not massive enough to directly perturb the galactic disc but we show that the density field of the host dark matter halo responds to this interaction resulting in a strong amplification of the perturbative effects. This subsequently causes the onset and development of the Monoceros-like feature.

  8. Supersymmetry and Lorentz Violation in 5D

    SciTech Connect

    Garcia-Aguilar, J. D.; Perez-Lorenzana, A.; Pedraza-Ortega, O.

    2011-10-14

    We present a study for a Supersymmetric field theory with Lorentz-Violation terms in 5D. We perform the analysis in the context of the Berger-Kostelecky model (BK), adding one compactified dimension that explicitly breaks the Lorentz invariance. We introduce terms that encode this breaking, and find non trivial restrictions over boundary conditions of fields that one needs to close the supersymmetric algebra.

  9. (An)Isotropic models in scalar and scalar-tensor cosmologies

    NASA Astrophysics Data System (ADS)

    Belinchón, José Antonio

    2012-04-01

    We study how the constants G and Λ may vary in different theoretical models (general relativity with a perfect fluid, scalar cosmological models ("quintessence") with and without interacting scalar and matter fields and a scalar-tensor model with a dynamical Λ) in order to explain some observational results. We apply the program outlined in section II to study three different geometries which generalize the FRW ones, which are Bianchi V, VII0 and IX, under the self-similarity hypothesis. We put special emphasis on calculating exact power-law solutions which allow us to compare the different models. In all the studied cases we arrive at the conclusion that the solutions are isotropic and noninflationary while the cosmological constant behaves as a positive decreasing time function (in agreement with the current observations) and the gravitational constant behaves as a growing time function.

  10. Cosmological properties and reconstruction of scalar field models of the Holographic Dark Energy model with Granda-Oliveros cut-off in Kaluza-Klein cosmology

    NASA Astrophysics Data System (ADS)

    Pasqua, Antonio; Chattopadhyay, Surajit; Assaf, Khudhair A.; Salako, Ines G.

    2016-06-01

    In this paper, we study the properties of the Holographic Dark Energy (HDE) model in the context of Kaluza-Klein (KK) cosmology with infrared cut-off given by the recently proposed by Granda-Oliveros cut-off, which contains a term proportional to the time derivative of the Hubble parameter and one proportional to the Hubble parameter squared. Moreover, this cut-off is characterized by two free parameters which are the proportional constants of the two terms of the cut-off. We derive the expression of the Equation of State (EoS) parameter ωD and of the deceleration parameter q for both non-interacting and interacting Dark Sectors and in the limiting case of a flat Dark Dominated Universe. Moreover, we study the squared speed of the sound vs2 and the statefinder diagnostic \\{r,s\\} in order to understand the cosmological properties of the model considered. We also develop a correspondence between the model considered and three scalar field models: the tachyon, the k-essence and the quintessence ones.

  11. LRS Bianchi type-I string cosmological models in f (R, T) gravity

    NASA Astrophysics Data System (ADS)

    Kanakavalli, T.; Ananda Rao, G.

    2016-07-01

    Spatially homogeneous and anisotropic LRS Bianchi type-I space time is investigated in the presence of cosmic string source in a modified theory of gravitation formulated by Harko et al. (Phys. Rev. D 84:024020, 2011). We have solved the field equations using the equations of state for strings and presented cosmological models which describe geometric string, Takabayasi string and Reddy string in this particular theory. Some physical and kinematical parameters of the models are computed and discussed their physical significance.

  12. Viability of an arctan model of f (R ) gravity for late-time cosmology

    NASA Astrophysics Data System (ADS)

    Dutta, Koushik; Panda, Sukanta; Patel, Avani

    2016-07-01

    f (R ) modification of Einstein's gravity is an interesting possibility to explain the late-time acceleration of the Universe. In this work we explore the cosmological viability of one such f (R ) modification proposed by Kruglov [Phys. Rev. D 89, 064004 (2014)]. We show that the model violates fifth-force constraints. The model is also plagued with the issue of a curvature singularity in a spherically collapsing object, where the effective scalar field reaches the point of diverging scalar curvature.

  13. Does the diffusion dark matter-dark energy interaction model solve cosmological puzzles?

    NASA Astrophysics Data System (ADS)

    Szydłowski, Marek; Stachowski, Aleksander

    2016-08-01

    We study dynamics of cosmological models with diffusion effects modeling dark matter and dark energy interactions. We show the simple model with diffusion between the cosmological constant sector and dark matter, where the canonical scaling law of dark matter (ρd m ,0a-3(t )) is modified by an additive ɛ (t )=γ t a-3(t ) to the form ρd m=ρd m ,0a-3(t )+ɛ (t ). We reduced this model to the autonomous dynamical system and investigate it using dynamical system methods. This system possesses a two-dimensional invariant submanifold on which the dark matter-dark energy (DM-DE) interaction can be analyzed on the phase plane. The state variables are density parameter for matter (dark and visible) and parameter δ characterizing the rate of growth of energy transfer between the dark sectors. A corresponding dynamical system belongs to a general class of jungle type of cosmologies represented by coupled cosmological models in a Lotka-Volterra framework. We demonstrate that the de Sitter solution is a global attractor for all trajectories in the phase space and there are two repellers: the Einstein-de Sitter universe and the de Sitter universe state dominating by the diffusion effects. We distinguish in the phase space trajectories, which become in good agreement with the data. They should intersect a rectangle with sides of Ωm ,0∈[0.2724 ,0.3624 ] , δ ∈[0.0000 ,0.0364 ] at the 95% CL. Our model could solve some of the puzzles of the Λ CDM model, such as the coincidence and fine-tuning problems. In the context of the coincidence problem, our model can explain the present ratio of ρm to ρd e, which is equal 0.457 6-0.0831+0.1109 at a 2 σ confidence level.

  14. Lagrangian theory of structure formation in relativistic cosmology. II. Average properties of a generic evolution model

    NASA Astrophysics Data System (ADS)

    Buchert, Thomas; Nayet, Charly; Wiegand, Alexander

    2013-06-01

    Kinematical and dynamical properties of a generic inhomogeneous cosmological model, spatially averaged with respect to free-falling (generalized fundamental) observers, are investigated for the matter model “irrotational dust.” Paraphrasing a previous Newtonian investigation, we present a relativistic generalization of a backreaction model based on volume-averaging the “relativistic Zel’dovich approximation.” In this model we investigate the effect of “kinematical backreaction” on the evolution of cosmological parameters as they are defined in an averaged inhomogeneous cosmology, and we show that the backreaction model interpolates between orthogonal symmetry properties by covering subcases of the plane-symmetric solution, the Lemaître-Tolman-Bondi solution and the Szekeres solution. We so obtain a powerful model that lays the foundations for quantitatively addressing curvature inhomogeneities as they would be interpreted as “dark energy” or “dark matter” in a quasi-Newtonian cosmology. The present model, having a limited architecture due to an assumed Friedmann-Lemaître-Robertson-Walker background, is nevertheless capable of replacing 1/4 of the needed amount for dark energy on domains of 200 Mpc in diameter for typical (one-sigma) fluctuations in a cold dark matter initial power spectrum. However, the model is far from explaining dark energy on larger scales (spatially), where a 6% effect on 400 Mpc domains is identified that can be traced back to an on average negative intrinsic curvature today. One drawback of the quantitative results presented is the fact that the epoch when backreaction is effective on large scales and leads to volume acceleration lies in the future. We discuss this issue in relation to the initial spectrum, the dark matter problem, the coincidence problem, and the fact that large-scale dark energy is an effect on the past light cone (not spatial), and we pinpoint key elements of future research.

  15. Dynamics of gravitating hadron matter in a Bianchi-IX cosmological model

    NASA Astrophysics Data System (ADS)

    Pavluchenko, Sergey A.

    2016-08-01

    We perform an analysis of the Einstein-Skyrme cosmological model in the Bianchi-IX background. We analytically describe asymptotic regimes and semianalytically describe generic regimes. It appears that depending on the product of the Newtonian constant κ with Skyrme coupling K , in the absence of the cosmological term, there are three possible regimes: recollapse with κ K <2 and two power-law regimes, ∝t1 /2 for κ K =2 and ∝t for κ K >2 . In the presence of the positive cosmological term, power-law regimes turn to the exponential (de Sitter) ones, while the recollapse regime turns to the exponential if the value for the Λ -term is sufficiently large, otherwise the regime remains recollapse. The negative cosmological term leads to the recollapse regardless of κ K . All nonsingular regimes have the squashing coefficient a (t )→1 at late times, which is associated with restoring symmetry dynamics. Also all nonsingular regimes appear to be linearly stable exponential solutions always, while power-law regimes for an open region of the initial conditions.

  16. A MAGNIFIED GLANCE INTO THE DARK SECTOR: PROBING COSMOLOGICAL MODELS WITH STRONG LENSING IN A1689

    SciTech Connect

    Magaña, Juan; Motta, V.; Cárdenas, Victor H.; Verdugo, T.; Jullo, Eric E-mail: veronica.motta@uv.cl E-mail: tomasverdugo@gmail.com

    2015-11-01

    In this paper we constrain four alternative models to the late cosmic acceleration in the universe: Chevallier–Polarski–Linder (CPL), interacting dark energy (IDE), Ricci holographic dark energy (HDE), and modified polytropic Cardassian (MPC). Strong lensing (SL) images of background galaxies produced by the galaxy cluster Abell 1689 are used to test these models. To perform this analysis we modify the LENSTOOL lens modeling code. The value added by this probe is compared with other complementary probes: Type Ia supernovae (SN Ia), baryon acoustic oscillations (BAO), and cosmic microwave background (CMB). We found that the CPL constraints obtained for the SL data are consistent with those estimated using the other probes. The IDE constraints are consistent with the complementary bounds only if large errors in the SL measurements are considered. The Ricci HDE and MPC constraints are weak, but they are similar to the BAO, SN Ia, and CMB estimations. We also compute the figure of merit as a tool to quantify the goodness of fit of the data. Our results suggest that the SL method provides statistically significant constraints on the CPL parameters but is weak for those of the other models. Finally, we show that the use of the SL measurements in galaxy clusters is a promising and powerful technique to constrain cosmological models. The advantage of this method is that cosmological parameters are estimated by modeling the SL features for each underlying cosmology. These estimations could be further improved by SL constraints coming from other galaxy clusters.

  17. A Magnified Glance into the Dark Sector: Probing Cosmological Models with Strong Lensing in A1689

    NASA Astrophysics Data System (ADS)

    Magaña, Juan; Cárdenas, V. Motta ´ctor H., Vi; Verdugo, T.; Jullo, Eric

    2015-11-01

    In this paper we constrain four alternative models to the late cosmic acceleration in the universe: Chevallier–Polarski–Linder (CPL), interacting dark energy (IDE), Ricci holographic dark energy (HDE), and modified polytropic Cardassian (MPC). Strong lensing (SL) images of background galaxies produced by the galaxy cluster Abell 1689 are used to test these models. To perform this analysis we modify the LENSTOOL lens modeling code. The value added by this probe is compared with other complementary probes: Type Ia supernovae (SN Ia), baryon acoustic oscillations (BAO), and cosmic microwave background (CMB). We found that the CPL constraints obtained for the SL data are consistent with those estimated using the other probes. The IDE constraints are consistent with the complementary bounds only if large errors in the SL measurements are considered. The Ricci HDE and MPC constraints are weak, but they are similar to the BAO, SN Ia, and CMB estimations. We also compute the figure of merit as a tool to quantify the goodness of fit of the data. Our results suggest that the SL method provides statistically significant constraints on the CPL parameters but is weak for those of the other models. Finally, we show that the use of the SL measurements in galaxy clusters is a promising and powerful technique to constrain cosmological models. The advantage of this method is that cosmological parameters are estimated by modeling the SL features for each underlying cosmology. These estimations could be further improved by SL constraints coming from other galaxy clusters.

  18. Randall-Sundrum cosmological model with nonminimal derivative coupling of scalar field

    SciTech Connect

    Widiyani, Agustina Suroso, Agus Zen, Freddy P.

    2015-04-16

    Nonminimal derivative coupling (NMDC) of scalar field in time-dependent Randall-Sundrum model is investigated. Firstly, we take a simple relation between the scale factor on the brane, a(t), and the scale factor of the extradimension, b(t), as b = a{sup γ} where γ is a constant. Then, we derive the Einstein equation and find its cosmological solution for a special case of static extra dimension, γ = 0. As the result, we find that de Sitter solution is a typical solution of our model. We also find that the brane tension which is related to cosmological constant on the brane is related to the coupling constant of the model.

  19. Squeezed States, Uncertainty Relations and the Pauli Principle in Composite and Cosmological Models

    NASA Technical Reports Server (NTRS)

    Terazawa, Hidezumi

    1996-01-01

    The importance of not only uncertainty relations but also the Pauli exclusion principle is emphasized in discussing various 'squeezed states' existing in the universe. The contents of this paper include: (1) Introduction; (2) Nuclear Physics in the Quark-Shell Model; (3) Hadron Physics in the Standard Quark-Gluon Model; (4) Quark-Lepton-Gauge-Boson Physics in Composite Models; (5) Astrophysics and Space-Time Physics in Cosmological Models; and (6) Conclusion. Also, not only the possible breakdown of (or deviation from) uncertainty relations but also the superficial violation of the Pauli principle at short distances (or high energies) in composite (and string) models is discussed in some detail.

  20. Off The Beaten Path: Modeling the Dynamics of Supermassive Black Holes in Cosmological Simulations

    NASA Astrophysics Data System (ADS)

    Tremmel, Michael J.; Governato, Fabio; Volonteri, Marta; Quinn, Thomas R.

    2015-01-01

    Cosmological simulations are an essential tool to understand the co-evolution of supermassive black holes (SMBHs) and their host galaxies. However, the limited resolution of these simulations presents unique challenges to successfully modeling black hole dynamics. We present a novel, physically motivated method for improving the dynamics of black holes in cosmological simulations, by accounting for the unresolved dynamical friction that SMBHs feel from stars and dark matter. We show how this approach, which naturally scales with resolution, is a major step forward compared to more commonly used 'advection' models that often assume SMBHs sink very rapidly toward the center of their host galaxies. Here, we demonstrate that our method is able to prevent numerical heating of SMBHs while allowing for realistic dynamics.Our implementation will allow us to more realistically model SMBH dynamics, accretion, and mergers in cosmological simulations, giving us the ability to better understand how SMBHs grow with their host galaxies. This also provides an opportunity for more detailed studies of SMBHs in dwarf galaxies, which can give crucial insight into constraining black hole seed formation models.

  1. Ghost instabilities of cosmological models with vector fields nonminimally coupled to the curvature

    SciTech Connect

    Himmetoglu, Burak; Peloso, Marco; Contaldi, Carlo R.

    2009-12-15

    We prove that many cosmological models characterized by vectors nonminimally coupled to the curvature (such as the Turner-Widrow mechanism for the production of magnetic fields during inflation, and models of vector inflation or vector curvaton) contain ghosts. The ghosts are associated with the longitudinal vector polarization present in these models and are found from studying the sign of the eigenvalues of the kinetic matrix for the physical perturbations. Ghosts introduce two main problems: (1) they make the theories ill defined at the quantum level in the high energy/subhorizon regime (and create serious problems for finding a well-behaved UV completion), and (2) they create an instability already at the linearized level. This happens because the eigenvalue corresponding to the ghost crosses zero during the cosmological evolution. At this point the linearized equations for the perturbations become singular (we show that this happens for all the models mentioned above). We explicitly solve the equations in the simplest cases of a vector without a vacuum expectation value in a Friedmann-Robertson-Walker geometry, and of a vector with a vacuum expectation value plus a cosmological constant, and we show that indeed the solutions of the linearized equations diverge when these equations become singular.

  2. A TEST OF COSMOLOGICAL MODELS USING HIGH-z MEASUREMENTS OF H(z)

    SciTech Connect

    Melia, Fulvio; McClintock, Thomas M. E-mail: tmcclintock89@gmail.com

    2015-10-15

    The recently constructed Hubble diagram using a combined sample of SNLS and SDSS-II SNe Ia, and an application of the Alcock–Paczyński (AP) test using model-independent Baryon Acoustic Oscillation (BAO) data, have suggested that the principal constraint underlying the cosmic expansion is the total equation-of-state of the cosmic fluid, rather than that of its dark energy. These studies have focused on the critical redshift range (0 ≲ z ≲ 2) within which the transition from decelerated to accelerated expansion is thought to have occurred, and they suggest that the cosmic fluid has zero active mass, consistent with a constant expansion rate. The evident impact of this conclusion on cosmological theory calls for an independent confirmation. In this paper, we carry out this crucial one-on-one comparison between the R{sub h} = ct universe (a Friedmann–Robertson–Walker cosmology with zero active mass) and wCDM/ΛCDM, using the latest high-z measurements of H(z). Whereas the SNe Ia yield the integrated luminosity distance, while the AP diagnostic tests the geometry of the universe, the Hubble parameter directly samples the expansion rate itself. We find that the model-independent cosmic chronometer data prefer R{sub h} = ct over wCDM/ΛCDM with a Bayes Information Criterion likelihood of ∼95% versus only ∼5%, in strong support of the earlier SNe Ia and AP results. This contrasts with a recent analysis of H(z) data based solely on BAO measurements which, however, strongly depend on the assumed cosmology. We discuss why the latter approach is inappropriate for model comparisons, and emphasize again the need for truly model-independent observations to be used in cosmological tests.

  3. Exact string theory model of closed timelike curves and cosmological singularities

    SciTech Connect

    Johnson, Clifford V.; Svendsen, Harald G.

    2004-12-15

    We study an exact model of string theory propagating in a space-time containing regions with closed timelike curves (CTCs) separated from a finite cosmological region bounded by a big bang and a big crunch. The model is an nontrivial embedding of the Taub-NUT geometry into heterotic string theory with a full conformal field theory (CFT) definition, discovered over a decade ago as a heterotic coset model. Having a CFT definition makes this an excellent laboratory for the study of the stringy fate of CTCs, the Taub cosmology, and the Milne/Misner-type chronology horizon which separates them. In an effort to uncover the role of stringy corrections to such geometries, we calculate the complete set of {alpha}{sup '} corrections to the geometry. We observe that the key features of Taub-NUT persist in the exact theory, together with the emergence of a region of space with Euclidean signature bounded by timelike curvature singularities. Although such remarks are premature, their persistence in the exact geometry is suggestive that string theory is able to make physical sense of the Milne/Misner singularities and the CTCs, despite their pathological character in general relativity. This may also support the possibility that CTCs may be viable in some physical situations, and may be a natural ingredient in pre-big bang cosmological scenarios.

  4. Comparison and Historical Evolution of Ancient Greek Cosmological Ideas and Mathematical Models

    NASA Astrophysics Data System (ADS)

    Pinotsis, Antonios D.

    2005-12-01

    We present a comparative study of the cosmological ideas and mathematical models in ancient Greece. We show that the heliocentric system introduced by Aristarchus of Samos was the outcome of much intellectual activity. Many Greek philosophers, mathematicians and astronomers such as Anaximander, Philolaus, Hicetas, Ecphantus and Heraclides of Pontus contributed to this. Also, Ptolemy was influenced by the cosmological model of Heraclides of Pontus for the explanation of the apparent motions of Mercury and Venus. Apollonius, who wrote the definitive work on conic sections, introduced the theory of eccentric circles and implemented them together with epicycles instead of considering that the celestial bodies travel in elliptic orbits. This is due to the deeply rooted belief that the orbits of the celestial bodies were normal circular motions around the Earth, which was still. There was also a variety of important ideas which are relevant to modern science. We present the ideas of Plato that are consistent with modern relativity theories, as well as Aristarchus' estimations of the size of the Universe in comparison with the size of the planetary system. As a first approximation, Hipparchus' theory of eccentric circles was equivalent to the first two laws of Kepler. The significance of the principle of independence and superposition of motions in the formulation of ancient cosmological models is also clarified.

  5. Non-singular string cosmology in a 2d hybrid model

    NASA Astrophysics Data System (ADS)

    Florakis, I.; Kounnas, C.; Partouche, H.; Toumbas, N.

    2011-03-01

    The existence of non-singular string cosmologies is established in a class of two-dimensional supersymmetric Hybrid models at finite temperature. The left-moving sector of the Hybrid models gives rise to 16 real (N=4) spacetime supercharges as in the usual superstring models. The right-moving sector is non-supersymmetric at the massless level, but is characterized by MSDS symmetry, which ensures boson/fermion degeneracy of the right-moving massive levels. Finite temperature configurations, which are free of Hagedorn instabilities, are constructed in the presence of non-trivial “gravito-magnetic” fluxes. These fluxes inject non-trivial winding charge into the thermal vacuum and restore the thermal T-duality symmetry associated with the Euclidean time circle. Thanks to the unbroken right-moving MSDS symmetry, the one-loop string partition function is exactly calculable beyond any α‧-approximation. At the self-dual point new massless thermal states appear, sourcing localized spacelike branes, which can be used to connect a contracting thermal Universe to an expanding one. The resulting bouncing cosmology is free of any curvature singularities and the string coupling remains perturbative throughout the cosmological evolution.

  6. Modified-Gravity-GADGET: a new code for cosmological hydrodynamical simulations of modified gravity models

    NASA Astrophysics Data System (ADS)

    Puchwein, Ewald; Baldi, Marco; Springel, Volker

    2013-11-01

    We present a new massively parallel code for N-body and cosmological hydrodynamical simulations of modified gravity models. The code employs a multigrid-accelerated Newton-Gauss-Seidel relaxation solver on an adaptive mesh to efficiently solve for perturbations in the scalar degree of freedom of the modified gravity model. As this new algorithm is implemented as a module for the P-GADGET3 code, it can at the same time follow the baryonic physics included in P-GADGET3, such as hydrodynamics, radiative cooling and star formation. We demonstrate that the code works reliably by applying it to simple test problems that can be solved analytically, as well as by comparing cosmological simulations to results from the literature. Using the new code, we perform the first non-radiative and radiative cosmological hydrodynamical simulations of an f (R)-gravity model. We also discuss the impact of active galactic nucleus feedback on the matter power spectrum, as well as degeneracies between the influence of baryonic processes and modifications of gravity.

  7. Galactic entropy in extended Kaluza-Klein cosmology

    NASA Astrophysics Data System (ADS)

    Yanar, Hilmi; Salti, Mustafa; Aydogdu, Oktay; Acikgoz, Irfan; Yasar, Erol

    2016-02-01

    We use a Kaluza-Klein model with variable cosmological and gravitational terms to discuss the nature of galactic entropy function. For this purpose, we assume a universe filled with dark fluid and consider five-dimensional (5D) field equations using the Gamma law equation. We mainly discuss the validity of the first and generalized second laws of galactic thermodynamics for viable Kaluza-Klein models.

  8. The Scalar-photon Coupling with Mie Invariant Within the Scope of Bianchi Type-I Cosmological Model

    NASA Astrophysics Data System (ADS)

    Muharlyamov, Ruslan K.; Pankratyeva, Tatiana N.

    2016-02-01

    We investigate the Bianchi type-I cosmological model with the scalar and electromagnetic fields possessing non-minimal couplings. They contain the Mie invariant that leads to the flat Friedman's cosmological model. We found the lagrangian for interaction, which the isotropization process of the expansion takes place. Two cases are considered, when the Mie invariant is constat or time-dependent. We study the canonical scalar field and the phantom one.

  9. An accurate halo model for fitting non-linear cosmological power spectra and baryonic feedback models

    NASA Astrophysics Data System (ADS)

    Mead, A. J.; Peacock, J. A.; Heymans, C.; Joudaki, S.; Heavens, A. F.

    2015-12-01

    We present an optimized variant of the halo model, designed to produce accurate matter power spectra well into the non-linear regime for a wide range of cosmological models. To do this, we introduce physically motivated free parameters into the halo-model formalism and fit these to data from high-resolution N-body simulations. For a variety of Λ cold dark matter (ΛCDM) and wCDM models, the halo-model power is accurate to ≃ 5 per cent for k ≤ 10h Mpc-1 and z ≤ 2. An advantage of our new halo model is that it can be adapted to account for the effects of baryonic feedback on the power spectrum. We demonstrate this by fitting the halo model to power spectra from the OWLS (OverWhelmingly Large Simulations) hydrodynamical simulation suite via parameters that govern halo internal structure. We are able to fit all feedback models investigated at the 5 per cent level using only two free parameters, and we place limits on the range of these halo parameters for feedback models investigated by the OWLS simulations. Accurate predictions to high k are vital for weak-lensing surveys, and these halo parameters could be considered nuisance parameters to marginalize over in future analyses to mitigate uncertainty regarding the details of feedback. Finally, we investigate how lensing observables predicted by our model compare to those from simulations and from HALOFIT for a range of k-cuts and feedback models and quantify the angular scales at which these effects become important. Code to calculate power spectra from the model presented in this paper can be found at https://github.com/alexander-mead/hmcode.

  10. Parameters of cosmological models and recent astronomical observations

    SciTech Connect

    Sharov, G.S.; Vorontsova, E.G. E-mail: elenavor@inbox.ru

    2014-10-01

    For different gravitational models we consider limitations on their parameters coming from recent observational data for type Ia supernovae, baryon acoustic oscillations, and from 34 data points for the Hubble parameter H(z) depending on redshift. We calculate parameters of 3 models describing accelerated expansion of the universe: the ΛCDM model, the model with generalized Chaplygin gas (GCG) and the multidimensional model of I. Pahwa, D. Choudhury and T.R. Seshadri. In particular, for the ΛCDM model 1σ estimates of parameters are: H{sub 0}=70.262±0.319 km {sup -1}Mp {sup -1}, Ω{sub m}=0.276{sub -0.008}{sup +0.009}, Ω{sub Λ}=0.769±0.029, Ω{sub k}=-0.045±0.032. The GCG model under restriction 0α≥ is reduced to the ΛCDM model. Predictions of the multidimensional model essentially depend on 3 data points for H(z) with z≥2.3.

  11. Rigorous Newtonian 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.

  12. Isotropic cosmological models in F(T,TG) theory

    NASA Astrophysics Data System (ADS)

    Sharif, M.; Nazir, Kanwal

    2016-09-01

    This paper is devoted to study evolution of the isotropic universe models in the framework of F(T,TG) gravity (T represents torsion scalar and TG is the teleparallel equivalent of the Gauss-Bonnet (GB) term). We construct F(T,TG) models by taking different eras of the universe like non-relativistic and relativistic matter eras, dark energy (DE) dominated era and their combinations. It is found that the reconstructed models indicate decreasing behavior for DE dominated era and its combination with other eras. We also discuss stability of each reconstructed model. Finally, we evaluate equation of state (EoS) parameter by considering two models and study its behavior graphically.

  13. Behavior of nonlinear anisotropies in bouncing Bianchi I models of loop quantum cosmology

    SciTech Connect

    Chiou, D.-W.; Vandersloot, Kevin

    2007-10-15

    In homogeneous and isotropic loop quantum cosmology, gravity can behave repulsively at Planckian energy densities leading to the replacement of the big bang singularity with a big bounce. Yet in any bouncing scenario it is important to include nonlinear effects from anisotropies which typically grow during the collapsing phase. We investigate the dynamics of a Bianchi I anisotropic model within the framework of loop quantum cosmology. Using effective semiclassical equations of motion to study the dynamics, we show that the big bounce is still predicted with only differences in detail arising from the inclusion of anisotropies. We show that the anisotropic shear term grows during the collapsing phase, but remains finite through the bounce. Immediately following the bounce, the anisotropies decay and with the inclusion of matter with equation of state w<+1, the universe isotropizes in the expanding phase.

  14. Spherically symmetric solutions of a (4 + n)-dimensional Einstein Yang Mills model with cosmological constant

    NASA Astrophysics Data System (ADS)

    Brihaye, Yves; Hartmann, Betti

    2005-01-01

    We construct solutions of an Einstein Yang Mills system including a cosmological constant in 4 + n spacetime dimensions, where the n-dimensional manifold associated with the extra dimensions is taken to be Ricci flat. Assuming the matter and metric fields to be independent of the n extra coordinates, a spherical symmetric ansatz for the fields leads to a set of coupled ordinary differential equations. We find that for n > 1 only solutions with either one non-zero Higgs field or with all Higgs fields constant and zero gauge field function (corresponding to a Wu Yang-type ansatz) exist. We give the analytic solutions available in this model. These are 'embedded' Abelian solutions with a diverging size of the manifold associated with the extra n dimensions. Depending on the choice of parameters, these latter solutions either represent naked singularities or they possess a single horizon. We also present solutions of the effective four-dimensional Einstein Yang Mills Higgs-dilaton model, where the higher-dimensional cosmological constant induces a Liouville-type potential. The solutions are non-Abelian solutions with diverging Higgs fields, which exist only up to a maximal value of the cosmological constant.

  15. Models of quintessence coupled to the electromagnetic field and the cosmological evolution of alpha

    NASA Astrophysics Data System (ADS)

    Copeland, E. J.; Nunes, N. J.; Pospelov, M.

    2004-01-01

    We study the change of the effective fine structure constant in the cosmological models of a scalar field with a nonvanishing coupling to the electromagnetic field. Combining cosmological data and terrestrial observations we place empirical constraints on the size of the possible coupling and explore a large class of models that exhibit tracking behavior. The change of the fine structure constant implied by the quasar absorption spectra together with the requirement of tracking behavior impose a lower bound of the size of this coupling. Furthermore, the transition to the quintessence regime implies a narrow window for this coupling around 10-5 in units of the inverse Planck mass. We also propose a nonminimal coupling between electromagnetism and quintessence which has the effect of leading only to changes of alpha determined from atomic physics phenomena, but leaving no observable consequences through nuclear physics effects. In doing so we are able to reconcile the claimed cosmological evidence for a changing fine structure constant with the tight constraints emerging from the Oklo natural nuclear reactor.

  16. Inflation in a renormalizable cosmological model and the cosmic no hair conjecture

    NASA Technical Reports Server (NTRS)

    Maeda, Kei-Ichi; Stein-Schabes, Jaime A.; Futamase, Toshifumi

    1988-01-01

    The possibility of having inflation in a renormalizable cosmological model is investigated. The Cosmic No Hair Conjecture is proved to hold for all Bianchi types except Bianchi IX. By the use of a conformal transformation on the metric it is shown that these models are equivalent to the ones described by the Einstein-Hilbert action for gravity minimally coupled to a set of scalar fields with inflationary potentials. Henceforth, it is proven that inflationary solutions behave as attractors in solution space, making it a natural event in the evolution of such models.

  17. Unified Dark Matter and Dark Energy Description in a Chiral Cosmological Model

    NASA Astrophysics Data System (ADS)

    Abbyazov, Renat R.; Chervon, Sergey V.

    2013-03-01

    We show the way of dark matter and dark energy presentation via ansatzs on the kinetic energies of the fields in the two-component chiral cosmological model (CCM). To connect a kinetic interaction of dark matter and dark energy with observational data the reconstruction procedure for the chiral metric component h22 and the potential of (self-)interaction V has been developed. The reconstruction of h22 and V for the early and later inflation have been performed. The proposed model is confronted to ΛCDM model as well.

  18. A new approach to cosmological perturbations in f(R) models

    SciTech Connect

    Bertacca, Daniele; Bartolo, Nicola; Matarrese, Sabino E-mail: nicola.bartolo@pd.infn.it

    2012-08-01

    We propose an analytic procedure that allows to determine quantitatively the deviation in the behavior of cosmological perturbations between a given f(R) modified gravity model and a ΛCDM reference model. Our method allows to study structure formation in these models from the largest scales, of the order of the Hubble horizon, down to scales deeply inside the Hubble radius, without employing the so-called 'quasi-static' approximation. Although we restrict our analysis here to linear perturbations, our technique is completely general and can be extended to any perturbative order.

  19. Cosmological ``Truths''

    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

  20. Cold Galaxies on FIRE: Modeling the Most Luminous Starbursts in the Universe with Cosmological Zoom Simulations

    NASA Astrophysics Data System (ADS)

    Narayanan, Desika

    2014-10-01

    As the most luminous, heavily star-forming galaxies in the Universe, Submillimeter Galaxies at z 2-4 are key players in galaxy evolution. Since their discovery, SMGs have received significant attention from HST in characterizing their physical morphology, stellar masses, and star formation histories. Unfortunately, these physical constraints have been difficult for theorists to reconcile with galaxy formation simulations. Previous generations of simulations have all either {a} neglected baryons; {b} neglected radiative transfer {and connecting to observations}; or {c} neglected cosmological conditions. Here, we propose to conduct the first ever cosmological hydrodynamic simulations of Submillimeter Galaxy formation that couple with bona fide 3D dust radiative transfer calculations. These ultra-high resolution simulations {parsec-scale} will be the first to resolve the sites of dust obscuration, the cosmic growth history of SMGs, and their evolutionary destiny. Our proposal has two principle goals: {1} Develop the first ever model for SMG formation from cosmological simulations that include both baryons and dust radiative transfer; {2} Capitalize on our parsec-scale resolution to understand the connection between the physical properties of star-forming regions in high-z starbursts, and recent IMF constraints from present-epoch massive galaxies.

  1. Compatibility of the large quasar groups with the concordance cosmological model

    NASA Astrophysics Data System (ADS)

    Marinello, Gabriel E.; Clowes, Roger G.; Campusano, Luis E.; Williger, Gerard M.; Söchting, Ilona K.; Graham, Matthew J.

    2016-09-01

    We study the compatibility of large quasar groups with the concordance cosmological model. Large quasar groups are very large spatial associations of quasars in the cosmic web, with sizes of 50-250 h-1 Mpc. In particular, the largest large quasar group known, named Huge-LQG, has a longest axis of ˜860 h-1 Mpc, larger than the scale of homogeneity (˜260 Mpc), which has been noted as a possible violation of the cosmological principle. Using mock catalogues constructed from the Horizon Run 2 cosmological simulation, we found that large quasar groups size, quasar member number and mean overdensity distributions in the mocks agree with observations. The Huge-LQG is found to be a rare group with a probability of 0.3 per cent of finding a group as large or larger than the observed, but an extreme value analysis shows that it is an expected maximum in the sample volume with a probability of 19 per cent of observing a largest quasar group as large or larger than Huge-LQG. The Huge-LQG is expected to be the largest structure in a volume at least 5.3 ± 1 times larger than the one currently studied.

  2. Machine learning and cosmological simulations - I. Semi-analytical models

    NASA Astrophysics Data System (ADS)

    Kamdar, Harshil M.; Turk, Matthew J.; Brunner, Robert J.

    2016-01-01

    We present a new exploratory framework to model galaxy formation and evolution in a hierarchical Universe by using machine learning (ML). Our motivations are two-fold: (1) presenting a new, promising technique to study galaxy formation, and (2) quantitatively analysing the extent of the influence of dark matter halo properties on galaxies in the backdrop of semi-analytical models (SAMs). We use the influential Millennium Simulation and the corresponding Munich SAM to train and test various sophisticated ML algorithms (k-Nearest Neighbors, decision trees, random forests, and extremely randomized trees). By using only essential dark matter halo physical properties for haloes of M > 1012 M⊙ and a partial merger tree, our model predicts the hot gas mass, cold gas mass, bulge mass, total stellar mass, black hole mass and cooling radius at z = 0 for each central galaxy in a dark matter halo for the Millennium run. Our results provide a unique and powerful phenomenological framework to explore the galaxy-halo connection that is built upon SAMs and demonstrably place ML as a promising and a computationally efficient tool to study small-scale structure formation.

  3. Nonparametric test of consistency between cosmological models and multiband CMB measurements

    SciTech Connect

    Aghamousa, Amir; Shafieloo, Arman E-mail: shafieloo@kasi.re.kr

    2015-06-01

    We present a novel approach to test the consistency of the cosmological models with multiband CMB data using a nonparametric approach. In our analysis we calibrate the REACT (Risk Estimation and Adaptation after Coordinate Transformation) confidence levels associated with distances in function space (confidence distances) based on the Monte Carlo simulations in order to test the consistency of an assumed cosmological model with observation. To show the applicability of our algorithm, we confront Planck 2013 temperature data with concordance model of cosmology considering two different Planck spectra combination. In order to have an accurate quantitative statistical measure to compare between the data and the theoretical expectations, we calibrate REACT confidence distances and perform a bias control using many realizations of the data. Our results in this work using Planck 2013 temperature data put the best fit ΛCDM model at 95% (∼ 2σ) confidence distance from the center of the nonparametric confidence set while repeating the analysis excluding the Planck 217 × 217 GHz spectrum data, the best fit ΛCDM model shifts to 70% (∼ 1σ) confidence distance. The most prominent features in the data deviating from the best fit ΛCDM model seems to be at low multipoles  18 < ℓ < 26 at greater than 2σ, ℓ ∼ 750 at ∼1 to 2σ and ℓ ∼ 1800 at greater than 2σ level. Excluding the 217×217 GHz spectrum the feature at ℓ ∼ 1800 becomes substantially less significance at ∼1 to 2σ confidence level. Results of our analysis based on the new approach we propose in this work are in agreement with other analysis done using alternative methods.

  4. Cosmological constraints on nonstandard inflationary quantum collapse models

    NASA Astrophysics Data System (ADS)

    Landau, Susana J.; Scóccola, Claudia G.; Sudarsky, Daniel

    2012-06-01

    We briefly review an important shortcoming—unearthed in previous works—of the standard version of the inflationary model for the emergence of the seeds of cosmic structure. We consider here some consequences emerging from a proposal inspired on ideas of Penrose and Diósi [R. Penrose, The Emperor’s New Mind. Concerning Computers, Minds and Laws of Physics (1989).][R. Penrose, in Physics meets Philosophy at the Planck Scale: Contemporary Theories in Quantum Gravity, edited by C. Callendar and N. Huggett (2001), pp. 290-+.][L. Diósi, Phys. Lett. A 120, 377 (1987).PYLAAG0375-960110.1016/0375-9601(87)90681-5][L. Diósi, Phys. Rev. A 40, 1165 (1989).PLRAAN0556-279110.1103/PhysRevA.40.1165] about a quantum-gravity induced reduction of the wave function, which has been put forward to address the shortcomings, arguing that its effect on the inflaton field is what can lead to the emergence of the seeds of cosmic structure [A. Perez, H. Sahlmann, and D. Sudarsky, Classical Quantum Gravity 23, 2317 (2006).CQGRDG0264-938110.1088/0264-9381/23/7/008]. The proposal leads to a deviation of the primordial spectrum from the scale-invariant Harrison-Zel’dovich one, and consequently, to a different CMB power spectrum. We perform statistical analyses to test two quantum collapse schemes with recent data from the CMB, including the 7-yr release of WMAP and the matter power spectrum measured using LRGs by the Sloan Digital Sky Survey. Results from the statistical analyses indicate that several collapse models are compatible with CMB and LRG data, and establish constraints on the free parameters of the models. The data put no restriction on the timescale for the collapse of the scalar field modes.

  5. Cosmology in one dimension: A two-component model

    NASA Astrophysics Data System (ADS)

    Shiozawa, Yui; Miller, Bruce N.

    2016-10-01

    We investigate structure formation in a one dimensional model of a matter-dominated universe using a quasi-newtonian formulation. In addition to dark matter, luminous matter is introduced to examine the potential bias in the distributions. We use multifractal analysis techniques to identify structures, including clusters and voids. Both dark matter and luminous matter exhibit fractal geometry as the universe evolves over a finite range. We present the results for the generalized dimensions computed on various scales for each matter distribution. We compare and contrast the fractal dimensions of two types of matter for the first time and show how dynamical considerations cause them to differ.

  6. The Compatibility of Friedmann Cosmological Models with Observed Properties of Gamma-Ray Bursts and a Large Hubble Constant

    NASA Technical Reports Server (NTRS)

    Horack, John M.; Koshut, Thomas M.; Mallozzi, Robert S.; Emslie, A. Gordon; Meegan, Charles A.

    1996-01-01

    The distance scale to cosmic gamma-ray bursts (GRB's) is still uncertain by many orders of magnitude; however, one viable scenario places GRB's at cosmological distances, thereby permitting them to be used as tracers of the cosmological expansion over a significant range of redshifts zeta. Also, several recent measurements of the Hubble constant H(sub 0) appearing in the referred literature report values of 70-80 km/s /Mpc. Although there is significant debate regarding these measurements, we proceed here under the assumption that they are evidence of a large value for H(sub 0). This is done in order to investigate the additional constraints on cosmological models that can be obtained under this hypothesis when combined with the age of the universe and the brightness distribution of cosmological gamma-ray bursts. We show that the range of cosmological models that can be consistent with the GRB brightness distribution, a Hubble constant of 70-80 km/s/Mpc, and a minimum age of the universe of 13-15 Gyr is constrained significantly, largely independent of a wide range of assumptions regarding the evolutionary nature of the burst population. Low-density, Lambda greater than 0 cosmological models with deceleration parameter in the range -1 less than q(sub 0) less than 0 and density parameter sigma(sub 0) in the range approximately equals 0.10-0.25(Omega(sub 0) approximately equals 0.2-0.5) are strongly favored.

  7. Cosmology of a holographic induced gravity model with curvature effects

    SciTech Connect

    Bouhmadi-Lopez, Mariam; Errahmani, Ahmed; Ouali, Taoufiq

    2011-10-15

    We present a holographic model of the Dvali-Gabadadze-Porrati scenario with a Gauss-Bonnet term in the bulk. We concentrate on the solution that generalizes the normal Dvali-Gabadadze-Porrati branch. It is well known that this branch cannot describe the late-time acceleration of the universe even with the inclusion of a Gauss-Bonnet term. Here, we show that this branch in the presence of a Gauss-Bonnet curvature effect and a holographic dark energy with the Hubble scale as the infrared cutoff can describe the late-time acceleration of the universe. It is worthwhile to stress that such an energy density component cannot do the same job on the normal Dvali-Gabadadze-Porrati branch (without Gauss-Bonnet modifications) nor in a standard four-dimensional relativistic model. The acceleration on the brane is also presented as being induced through an effective dark energy which corresponds to a balance between the holographic one and geometrical effects encoded through the Hubble parameter.

  8. Axion cosmology

    NASA Astrophysics Data System (ADS)

    Marsh, David J. E.

    2016-07-01

    Axions comprise a broad class of particles that can play a major role in explaining the unknown aspects of cosmology. They are also well-motivated within high energy physics, appearing in theories related to CP-violation in the standard model, supersymmetric theories, and theories with extra-dimensions, including string theory, and so axion cosmology offers us a unique view onto these theories. I review the motivation and models for axions in particle physics and string theory. I then present a comprehensive and pedagogical view on the cosmology and astrophysics of axion-like particles, starting from inflation and progressing via BBN, the CMB, reionization and structure formation, up to the present-day Universe. Topics covered include: axion dark matter (DM); direct and indirect detection of axions, reviewing existing and future experiments; axions as dark radiation; axions and the cosmological constant problem; decays of heavy axions; axions and stellar astrophysics; black hole superradiance; axions and astrophysical magnetic fields; axion inflation, and axion DM as an indirect probe of inflation. A major focus is on the population of ultralight axions created via vacuum realignment, and its role as a DM candidate with distinctive phenomenology. Cosmological observations place robust constraints on the axion mass and relic density in this scenario, and I review where such constraints come from. I next cover aspects of galaxy formation with axion DM, and ways this can be used to further search for evidence of axions. An absolute lower bound on DM particle mass is established. It is ma > 10-24eV from linear observables, extending to ma ≳ 10-22eV from non-linear observables, and has the potential to reach ma ≳ 10-18eV in the future. These bounds are weaker if the axion is not all of the DM, giving rise to limits on the relic density at low mass. This leads to the exciting possibility that the effects of axion DM on structure formation could one day be detected

  9. Homoclinic chaos in axisymmetric Bianchi-IX cosmological models with an ad hoc quantum potential

    SciTech Connect

    Correa, G. C.; Stuchi, T. J.; Joras, S. E.

    2010-04-15

    In this work we study the dynamics of the axisymmetric Bianchi-IX cosmological model with a term of quantum potential added. As it is well known, this class of Bianchi-IX models is homogeneous and anisotropic with two scale factors, A(t) and B(t), derived from the solution of Einstein's equation for general relativity. The model we use in this work has a cosmological constant and the matter content is dust. To this model we add a quantum-inspired potential that is intended to represent short-range effects due to the general relativistic behavior of matter in small scales and play the role of a repulsive force near the singularity. We find that this potential restricts the dynamics of the model to positive values of A(t) and B(t) and alters some qualitative and quantitative characteristics of the dynamics studied previously by several authors. We make a complete analysis of the phase space of the model finding critical points, periodic orbits, stable/unstable manifolds using numerical techniques such as Poincare section, numerical continuation of orbits, and numerical globalization of invariant manifolds. We compare the classical and the quantum models. Our main result is the existence of homoclinic crossings of the stable and unstable manifolds in the physically meaningful region of the phase space [where both A(t) and B(t) are positive], indicating chaotic escape to inflation and bouncing near the singularity.

  10. Bianchi type-VIh string cloud cosmological models with bulk viscosity

    NASA Astrophysics Data System (ADS)

    Tripathy, Sunil K.; Behera, Dipanjali

    2010-11-01

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

  11. Cosmological models in alternative theory of gravity with bilinear deceleration parameter

    NASA Astrophysics Data System (ADS)

    Mishra, R. K.; Chand, Avtar

    2016-08-01

    In this paper we have studied the exact solution of modified EFE (Einstein's field equations) within the scope of spatially homogeneous and isotropic FLRW (Friedmann-Lemaître-Robertson-Walker) space-time in scalar-tensor BD (Brans-Dicke) theory of gravity. For the purpose we have proposed DP (Deceleration Parameter) q as a bilinear function of proper cosmic time t as q = α (1-t)/1+t and q = -α t/1+t, here α is a non-negative constant. As per requirement we have already addressed the various aspects of cosmological models. Physical and geometric properties of the models have been also presented.

  12. An Early Universe Model with Stiff Matter and a Cosmological Constant

    NASA Astrophysics Data System (ADS)

    Oliveira-Neto, G.; Monerat, G. A.; Corrêa Silva, E. V.; Neves, C.; Ferreira Filho, L. G.

    2011-06-01

    In the present work, we study the quantum cosmology description of a Friedmann-Robertson-Walker model in the presence of a stiff matter perfect fluid and a negative cosmological constant. We work in the Schutz's variational formalism and the spatial sections have constant negative curvature. We quantize the model and obtain the appropriate Wheeler-DeWitt equation. In this model the states are bounded therefore we compute the discrete energy spectrum and the corresponding eigenfunctions. In the present work, we consider only the negative eigenvalues and their corresponding eigenfunctions. This choice implies that the energy density of the perfect fluid is negative. A stiff matter perfect fluid with this property produces a model with a bouncing solution, at the classical level, free from an initial singularity. After that, we use the eigenfunctions in order to construct wave packets and evaluate the time-dependent expectation value of the scale factor. We find that it oscillates between maximum and minimum values. Since the expectation value of the scale factor never vanishes, we confirm that this model is free from an initial singularity, also, at the quantum level.

  13. Initial development of 5D COGENT

    NASA Astrophysics Data System (ADS)

    Cohen, R. H.; Lee, W.; Dorf, M.; Dorr, M.

    2015-11-01

    COGENT is a continuum gyrokinetic edge code being developed by the by the Edge Simulation Laboratory (ESL) collaboration. Work to date has been primarily focussed on a 4D (axisymmetric) version that models transport properties of edge plasmas. We have begun development of an initial 5D version to study edge turbulence, with initial focus on kinetic effects on blob dynamics and drift-wave instability in a shearless magnetic field. We are employing compiler directives and preprocessor macros to create a single source code that can be compiled in 4D or 5D, which helps to ensure consistency of physics representation between the two versions. A key aspect of COGENT is the employment of mapped multi-block grid capability to handle the complexity of diverter geometry. It is planned to eventually exploit this capability to handle magnetic shear, through a series of successively skewed unsheared grid blocks. The initial version has an unsheared grid and will be used to explore the degree to which a radial domain must be block decomposed. We report on the status of code development and initial tests. Work performed for USDOE, at LLNL under contract DE-AC52-07NA27344.

  14. Constraints on cosmological models and reconstructing the acceleration history of the Universe with gamma-ray burst distance indicators

    SciTech Connect

    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.

  15. Dark Energy and Dark Matter in Some Cosmological Models (as remnants of visible universe)

    NASA Astrophysics Data System (ADS)

    El Fady Morcos, Abd

    2016-07-01

    Homogeneity and isotropy distribution of matter, have been considered in most of cosmological models. The formation possibility of clusters of galaxies in some stable models, have been studied. In the present work we are going to consider the dark energy and dark matter as the rest of the visible universe. The self-consistent model formulated in the context of the Generalized Field Theory , the standard model built in the General Theory of Relativity, and Saez and de Juan model constructed in the background of Møller Tetrad Theory of gravitation have been used. It is found these the dark matter and dark energy is related to a parameter ɛ. This parameter depends on the used model and availability of formation of condensations in it.

  16. How robust are inflation model and dark matter constraints from cosmological data?

    SciTech Connect

    Hamann, Jan; Hannestad, Steen; Sloth, Martin S.; Wong, Yvonne Y. Y.

    2007-01-15

    High-precision data from observation of the cosmic microwave background and the large scale structure of the universe provide very tight constraints on the effective parameters that describe cosmological inflation. Indeed, within a constrained class of {lambda}CDM models, the simple {lambda}{phi}{sup 4} chaotic inflation model already appears to be ruled out by cosmological data. In this paper, we compute constraints on inflationary parameters within a more general framework that includes other physically motivated parameters such as a nonzero neutrino mass. We find that a strong degeneracy between the tensor-to-scalar ratio r and the neutrino mass prevents {lambda}{phi}{sup 4} from being excluded by present data. Reversing the argument, if {lambda}{phi}{sup 4} is the correct model of inflation, it predicts a sum of neutrino masses at 0.3{yields}0.5 eV, a range compatible with present experimental limits and within the reach of the next generation of neutrino mass measurements. We also discuss the associated constraints on the dark matter density, the dark energy equation of state, and spatial curvature, and show that the allowed regions are significantly altered. Importantly, we find an allowed range of 0.094<{omega}{sub c}h{sup 2}<0.136 for the dark matter density, a factor of 2 larger than that reported in previous studies. This expanded parameter space may have implications for constraints on SUSY dark matter models.

  17. Kaluza-Klein cosmological model in f(R, T) gravity with Λ(T)

    NASA Astrophysics Data System (ADS)

    Sahoo, P. K.; Mishra, B.; Tripathy, S. K.

    2016-04-01

    A class of Kaluza-Klein cosmological models in $f(R,T)$ theory of gravity have been investigated. In the work, we have considered the functional $f(R,T)$ to be in the form $f(R,T)=f(R)+f(T)$ with $f(R)=\\lambda R$ and $f(T)=\\lambda T$. Such a choice of the functional $f(R,T)$ leads to an evolving effective cosmological constant $\\Lambda$ which depends on the stress energy tensor. The source of the matter field is taken to be a perfect cosmic fluid. The exact solutions of the field equations are obtained by considering a constant deceleration parameter which leads two different aspects of the volumetric expansion namely a power law and an exponential volumetric expansion. Keeping an eye on the accelerating nature of the universe in the present epoch, the dynamics and physical behaviour of the models have been discussed. From statefinder diagnostic pair we found that the model with exponential volumetric expansion behaves more like a $\\Lambda$CDM model.

  18. Some implications of signature-change in cosmological models of loop quantum gravity

    SciTech Connect

    Bojowald, Martin; Mielczarek, Jakub E-mail: jakub.mielczarek@uj.edu.pl

    2015-08-01

    Signature change at high density has been obtained as a possible consequence of deformed space-time structures in models of loop quantum gravity. This article provides a conceptual discussion of implications for cosmological scenarios, based on an application of mathematical results for mixed-type partial differential equations (the Tricomi problem). While the effective equations from which signature change has been derived are shown to be locally regular and therefore reliable, the underlying theory of loop quantum gravity may face several global problems in its semiclassical solutions.

  19. Schrödinger Wheeler DeWitt Equation in Chaplygin Gas FRW Cosmological Model

    NASA Astrophysics Data System (ADS)

    Pedram, P.; Jalalzadeh, S.; Gousheh, S. S.

    2007-12-01

    We present a Chaplygin gas Friedmann Robertson Walker quantum cosmological model. In this work the Schutz’s variational formalism is applied with positive, negative, and zero constant spatial curvature. In this approach the notion of time can be recovered. These give rise to Schrödinger Wheeler DeWitt equation for the scale factor. We use the eigenfunctions in order to construct wave packets for each case. We study the time dependent behavior of the expectation value of the scale factor, using the many-worlds interpretations of quantum mechanics.

  20. Sociology of Modern Cosmology

    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.

  1. Mental models of the Earth, Sun and Moon: Indian children's cosmologies

    NASA Astrophysics Data System (ADS)

    Samarapungavan, A.; Vosniadou, S.; Brewer, W. F.

    Indian children were interviewed. In places where both folk and scientific cosmologies are accessible to the children, aspects of the folk cosmologies are often incorporated into the children's ideas. Hyderabad children often describe a spherical Earth supported by a body of water, a description that is not found in American children's initial cosmologies.

  2. Bianchi type-V bulk viscous string cosmological model in f( R, T) gravity

    NASA Astrophysics Data System (ADS)

    Naidu, R. L.; Reddy, D. R. K.; Ramprasad, T.; Ramana, K. V.

    2013-11-01

    In this paper, we investigate a spatially homogeneous and anisotropic Bianchi type-V cosmological model in a scalar-tensor theory of gravitation proposed by Harko et al. (Phys. Rev. D 84:024020, 2011) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. To obtain a determinate solution, a special law of variation proposed by Berman (Nuovo Cimento B 74:182, 1983) is used. We have also used the barotropic equation of state for the pressure and density and bulk viscous pressure is assumed to be proportional to energy density. It is interesting to note that the strings in this model do not survive. Also the model does not remain anisotropic throughout the evolution of the universe. Some physical and kinematical properties of the model are also discussed.

  3. Cosmological effects of scalar-photon couplings: dark energy and varying-α Models

    SciTech Connect

    Avgoustidis, A.; Martins, C.J.A.P.; Monteiro, A.M.R.V.L.; Vielzeuf, P.E.; Luzzi, G. E-mail: Carlos.Martins@astro.up.pt E-mail: up110370652@alunos.fc.up.pt

    2014-06-01

    We study cosmological models involving scalar fields coupled to radiation and discuss their effect on the redshift evolution of the cosmic microwave background temperature, focusing on links with varying fundamental constants and dynamical dark energy. We quantify how allowing for the coupling of scalar fields to photons, and its important effect on luminosity distances, weakens current and future constraints on cosmological parameters. In particular, for evolving dark energy models, joint constraints on the dark energy equation of state combining BAO radial distance and SN luminosity distance determinations, will be strongly dominated by BAO. Thus, to fully exploit future SN data one must also independently constrain photon number non-conservation arising from the possible coupling of SN photons to the dark energy scalar field. We discuss how observational determinations of the background temperature at different redshifts can, in combination with distance measures data, set tight constraints on interactions between scalar fields and photons, thus breaking this degeneracy. We also discuss prospects for future improvements, particularly in the context of Euclid and the E-ELT and show that Euclid can, even on its own, provide useful dark energy constraints while allowing for photon number non-conservation.

  4. Local equilibrium solutions in simple anisotropic cosmological models, as described by relativistic fluid dynamics

    NASA Astrophysics Data System (ADS)

    Shogin, Dmitry; Amund Amundsen, Per

    2016-10-01

    We test the physical relevance of the full and the truncated versions of the Israel–Stewart (IS) theory of irreversible thermodynamics in a cosmological setting. Using a dynamical systems method, we determine the asymptotic future of plane symmetric Bianchi type I spacetimes with a viscous mathematical fluid, keeping track of the magnitude of the relative dissipative fluxes, which determines the applicability of the IS theory. We consider the situations where the dissipative mechanisms of shear and bulk viscosity are involved separately and simultaneously. It is demonstrated that the only case in the given model when the fluid asymptotically approaches local thermal equilibrium, and the underlying assumptions of the IS theory are therefore not violated, is that of a dissipative fluid with vanishing bulk viscosity. The truncated IS equations for shear viscosity are found to produce solutions which manifest pathological dynamical features and, in addition, to be strongly sensitive to the choice of initial conditions. Since these features are observed already in the case of an oversimplified mathematical fluid model, we have no reason to assume that the truncation of the IS transport equations will produce relevant results for physically more realistic fluids. The possible role of bulk and shear viscosity in cosmological evolution is also discussed.

  5. The accelerating universe and other cosmological aspects of modified gravity models

    NASA Astrophysics Data System (ADS)

    de Felice, Antonio

    I give a short introduction to standard cosmology and a review of what it is meant by "the dark energy enigma" in chapter l. In chapter 2, I mention and describe some attempts found in the literature of the past few years to attack this problem. Dark energy candidates for which the equation-of-state parameter w is less than -1 violate the dominant energy condition. In scalar-tensor theories of gravity, however, the expansion of the universe can mimic the behavior of general relativity with w < -1 dark energy, without violating any energy conditions. I examine, in chapter 3, whether this possibility is phenomenologically viable by studying Brans-Dicke models and characterizing both the naturalness of the models themselves, and additional observational constraints from limits on the time-dependence of Newton's constant. I find that only highly contrived models would lead observers to measure w < -1. In chapter 4, I consider general curvature-invariant modifications of the Einstein-Hilbert action that become important only in regions of extremely low space-time curvature. I investigate the far future evolution of the universe in such models, examining the possibilities for cosmic acceleration and other ultimate destinies. The models generically possess de Sitter space as an unstable solution and exhibit an interesting set of attractor solutions which, in some cases, provide alternatives to dark energy models. In chapter 5, I study a baryogenesis mechanism operating in the context of hyperextended inflation and making use of a coupling between the scalar field and a standard model global current, such as B or B - L . The method is efficient at temperatures at which these currents are not conserved due to some higher dimensional operator. The particle physics and cosmological phenomenology are discussed. I consider constraints stemming from nucleosynthesis and solar system experiments.

  6. COSMOLOGICAL SIMULATIONS OF INTERGALACTIC MEDIUM EVOLUTION. I. TEST OF THE SUBGRID CHEMICAL ENRICHMENT MODEL

    SciTech Connect

    Côté, Benoit; Martel, Hugo; Drissen, Laurent

    2013-11-10

    We present a one-zone galactic chemical enrichment model that takes into account the contribution of stellar winds from massive stars under the effect of rotation, Type II supernovae, hypernovae, stellar winds from low- and intermediate-mass stars, and Type Ia supernovae. This enrichment model will be implemented in a galactic model designed to be used as a subgrid treatment for galaxy evolution and outflow generation in large-scale cosmological simulations, in order to study the evolution of the intergalactic medium. We test our enrichment prescription by comparing its predictions with the metallicity distribution function and the abundance patterns of 14 chemical elements observed in the Milky Way stars. To do so, we combine the effect of many stellar populations created from the star formation history of the Galaxy in the solar neighborhood. For each stellar population, we keep track of its specific mass, initial metallicity, and age. We follow the time evolution of every population in order to respect the time delay between the various stellar phases. Our model is able to reproduce the observed abundances of C, O, Na, Mg, Al, S, and Ca. For Si, Cr, Mn, Ni, Cu, and Zn, the fits are still reasonable, but improvements are needed. We marginally reproduce the nitrogen abundance in very low metallicity stars. Overall, our results are consistent with the predicted abundance ratios seen in previous studies of the enrichment history of the Milky Way. We have demonstrated that our semi-analytic one-zone model, which cannot deal with spatial information such as the metallicity gradient, can nevertheless successfully reproduce the global Galactic enrichment evolution obtained by more complex models, at a fraction of the computational cost. This model is therefore suitable for a subgrid treatment of chemical enrichment in large-scale cosmological simulations.

  7. Towards scaling cosmological solutions with full coupled Horndeski Lagrangian: the KGB model

    SciTech Connect

    Gomes, A.R.; Amendola, Luca E-mail: l.amendola@thphys.uni-heidelberg.de

    2014-03-01

    We study a general scalar field Lagrangian coupled with matter and linear in □φ (also called KGB model). Within this class of models, we find the most general form of the Lagrangian that allows for cosmological scaling solutions, i.e. solutions where the ratio of matter to field density and the equation of state remain constant. Scaling solutions of this kind may help solving the coincidence problem since in this case the presently observed ratio of matter to dark energy does not depend on initial conditions, but rather on the theoretical parameters. Extending previous results we find that it is impossible to join in a single solution a matter era and the scaling attractor. This is an additional step towards finding the most general scaling Lagrangian within the Horndeski class, i.e. general scalar-tensor models with second order equations of motion.

  8. Thermodynamics and classification of cosmological models in the Horava-Lifshitz theory of gravity

    SciTech Connect

    Wang, Anzhong; Wu, Yumei E-mail: yumei_wu@baylor.edu

    2009-07-01

    We study thermodynamics of cosmological models in the Horava-Lifshitz theory of gravity, and systematically investigate the evolution of the universe filled with a perfect fluid that has the equation of state p = wρ, where p and ρ denote, respectively, the pressure and energy density of the fluid, and w is an arbitrary real constant. Depending on specific values of the free parameters involved in the models, we classify all of them into various cases. In each case the main properties of the evolution are studied in detail, including the periods of deceleration and/or acceleration, and the existence of big bang, big crunch, and big rip singularities. We pay particular attention on models that may give rise to a bouncing universe.

  9. Bianchi type string cosmological models in f(R,T) gravity

    NASA Astrophysics Data System (ADS)

    Sahoo, P. K.; Mishra, B.; Sahoo, Parbati; Pacif, S. K. J.

    2016-09-01

    In this work we have studied Bianchi-III and - VI 0 cosmological models with string fluid source in f( R, T) gravity (T. Harko et al., Phys. Rev. D 84, 024020 (2011)), where R is the Ricci scalar and T the trace of the stress energy-momentum tensor in the context of late time accelerating expansion of the universe as suggested by the present observations. The exact solutions of the field equations are obtained by using a time-varying deceleration parameter. The universe is anisotropic and free from initial singularity. Our model initially shows acceleration for a certain period of time and then decelerates consequently. Several dynamical and physical behaviors of the model are also discussed in detail.

  10. More on cosmological constraints on spontaneous R-symmetry breaking models

    SciTech Connect

    Hamada, Yuta; Kobayashi, Tatsuo; Kamada, Kohei; Ookouchi, Yutaka E-mail: kohei.kamada@epfl.ch E-mail: yutaka.ookouchi@artsci.kyushu-u.ac.jp

    2014-01-01

    We study the spontaneous R-symmetry breaking model and investigate the cosmological constraints on this model due to the pseudo Nambu-Goldstone boson, R-axion. We consider the R-axion which has relatively heavy mass in order to complement our previous work. In this regime, model parameters, R-axions mass and R-symmetry breaking scale, are constrained by Big Bang Nucleosynthesis and overproduction of the gravitino produced from R-axion decay and thermal plasma. We find that the allowed parameter space is very small for high reheating temperature. For low reheating temperature, the U(1){sub R} breaking scale f{sub a} is constrained as f{sub a} < 10{sup 12−14} GeV regardless of the value of R-axion mass.

  11. The three-loop Yang-Mills condensate dark energy model and its cosmological constraints

    SciTech Connect

    Wang, S; Zhang, Y; Xia, T Y E-mail: yzh@ustc.edu.cn

    2008-10-15

    This work is a comprehensive investigation of the Yang-Mills condensate (YMC) dark energy (DE) model, which is extended to include the three-loop quantum corrections. We study its cosmic evolution and the possibility of crossing the phantom divide w = -1, examine in detail the Hubble parameter H, the deceleration parameter q, the statefinder (r,s) diagnostic and the w-w{sup '} diagnostic for the model without and with interaction, and compare our results with other DE models. Also, using the observational data for type Ia supernovae (SNIa), the shift parameter from the cosmic microwave background (CMB), and the baryon acoustic oscillation peak from large scale structures (LSS), we give the cosmological constraints on the three-loop YMC model. It is found that the model can solve the coincidence problem naturally, and its prediction of the aforementioned parameter is much closer to the {Lambda}CDM (CDM: cold dark matter) model one than those from other dynamical DE models; the introduction of the matter-DE interaction will make the YMC model deviate from the {Lambda}CDM model, and will give an equation of state crossing -1. Moreover, it is also found that, for fitting the latest SNIa data alone, the {Lambda}CDM model is slightly better than the three-loop YMC model; but in fitting the combination of SNIa, CMB and LSS data, the three-loop YMC model performs better than the {Lambda}CDM model.

  12. The three-loop Yang-Mills condensate dark energy model and its cosmological constraints

    NASA Astrophysics Data System (ADS)

    Wang, S.; Zhang, Y.; Xia, T. Y.

    2008-10-01

    This work is a comprehensive investigation of the Yang-Mills condensate (YMC) dark energy (DE) model, which is extended to include the three-loop quantum corrections. We study its cosmic evolution and the possibility of crossing the phantom divide w = -1, examine in detail the Hubble parameter H, the deceleration parameter q, the statefinder (r,s) diagnostic and the w-w' diagnostic for the model without and with interaction, and compare our results with other DE models. Also, using the observational data for type Ia supernovae (SNIa), the shift parameter from the cosmic microwave background (CMB), and the baryon acoustic oscillation peak from large scale structures (LSS), we give the cosmological constraints on the three-loop YMC model. It is found that the model can solve the coincidence problem naturally, and its prediction of the aforementioned parameter is much closer to the ΛCDM (CDM: cold dark matter) model one than those from other dynamical DE models; the introduction of the matter-DE interaction will make the YMC model deviate from the ΛCDM model, and will give an equation of state crossing -1. Moreover, it is also found that, for fitting the latest SNIa data alone, the ΛCDM model is slightly better than the three-loop YMC model; but in fitting the combination of SNIa, CMB and LSS data, the three-loop YMC model performs better than the ΛCDM model.

  13. The Evolution of Cosmology

    NASA Astrophysics Data System (ADS)

    Hewett, Lionel

    2008-10-01

    Throughout the centuries numerous models of cosmology have been proposed and discarded as mankind's understanding of the cosmos has grown through improved observations. It is interesting to follow how the scientific consensus regarding cosmology has changed over time so as to favor first one of these models, then another and another up to the present day. This paper describes many of these historical models, explains why so few of them are still considered viable today, and shows what the surviving models have to say about the creation, evolution, and fate of our universe. Included in the discussion are such modern topics as inflationary cosmology, accelerating universe, dark energy, dark matter, and time symmetry.

  14. Scale covariance and G-varying cosmology. IV - The log N-log S relation. [radio source models

    NASA Technical Reports Server (NTRS)

    Canuto, V. M.; Owen, J. R.

    1979-01-01

    The traditional radio counts N(S) and radio source models are studied within the framework of the scale-covariant cosmology developed to investigate whether the relative strength of the gravitational and electromagnetic constants is a function of cosmological epoch. It is found that a gravitational constant G varying as the inverse of t, where t is the epoch in atomic units, is consistent with all the data analyzed. For a wide class of models the present cosmology allows a finer discrimination of the deceleration parameter than does standard theory. The results, when combined with those of previous papers, namely, those from radio and optical flux and angular-diameter data analysis, favor an open universe.

  15. The cosmological constant problem

    SciTech Connect

    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.

  16. 2.5D/3D Models for the enhancement of architectural-urban heritage. An Virtual Tour of design of the Fascist headquarters in Littoria

    NASA Astrophysics Data System (ADS)

    Ippoliti, E.; Calvano, M.; Mores, L.

    2014-05-01

    Enhancement of cultural heritage is not simply a matter of preserving material objects but comes full circle only when the heritage can be enjoyed and used by the community. This is the rationale behind this presentation: an urban Virtual Tour to explore the 1937 design of the Fascist Headquarters in Littoria, now part of Latina, by the architect Oriolo Frezzotti. Although the application is deliberately "simple", it was part of a much broader framework of goals. One such goal was to create "friendly and perceptively meaningful" interfaces by integrating different "3D models" and so enriching. In fact, by exploiting the activation of natural mechanisms of visual perception and the ensuing emotional emphasis associated with vision, the illusionistic simulation of the scene facilitates access to the data even for "amateur" users. A second goal was to "contextualise the information" on which the concept of cultural heritage is based. In the application, communication of the heritage is linked to its physical and linguistic context; the latter is then used as a basis from which to set out to explore and understand the historical evidence. A third goal was to foster the widespread dissemination and sharing of this heritage of knowledge. On the one hand we worked to make the application usable from the Web, on the other, we established a reliable, rapid operational procedure with high quality processed data and ensuing contents. The procedure was also repeatable on a large scale.

  17. SN1987A-Neutrino emission from Supernova': in Dynamic universe model of cosmology

    NASA Astrophysics Data System (ADS)

    Naga Parameswara Gupta, Satyavarapu

    SN1987A-Neutrino emission from supernova before the star bursts' is an important discovery, when viewed from `Dynamic universe model of cosmology' point of view. In OMEG05, we have successfully presented the reasons for calculation error called `missing mass' in an inhomoge-neous, anisotropic and multi-body Dynamic universe Model, where this error is not occurring. But there are some new voices that say about generation of some flavors of neutrinos during Bigbang. We find from SN1987A Neutrino generation covers all flavors. Remaining flavors of Neutrinos are generated from sun and stars. This covers the whole spectrum. This paper covers all these aspects. And other earlier results by Dynamic Universe Model 1. Offers Singularity free solutions 2. Non-collapsing Galaxy structures 3. Solving Missing mass in Galaxies, and it finds reason for Galaxy circular velocity curves. . . . 4. Blue shifted and red shifted Galaxies co-existence. . . 5. Explains the force behind expansion of universe. 6. Explains the large voids and non-uniform matter densities. 7. Explains the Pioneer anomaly 8. Predicts the trajectory of New Horizons satellite. 9 Jeans swindle test 10. Existence of large number of blue shifted Galaxies `SITA Simulations' software was developed about 18 years back for Dynamic Universe Model of Cosmology. It is based on Newtonian physics. It is Classical singularity free N-body tensor solution to the old problem announced by King Oscar II and tried by Poincare in year AD1888 for 133 masses, tested extensively for so many years. This was developed on 486 based PC of those days; the same software was used repeatedly for so many years for solving different Physical problems on Different PCs and Laptops. It is based on Dynamic Universe Model's mathematical back ground.

  18. How many parameters in the cosmological models with dark energy? [rapid communication

    NASA Astrophysics Data System (ADS)

    Godłowski, Włodzimierz; Szydłowski, Marek

    2005-09-01

    In cosmology many dramatically different scenarios in the past (big bang versus bounce) and in the future (de Sitter versus big rip) are compatible with the present day observations. This difficulties are called the degeneracy problem. We use the Akaike (AIC) and Bayesian (BIC) information criteria of model selection to avoid this degeneracy and to determine the model with such a set of parameters which gives the most preferred fit to the data. We consider seven representative scenarios, namely: the ΛCDM, CDM model with topological defect, phantom CDM model, bouncing ΛCDM model, bouncing phantom CDM model, brane ΛCDM model and model with the dynamical equation of state parameter linearized around the present epoch. Applying the information criteria to the currently available SNIa data we show that AIC indicates the flat phantom model while BIC indicates both flat phantom CDM and flat ΛCDM models. Finally we conclude that number of essential parameters chosen by dark energy models which are compared with SNIa data is two.

  19. Gowdy-symmetric cosmological models with Cauchy horizons ruled by non-closed null generators

    NASA Astrophysics Data System (ADS)

    Hennig, Jörg

    2016-08-01

    Smooth Gowdy-symmetric generalized Taub-NUT solutions are a class of inhomogeneous cosmological models with spatial three-sphere topology. They have a past Cauchy horizon with closed null-generators, and they have been shown to develop a second, regular Cauchy horizon in the future, unless in special, well-defined singular cases. Here we generalize these models to allow for past Cauchy horizons ruled by non-closed null generators. In particular, we show local and global existence of such a class of solutions with two functional degrees of freedom. This removes a periodicity condition for the asymptotic data at the past Cauchy horizon that was required before. Moreover, we derive a three-parametric family of exact solutions within that class and study its properties.

  20. SLOWMOVE - A numerical model for the propagation of slow-moving landslides: a spatially distributed 2.5D approach and its application to the analysis of the Super-Sauze landslide (French Alps).

    NASA Astrophysics Data System (ADS)

    Travelletti, Julien; Bégueria, Santiago; van Asch, Theo; Spickermann, Anke; Malet, Jean-Philippe

    2010-05-01

    Process-based models are common tools for understanding and forecasting landslide behaviour. The objective of this study is to describe the implementation of the dynamic SLOWMOVE model in 2.5 dimensions using the GIS scripting language PCRaster. This environment provides visualization of the results through map animations and time series, and a user-friendly interface. The model performance is evaluated on multi-temporal datasets of landslide displacements for the period of summer 2009. The Super-Sauze landslide is triggered in Callovo-Oxfordian black marls and is composed of a silty-sand matrix mixed with moraine debris. It extends over a horizontal distance of 850 m with an average 25° slope. The total volume is estimated at 750,000 m3 and creeping velocities range from 0.01 to 0.40 m day-1. The complex paleo-topography covered by the landslide is made by successions of crests and gullies which play an essential role in the behavior by creating sections with distinct kinematical, mechanical and hydrological characteristics. Observational data showed that the velocity rates are mainly controlled by changes in excess pore water pressure. The SLOWMOVE model has been implemented in 2.5D in order to take into account of complex basal topography represented through a DEM. The landslide is treated as a one-phase material, whose behavior is controlled by rheological properties following a Coulomb-viscous model. SLOWMOVE 2.5D is based on a two dimensional finite difference solution (2D Eulerian space with Cartesian coordinates) of the Saint Venant equations that are derived from a depth-integration of the Navier-Stokes equations of fluid motion. Important assumptions in the model are that: (1) the inertia term in the equation of motion can be cancelled without a significant effect in the velocity field; (2) the acceleration due to internal pressure is controlled by strain; (3) undrained loading generates excess pore water pressure.

  1. 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.

  2. Taylor expansion of luminosity distance in Szekeres cosmological models: effects of local structures evolution on cosmographic parameters

    SciTech Connect

    Villani, Mattia

    2014-06-01

    We consider the Goode-Wainwright representation of the Szekeres cosmological models and calculate the Taylor expansion of the luminosity distance in order to study the effects of the inhomogeneities on cosmographic parameters. Without making a particular choice for the arbitrary functions defining the metric, we Taylor expand up to the second order in redshift for Family I and up to the third order for Family II Szekeres metrics under the hypotesis, based on observation, that local structure formation is over. In a conservative fashion, we also allow for the existence of a non null cosmological constant.

  3. Departures from the Friedmann-Lemaitre-Robertston-Walker Cosmological Model in an Inhomogeneous Universe: A Numerical Examination.

    PubMed

    Giblin, John T; Mertens, James B; Starkman, Glenn D

    2016-06-24

    While the use of numerical general relativity for modeling astrophysical phenomena and compact objects is commonplace, the application to cosmological scenarios is only just beginning. Here, we examine the expansion of a spacetime using the Baumgarte-Shapiro-Shibata-Nakamura formalism of numerical relativity in synchronous gauge. This work represents the first numerical cosmological study that is fully relativistic, nonlinear, and without symmetry. The universe that emerges exhibits an average Friedmann-Lemaître-Robertson-Walker (FLRW) behavior; however, this universe also exhibits locally inhomogeneous expansion beyond that expected in linear perturbation theory around a FLRW background. PMID:27391710

  4. Departures from the Friedmann-Lemaitre-Robertston-Walker Cosmological Model in an Inhomogeneous Universe: A Numerical Examination

    NASA Astrophysics Data System (ADS)

    Giblin, John T.; Mertens, James B.; Starkman, Glenn D.

    2016-06-01

    While the use of numerical general relativity for modeling astrophysical phenomena and compact objects is commonplace, the application to cosmological scenarios is only just beginning. Here, we examine the expansion of a spacetime using the Baumgarte-Shapiro-Shibata-Nakamura formalism of numerical relativity in synchronous gauge. This work represents the first numerical cosmological study that is fully relativistic, nonlinear, and without symmetry. The universe that emerges exhibits an average Friedmann-Lemaître-Robertson-Walker (FLRW) behavior; however, this universe also exhibits locally inhomogeneous expansion beyond that expected in linear perturbation theory around a FLRW background.

  5. Departures from the Friedmann-Lemaitre-Robertston-Walker Cosmological Model in an Inhomogeneous Universe: A Numerical Examination.

    PubMed

    Giblin, John T; Mertens, James B; Starkman, Glenn D

    2016-06-24

    While the use of numerical general relativity for modeling astrophysical phenomena and compact objects is commonplace, the application to cosmological scenarios is only just beginning. Here, we examine the expansion of a spacetime using the Baumgarte-Shapiro-Shibata-Nakamura formalism of numerical relativity in synchronous gauge. This work represents the first numerical cosmological study that is fully relativistic, nonlinear, and without symmetry. The universe that emerges exhibits an average Friedmann-Lemaître-Robertson-Walker (FLRW) behavior; however, this universe also exhibits locally inhomogeneous expansion beyond that expected in linear perturbation theory around a FLRW background.

  6. Combined cosmological tests of a bivalent tachyonic dark energy scalar field model

    SciTech Connect

    Keresztes, Zoltán; Gergely, László Á. E-mail: gergely@physx.u-szeged.hu

    2014-11-01

    A recently investigated tachyonic scalar field dark energy dominated universe exhibits a bivalent future: depending on initial parameters can run either into a de Sitter exponential expansion or into a traversable future soft singularity followed by a contraction phase. We also include in the model (i) a tiny amount of radiation, (ii) baryonic matter (Ω{sub b}h{sup 2} = 0.022161, where the Hubble constant is fixed as h = 0.706) and (iii) cold dark matter (CDM). Out of a variety of six types of evolutions arising in a more subtle classification, we identify two in which in the past the scalar field effectively degenerates into a dust (its pressure drops to an insignificantly low negative value). These are the evolutions of type IIb converging to de Sitter and type III hitting the future soft singularity. We confront these background evolutions with various cosmological tests, including the supernova type Ia Union 2.1 data, baryon acoustic oscillation distance ratios, Hubble parameter-redshift relation and the cosmic microwave background (CMB) acoustic scale. We determine a subset of the evolutions of both types which at 1σ confidence level are consistent with all of these cosmological tests. At perturbative level we derive the CMB temperature power spectrum to find the best agreement with the Planck data for Ω{sub CDM} = 0.22. The fit is as good as for the ΛCDM model at high multipoles, but the power remains slightly overestimated at low multipoles, for both types of evolutions. The rest of the CDM is effectively generated by the tachyonic field, which in this sense acts as a combined dark energy and dark matter model.

  7. FRW Like Cosmological Model and Accelerated Expansion of the Universe from Non Commutative Seiberg-Witten Geometry

    SciTech Connect

    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.

  8. Why the Rh = ct cosmology is a vacuum solution in disguise and why all big bang models should be so

    NASA Astrophysics Data System (ADS)

    Mitra, Abhas

    2014-07-01

    Recently, Melia and his coworkers have proposed the so-called Rh = ct cosmology where the scale factor of the universe is a(t) ∝ t and the spatial part is flat. Here, we look at this proposal from a fundamental angle. First, we note that Melia cosmology looks strikingly similar to the old Milne cosmology where a(t) ∝ t and the spatial part is negatively curved. It is known that though Milne cosmology is a valid Friedmann solution, it actually corresponds to ρ = 0 and can be described by a globally static Minkowski metric. Secondly, we note that for the Melia model, Ricci & Kretschmann scalars assume their perfect static form hinting that it too may tacitly correspond to vacuum. To compare Melia universe with the Milne universe, we express Melia metric too in curvature/Schwarzschild coordinates. Finally, by using the fact for such coordinate transformations dx'4 = Jdx4, where J is the appropriate Jacobian, we explicitly show that Melia metric is static, which for k = 0 case implies vacuum. This shows that even apparently meaningful general relativistic solutions could be illusory as far as physical reality is concerned. And since Melia model is the unique solution for the big bang model, eventually, all big bang models could be mathematical illusions.

  9. ITVO and BaSTI: databases and services for cosmological and stellar models.

    NASA Astrophysics Data System (ADS)

    Manzato, P.; Molinaro, M.; Gasparo, F.; Pasian, F.; Pietrinferni, A.; Cassisi, S.; Gheller, C.; Ameglio, S.; Murante, G.; Borgani, S.

    We have created a database structure to store the metadata of different types of cosmological simulations (Gadget, Enzo, FLY) and the first relational database for stellar evolution models BaSTI, it includes tracks and isochrones computed with the FRANEC code. We are also studying the feasibility of including different sets of theory data and services in the Virtual Observatory (VObs). Some examples of services are: the calculation on-the-fly of the profiles of some quantities for the simulated galaxy clusters, the preview of the object image opened with a VObs tool and retrieve a VOTable standard format. Furthermore, the BaSTI database development is the use case for studying the feasibility of storing in it the output of new simulations performed using the Grid infrastructure as demonstrating in the VO-DCA WP5, EU funded project. All that could be matter of discussion between the tool developers and the users, the scientists.

  10. Cosmological backreaction for a test field observer in a chaotic inflationary model

    SciTech Connect

    Marozzi, Giovanni; Vacca, Gian Paolo; Brandenberger, Robert H. E-mail: vacca@bo.infn.it

    2013-02-01

    In an inhomogeneous universe, an observer associated with a particular matter field does not necessarily measure the same cosmological evolution as an observer in a homogeneous and isotropic universe. Here we consider, in the context of a chaotic inflationary background model, a class of observers associated with a ''clock field'' for which we use a light test field. We compute the effective expansion rate and fluid equation of state in a gauge invariant way, taking into account the quantum fluctuations of the long wavelength modes, and working up to second order in perturbation theory and in the slow-roll approximation. We find that the effective expansion rate is smaller than what would be measured in the absence of fluctuations. Within the stochastic approach we study the bounds for which the approximations we make are consistent.

  11. Cosmological Parameter Uncertainties from SALT-II Type Ia Supernova Light Curve Models

    SciTech Connect

    Mosher, J.; Guy, J.; Kessler, R.; Astier, P.; Marriner, J.; Betoule, M.; Sako, M.; El-Hage, P.; Biswas, R.; Pain, R.; Kuhlmann, S.; Regnault, N.; Frieman, J. A.; Schneider, D. P.

    2014-08-29

    We use simulated type Ia supernova (SN Ia) samples, including both photometry and spectra, to perform the first direct validation of cosmology analysis using the SALT-II light curve model. This validation includes residuals from the light curve training process, systematic biases in SN Ia distance measurements, and a bias on the dark energy equation of state parameter w. Using the SN-analysis package SNANA, we simulate and analyze realistic samples corresponding to the data samples used in the SNLS3 analysis: ~120 low-redshift (z < 0.1) SNe Ia, ~255 Sloan Digital Sky Survey SNe Ia (z < 0.4), and ~290 SNLS SNe Ia (z ≤ 1). To probe systematic uncertainties in detail, we vary the input spectral model, the model of intrinsic scatter, and the smoothing (i.e., regularization) parameters used during the SALT-II model training. Using realistic intrinsic scatter models results in a slight bias in the ultraviolet portion of the trained SALT-II model, and w biases (w (input) – w (recovered)) ranging from –0.005 ± 0.012 to –0.024 ± 0.010. These biases are indistinguishable from each other within the uncertainty, the average bias on w is –0.014 ± 0.007.

  12. Modelling the cosmological co-evolution of supermassive black holes and galaxies

    NASA Astrophysics Data System (ADS)

    Marulli, F.; Bonoli, S.; Branchini, E.; Moscardini, L.; Springel, V.; White, S. D. M.

    2008-10-01

    We model the cosmological co-evolution of galaxies and their central supermassive black holes (BHs) within a semi-analytical framework developed on the outputs of the Millennium Simulation. This model, described in detail by Croton et al. and De Lucia and Blaizot, introduces a `radio mode' feedback from AGN at the centre of X-ray emitting atmospheres in galaxy groups and clusters. We investigate how well this model can reproduce the physical properties of BHs and AGN. We analyse the scaling relations, the fundamental plane and the mass function of BHs, and compare them with the most recent observational data. Moreover, we extend the semi-analytic model to follow the evolution of the BH mass accretion and its conversion into radiation, and compare the derived AGN bolometric luminosity function with the observed one. While we find for the most part a very good agreement between predicted and observed BH properties, the semi-analytic model underestimates the number density of luminous AGN at high redshifts, independently of the adopted Eddington factor and accretion efficiency. However, an agreement with the observations is possible within the framework of our model, provided it is assumed that the cold gas fraction accreted by BHs at high redshifts is larger than at low redshifts.

  13. Cosmological parameter uncertainties from SALT-II type Ia supernova light curve models

    SciTech Connect

    Mosher, J.; Sako, M.; Guy, J.; Astier, P.; Betoule, M.; El-Hage, P.; Pain, R.; Regnault, N.; Marriner, J.; Biswas, R.; Kuhlmann, S.; Schneider, D. P.

    2014-09-20

    We use simulated type Ia supernova (SN Ia) samples, including both photometry and spectra, to perform the first direct validation of cosmology analysis using the SALT-II light curve model. This validation includes residuals from the light curve training process, systematic biases in SN Ia distance measurements, and a bias on the dark energy equation of state parameter w. Using the SN-analysis package SNANA, we simulate and analyze realistic samples corresponding to the data samples used in the SNLS3 analysis: ∼120 low-redshift (z < 0.1) SNe Ia, ∼255 Sloan Digital Sky Survey SNe Ia (z < 0.4), and ∼290 SNLS SNe Ia (z ≤ 1). To probe systematic uncertainties in detail, we vary the input spectral model, the model of intrinsic scatter, and the smoothing (i.e., regularization) parameters used during the SALT-II model training. Using realistic intrinsic scatter models results in a slight bias in the ultraviolet portion of the trained SALT-II model, and w biases (w {sub input} – w {sub recovered}) ranging from –0.005 ± 0.012 to –0.024 ± 0.010. These biases are indistinguishable from each other within the uncertainty; the average bias on w is –0.014 ± 0.007.

  14. Cosmological Simulations of the Intergalactic Medium Evolution. II. Galaxy Model and Feedback

    NASA Astrophysics Data System (ADS)

    Côté, Benoit; Martel, Hugo; Drissen, Laurent

    2015-04-01

    We present a semi-analytical model designed to be included in large-scale cosmological simulations to treat the evolution of galaxies. The goal of this paper is to test our model to make sure that it behaves in a realistic manner. We consider galaxies with current stellar masses between {{10}6.54} and {{10}11.65} {{M}⊙ }. Our model includes radiative cooling, gas inflow, star formation, chemical enrichment, and stellar and AGN feedback. The evolution of each stellar population that forms in our model is individually followed in time by using stellar models found in the literature. Our stellar feedback prescription is based on the production of galactic outflows, which are powered by the mechanical energy (Energy-driven) and the radiative pressure (Momentum-driven). We implemented the physics of bubbles blown by stars to treat the feedback generated by mechanical energy. By keeping track of the energy gained and lost inside bubbles, we can compute the fraction of the stellar mechanical energy that is used to launch an outflow. Our model predicts that E-driven outflows dominate the evolution of low-mass galaxies with current stellar masses below {{10}10} {{M}⊙ }, whereas intermediate-mass galaxies with current stellar masses up to {{10}10.7} {{M}⊙ } are dominated by M-driven outflows. AGN feedback dominates the evolution of the most massive galaxies. With these three sources of feedback, we are able to reproduce the current observed stellar-to-dark-halo mass relation, as well as the current average stellar metallicity of galaxies. Outflows are very efficient in expelling metals out of galaxies, especially with E-driven outflows, which is consistent with the observed trend that metals are ejected more efficiently in low-mass galaxies. At the end of our simulations, a significant fraction of the metals produced by stars is located in the halos of galaxies. Metals can escape efficiently into the intergalactic medium for galaxies with current stellar masses below

  15. Testing the Standard Model of Cosmology with Strong Lensing Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Bayliss, Matthew; Oguri, M.; Gladders, M. D.; Sharon, K.; Koester, B.; Gralla, M.; Garcia, C. J.; Barrientos, F.; Carrasco, M.

    2012-01-01

    Galaxy cluster strong lenses are powerful probes of cosmology, large scale structure, and the high-z universe. They are also, however, extremely rare, and their value has historically been limited as a result of the dearth of known cluster lenses. We present results using a new, well-defined sample of hundreds of galaxy-cluster-scale strong lenses that were identified in the Sloan Digital Sky Survey (SDSS) and the Red-Sequence Cluster Survey 2 (RCS2). We use strong lens model constraints on the matter distribution in the cores of dozens of lensing clusters, and combine these measurements at small radius with multiple mass observables on virial radius scales to empirically recover the mass-concentration relation for clusters spanning more than an order of magnitude in mass. Contrary to previous claims based on small samples of clusters, we find that the mass-concentration relation is generally in good agreement with theoretical expectations for a strong lensing selected sample of clusters. We also use the ensemble statistics of a complete sample of hundreds of giant arcs to provide a new measurement of the abundance of clusters forming giant arcs in a well-defined cosmological volume, and we measure the redshift distribution of our giant arc sample. We find that the median redshift of bright (g < 24) giant arcs is z 2, which provides some relief of the previously claimed "giant arc problem", while simultaneously establishing that our large sample of giant arcs provides the observational community with hundreds of highly magnified galaxies at high redshift.

  16. A toy model to test the accuracy of cosmological N-body simulations

    NASA Astrophysics Data System (ADS)

    Sylos Labini, F.

    2013-04-01

    The evolution of an isolated over-density represents a useful toy model to test the accuracy of a cosmological N-body code in the non-linear regime as it is approximately equivalent to that of a truly isolated cloud of particles, with same density profile and velocity distribution, in a non-expanding background. This is the case as long as the system size is smaller than the simulation box side, so that its interaction with the infinite copies can be neglected. In such a situation, the over-density rapidly undergoes to a global collapse forming a quasi stationary state in virial equilibrium. However, by evolving the system with a cosmological code (GADGET) for a sufficiently long time, a clear deviation from such quasi-equilibrium configuration is observed. This occurs in a time tLI that depends on the values of the simulation numerical parameters such as the softening length and the time-stepping accuracy, i.e. it is a numerical artifact related to the limited spatial and temporal resolutions. The analysis of the Layzer-Irvine cosmic energy equation confirms that this deviation corresponds to an unphysical dynamical regime. By varying the numerical parameters of the simulation and the physical parameters of the system we show that the unphysical behaviour originates from badly integrated close scatterings of high-velocity particles. We find that, while the structure may remain virialized in the unphysical regime, its density and velocity profiles are modified with respect to the quasi-equilibrium configurations, converging, however, to well defined shapes, the former characterised by a Navarro Frenk White-type behaviour.

  17. The fine tuning of the cosmological constant in a conformal model

    NASA Astrophysics Data System (ADS)

    Jain, Pankaj; Kashyap, Gopal; Mitra, Subhadip

    2015-10-01

    We consider a conformal model involving two real scalar fields in which the conformal symmetry is broken by a soft mechanism and is not anomalous. One of these scalar fields is representative of the standard model Higgs. The model predicts exactly zero cosmological constant. In the simplest version of the model, some of the couplings need to be fine-tuned to very small values. We formulate the problem of fine tuning of these couplings. We argue that the problem arises since we require a soft mechanism to break conformal symmetry. The symmetry breaking is possible only if the scalar fields do not evolve significantly over the time scale of the Universe. Ignoring contributions due to quantum gravity, we present two solutions to this fine tuning problem. We argue that the problem is solved if the classical value of one of the scalar fields is super-Planckian, i.e. takes a value much larger than the Planck mass. The second solution involves introduction of a strongly coupled hidden sector that we call hypercolor. In this case, the conformal invariance is broken dynamically and triggers the breakdown of the electroweak symmetry. We argue that our analysis applies also to the case of the standard model Higgs multiplet.

  18. How real-time cosmology can distinguish between different anisotropic models

    NASA Astrophysics Data System (ADS)

    Amendola, Luca; Eggers Bjæ lde, Ole; Valkenburg, Wessel; Wong, Yvonne Y. Y.

    2013-12-01

    We present a new analysis on how to distinguish between isotropic and anisotropic cosmological models based on tracking the angular displacements of a large number of distant quasars over an extended period of time, and then performing a multipole-vector decomposition of the resulting displacement maps. We find that while the GAIA mission operating at its nominal specifications does not have sufficient angular resolution to resolve anisotropic universes from isotropic ones using this method within a reasonable timespan of ten years, a next-generation GAIA-like survey with a resolution ten times better should be equal to the task. Distinguishing between different anisotropic models is however more demanding. Keeping the observational timespan to ten years, we find that the angular resolution of the survey will need to be of order 0.1 μas in order for certain rotating anisotropic models to produce a detectable signature that is also unique to models of this class. However, should such a detection become possible, it would immediately allow us to rule out large local void models.

  19. Analytical model for non-thermal pressure in galaxy clusters - II. Comparison with cosmological hydrodynamics simulation

    NASA Astrophysics Data System (ADS)

    Shi, Xun; Komatsu, Eiichiro; Nelson, Kaylea; Nagai, Daisuke

    2015-03-01

    Turbulent gas motion inside galaxy clusters provides a non-negligible non-thermal pressure support to the intracluster gas. If not corrected, it leads to a systematic bias in the estimation of cluster masses from X-ray and Sunyaev-Zel'dovich (SZ) observations assuming hydrostatic equilibrium, and affects interpretation of measurements of the SZ power spectrum and observations of cluster outskirts from ongoing and upcoming large cluster surveys. Recently, Shi & Komatsu developed an analytical model for predicting the radius, mass, and redshift dependence of the non-thermal pressure contributed by the kinetic random motions of intracluster gas sourced by the cluster mass growth. In this paper, we compare the predictions of this analytical model to a state-of-the-art cosmological hydrodynamics simulation. As different mass growth histories result in different non-thermal pressure, we perform the comparison on 65 simulated galaxy clusters on a cluster-by-cluster basis. We find an excellent agreement between the modelled and simulated non-thermal pressure profiles. Our results open up the possibility of using the analytical model to correct the systematic bias in the mass estimation of galaxy clusters. We also discuss tests of the physical picture underlying the evolution of intracluster non-thermal gas motions, as well as a way to further improve the analytical modelling, which may help achieve a unified understanding of non-thermal phenomena in galaxy clusters.

  20. Model Selection and Parameter Estimation in Neutrino Cosmology and High Energy Astrophysics Around the Galactic Center

    NASA Astrophysics Data System (ADS)

    Canac, Nicolas

    Understanding the particle nature of dark matter and determining the properties of neutrinos remain two of the most important questions within the physics community. Both problems lie within the intersection between astrophysics and particle physics, a fact which gives rise to a rich set of independent and complementary approaches to making progress on both fronts. This thesis presents three works that attempt to construct models and constrain the properties of these particles using empirical data from a large host of astronomical observations. The first work uses observations from the Fermi Gamma-ray Space Telescope's Large Area Telescope (Fermi LAT) to construct empirical models of the diffuse gamma-ray background in the Galactic Center (GC). A new template associated with cosmic rays interacting with molecular gas is detected with high significance. Using this new template along with other known sources of gamma-ray emission in the GC, I find that the previously detected extended gamma-ray excess is still detected for all permutations of the background model, although its properties vary significantly within the observed range of models. The second work presents a detection of a new source of gamma-ray emission in the GC that traces the morphology of infrared starlight, again using observations from the Fermi LAT. I argue that this emission is likely due to the same source of cosmic rays responsible for producing the emission associated with the molecular gas template in the previous work, and further make the case that this population of cosmic rays could be produced by the same source responsible for the GC excess. The last work explores how derived neutrino parameter constraints depend on the assumed form of the primordial power spectrum, using constraints derived from a host of cosmological data sets, including cosmic microwave background, baryon acoustic oscillation, power spectrum, cluster counts, and hubble constant measurements. I find that for a model

  1. Controlling chaos through compactification in cosmological models with a collapsing phase

    SciTech Connect

    Wesley, Daniel H.; Steinhardt, Paul J.; Turok, Neil

    2005-09-15

    We consider the effect of compactification of extra dimensions on the onset of classical chaotic mixmaster behavior during cosmic contraction. Assuming a universe that is well-approximated as a four-dimensional Friedmann-Robertson-Walker model (with negligible Kaluza-Klein excitations) when the contraction phase begins, we identify compactifications that allow a smooth contraction and delay the onset of chaos until arbitrarily close to the big crunch. These compactifications are defined by the de Rham cohomology (Betti numbers) and Killing vectors of the compactification manifold. We find compactifications that control chaos in vacuum Einstein gravity, as well as in string theories with N=1 supersymmetry and M-theory. In models where chaos is controlled in this way, the universe can remain homogeneous and flat until it enters the quantum gravity regime. At this point, the classical equations leading to chaotic behavior can no longer be trusted, and quantum effects may allow a smooth approach to the big crunch and transition into a subsequent expanding phase. Our results may be useful for constructing cosmological models with contracting phases, such as the ekpyrotic/cyclic and pre-big bang models.

  2. Flow in cyclic cosmology

    SciTech Connect

    Kinney, William H.; Dizgah, Azadeh Moradinezhad

    2010-10-15

    In this paper, we use a known duality between expanding and contracting cosmologies to construct a dual of the inflationary flow hierarchy applicable to contracting cosmologies such as ekpyrotic and cyclic models. We show that the inflationary flow equations are invariant under the duality and therefore apply equally well to inflation or to cyclic cosmology. We construct a self-consistent small-parameter approximation dual to the slow-roll approximation in inflation, and calculate the power spectrum of perturbations in this limit. We also recover the matter-dominated contracting solution of Wands, and the recently proposed adiabatic ekpyrosis solution.

  3. Higgs Physics and Cosmology

    NASA Astrophysics Data System (ADS)

    Roberts, Alex

    class of scenarios at the LHC. Comparing limits, we find that current LHC results only exclude regions in parameter space which were already disfavored by precision electroweak data.. Recent LHC data, together with the electroweak naturalness argument, suggest that the top squarks may be significantly lighter than the other sfermions. We present supersymmetric models in which such a split spectrum is obtained through ''geometries'': being ''close to'' electroweak symmetry breaking implies being ''away from'' supersymmetry breaking, and vice versa. In particular, we present models in 5D warped spacetime, in which supersymmetry breaking and Higgs fields are located on the ultraviolet and infrared branes, respectively, and the top multiplets are localized to the infrared brane. The hierarchy of the Yukawa matrices can be obtained while keeping near flavor degeneracy between the first two generation sfermions, avoiding stringent constraints from flavor and CP violation. Through the AdS/CFT correspondence, the models can be interpreted as purely 4D theories in which the top and Higgs multiplets are composites of some strongly interacting sector exhibiting nontrivial dynamics at a low energy. Because of the compositeness of the Higgs and top multiplets, Landau pole constraints for the Higgs and top couplings apply only up to the dynamical scale, allowing for a relatively heavy Higgs boson, including mh = 125 GeV as suggested by the recent LHC data. We analyze electroweak symmetry breaking for a well-motivated subset of these models, and find that fine-tuning in electroweak symmetry breaking is indeed ameliorated. We also discuss a flat space realization of the scenario in which supersymmetry is broken by boundary conditions, with the top multiplets localized to a brane while other matter multiplets delocalized in the bulk.

  4. The Coyote Universe. II. Cosmological Models and Precision Emulation of the Nonlinear Matter Power Spectrum

    NASA Astrophysics Data System (ADS)

    Heitmann, Katrin; Higdon, David; White, Martin; Habib, Salman; Williams, Brian J.; Lawrence, Earl; Wagner, Christian

    2009-11-01

    The power spectrum of density fluctuations is a foundational source of cosmological information. Precision cosmological probes targeted primarily at investigations of dark energy require accurate theoretical determinations of the power spectrum in the nonlinear regime. To exploit the observational power of future cosmological surveys, accuracy demands on the theory are at the 1% level or better. Numerical simulations are currently the only way to produce sufficiently error-controlled predictions for the power spectrum. The very high computational cost of (precision) N-body simulations is a major obstacle to obtaining predictions in the nonlinear regime, while scanning over cosmological parameters. Near-future observations, however, are likely to provide a meaningful constraint only on constant dark energy equation of state, "wCDM", cosmologies. In this paper, we demonstrate that a limited set of only 37 cosmological models—the "Coyote Universe" suite—can be used to predict the nonlinear matter power spectrum to 1% over a prior parameter range set by current cosmic microwave background observations. This paper is the second in a series of three, with the final aim to provide a high-accuracy prediction scheme for the nonlinear matter power spectrum for wCDM cosmologies.

  5. 5-D Choptuik critical exponent and holography

    NASA Astrophysics Data System (ADS)

    Bland, J.; Kunstatter, G.

    2007-05-01

    Recently, a holographic argument was used to relate the saturation exponent, γBFKL, of 4-dimensional Yang-Mills theory in the Regge limit to the Choptuik critical scaling exponent, γ5d, in 5-dimensional black hole formation via scalar field collapse [L. Álvarez-Gaumé, C. Gómez, and M. A. Vázquez-Mozo, arXiv:hep-th/0611312.]. Remarkably, the numerical value of the former agreed quite well with previous calculations of the latter. We present new results of an improved calculation of γ5d with substantially decreased numerical error. Our current result is γ5d=0.4131±0.0001, which is close to, but not in strict agreement with, the value of γBFKL=0.409552 quoted in [L. Álvarez-Gaumé, C. Gómez, and M. A. Vázquez-Mozo, arXiv:hep-th/0611312.].

  6. Einstein's cosmology review of 1933: a new perspective on the Einstein-de Sitter model of the cosmos

    NASA Astrophysics Data System (ADS)

    O'Raifeartaigh, Cormac; O'Keeffe, Michael; Nahm, Werner; Mitton, Simon

    2015-09-01

    We present a first English translation and analysis of a little-known review of relativistic cosmology written by Albert Einstein in late 1932. The article, which was published in 1933 in a book of Einstein papers translated into French, contains a substantial review of static and dynamic relativistic models of the cosmos, culminating in a discussion of the Einstein-de Sitter model. The article offers a valuable contemporaneous insight into Einstein's cosmology in the early 1930s and confirms that his interest lay in the development of the simplest model of the cosmos that could account for observation. The article also confirms that Einstein did not believe that simplified relativistic models could give an accurate description of the early universe.

  7. A Cosmological Model with Negative Constant Deceleration Parameter in a General Scalar-Tensor Theory of Gravitation

    NASA Astrophysics Data System (ADS)

    Rao, V. U. M.; Sree Devi Kumari, G.

    2012-01-01

    Spatially homogeneous and anisotropic LRS Bianchi type-I metric is considered in the framework of Nordtvedt-Barker's general scalar-tensor theory of gravitation when the source for the energy momentum tensor is a perfect fluid. With the help of a special law of variation for Hubble's parameter proposed by Berman (Nuovo Cim. B. 74:182, 1983) a cosmological model with negative constant deceleration parameter is obtained. Some physical and kinematical properties of the model are also discussed.

  8. FAST TRACK COMMUNICATION: An effective gravity model and singularity avoidance in quantum FRW cosmologies

    NASA Astrophysics Data System (ADS)

    Haro, Jaume; Elizalde, Emilio

    2009-05-01

    An effective formulation of gravity is discussed, which lies in between the Wheeler-DeWitt approach and that of classical cosmology. It has the virtue of naturally avoiding the singularity that appears in Friedman-Robertson-Walker cosmologies. The mechanism is made explicit in specific examples, where it is compared with the quantization provided by loop quantum cosmology. It is argued that it is the regularization of the classical Hamiltonian, performed in that theory, that avoids the singularity, rather than usually invoked quantum effects. However, a deeper study of the quantum nature of geometry in that framework should help to completely clarify the issue.

  9. Cosmology between two wars. Einstein's revolution and alternative models of the Universe

    NASA Astrophysics Data System (ADS)

    Curir, Anna

    2011-06-01

    The personality of Edward Milne is examined, deepening the historical period in which his Cosmological theory was produced. Is suggested that Milne's kinematical Cosmology can be regarded as a kind of `resistance' to the scientific revolution deriving from the new Einstein's theory of gravitation. Is investigated the deep philosophical meaning of the metrics on curved manifolds as far as the representation of the universe is concerned, and the importance of the cosmological theories in the epistemology and in the evolution of science is stressed.

  10. The influence of primordial magnetic fields on the spherical collapse model in cosmology

    SciTech Connect

    Shibusawa, Y.; Ichiki, K.; Kadota, K. E-mail: ichiki@a.phys.nagoya-u.ac.jp

    2014-08-01

    Despite the ever growing observational evidence for the existence of the large scale magnetic fields, their origin and the evolution are not fully understood. If the magnetic fields are of primordial origin, they result in the generation of the secondary matter density perturbations and the previous studies show that such density perturbations enhance the number of dark matter halos. We extend the conventional spherical collapse model by including the Lorentz force which has not been implemented in the previous analysis to study the evolution of density perturbations produced by primordial magnetic fields. The critical over-density δ{sub c} characterizing the halo mass function turns out to be a bigger value, δ{sub c}≅ 1.78, than the conventional one δ{sub c}≅ 1.69 for the perturbations evolved only by the gravitational force. The difference in δ{sub c} between our model and the fully matter dominated cosmological model is small at a low redshift and, hence, only the high mass tail of the mass function is affected by the magnetic fields. At a high redshift, on the other hand, the difference in δ{sub c} becomes large enough to suppress the halo abundance over a wide range of mass scales. The halo abundance is reduced for instance by as large a factor as ∼10{sup 5} at z=9.

  11. Emergent cosmology revisited

    SciTech Connect

    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.

  12. 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.

  13. Coarse-grained cosmological perturbation theory: Stirring up the dust model

    NASA Astrophysics Data System (ADS)

    Uhlemann, Cora; Kopp, Michael

    2015-04-01

    We study the effect of coarse graining the dynamics of a pressureless self-gravitating fluid (coarse-grained dust) in the context of cosmological perturbation theory, in both the Eulerian and Lagrangian frameworks. We obtain recursion relations for the Eulerian perturbation kernels of the coarse-grained dust model by relating them to those of the standard pressureless fluid model. The effect of the coarse graining is illustrated by means of power and cross spectra for the density and velocity, which are computed up to one-loop order. In particular, the large-scale vorticity power spectrum that arises naturally from a mass-weighted velocity is derived from first principles. We find qualitatively good agreement for the magnitude, shape, and spectral index of the vorticity power spectrum with recent measurements from N -body simulations and results from the effective field theory of large-scale structure. To lay the ground for applications in the context of Lagrangian perturbation theory, we finally describe how the kernels obtained in Eulerian space can be mapped to Lagrangian ones.

  14. Searching for features of a string-inspired inflationary model with cosmological observations

    NASA Astrophysics Data System (ADS)

    Cai, Yi-Fu; Ferreira, Elisa G. M.; Hu, Bin; Quintin, Jerome

    2015-12-01

    The latest Planck results show a power deficit in the temperature anisotropies near ℓ≈20 in the cosmic microwave background (CMB). This observation can hardly be explained within the standard inflationary Λ -cold-dark-matter (Λ CDM ) scenario. In this paper we consider a string theory inspired inflationary model (axion monodromy inflation) with a step-like modulation in the potential which gives rise to observable signatures in the primordial perturbations. One interesting phenomenon is that the primordial scalar modes experience a sudden suppression at a critical scale when the modulation occurs. By fitting to the CMB data, we find that the model can nicely explain the ℓ≈20 power deficit anomaly as well as predict specific patterns in the temperature-polarization correlation and polarization autocorrelation spectra. Though the significance of the result is not sufficient to claim a detection, our analysis reveals that fundamental physics at extremely high energy scales, namely, some effects inspired by string theory, may be observationally testable in forthcoming cosmological experiments.

  15. The fate of the mixmaster behaviour in vacuum inhomogeneous Kaluza-Klein cosmological models

    NASA Astrophysics Data System (ADS)

    Demaret, Jacques; Hanquin, Jean-Luc; Henneaux, Marc; Spindel, Philipe; Taormina, Anne

    1986-07-01

    The generic behaviour of vacuum inhomogeneous Kaluza-Klein cosmologies is studied in the vicinity of the cosmological singularity. The collision law for the Kasner exponents is calculated in any number of spatial dimensions d. Its properties are investigated both theoretically and numerically. It is argued that the chaotic oscillatory behaviour disappears for d >= 10. This regime is replaced by the monotonic Kasner behaviour found previously.

  16. The Dirac-Milne cosmology

    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.

  17. Cosmology. A first course

    NASA Astrophysics Data System (ADS)

    Lachieze-Rey, Marc

    This book delivers a quantitative account of the science of cosmology, designed for a non-specialist audience. The basic principles are outlined using simple maths and physics, while still providing rigorous models of the Universe. It offers an ideal introduction to the key ideas in cosmology, without going into technical details. The approach used is based on the fundamental ideas of general relativity such as the spacetime interval, comoving coordinates, and spacetime curvature. It provides an up-to-date and thoughtful discussion of the big bang, and the crucial questions of structure and galaxy formation. Questions of method and philosophical approaches in cosmology are also briefly discussed. Advanced undergraduates in either physics or mathematics would benefit greatly from use either as a course text or as a supplementary guide to cosmology courses.

  18. 2.5D dictionary learning based computed tomography reconstruction

    NASA Astrophysics Data System (ADS)

    Luo, Jiajia; Eri, Haneda; Can, Ali; Ramani, Sathish; Fu, Lin; De Man, Bruno

    2016-05-01

    A computationally efficient 2.5D dictionary learning (DL) algorithm is proposed and implemented in the model- based iterative reconstruction (MBIR) framework for low-dose CT reconstruction. MBIR is based on the minimization of a cost function containing data-fitting and regularization terms to control the trade-off between data-fidelity and image noise. Due to the strong denoising performance of DL, it has previously been considered as a regularizer in MBIR, and both 2D and 3D DL implementations are possible. Compared to the 2D case, 3D DL keeps more spatial information and generates images with better quality although it requires more computation. We propose a novel 2.5D DL scheme, which leverages the computational advantage of 2D-DL, while attempting to maintain reconstruction quality similar to 3D-DL. We demonstrate the effectiveness of this new 2.5D DL scheme for MBIR in low-dose CT. By applying the 2D DL method in three different orthogonal planes and calculating the sparse coefficients accordingly, much of the 3D spatial information can be preserved without incurring the computational penalty of the 3D DL method. For performance evaluation, we use baggage phantoms with different number of projection views. In order to quantitatively compare the performance of different algorithms, we use PSNR, SSIM and region based standard deviation to measure the noise level, and use the edge response to calculate the resolution. Experimental results with full view datasets show that the different DL based algorithms have similar performance and 2.5D DL has the best resolution. Results with sparse view datasets show that 2.5D DL outperforms both 2D and 3D DL in terms of noise reduction. We also compare the computational costs, and 2.5D DL shows strong advantage over 3D DL in both full-view and sparse-view cases.

  19. Compatibility of the chameleon-field model with fifth-force experiments, cosmology, and PVLAS and CAST results.

    PubMed

    Brax, Philippe; van de Bruck, Carsten; Davis, Anne-Christine

    2007-09-21

    We analyze the PVLAS results using a chameleon field whose properties depend on the environment. We find that, assuming a runaway bare potential V(phi) and a universal coupling to matter, the chameleon potential is such that the scalar field can act as dark energy. Moreover, the chameleon-field model is compatible with the CERN Axion Solar Telescope results, fifth-force experiments, and cosmology. PMID:17930493

  20. Compatibility of the chameleon-field model with fifth-force experiments, cosmology, and PVLAS and CAST results.

    PubMed

    Brax, Philippe; van de Bruck, Carsten; Davis, Anne-Christine

    2007-09-21

    We analyze the PVLAS results using a chameleon field whose properties depend on the environment. We find that, assuming a runaway bare potential V(phi) and a universal coupling to matter, the chameleon potential is such that the scalar field can act as dark energy. Moreover, the chameleon-field model is compatible with the CERN Axion Solar Telescope results, fifth-force experiments, and cosmology.

  1. CDM accelerating cosmology as an alternative to ΛCDM model

    SciTech Connect

    Lima, J.A.S.; Jesus, J.F.; Oliveira, F.A. E-mail: jfernando@astro.iag.usp.br

    2010-11-01

    A new accelerating cosmology driven only by baryons plus cold dark matter (CDM) is proposed in the framework of general relativity. In this scenario the present accelerating stage of the Universe is powered by the negative pressure describing the gravitationally-induced particle production of cold dark matter particles. This kind of scenario has only one free parameter and the differential equation governing the evolution of the scale factor is exactly the same of the ΛCDM model. For a spatially flat Universe, as predicted by inflation (Ω{sub dm}+Ω{sub baryon} = 1), it is found that the effectively observed matter density parameter is Ω{sub meff} = 1−α, where α is the constant parameter specifying the CDM particle creation rate. The supernovae test based on the Union data (2008) requires α ∼ 0.71 so that Ω{sub meff} ∼ 0.29 as independently derived from weak gravitational lensing, the large scale structure and other complementary observations.

  2. Origin of inflation in CFT driven cosmology: R^2-gravity and non-minimally coupled inflaton models

    NASA Astrophysics Data System (ADS)

    Barvinsky, A. O.; Kamenshchik, A. Yu.; Nesterov, D. V.

    2015-12-01

    We present a detailed derivation of the recently suggested new type of hill-top inflation [arXiv:1509.07270] originating from the microcanonical density matrix initial conditions in cosmology driven by conformal field theory (CFT). The cosmological instantons of topology S^1× S^3, which set up these initial conditions, have the shape of a garland with multiple periodic oscillations of the scale factor of the spatial S^3-section. They describe underbarrier oscillations of the inflaton and scale factor in the vicinity of the inflaton potential maximum, which gives a sufficient amount of inflation required by the known CMB data. We build the approximation of two coupled harmonic oscillators for these garland instantons and show that they can generate inflation consistent with the parameters of the CMB primordial power spectrum in the non-minimal Higgs inflation model and in R^2 gravity. In particular, the instanton solutions provide smallness of inflationary slow-roll parameters ɛ and η <0 and their relation ɛ ˜ η ^2 characteristic of these two models. We present the mechanism of formation of hill-like inflaton potentials, which is based on logarithmic loop corrections to the asymptotically shift-invariant tree-level potentials of these models in the Einstein frame. We also discuss the role of R^2-gravity as an indispensable finite renormalization tool in the CFT driven cosmology, which guarantees the non-dynamical (ghost free) nature of its scale factor and special properties of its cosmological garland-type instantons. Finally, as a solution to the problem of hierarchy between the Planckian scale and the inflation scale we discuss the concept of a hidden sector of conformal higher spin fields.

  3. Cosmology for high energy physicists

    SciTech Connect

    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.

  4. Model-independent plotting of the cosmological scale factor as a function of lookback time

    SciTech Connect

    Ringermacher, H. I.; Mead, L. R. E-mail: Lawrence.mead@usm.edu

    2014-11-01

    In this work we describe a model-independent method of developing a plot of scale factor a(t) versus lookback time t{sub L} from the usual Hubble diagram of modulus data against redshift. This is the first plot of this type. We follow the model-independent methodology of Daly and Djorgovski used for their radio-galaxy data. Once the a(t)data plot is completed, any model can be applied and will display as described in the standard literature. We then compile an extensive data set to z = 1.8 by combining Type Ia supernovae (SNe Ia) data from SNLS3 of Conley et al., high-z SNe data of Riess et al., and radio-galaxy data of Daly and Djorgovski to validate the new plot. We first display these data on a standard Hubble diagram to confirm the best fit for ΛCDM cosmology, and thus validate the joined data set. The scale factor plot is then developed from the data and the ΛCDM model is again displayed from a least-squares fit. The fit parameters are in agreement with the Hubble diagram fit confirming the validity of the new plot. Of special interest is the transition time of the universe, which in the scale factor plot will appear as an inflection point in the data set. Noise is more visible in this presentation, which is particularly sensitive to inflection points of any model displayed in the plot, unlike on a modulus-z diagram, where there are no inflection points and the transition-z is not at all obvious by inspection. We obtain a lower limit of z ≥ 0.6. It is evident from this presentation that there is a dearth of SNe data in the range z = 1-2, exactly the range necessary to confirm a ΛCDM transition-z around z = 0.76. We then compare a 'toy model' wherein dark matter is represented as a perfect fluid with an equation of state p = –(1/3) ρ to demonstrate the plot sensitivity to model choice. Its density varies as 1/t {sup 2} and it enters the Friedmann equations as Ω{sub dark}/t {sup 2}, replacing only the Ω{sub dark}/a {sup 3} term. The toy model is a

  5. Current Issues in Cosmology

    NASA Astrophysics Data System (ADS)

    Pecker, Jean-Claude; Narlikar, Jayant

    2006-06-01

    Part I. Observational Facts Relating to Discrete Sources: 1. The state of cosmology G. Burbidge; 2. The redshifts of galaxies and QSOs E. M. Burbidge and G. Burbidge; 3. Accretion discs in quasars J. Sulentic; Part II. Observational Facts Relating to Background Radiation: 4. CMB observations and consequences F. Bouchet; 5. Abundances of light nuclei K. Olive; 6. Evidence for an accelerating universe or lack of A. Blanchard; Part III. Standard Cosmology: 7. Cosmology, an overview of the standard model F. Bernardeau; 8. What are the building blocks of our universe? K. C. Wali; Part IV. Large-Scale Structure: 9. Observations of large-scale structure V. de Lapparent; 10. Reconstruction of large-scale peculiar velocity fields R. Mohayaee, B. Tully and U. Frisch; Part V. Alternative Cosmologies: 11. The quasi-steady state cosmology J. V. Narlikar; 12. Evidence for iron whiskers in the universe N. C. Wickramasinghe; 13. Alternatives to dark matter: MOND + Mach D. Roscoe; 14. Anthropic principle in cosmology B. Carter; Part VI. Evidence for Anomalous Redshifts: 15. Anomalous redshifts H. C. Arp; 16. Redshifts of galaxies and QSOs: the problem of redshift periodicities G. Burbidge; 17. Statistics of redshift periodicities W. Napier; 18. Local abnormal redshifts J.-C. Pecker; 19. Gravitational lensing and anomalous redshifts J. Surdej, J.-F. Claeskens and D. Sluse; Panel discussion; General discussion; Concluding remarks.

  6. Current Issues in Cosmology

    NASA Astrophysics Data System (ADS)

    Pecker, Jean-Claude; Narlikar, Jayant

    2011-09-01

    Part I. Observational Facts Relating to Discrete Sources: 1. The state of cosmology G. Burbidge; 2. The redshifts of galaxies and QSOs E. M. Burbidge and G. Burbidge; 3. Accretion discs in quasars J. Sulentic; Part II. Observational Facts Relating to Background Radiation: 4. CMB observations and consequences F. Bouchet; 5. Abundances of light nuclei K. Olive; 6. Evidence for an accelerating universe or lack of A. Blanchard; Part III. Standard Cosmology: 7. Cosmology, an overview of the standard model F. Bernardeau; 8. What are the building blocks of our universe? K. C. Wali; Part IV. Large-Scale Structure: 9. Observations of large-scale structure V. de Lapparent; 10. Reconstruction of large-scale peculiar velocity fields R. Mohayaee, B. Tully and U. Frisch; Part V. Alternative Cosmologies: 11. The quasi-steady state cosmology J. V. Narlikar; 12. Evidence for iron whiskers in the universe N. C. Wickramasinghe; 13. Alternatives to dark matter: MOND + Mach D. Roscoe; 14. Anthropic principle in cosmology B. Carter; Part VI. Evidence for Anomalous Redshifts: 15. Anomalous redshifts H. C. Arp; 16. Redshifts of galaxies and QSOs: the problem of redshift periodicities G. Burbidge; 17. Statistics of redshift periodicities W. Napier; 18. Local abnormal redshifts J.-C. Pecker; 19. Gravitational lensing and anomalous redshifts J. Surdej, J.-F. Claeskens and D. Sluse; Panel discussion; General discussion; Concluding remarks.

  7. Cosmological antigravity.

    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.

  8. A unified model with a generalized gauge symmetry and its cosmological implications

    NASA Astrophysics Data System (ADS)

    Hsu, Jong-Ping; Cottrell, Kazuo O.

    2015-10-01

    A unified model is based on a generalized gauge symmetry with groups [SU3c]color×(SU2×U1)× [U1b×U1l]. It implies that all interactions should preserve conservation laws of baryon number, lepton number, and electric charge, etc. The baryonic U1b, leptonic U1l and color SU3c gauge transformations are generalized to involve nonintegrable phase factors. One has gauge invariant fourth-order equations for massless gauge fields, which leads to linear potentials in the [U1b×U1l] and color [SU3c] sectors. We discuss possible cosmological implications of the new baryonic gauge field. It can produce a very small constant repulsive force between two baryon galaxies (or between two anti-baryon galaxies), where the baryon force can overcome the gravitational force at very large distances and leads to an accelerated cosmic expansion. Based on conservation laws in the unified model, we discuss a simple rotating dumbbell universe with equal amounts of matter and anti-matter, which may be pictured as two gigantic rotating clusters of galaxies. Within the gigantic baryonic cluster, a galaxy will have an approximately linearly accelerated expansion due to the effective force of constant density of all baryonic matter. The same expansion happens in the gigantic anti-baryonic cluster. Physical implications of the generalized gauge symmetry on charmonium confining potentials due to new SU3c field equations, frequency shift of distant supernovae Ia and their experimental tests are discussed.

  9. The Jungle Universe: coupled cosmological models in a Lotka-Volterra framework

    NASA Astrophysics Data System (ADS)

    Perez, Jérôme; Füzfa, André; Carletti, Timoteo; Mélot, Laurence; Guedezounme, Lazare

    2014-06-01

    In this paper, we exploit the fact that the dynamics of homogeneous and isotropic Friedmann-Lemaître universes is a special case of generalized Lotka-Volterra system where the competitive species are the barotropic fluids filling the Universe. Without coupling between those fluids, Lotka-Volterra formulation offers a pedagogical and simple way to interpret usual Friedmann-Lemaître cosmological dynamics. A natural and physical coupling between cosmological fluids is proposed which preserves the structure of the dynamical equations. Using the standard tools of Lotka-Volterra dynamics, we obtain the general Lyapunov function of the system when one of the fluids is coupled to dark energy. This provides in a rigorous form a generic asymptotic behavior for cosmic expansion in presence of coupled species, beyond the standard de Sitter, Einstein-de Sitter and Milne cosmologies. Finally, we conjecture that chaos can appear for at least four interacting fluids.

  10. Cosmological implications of interacting group field theory models: Cyclic universe and accelerated expansion

    NASA Astrophysics Data System (ADS)

    de Cesare, Marco; Pithis, Andreas G. A.; Sakellariadou, Mairi

    2016-09-01

    We study the cosmological implications of interactions between spacetime quanta in the group field theory (GFT) approach to quantum gravity from a phenomenological perspective. Our work represents a first step towards understanding early Universe cosmology by studying the dynamics of the emergent continuum spacetime, as obtained from a fundamentally discrete microscopic theory. In particular, we show how GFT interactions lead to a recollapse of the Universe while preserving the bounce replacing the initial singularity, which has already been shown to occur in the free case. It is remarkable that cyclic cosmologies are thus obtained in this framework without any a priori assumption on the geometry of spatial sections of the emergent spacetime. Furthermore, we show how interactions make it possible to have an early epoch of accelerated expansion, which can be made to last for an arbitrarily large number of e -folds, without the need to introduce an ad hoc potential for the scalar field.

  11. A philosophy for big-bang cosmology.

    PubMed

    McCrea, W H

    1970-10-01

    According to recent developments in cosmology we seem bound to find a model universe like the observed universe, almost independently of how we suppose it started. Such ideas, if valid, provide fresh justification for the procedures of current cosmological theory.

  12. Vector theories in cosmology

    SciTech Connect

    Esposito-Farese, Gilles; Pitrou, Cyril; Uzan, Jean-Philippe

    2010-03-15

    This article provides a general study of the Hamiltonian stability and the hyperbolicity of vector field models involving both a general function of the Faraday tensor and its dual, f(F{sup 2},FF-tilde), as well as a Proca potential for the vector field, V(A{sup 2}). In particular it is demonstrated that theories involving only f(F{sup 2}) do not satisfy the hyperbolicity conditions. It is then shown that in this class of models, the cosmological dynamics always dilutes the vector field. In the case of a nonminimal coupling to gravity, it is established that theories involving Rf(A{sup 2}) or Rf(F{sup 2}) are generically pathologic. To finish, we exhibit a model where the vector field is not diluted during the cosmological evolution, because of a nonminimal vector field-curvature coupling which maintains second-order field equations. The relevance of such models for cosmology is discussed.

  13. Oscillating cosmological model with a varying Λ term in Barber's second self-creation theory of gravitation

    NASA Astrophysics Data System (ADS)

    Shen, M.

    2016-09-01

    We investigate the spatially homogeneous and isotropic FRW cosmological model with a time varying Λ term in Barber's second self-creation theory. The field equations of this theory are solved by using a time periodic varying deceleration parameter q=m cos kx -1 with m and k being positive constants. From the derivation of the expressions for the statefinder parameters r and s, it is obtained that the values of r and s of the present model can reduce to statefinder parameters of standard Λ CDM model r=1 and s=0 only when m=3/2.

  14. Stable clustering, the halo model and non-linear cosmological power spectra

    NASA Astrophysics Data System (ADS)

    Smith, R. E.; Peacock, J. A.; Jenkins, A.; White, S. D. M.; Frenk, C. S.; Pearce, F. R.; Thomas, P. A.; Efstathiou, G.; Couchman, H. M. P.

    2003-06-01

    We present the results of a large library of cosmological N-body simulations, using power-law initial spectra. The non-linear evolution of the matter power spectra is compared with the predictions of existing analytic scaling formulae based on the work of Hamilton et al. The scaling approach has assumed that highly non-linear structures obey `stable clustering' and are frozen in proper coordinates. Our results show that, when transformed under the self-similarity scaling, the scale-free spectra define a non-linear locus that is clearly shallower than would be required under stable clustering. Furthermore, the small-scale non-linear power increases as both the power spectrum index n and the density parameter Ω decrease, and this evolution is not well accounted for by the previous scaling formulae. This breakdown of stable clustering can be understood as resulting from the modification of dark matter haloes by continuing mergers. These effects are naturally included in the analytic `halo model' for non-linear structure; we use this approach to fit both our scale-free results and also our previous cold dark matter data. This method is more accurate than the commonly used Peacock-Dodds formula and should be applicable to more general power spectra. Code to evaluate non-linear power spectra using this method is available from http://as1.chem.nottingham.ac.uk/~res/software.html. Following publication, we will make the power-law simulation data publically available through the Virgo website http://www.mpa-garching.mpg.de/Virgo/.

  15. Cosmological daemon

    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.

  16. FRW cosmological models in Brans-Dicke theory of gravity with variable q and dynamical \\varLambda-term

    NASA Astrophysics Data System (ADS)

    Chand, Avtar; Mishra, R. K.; Pradhan, Anirudh

    2016-02-01

    Exact solution of modified Einstein's field equations are considered within the scope of spatially homogeneous and isotropic Fraidmann-Robertson-Walker (FRW) space-time filled with perfect fluid in the frame work of Brans-Dicke scalar-tensor theory of gravity. In this paper we have investigated the flat, open and closed FRW models and the effect of dynamic cosmological term on the evolution of the universe. Two types of FRW cosmological models are obtained by setting the power law between the scalar field φ and the scale factor a and deceleration parameter (DP) q as a time dependent. The concept of time dependent DP with some proper assumptions yield two type of the average scale factors (i) a(t)=[sinh(α t)]^{1/n} and (ii) a(t)=[t^{α}et]^{1/n}, α and n≠ 0 are arbitrary constants. In case (i), for 0 < n ≤ 1, it generates a class of accelerating models while for n > 1, the models of the universe exhibit phase transition from early decelerating to present accelerating phase and the transition redshift zt has been calculated and found to be in good agreement with the results from recent astrophysical observations. In case (ii), for n ≥ 2 and α = 1, we obtain a class of transit models of the universe from early decelerating to present accelerating phase. Taking into consideration the observational data, we conclude that the cosmological constant behaves as a positive decreasing function of time. The physical and geometric properties of the models are also discussed with the help of graphical presentations.

  17. Quantum phantom cosmology

    SciTech Connect

    DaPbrowski, Mariusz P.; Kiefer, Claus; Sandhoefer, Barbara

    2006-08-15

    We apply the formalism of quantum cosmology to models containing a phantom field. Three models are discussed explicitly: a toy model, a model with an exponential phantom potential, and a model with phantom field accompanied by a negative cosmological constant. In all these cases we calculate the classical trajectories in configuration space and give solutions to the Wheeler-DeWitt equation in quantum cosmology. In the cases of the toy model and the model with exponential potential we are able to solve the Wheeler-DeWitt equation exactly. For comparison, we also give the corresponding solutions for an ordinary scalar field. We discuss, in particular, the behavior of wave packets in minisuperspace. For the phantom field these packets disperse in the region that corresponds to the big-rip singularity. This thus constitutes a genuine quantum region at large scales, described by a regular solution of the Wheeler-DeWitt equation. For the ordinary scalar field, the big-bang singularity is avoided. Some remarks on the arrow of time in phantom models as well as on the relation of phantom models to loop quantum cosmology are given.

  18. Cosmological perturbations in teleparallel Loop Quantum Cosmology

    SciTech Connect

    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.

  19. 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.

  20. QCD Phase Transition in Dgp Brane Cosmology

    NASA Astrophysics Data System (ADS)

    Atazadeh, K.; Ghezelbash, A. M.; Sepangi, H. R.

    2012-08-01

    In the standard picture of cosmology it is predicted that a phase transition, associated with chiral symmetry breaking after the electroweak transition, has occurred at approximately 10μ seconds after the Big Bang to convert a plasma of free quarks and gluons into hadrons. We consider the quark-hadron phase transition in a Dvali, Gabadadze and Porrati (DGP) brane world scenario within an effective model of QCD. We study the evolution of the physical quantities useful for the study of the early universe, namely, the energy density, temperature and the scale factor before, during and after the phase transition. Also, due to the high energy density in the early universe, we consider the quadratic energy density term that appears in the Friedmann equation. In DGP brane models such a term corresponds to the negative branch (ɛ = -1) of the Friedmann equation when the Hubble radius is much smaller than the crossover length in 4D and 5D regimes. We show that for different values of the cosmological constant on a brane, λ, phase transition occurs and results in decreasing the effective temperature of the quark-gluon plasma and of the hadronic fluid. We then consider the quark-hadron transition in the smooth crossover regime at high and low temperatures and show that such a transition occurs along with decreasing the effective temperature of the quark-gluon plasma during the process of the phase transition.

  1. Missing Mass in Galaxies in Dynamic Universe Model of Cosmology (Part 3)

    NASA Astrophysics Data System (ADS)

    Gupta, S. N. P.

    2006-07-01

    In this present work SITA simulations were used to find out Theoretical star circular velocity curves in a Galaxy (star circular velocity verses star distance from the center of galaxy), depends on various initial conditions and are never half bell shaped curves as predicted by Bigbang cosmologies. Here we are presenting four main cases. In the first case A Galaxy with a huge central mass with star like masses in presence of external galaxies were taken. Theoretical prediction of circular velocities were matching with the observed velocities. In the later cases either Huge central mass was absent or external galaxies were absent or both were absent, the theoretical circular velocities did not match the observations. Hence the question of missing mass does not arise. Large-scale structures of universe could not be explained by Big bang based theories using additional repulsive forces like ``Einstein's λ'', as it requires isotropy and homogeneity. Our universe is neither isotropic nor homogeneous. It is LUMPY. And there is no gravitational repulsive force found in the universe even after almost a century after publication of General theory of Relativity. We find that for all fringe effects, Special theory of Relativity is sufficient. Things can be explained by Newtonian gravitation. This proves Galaxy disk formation require some external forces other than self-gravitation of Galaxy it self. Here the there is universal gravitational effect at that position and time are calculated due to ALL the bodies present in the universe. This forms a repulsive force. And this force varies with time, position, structure, masses, their distances, their dynamic movement etc. SITA (Simulation of Inter-intra-Galaxy Tautness and Attraction forces) was successful in the formation of Dynamic universe model where Blue shifted Galaxies were also present (Paper presented by SNP. Gupta, GR17, Dublin, 2004 & Presented in ICR 2005 International Conference on Relativity) , at Amravati

  2. Cosmic microwave background anisotropies in cold dark matter models with cosmological constant: The intermediate versus large angular scales

    NASA Technical Reports Server (NTRS)

    Stompor, Radoslaw; Gorski, Krzysztof M.

    1994-01-01

    We obtain predictions for cosmic microwave background anisotropies at angular scales near 1 deg in the context of cold dark matter models with a nonzero cosmological constant, normalized to the Cosmic Background Explorer (COBE) Differential Microwave Radiometer (DMR) detection. The results are compared to those computed in the matter-dominated models. We show that the coherence length of the Cosmic Microwave Background (CMB) anisotropy is almost insensitive to cosmological parameters, and the rms amplitude of the anisotropy increases moderately with decreasing total matter density, while being most sensitive to the baryon abundance. We apply these results in the statistical analysis of the published data from the UCSB South Pole (SP) experiment (Gaier et al. 1992; Schuster et al. 1993). We reject most of the Cold Dark Matter (CDM)-Lambda models at the 95% confidence level when both SP scans are simulated together (although the combined data set renders less stringent limits than the Gaier et al. data alone). However, the Schuster et al. data considered alone as well as the results of some other recent experiments (MAX, MSAM, Saskatoon), suggest that typical temperature fluctuations on degree scales may be larger than is indicated by the Gaier et al. scan. If so, CDM-Lambda models may indeed provide, from a point of view of CMB anisotropies, an acceptable alternative to flat CDM models.

  3. A 5-D hyperchaotic Rikitake dynamo system with hidden attractors

    NASA Astrophysics Data System (ADS)

    Vaidyanathan, S.; Pham, V.-T.; Volos, C. K.

    2015-07-01

    This paper presents a 5-D hyperchaotic Rikitake dynamo system with three positive Lyapunov exponents which is derived by adding two state feedback controls to the famous 3-D Rikitake two-disk dynamo system. It is noted that the proposed hyperchaotic system has no equilibrium points and hence it exhibits hidden attractors. In addition, the qualitative properties, as well as the adaptive synchronization of the hyperchaotic Rikitake dynamo system with unknown system parameters, are discussed in details. The main results are proved using Lyapunov stability theory and numerical simulations are shown using MATLAB. Moreover, an electronic circuit realization in SPICE has been detailed to confirm the feasibility of the theoretical 5-D hyperchaotic Rikitake dynamo model.

  4. BOOK REVIEW: Cosmology

    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

  5. The Case for a Hierarchical Cosmology

    ERIC Educational Resources Information Center

    Vaucouleurs, G. de

    1970-01-01

    The development of modern theoretical cosmology is presented and some questionable assumptions of orthodox cosmology are pointed out. Suggests that recent observations indicate that hierarchical clustering is a basic factor in cosmology. The implications of hierarchical models of the universe are considered. Bibliography. (LC)

  6. 5D supergravity and projective superspace

    NASA Astrophysics Data System (ADS)

    Kuzenko, Sergei M.; Tartaglino-Mazzucchelli, Gabriele

    2008-02-01

    This paper is a companion to our earlier work [1] in which the projective superspace formulation for matter-coupled simple supergravity in five dimensions was presented. For the minimal multiplet of 5D Script N = 1 supergravity introduced by Howe in 1981, we give a complete solution of the Bianchi identities. The geometry of curved superspace is shown to allow the existence of a large family of off-shell supermultiplets that can be used to describe supersymmetric matter, including vector multiplets and hypermultiplets. We formulate a manifestly locally supersymmetric action principle. Its natural property turns out to be the invariance under so-called projective transformations of the auxiliary isotwistor variables. We then demonstrate that the projective invariance allows one to uniquely restore the action functional in a Wess-Zumino gauge. The latter action is well-suited for reducing the supergravity-matter systems to components.

  7. 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.

  8. Transition probabilities for 5s-5p, 5p-5d, 4f-5d, and 5d-5f transitions in Ag-like ions with Z = 50-86

    SciTech Connect

    Ivanova, E.P.

    2011-01-15

    The wavelengths, electric dipole transition probabilities, and oscillator strengths are calculated for transitions between low-lying states (5s-5p, 5p-5d, 4f-5d, and 5d-5f) in the silver isoelectronic sequence (50 {<=} Z {<=} 86) using relativistic perturbation theory with a zero-approximation model potential. The results are compared with the corresponding data of the relativistic Hartree-Fock theory and the relativistic many-body perturbation theory. The results of these three theoretical approaches are compared with available experimental data for the level lifetimes. Possible reasons for some disagreements are discussed.

  9. The cosmological model of eternal inflation and the transition from chance to biological evolution in the history of life

    PubMed Central

    Koonin, Eugene V

    2007-01-01

    Background Recent developments in cosmology radically change the conception of the universe as well as the very notions of "probable" and "possible". The model of eternal inflation implies that all macroscopic histories permitted by laws of physics are repeated an infinite number of times in the infinite multiverse. In contrast to the traditional cosmological models of a single, finite universe, this worldview provides for the origin of an infinite number of complex systems by chance, even as the probability of complexity emerging in any given region of the multiverse is extremely low. This change in perspective has profound implications for the history of any phenomenon, and life on earth cannot be an exception. Hypothesis Origin of life is a chicken and egg problem: for biological evolution that is governed, primarily, by natural selection, to take off, efficient systems for replication and translation are required, but even barebones cores of these systems appear to be products of extensive selection. The currently favored (partial) solution is an RNA world without proteins in which replication is catalyzed by ribozymes and which serves as the cradle for the translation system. However, the RNA world faces its own hard problems as ribozyme-catalyzed RNA replication remains a hypothesis and the selective pressures behind the origin of translation remain mysterious. Eternal inflation offers a viable alternative that is untenable in a finite universe, i.e., that a coupled system of translation and replication emerged by chance, and became the breakthrough stage from which biological evolution, centered around Darwinian selection, took off. A corollary of this hypothesis is that an RNA world, as a diverse population of replicating RNA molecules, might have never existed. In this model, the stage for Darwinian selection is set by anthropic selection of complex systems that rarely but inevitably emerge by chance in the infinite universe (multiverse). Conclusion The

  10. Computation of inflationary cosmological perturbations in the power-law inflationary model using the phase-integral method

    SciTech Connect

    Rojas, Clara; Villalba, Victor M.

    2007-03-15

    The phase-integral approximation devised by Froeman and Froeman, is used for computing cosmological perturbations in the power-law inflationary model. The phase-integral formulas for the scalar and tensor power spectra are explicitly obtained up to ninth-order of the phase-integral approximation. We show that, the phase-integral approximation exactly reproduces the shape of the power spectra for scalar and tensor perturbations as well as the spectral indices. We compare the accuracy of the phase-integral approximation with the results for the power spectrum obtained with the slow-roll and uniform-approximation methods.

  11. Large-basis shell-model technology in nucleosynthesis and cosmology

    SciTech Connect

    Mathews, G.J.; Bloom, S.D.; Takahashi, K.; Fuller, G.M.; Hausman, R.F. Jr.

    1985-05-01

    We discuss various applications of the Lanczos method to describe properties of many-body microscopic systems in nucleosynthesis and cosmology. These calculations include: solar neutrino detectors; beta-decay of excited nuclear states; electron-capture rates during a core-bounce supernova; exotic quarked nuclei as a catalyst for hydrogen burning; and the quark-hadron phase transition during the early universe. 27 refs., 3 figs.

  12. A Cosmological Model of the Early Universe Based on ECG with Variable Λ-Term in Lyra Geometry

    NASA Astrophysics Data System (ADS)

    Saadat, H.

    2016-05-01

    In this paper, we study interacting extended Chaplygin gas as dark matter and quintessence scalar field as dark energy with an effective Λ-term in Lyra manifold. As we know Chaplygin gas behaves as dark matter at the early universe while cosmological constant at the late time. Modified field equations are given and motivation of the phenomenological models discussed in details. Four different models based on the interaction term are investigated in this work. Then, we consider other models where Extended Chaplygin gas and quintessence field play role of dark matter and dark energy respectively with two different forms of interaction between the extended Chaplygin gas and quintessence scalar field for both constant and varying Λ. Concerning to the mathematical hardness of the problems we discuss results numerically and graphically. Obtained results give us hope that proposed models can work as good models for the early universe with later stage of evolution containing accelerated expansion.

  13. Cosmology with the Cosmic Microwave Background

    NASA Astrophysics Data System (ADS)

    Souradeep, Tarun

    The standard model of cosmology must not only explain the dynamics of the homogeneous background universe, but also satisfactorily describe the perturbed universe - the generation, evolution and finally, the formation of large-scale structures in the universe. Cosmic microwave background (CMB) has been by far the most influential cosmological observation driving advances in current cosmology. Exquisite measurements from CMB experiments have seen the emergence of a concordant cosmological model. Besides precise determination of various parameters of the standard cosmological model, observations have also established some important basic tenets that underlie models of cosmology and structure formation in the universe. The article reviews this aspect of recent progress in cosmology for a general science reader.

  14. Cosmological perturbations in massive bigravity

    SciTech Connect

    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.

  15. Expanding wave solutions of the Einstein equations that induce an anomalous acceleration into the Standard Model of Cosmology.

    PubMed

    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.

  16. Expanding wave solutions of the Einstein equations that induce an anomalous acceleration into the Standard Model of Cosmology

    PubMed Central

    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

  17. Expanding wave solutions of the Einstein equations that induce an anomalous acceleration into the Standard Model of Cosmology.

    PubMed

    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. PMID:19706502

  18. Cosmological interrelations in nature.

    NASA Astrophysics Data System (ADS)

    Błaszkiewicz, L. P.

    1996-06-01

    Modern cosmology came into existence in the 20-th century when Albert Einstein introduced the static Universe model (1917), and when Edwin Hubble published the observations of spectra of galaxies together with the Dopplerian redshift interpretations (1929). These observational data were in accordance with the hypotheses of Alexander Friedman.

  19. 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…

  20. Why the Big Bang Model does not allow inflationary and cyclic cosmologies though mathematically one can obtain any model with favourable assumptions

    NASA Astrophysics Data System (ADS)

    Mitra, Abhas

    2014-07-01

    Various versions of standard Big Bang Model (BBM) including the current LCDM cosmology require an “inflationary” phase for the nascent universe (Δt∼10-32 s) during which the size of the universe blows up by a factor of ∼1078. However, the so-called Rh=ct cosmology (Melia, 2013a) claims that the isotropy and homogeneity of the present universe can be understood without assuming any inflationary phase. To this effect, Melia and his coworkers have often invoked “Weyl’s Postulate” and “Birkhoff’s Theorem” to qualitatively argue for this novel model. On the other hand, here, we explore for a cogent analytical basis of the Rh=ct proposal which is claimed to have such a profound implication. First we show that (i) if the spatial flatness of the BBM would be presumed, Rh=ct cosmology may indeed follow. To further explore this issue without prior assumption of flatness (ii) we equate the twin expressions for the Energy Complex (EC) associated with BBM computed by using the same Einstein pseudo-tensor and quasi-Cartesian coordinates (Mitra, 2013b). This exercise surprisingly shows that BBM has tacit and latent self-consistency constraints: it is spatially flat and its scale factor a(t)∝t. Accordingly, it seems that, there is no scope for the other models including inflationary and cyclic ones. The real lumpy universe may be too complex for the simplistic Big Bang model.

  1. Crossing the cosmological constant line in a dilatonic brane-world model with and without curvature corrections

    SciTech Connect

    Bouhmadi-Lopez, Mariam; Ferrera, Antonio E-mail: a.ferrera.pardo@gmail.com

    2008-10-15

    We construct a new brane-world model composed of a bulk with a dilatonic field, plus a brane with brane tension coupled to the dilaton, cold dark matter and an induced gravity term. It is possible to show that, depending on the nature of the coupling between the brane tension and the dilaton, this model can describe the late time acceleration of the brane expansion (for the normal branch) as it moves within the bulk. The acceleration is produced together with a mimicry of the crossing of the cosmological constant line (w = -1) on the brane, although this crossing of the phantom divide is obtained without invoking any phantom matter either on the brane or in the bulk. The role of dark energy is played by the brane tension, which reaches a maximum positive value along the cosmological expansion of the brane. It is precisely at that maximum that the crossing of the phantom divide takes place. We also show that these results remain valid when the induced gravity term on the brane is switched off.

  2. Cosmological moduli problem, supersymmetry breaking, and stability in postinflationary cosmology

    NASA Astrophysics Data System (ADS)

    Banks, T.; Berkooz, M.; Steinhardt, P. J.

    1995-07-01

    We review scenarios that have been proposed to solve the cosmological problem caused by moduli in string theory, the postmodern Polonyi problem (PPP). In particular, we discuss the difficulties encountered by the apparently ``trivial'' solution of this problem, in which moduli masses are assumed to arise from nonperturbative, SUSY-preserving, dynamics at a scale higher than that of SUSY breaking. This suggests a powerful cosmological vacuum selection principle in superstring theory. However, we argue that if one eschews the possibility of cancellations between different exponentials of the inverse string coupling, the mechanism described above cannot stabilize the dilaton. Thus, even if supersymmetric dynamics gives mass to the other moduli in string theory, the dilaton mass must be generated by SUSY breaking, and dilaton domination of the energy density of the Universe cannot be avoided. We conclude that the only proposal for solving the PPP that works is the intermediate scale inflation scenario of Randall and Thomas. However, we point out that all extant models have ignored unavoidably large inhomogeneities in the cosmological moduli density at very early times, and speculate that the effects associated with nonlinear gravitational collapse of these inhomogeneities may serve as an efficient mechanism for converting moduli into ordinary matter. As an important by-product of this investigation we show that in a postinflationary universe minima of the effective potential with a negative cosmological constant are not stationary points of the classical equations of scalar field cosmology. Instead, such points lead to catastrophic gravitational collapse of that part of the Universe which is attracted to them. Thus postinflationary cosmology dynamically chooses non-negative values of the cosmological constant. This implies that supersymmetry must be broken in any sensible inflationary cosmology. We suggest that further study of the cosmology of moduli will lead to

  3. Late time cosmological phase transitions 1: Particle physics models and cosmic evolution

    NASA Technical Reports Server (NTRS)

    Frieman, Joshua A.; Hill, Christopher T.; Watkins, Richard

    1991-01-01

    We described a natural particle physics basis for late-time phase transitions in the universe. Such a transition can seed the formation of large-scale structure while leaving a minimal imprint upon the microwave background anisotropy. The key ingredient is an ultra-light pseudo-Nambu-Goldstone boson with an astronomically large (O(kpc-Mpc)) Compton wavelength. We analyze the cosmological signatures of and constraints upon a wide class of scenarios which do not involve domain walls. In addition to seeding structure, coherent ultra-light bosons may also provide unclustered dark matter in a spatially flat universe, omega sub phi approx. = 1.

  4. Bianchi type-V bulk viscous string cosmological model in Saez-Ballester scalar-tensor theory of gravitation

    NASA Astrophysics Data System (ADS)

    Reddy, D. R. K.; Naidu, R. L.; Sobhan Babu, K.; Dasu Naidu, K.

    2014-01-01

    In this paper, a spatially homogeneous and anisotropic Bianchi type-V cosmological model is considered in a scalar-tensor theory of gravitation proposed by Saez and Ballester (in Phys. Lett. A 113:467, 1986) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. The field equations being highly non-linear, we obtain a determinate solution using the plausible physical conditions (i) the scalar of expansion of the space-time is proportional to shear scalar (ii) the baratropic equation of state for pressure and density and (iii) the bulk viscous pressure is proportional to the energy density. It is interesting to observe that cosmic strings do not survive in this model. Some physical and kinematical properties of the model are also discussed.

  5. A new statistical model for Population III supernova rates: discriminating between ΛCDM and WDM cosmologies

    NASA Astrophysics Data System (ADS)

    Magg, Mattis; Hartwig, Tilman; Glover, Simon C. O.; Klessen, Ralf S.; Whalen, Daniel J.

    2016-11-01

    With new observational facilities becoming available soon, discovering and characterizing supernovae from the first stars will open up alternative observational windows to the end of the cosmic dark ages. Based on a semi-analytical merger tree model of early star formation, we constrain Population III supernova rates. We find that our method reproduces the Population III supernova rates of large-scale cosmological simulations very well. Our computationally efficient model allows us to survey a large parameter space and to explore a wide range of different scenarios for Population III star formation. Our calculations show that observations of the first supernovae can be used to differentiate between cold and warm dark matter models and to constrain the corresponding particle mass of the latter. Our predictions can also be used to optimize survey strategies with the goal to maximize supernova detection rates.

  6. Area functional relation for 5D-Gauss-Bonnet-AdS black hole

    NASA Astrophysics Data System (ADS)

    Pradhan, Parthapratim

    2016-08-01

    We present area (or entropy) functional relation for multi-horizons five dimensional (5D) Einstein-Maxwell-Gauss-Bonnet-AdS black hole. It has been observed by exact and explicit calculation that some complicated function of two or three horizons area is mass-independent whereas the entropy product relation is not mass-independent. We also study the local thermodynamic stability of this black hole. The phase transition occurs at certain condition. Smarr mass formula and first law of thermodynamics have been derived. This mass-independent relation suggests they could turn out to be an universal quantity and further helps us to understanding the nature of black hole entropy (both interior and exterior) at the microscopic level. In the "Appendix", we have derived the thermodynamic products for 5D Einstein-Maxwell-Gauss-Bonnet black hole with vanishing cosmological constant.

  7. A coasting cosmology

    NASA Technical Reports Server (NTRS)

    Kolb, Edward W.

    1989-01-01

    A Friedmann-Robertson-Walker cosmology with energy density decreasing in expansion as 1/R-squared, where R is the Robertson-Walker scale factor, is studied. In such a model the universe expands with constant velocity; hence the term coasting cosmology. Observational consequences of such a model include the age of the universe, the luminosity distance-redshift relation (the Hubble diagram), the angular diameter distance-redshift relation, and the galaxy number count as a function of redshift. These observations are used to limit the parameters of the model. Among the interesting consequences of the model are the possibility of an ever-expanding closed universe, a model universe with multiple images at different redshifts of the same object, a universe with Omega - 1 not equal to 0 stable in expansion, and a closed universe with radius smaller than 1/H(0).

  8. Cosmological wormholes

    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.

  9. Medieval Cosmology

    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 ...

  10. Superheavy magnetic monopoles and the standard cosmology

    NASA Astrophysics Data System (ADS)

    Turner, M. S.

    1984-10-01

    The superheavy magnetic monopoles predicted to exist in grand unified theories (GUTs) are for particle physics, astrophysics and cosmology. Astrophysical and cosmological considerations are invaluable in the study of the properties of GUT monopoles. Because of the glut of monopoles predicted in the standard cosmology for the simplest GUTs. The simplest GUTs and the standard cosmology are not compatible. This is a very important piece of information about physics at unification energies and about the earliest movements of the Universe. The cosmological consequences of GUT monopoles within the context of the standard hot big bang model are reviewed.

  11. Twisted C⋆-algebra formulation of quantum cosmology with application to the Bianchi I model

    NASA Astrophysics Data System (ADS)

    Rosenbaum, Marcos; Vergara, J. David; Juárez, Román; Minzoni, A. A.

    2014-04-01

    A twisted C⋆-algebra of the extended (noncommutative) Heisenberg-Weyl group has been constructed which takes into account the uncertainty principle for coordinates in the Planck-length regime. This general construction is then used to generate an appropriate Hilbert space and observables for the noncommutative theory which, when applied to the Bianchi I cosmology, leads to a new set of equations that describe the quantum evolution of the Universe. We find that this formulation matches theories based on a reticular Heisenberg-Weyl algebra in the bouncing and expanding regions of a collapsing Bianchi universe. There is, however, an additional effect introduced by the dynamics generated by the noncommutativity. This is an oscillation in the spectrum of the volume operator of the Universe, within the bouncing region of the commutative theories. We show that this effect is generic and produced by the noncommutative momentum exchange between the degrees of freedom in the cosmology. We give asymptotic and numerical solutions which show the above mentioned effects of the noncommutativity.

  12. Bayesian Methods in Cosmology

    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.

  13. Bayesian Methods in Cosmology

    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.

  14. Topics in inflationary cosmologies

    SciTech Connect

    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.

  15. Cosmology and the Bispectrum

    SciTech Connect

    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.

  16. Cosmology from start to finish.

    PubMed

    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?

  17. 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.

  18. 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.

  19. Some cosmological models coming from gravitational theories having torsional degrees of freedom

    NASA Astrophysics Data System (ADS)

    Espiro, J. Lorca; Vásquez, Yerko

    2016-09-01

    In this work we consider gravitational theories in which the effect of coupling characteristic classes, appropriately introduced as operators in the Einstein-Hilbert action, has been taken into account. As it is well known, this approach strays from the framework of general relativity since it results in theories in which torsion can be present. We consider here all the characteristic classes that are consistent with a four-dimensional space-time manifold. Then, we present explicit expressions for the contortion 1-form and torsion 2-form for a broad class of conditions in various cases of interest. Additionally, we use the same framework to study cosmological scenarios that are obtained mainly by selecting the flat FLRW metric and an ideal fluid.

  20. Anisotropic matter in cosmology: locally rotationally symmetric Bianchi I and VII o models

    NASA Astrophysics Data System (ADS)

    Sloan, David

    2016-05-01

    We examine the behaviour of homogeneous, anisotropic space-times, specifically the locally rotationally symmetric Bianchi types I and VII o in the presence of anisotropic matter. By finding an appropriate constant of the motion, and transforming the equations of motion we are able to provide exact solutions in the presence of perfect fluids with anisotropic pressures. The solution space covers matter consisting of a single perfect fluid which satisfies the weak energy condition and is rich enough to contain solutions which exhibit behaviour which is qualitatively distinct from the isotropic sector. Thus we find that there is more ‘matter that matters’ close to a homogeneous singularity than the usual stiff fluid. Example metrics are given for cosmologies whose matter sources are magnetic fields, relativistic particles, cosmic strings and domain walls.

  1. Cosmology with massive neutrinos I: towards a realistic modeling of the relation between matter, haloes and galaxies

    SciTech Connect

    Villaescusa-Navarro, Francisco; Viel, Matteo; Marulli, Federico; Castorina, Emanuele; Sefusatti, Emiliano; Saito, Shun E-mail: federico.marulli3@unibo.it E-mail: branchin@fis.uniroma3.it E-mail: esefusat@ictp.it

    2014-03-01

    By using a suite of large box-size N-body simulations that incorporate massive neutrinos as an extra set of particles, with total masses of 0.15, 0.30, and 0.60 eV, we investigate the impact of neutrino masses on the spatial distribution of dark matter haloes and on the distribution of galaxies within the haloes. We compute the bias between the spatial distribution of dark matter haloes and the overall matter and cold dark matter distributions using statistical tools such as the power spectrum and the two-point correlation function. Overall we find a scale-dependent bias on large scales for the cosmologies with massive neutrinos. In particular, we find that the bias decreases with the scale, being this effect more important for higher neutrino masses and at high redshift. However, our results indicate that the scale-dependence in the bias is reduced if the latter is computed with respect to the cold dark matter distribution only. We find that the value of the bias on large scales is reasonably well reproduced by the Tinker fitting formula once the linear cold dark matter power spectrum is used, instead of the total matter power spectrum. We also investigate whether scale-dependent bias really comes from purely neutrino's effect or from nonlinear gravitational collapse of haloes. For this purpose, we address the Ω{sub ν}-σ{sub 8} degeneracy and find that such degeneracy is not perfect, implying that neutrinos imprint a slight scale dependence on the large-scale bias. Finally, by using a simple halo occupation distribution (HOD) model, we investigate the impact of massive neutrinos on the distribution of galaxies within dark matter haloes. We use the main galaxy sample in the Sloan Digital Sky Survey (SDSS) II Data Release 7 to investigate if the small-scale galaxy clustering alone can be used to discriminate among different cosmological models with different neutrino masses. Our results suggest that different choices of the HOD parameters can reproduce the

  2. 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.

  3. 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.

  4. Study of some cosmological parameters for interacting new holographic dark energy model in f(T) gravity

    NASA Astrophysics Data System (ADS)

    Ranjit, Chayan; Rudra, Prabir

    2016-10-01

    The present work is based on the idea of an interacting framework of new holographic dark energy (HDE) with cold dark matter in the background of f(T) gravity. Here, we have considered the flat modified Friedmann universe for f(T) gravity which is filled with new HDE and dark matter. We have derived some cosmological parameters like deceleration parameter, equation of state (EoS) parameter, state-finder parameters, cosmographic parameters, Om parameter and graphically investigated the nature of these parameters for the above mentioned interacting scenario. The results are found to be consistent with the accelerating universe. Also, we have graphically investigated the trajectories in ω-ω‧ plane for different values of the interacting parameter and explored the freezing region and thawing region in ω-ω‧ plane. Finally, we have analyzed the stability of this model.

  5. The new model of the Big Bang and the Universe expansion. A comparison with modern observational data and cosmological theories

    NASA Astrophysics Data System (ADS)

    Kraiko, A. N.; Valiyev, Kh. F.

    2016-10-01

    The new model of the Big Bang and the Universe expansion is constructed. It is based on solutions in classical and in relativistic statements of problem on the dispersion into the void of the gas compressed into a point or in a finite, but for further negligible, volume. If to restrict in relativistic statement gas speed value v by the speed of light (υ =| v | cosmological theories with the dark energy and the dark matter. The conclusion is drawn on uselessness of the dark energy.

  6. Impacts of different SNLS3 light-curve fitters on cosmological consequences of interacting dark energy models

    NASA Astrophysics Data System (ADS)

    Hu, Yazhou; Li, Miao; Li, Nan; Wang, Shuang

    2016-08-01

    We explore the cosmological consequences of interacting dark energy (IDE) models using the SNLS3 supernova samples. In particular, we focus on the impacts of different SNLS3 light-curve fitters (LCF; referred to in this paper as SALT2, SiFTO and combined sample). Firstly, making use of the three SNLS3 data sets, as well as the Planck distance priors data and the galaxy clustering data, we constrain the parameter spaces of three IDE models. Then, we study the cosmic evolutions of Hubble parameter H(z), deceleration diagram q(z), statefinder hierarchy S(1)3(z) and S(1)4(z), and check whether or not these dark energy diagnosis can distinguish the differences among the results of different SNLS3 LCF. Finally, we perform a high redshift cosmic age test using three old high redshift objects (OHRO), and explore the fate of the Universe. We find that the impacts of different SNLS3 LCF are rather small, and can not be distinguished using H(z), q(z), S(1)3(z), S(1)4(z), and the age data of OHRO. In addition, we infer, from the current observations, how far we are from a cosmic doomsday in the worst case, and find that the combined sample always gives the largest 2σ lower limit of the time interval between "big rip" and today, while the results given by the SALT2 and the SiFTO sample are similar. These conclusions are insensitive to a specific form of dark sector interaction. Our method can be used to distinguish the differences among various cosmological observations.

  7. Quantum cosmology on the worldsheet

    SciTech Connect

    Cooper, A.R.; Susskind, L.; Thorlacius, L.

    1991-08-01

    Two-dimensional quantum gravity coupled to conformally invariant matter central c > 25 provides a toy model for quantum gravity in four dimensions. Two-dimensional quantum cosmology can thus be studied in terms of string theory in background fields. The large scale cosmological constant depends on non-linear dynamics in the string theory target space and does not appear to be suppressed by wormhole effects. 13 refs.

  8. Equations on knot polynomials and 3d/5d duality

    SciTech Connect

    Mironov, A.; Morozov, A.

    2012-09-24

    We briefly review the current situation with various relations between knot/braid polynomials (Chern-Simons correlation functions), ordinary and extended, considered as functions of the representation and of the knot topology. These include linear skein relations, quadratic Plucker relations, as well as 'differential' and (quantum) A-polynomial structures. We pay a special attention to identity between the A-polynomial equations for knots and Baxter equations for quantum relativistic integrable systems, related through Seiberg-Witten theory to 5d super-Yang-Mills models and through the AGT relation to the q-Virasoro algebra. This identity is an important ingredient of emerging a 3d- 5d generalization of the AGT relation. The shape of the Baxter equation (including the values of coefficients) depend on the choice of the knot/braid. Thus, like the case of KP integrability, where (some, so far torus) knots parameterize particular points of the Universal Grassmannian, in this relation they parameterize particular points in the moduli space of many-body integrable systems of relativistic type.

  9. Nearly free electrons in a 5d delafossite oxide metal

    PubMed Central

    Kushwaha, Pallavi; Sunko, Veronika; Moll, Philip J. W.; Bawden, Lewis; Riley, Jonathon M.; Nandi, Nabhanila; Rosner, Helge; Schmidt, Marcus P.; Arnold, Frank; Hassinger, Elena; Kim, Timur K.; Hoesch, Moritz; Mackenzie, Andrew P.; King, Phil D. C.

    2015-01-01

    Understanding the role of electron correlations in strong spin-orbit transition-metal oxides is key to the realization of numerous exotic phases including spin-orbit–assisted Mott insulators, correlated topological solids, and prospective new high-temperature superconductors. To date, most attention has been focused on the 5d iridium-based oxides. We instead consider the Pt-based delafossite oxide PtCoO2. Our transport measurements, performed on single-crystal samples etched to well-defined geometries using focused ion beam techniques, yield a room temperature resistivity of only 2.1 microhm·cm (μΩ-cm), establishing PtCoO2 as the most conductive oxide known. From angle-resolved photoemission and density functional theory, we show that the underlying Fermi surface is a single cylinder of nearly hexagonal cross-section, with very weak dispersion along kz. Despite being predominantly composed of d-orbital character, the conduction band is remarkably steep, with an average effective mass of only 1.14me. Moreover, the sharp spectral features observed in photoemission remain well defined with little additional broadening for more than 500 meV below EF, pointing to suppressed electron-electron scattering. Together, our findings establish PtCoO2 as a model nearly-free–electron system in a 5d delafossite transition-metal oxide. PMID:26601308

  10. Stephani Schutz quantum cosmology

    NASA Astrophysics Data System (ADS)

    Pedram, P.; Jalalzadeh, S.; Gousheh, S. S.

    2007-11-01

    We study the Stephani quantum cosmological model in the presence of a cosmological constant in radiation dominated Universe. In the present work the Schutz's variational formalism which recovers the notion of time is applied. This gives rise to Wheeler DeWitt equations which can be cast in the form of Schrödinger equations for the scale factor. We find their eigenvalues and eigenfunctions by using the spectral method. Then we use the eigenfunctions in order to construct wave packets and evaluate the time-dependent expectation value of the scale factor, which is found to oscillate between non-zero finite maximum and minimum values. Since the expectation value of the scale factor never tends to the singular point, we have an initial indication that this model may not have singularities at the quantum level.

  11. Supplementary Investigation in the Langley Free-Spinning Tunnel of a 1/20-Scale Model of the Douglas XF4D-1 Airplane Including Spin-Recovery Parachute Tests of the Model Loaded to Simulate the Douglas F5D-1 Airplane

    NASA Technical Reports Server (NTRS)

    Klinar, Walter J.; Lee, Henry A.

    1955-01-01

    A supplementary investigation has been conducted in the Langley 20-foot free-spinning tunnel of a l/20-scale model of the Douglas XF4D-1 airplane to determine the effect of only neutralizing the rudder for recovery from an inverted spin, and the effect of partial aileron deflection with the spin for recovery from an erect spin. An estimation of the size parachute required for satisfactory recovery from a spin with the model ballasted to represent the Douglas F5D-1 (formerly the Douglas XF4D-2) airplane was also made. Results of the original investigation on the XF4D-1 design are presented in NACA RM SL50K30a. The results indicated that satisfactory recoveries from inverted spins of the airplane should be obtained by rudder neutralization when the longitudinal stick position is neutral or forward. Recoveries from erect spins from the normal-spin control configuration should be satisfactory by full rudder reversal with simultaneous movement of the ailerons to two-thirds with the spin. For the parachute tests with the model loaded to represent the F5D-1 airplane, the tests indicated that a 16.7-foot-diameter hemispherical-tail parachute (drag coefficient of 1.082 based on the projected area) with a towline 20.0 feet long (full- scale values) should be satisfactory for an emergency spin-recovery device during demonstration spins of the airplane.

  12. Average density in cosmology

    SciTech Connect

    Bonnor, W.B.

    1987-05-01

    The Einstein-Straus (1945) vacuole is here used to represent a bound cluster of galaxies embedded in a standard pressure-free cosmological model, and the average density of the cluster is compared with the density of the surrounding cosmic fluid. The two are nearly but not quite equal, and the more condensed the cluster, the greater the difference. A theoretical consequence of the discrepancy between the two densities is discussed. 25 references.

  13. 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.

  14. Cosmological implications of unimodular gravity

    SciTech Connect

    Jain, Pankaj; Jaiswal, Atul; Karmakar, Purnendu; Kashyap, Gopal; Singh, Naveen K. E-mail: atijazz@iitk.ac.in E-mail: gopal@iitk.ac.in

    2012-11-01

    We consider a model of gravity and matter fields which is invariant only under unimodular general coordinate transformations (GCT). The determinant of the metric is treated as a separate field which transforms as a scalar under unimodular GCT. Furthermore we also demand that the theory is invariant under a new global symmetry which we call generalized conformal invariance. We study the cosmological implications of the resulting theory. We show that this theory gives a fit to the high-z supernova data which is identical to the standard Big Bang model. Hence we require some other cosmological observations to test the validity of this model. We also consider some models which do not obey the generalized conformal invariance. In these models we can fit the supernova data without introducing the standard cosmological constant term. Furthermore these models introduce only one dark component and hence solve the coincidence problem of dark matter and dark energy.

  15. Competitive PCR for Quantification of BM5d Proviral DNA in Mice with AIDS

    PubMed Central

    Casabianca, Anna; Vallanti, Giuliana; Magnani, Mauro

    1998-01-01

    Murine AIDS in C57BL/6 mice is caused by a unique mixture of murine leukemia viruses. We report the use of a competitive PCR to detect and quantitate BM5d proviral DNA. This assay allowed discrimination among endogenous wild-type murine retroviruses and BM5d sequences. Furthermore, the method was subsequently used to evaluate the amount of BM5d in infected mice and in infected AZT (zidovudine)-treated mice, providing an effective way to quantitatively evaluate drug efficacy in the murine AIDS model. PMID:9666028

  16. Network Cosmology

    PubMed Central

    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

  17. Network cosmology.

    PubMed

    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.

  18. Loop quantum Brans-Dicke cosmology

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangdong; Artymowski, Michal; Ma, Yongge

    2013-04-01

    The spatially flat and isotropic cosmological model of Brans-Dicke theory with coupling parameter ω≠-(3)/(2) is quantized by the approach of loop quantum cosmology. An interesting feature of this model is that although the Brans-Dicke scalar field is nonminimally coupled with curvature, it can still play the role of an emergent time variable. In the quantum theory, the classical differential equation which represents cosmological evolution is replaced by a quantum difference equation. The effective Hamiltonian and modified dynamical equations of loop quantum Brans-Dicke cosmology are also obtained, which lay a foundation for the phenomenological investigation to possible quantum gravity effects in cosmology. The effective equations indicate that the classical big bang singularity is again replaced by a quantum bounce in loop quantum Brans-Dicke cosmology.

  19. A cosmological exclusion plot: towards model-independent constraints on modified gravity from current and future growth rate data

    SciTech Connect

    Taddei, Laura

    2015-02-01

    Most cosmological constraints on modified gravity are obtained assuming that the cosmic evolution was standard ΛCDM in the past and that the present matter density and power spectrum normalization are the same as in a ΛCDM model. Here we examine how the constraints change when these assumptions are lifted. We focus in particular on the parameter Y (also called G{sub eff}) that quantifies the deviation from the Poisson equation. This parameter can be estimated by comparing with the model-independent growth rate quantity fσ{sub 8}(z) obtained through redshift distortions. We reduce the model dependency in evaluating Y by marginalizing over σ{sub 8} and over the initial conditions, and by absorbing the degenerate parameter Ω{sub m,0} into Y. We use all currently available values of fσ{sub 8}(z). We find that the combination Y-circumflex =YΩ{sub m,0}, assumed constant in the observed redshift range, can be constrained only very weakly by current data, Y-circumflex =0.28{sub −0.23}{sup +0.35} at 68% c.l. We also forecast the precision of a future estimation of Y-circumflex in a Euclid-like redshift survey. We find that the future constraints will reduce substantially the uncertainty, Y-circumflex =0.30{sub −0.09}{sup +0.08} , at 68% c.l., but the relative error on Y-circumflex around the fiducial remains quite high, of the order of 30%. The main reason for these weak constraints is that Y-circumflex is strongly degenerate with the initial conditions, so that large or small values of Y-circumflex are compensated by choosing non-standard initial values of the derivative of the matter density contrast. Finally, we produce a forecast of a cosmological exclusion plot on the Yukawa strength and range parameters, which complements similar plots on laboratory scales but explores scales and epochs reachable only with large-scale galaxy surveys. We find that future data can constrain the Yukawa strength to within 3% of the Newtonian one if the range is around a few

  20. Nekrasov-Shatashvili limit of the 5D superconformal index

    NASA Astrophysics Data System (ADS)

    Papageorgakis, Constantinos; Pini, Alessandro; Rodríguez-Gómez, Diego

    2016-08-01

    We consider the Nekrasov-Shatashvili limit of the five-dimensional (5D) superconformal index and propose a novel prescription for selecting the finite contributions. Applying the latter to various examples of U(1) theories, we find that the 5D Nekrasov-Shatashvili index can be reproduced using recent techniques of Córdova and Shao, who related the 4D Schur index to the Bogomol'nyi-Prasad-Sommerfield (BPS) spectrum of the theory on the Coulomb branch. In this picture, the 5D instanton solitons are interpreted as additional flavor nodes in an associated 5D BPS quiver.

  1. Cosmology with hypervelocity stars

    SciTech Connect

    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.

  2. Culture and children's cosmology.

    PubMed

    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.

  3. Cosmological tests of modified gravity.

    PubMed

    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. PMID:27007681

  4. Cosmological tests of modified gravity.

    PubMed

    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.

  5. 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.

  6. Dynamical Cosmological Constant in R 3 Gravity

    NASA Astrophysics Data System (ADS)

    Zare, Nasser; Fathi, Mohsen

    2015-03-01

    In this paper, we go through the famous f( R) theories of gravity, but keeping a peculiar one, namely R 3 modification. Moreover, instead of a coordinate free cosmological parameter, we take it to be a function of time. Having all these stuff, we investigate the notions of standard cosmology model, in the context of R 3 modification to general relativity, and in various regimes, we study the dynamical cosmological constant.

  7. No hair theorem for inhomogeneous cosmologies

    SciTech Connect

    Jensen, L.G.; Stein-Schabes, J.A.

    1986-03-01

    We show that under very general conditions any inhomogeneous cosmological model with a positive cosmological constant, that can be described in a synchronous reference system will tend asymptotically in time towards the de Sitter solution. This is shown to be relevant in the context of inflationary models as it makes inflation very weakly dependent on initial conditions. 8 refs.

  8. C-Field Cosmology in Higher Dimensions

    NASA Astrophysics Data System (ADS)

    Chatterjee, S.; Banerjee, A.

    2004-02-01

    Hoyle and Narlikar's C-field cosmology is extended in the framework of higher dimensional spacetime and a class of exact solutions is obtained. Adjusting the arbitrary constants of integration one can show that our model is amenable to the desirable property of dimensional reduction so that the universe ends up in an effective 4D one. Further with matter creation from the C-field the mass density steadies with time and the usual bigbang singularity is avoided. An alternative mechanism is also suggested which seems to provide matter creation in the 4D spacetime although total matter in the 5D world remains conserved. Quintessence phenomenon and energy conditions are also discussed and it is found that in line with the physical requirements our model admits a solution with a decelerating phase in the early era followed by an accelerated expansion later. Moreover, as the contribution from the C-field is made negligible a class of our solutions reduces to the previously known higher dimensional models in the framework of Einstein's theory.

  9. 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

    2016-10-01

    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.

  10. Ekpyrotic loop quantum cosmology

    SciTech Connect

    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.

  11. 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.

  12. Cosmology and astroparticles

    SciTech Connect

    Gelmini, G.B.

    1996-02-01

    These lectures are devoted to elementary particle physicists and assume the reader has very little or no knowledge of cosmology and astrophysics. After a brief historical introduction to the development of modern cosmology and astro-particles in which the Hot Big Bang model is defined, the Robertson-Walker metric and the dynamics of the Friedmann-Robertson-Walker cosmology are discussed in section 2. In section 3 the main observational features of the Universe are reviewed, including a description of our neighborhood, homogeneity and isotropy, the cosmic background radiation, the expansion, the age and the matter content of the Universe. A brief account of the thermal history of the Universe follows in section 4, and relic abundances are discussed in section 5. Section 6 is devoted to primordial nucleosynthesis, section 7 to structure formation in the Universe and section 8 to the possibility of detection of the dark matter in the halo of our galaxy. In the relevant sections recent developments are included, such as several so called {open_quote}{open_quote}crisis{close_quote}{close_quote} (the age crisis, the cluster baryon crisis and the nucleosynthesis crisis), and the MACHO events that may constitute the first detection of dark matter in the halo of our galaxy. {copyright} {ital 1996 American Institute of Physics.}

  13. Cosmology and astroparticles

    SciTech Connect

    Gelmini, Graciela B.

    1996-02-20

    These lectures are devoted to elementary particle physicists and assume the reader has very little or no knowledge of cosmology and astrophysics. After a brief historical introduction to the development of modern cosmology and astro-particles in which the Hot Big Bang model is defined, the Robertson-Walker metric and the dynamics of the Friedmann-Robertson-Walker cosmology are discussed in section 2. In section 3 the main observational features of the Universe are reviewed, including a description of our neighborhood, homogeneity and isotropy, the cosmic background radiation, the expansion, the age and the matter content of the Universe. A brief account of the thermal history of the Universe follows in section 4, and relic abundances are discussed in section 5. Section 6 is devoted to primordial nucleosynthesis, section 7 to structure formation in the Universe and section 8 to the possibility of detection of the dark matter in the halo of our galaxy. In the relevant sections recent developments are included, such as several so called ''crisis'' (the age crisis, the cluster baryon crisis and the nucleosynthesis crisis), and the MACHO events that may constitute the first detection of dark matter in the halo of our galaxy.

  14. Cosmological tests of coupled Galileons

    SciTech Connect

    Brax, Philippe; Davis, Anne-Christine; Gubitosi, Giulia E-mail: Clare.Burrage@nottingham.ac.uk E-mail: g.gubitosi@imperial.ac.uk

    2015-03-01

    We investigate the cosmological properties of Galileon models which admit Minkowski space as a stable solution in vacuum. This is motivated by stable, positive tension brane world constructions that give rise to Galileons. We include both conformal and disformal couplings to matter and focus on constraints on the theory that arise because of these couplings. The disformal coupling to baryonic matter is extremely constrained by astrophysical and particle physics effects. The disformal coupling to photons induces a cosmological variation of the speed of light and therefore distorsions of the Cosmic Microwave Background spectrum which are known to be very small. The conformal coupling to baryons leads to a variation of particle masses since Big Bang Nucleosynthesis which is also tightly constrained. We consider the background cosmology of Galileon models coupled to Cold Dark Matter (CDM), photons and baryons and impose that the speed of light and particle masses respect the observational bounds on cosmological time scales. We find that requiring that the equation of state for the Galileon models must be close to -1 now restricts severely their parameter space and can only be achieved with a combination of the conformal and disformal couplings. This leads to large variations of particle masses and the speed of light which are not compatible with observations. As a result, we find that cosmological Galileon models are viable dark energy theories coupled to dark matter but their couplings, both disformal and conformal, to baryons and photons must be heavily suppressed making them only sensitive to CDM.

  15. Landscape predictions from cosmological vacuum selection

    SciTech Connect

    Bousso, Raphael; Yang, I-S.

    2007-06-15

    In Bousso-Polchinski models with hundreds of fluxes, we compute the effects of cosmological dynamics on the probability distribution of landscape vacua. Starting from generic initial conditions, we find that most fluxes are dynamically driven into a different and much narrower range of values than expected from landscape statistics alone. Hence, cosmological evolution will access only a tiny fraction of the vacua with small cosmological constant. This leads to a host of sharp predictions. Unlike other approaches to eternal inflation, the holographic measure employed here does not lead to staggering, an excessive spread of probabilities that would doom the string landscape as a solution to the cosmological constant problem.

  16. Landscape predictions from cosmological vacuum selection

    SciTech Connect

    Bousso, Raphael; Bousso, Raphael; Yang, Sheng

    2007-04-23

    In Bousso-Polchinski models with hundreds of fluxes, we compute the effects of cosmological dynamics on the probability distribution of landscape vacua. Starting from generic initial conditions, we find that most fluxes are dynamically driven into a different and much narrower range of values than expected from landscape statistics alone. Hence, cosmological evolution will access only a tiny fraction of the vacua with small cosmological constant. This leads to a host of sharp predictions. Unlike other approaches to eternal inflation, the holographic measure employed here does not lead to staggering, an excessive spread of probabilities that would doom the string landscape as a solution to the cosmological constant problem.

  17. Imperfect fluids, Lorentz violations, and Finsler cosmology

    SciTech Connect

    Kouretsis, A. P.; Stathakopoulos, M.; Stavrinos, P. C.

    2010-09-15

    We construct a cosmological toy model based on a Finslerian structure of space-time. In particular, we are interested in a specific Finslerian Lorentz violating theory based on a curved version of Cohen and Glashow's very special relativity. The osculation of a Finslerian manifold to a Riemannian manifold leads to the limit of relativistic cosmology, for a specified observer. A modified flat Friedmann-Robertson-Walker cosmology is produced. The analogue of a zero energy particle unfolds some special properties of the dynamics. The kinematical equations of motion are affected by local anisotropies. Seeds of Lorentz violations may trigger density inhomogeneities to the cosmological fluid.

  18. Cosmology with matter diffusion

    SciTech Connect

    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.

  19. Tilted string cosmologies

    NASA Astrophysics Data System (ADS)

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

    1999-04-01

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

  20. A multi-element cosmological model with a complex space-time topology

    NASA Astrophysics Data System (ADS)

    Kardashev, N. S.; Lipatova, L. N.; Novikov, I. D.; Shatskiy, A. A.

    2015-02-01

    Wormhole models with a complex topology having one entrance and two exits into the same space-time of another universe are considered, as well as models with two entrances from the same space-time and one exit to another universe. These models are used to build a model of a multi-sheeted universe (a multi-element model of the "Multiverse") with a complex topology. Spherical symmetry is assumed in all the models. A Reissner-Norström black-hole model having no singularity beyond the horizon is constructed. The strength of the central singularity of the black hole is analyzed.

  1. Cosmology with galaxy clusters

    NASA Astrophysics Data System (ADS)

    Sartoris, Barbara

    2015-08-01

    Clusters of galaxies are powerful probes to constrain parameters that describe the cosmological models and to distinguish among different models. Since, the evolution of the cluster mass function and large-scale clustering contain the informations about the linear growth rate of perturbations and the expansion history of the Universe, clusters have played an important role in establishing the current cosmological paradigm. It is crucial to know how to determine the cluster mass from observational quantities when using clusters as cosmological tools. For this, numerical simulations are helpful to define and study robust cluster mass proxies that have minimal and well understood scatter across the mass and redshift ranges of interest. Additionally, the bias in cluster mass determination can be constrained via observations of the strong and weak lensing effect, X-ray emission, the Sunyaev- Zel’dovic effect, and the dynamics of galaxies.A major advantage of X-ray surveys is that the observable-mass relation is tight. Moreover, clusters can be easily identified in X-ray as continuous, extended sources. As of today, interesting cosmological constraints have been obtained from relatively small cluster samples (~102), X-ray selected by the ROSAT satellite over a wide redshift range (0105 clusters with photometric redshifts from multi-band optical surveys (e.g. PanSTARRS, DES, and LSST). This will vastly improve upon current cosmological constraints, especially by the synergy with other cluster surveys that

  2. Cosmological parameter estimation using Particle Swarm Optimization

    NASA Astrophysics Data System (ADS)

    Prasad, J.; Souradeep, T.

    2014-03-01

    Constraining parameters of a theoretical model from observational data is an important exercise in cosmology. There are many theoretically motivated models, which demand greater number of cosmological parameters than the standard model of cosmology uses, and make the problem of parameter estimation challenging. It is a common practice to employ Bayesian formalism for parameter estimation for which, in general, likelihood surface is probed. For the standard cosmological model with six parameters, likelihood surface is quite smooth and does not have local maxima, and sampling based methods like Markov Chain Monte Carlo (MCMC) method are quite successful. However, when there are a large number of parameters or the likelihood surface is not smooth, other methods may be more effective. In this paper, we have demonstrated application of another method inspired from artificial intelligence, called Particle Swarm Optimization (PSO) for estimating cosmological parameters from Cosmic Microwave Background (CMB) data taken from the WMAP satellite.

  3. Bbb CP2 and Bbb CP1 sigma models in supergravity: Bianchi type IX instantons and cosmologies

    NASA Astrophysics Data System (ADS)

    Akbar, M. M.; D'Eath, P. D.

    2004-05-01

    We find instanton/cosmological solutions with biaxial Bianchi-IX symmetry, involving nontrivial spatial dependence of the {\\bb C} P^{1} - and {\\bb C} P^{2} -sigma-models coupled to gravity. Such manifolds arise in N = 1, d = 4 supergravity with supermatter actions and hence the solutions can be embedded in supergravity. There is a natural way in which the standard coordinates of these manifolds can be mapped into the four-dimensional physical space. Due to its special symmetry, we start with {\\bb C} P^{2} with its corresponding scalar ansatz; this further requires the spacetime to be SU(2) × U(1)-invariant. The problem then reduces to a set of ordinary differential equations whose analytical properties and solutions are discussed. Among the solutions there is a surprising, special family of exact solutions which owe their existence to the nontrivial topology of {\\bb C} P^{2} and are in 1-1 correspondence with matter-free Bianchi-IX metrics. These solutions can also be found by coupling {\\bb C} P^{1} to gravity. The regularity of these Euclidean solutions is discussed—the only possibility is bolt-type regularity. The Lorentzian solutions with similar scalar ansatz are all obtainable from the Euclidean solutions by Wick rotation.

  4. COSMOLOGICAL-MODEL-INDEPENDENT TESTS FOR THE DISTANCE-DUALITY RELATION FROM GALAXY CLUSTERS AND TYPE Ia SUPERNOVA

    SciTech Connect

    Li Zhengxiang; Yu Hongwei; Wu Puxun

    2011-03-01

    We perform a cosmological-model-independent test for the distance-duality (DD) relation {eta}(z) = D{sub L} (z)(1 + z){sup -2}/D{sub A} (z), where D{sub L} and D{sub A} are the luminosity distance and angular diameter distance, respectively, with a combination of observational data for D{sub L} taken from the latest Union2 SNe Ia and that for D{sub A} provided by two galaxy cluster samples compiled by De Filippis et al. and Bonamente et al. Two parameterizations for {eta}(z), i.e., {eta}(z) = 1 + {eta}{sub 0} z and {eta}(z) = 1 + {eta}{sub 0} z/(1 + z), are used. We find that the DD relation can be accommodated at 1{sigma} confidence level (CL) for the De Filippis et al. sample and at 3{sigma} CL for the Bonamente et al. sample. We also examine the DD relation by postulating two more general parameterizations: {eta}(z) = {eta}{sub 0} + {eta}{sub 1} z and {eta}(z) = {eta}{sub 0} + {eta}{sub 1} z/(1 + z), and find that the DD relation is compatible with the results from the De Filippis et al. and the Bonamente et al. samples at 1{sigma} and 2{sigma} CLs, respectively. Thus, we conclude that the DD relation is compatible with present observations.

  5. Theoretical Astrophysics - Volume 3, Galaxies and Cosmology

    NASA Astrophysics Data System (ADS)

    Padmanabhan, T.

    2002-12-01

    1. Overview: galaxies and cosmology; 2. Galactic structure and dynamics; 3. Friedmann model of the universe; 4. Thermal history of the universe; 5. Structure formation; 6. Cosmic microwave background radiation; 7. Formation of baryonic structures; 8. Active galactic nuclei; 9. Intergalactic medium and absorption systems; 10. Cosmological observations.

  6. The Cosmological Constant and its Interpretation

    NASA Astrophysics Data System (ADS)

    Liddle, A.; Murdin, P.

    2002-12-01

    The cosmological constant was first introduced into the equations of general relativity by Einstein himself, who later famously criticized this move as his `greatest blunder'. His main motivation had been to allow cosmological models featuring a static universe, but this possibility swiftly became redundant with Edwin Hubble's discovery of the expansion of the universe. Despite this, it has period...

  7. A philosophy for big-bang cosmology.

    PubMed

    McCrea, W H

    1970-10-01

    According to recent developments in cosmology we seem bound to find a model universe like the observed universe, almost independently of how we suppose it started. Such ideas, if valid, provide fresh justification for the procedures of current cosmological theory. PMID:16058406

  8. Multi-dimensional cosmology and GUP

    SciTech Connect

    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.

  9. String Theory and Primordial Cosmology

    NASA Astrophysics Data System (ADS)

    Gasperini, Maurizio

    String cosmology aims at providing a reliable description of the very early Universe in the regime where standard-model physics is no longer appropriate, and where we can safely apply the basic ingredients of superstring models such as dilatonic and axionic forces, duality symmetries, winding modes, limiting sizes and curvatures, higher dimensional interactions among elementary extended object. The sought target is that of resolving (or at least alleviating) the big problems of standard and inflationary cosmology like the spacetime singularity, the physics of the trans-Planckian regime, the initial condition for inflation, and so on.

  10. Tuning, ergodicity, equilibrium, and cosmology

    NASA Astrophysics Data System (ADS)

    Albrecht, Andreas

    2015-05-01

    I explore the possibility that the cosmos is fundamentally an equilibrium system and review the attractive features of such theories. Equilibrium cosmologies are commonly thought to fail due to the "Boltzmann brain" problem. I show that it is possible to evade the Boltzmann brain problem if there is a suitable coarse-grained relationship between the fundamental degrees of freedom and the cosmological observables. I make my main points with simple toy models and then review the de Sitter equilibrium model as an illustration.

  11. The cosmology of asymmetric brane modified gravity

    SciTech Connect

    O'Callaghan, Eimear; Gregory, Ruth; Pourtsidou, Alkistis E-mail: ppxap1@nottingham.ac.uk

    2009-09-01

    We consider the asymmetric branes model of modified gravity, which can produce late time acceleration of the universe and compare the cosmology of this model to the standard ΛCDM model and to the DGP braneworld model. We show how the asymmetric cosmology at relevant physical scales can be regarded as a one-parameter extension of the DGP model, and investigate the effect of this additional parameter on the expansion history of the universe.

  12. F5D-1 on ramp with flight technicians

    NASA Technical Reports Server (NTRS)

    1962-01-01

    The big block letters 'TEST' on the upper fuselage of this Douglas F5D-1 Skylancer (Bu. No. 139208/NASA tail number 212) denoted the craft as a test plane which was one of the fleet stabled at NASA Flight Research Center from 1961 to 1963 (redesignated the Dryden Flight Research Center in 1976). The calibration hangar, with the door partially open, is shown in the background while nearby the flight technicians are preparing the airplane for another research flight. In 1963 the F5D-1, NASA 212, was transferred to Ames Research Center, Mountain View, California, where it was flown on miscellaneous research projects including supersonic-transport landing studies. The F5D-1 was used to collect data on sink rates and approach characteristics. This particular F5D-1 was retired after several years, and in December 1975, it was loaned to Victor Valley College.

  13. Galileons on cosmological backgrounds

    SciTech Connect

    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.

  14. Soft inflation. [in cosmology

    NASA Technical Reports Server (NTRS)

    Berkin, Andrew L.; Maeda, Kei-Ichi; Yokoyama, Jun'ichi

    1990-01-01

    The cosmology resulting from two coupled scalar fields was studied, one which is either a new inflation or chaotic type inflation, and the other which has an exponentially decaying potential. Such a potential may appear in the conformally transformed frame of generalized Einstein theories like the Jordan-Brans-Dicke theory. The constraints necessary for successful inflation are examined. Conventional GUT models such as SU(5) were found to be compatible with new inflation, while restrictions on the self-coupling constant are significantly loosened for chaotic inflation.

  15. DBI analog of a decaying vacuum cosmology

    NASA Astrophysics Data System (ADS)

    Bessada, Dennis

    2013-07-01

    In this work I discuss the dynamical and thermodynamical equivalence between a general k-essence scalar field cosmology and an arbitrary cosmological model with a decaying vacuum, thus generalizing the approach proposed by Maia and Lima [Phys. Rev. D 65, 083513 (2002)]. The formalism obtained is quite general and holds for any noncanonical scalar field model. As a special case I derive a Dirac-Born-Infeld model with an exponential potential and constant speed of sound, and show that it is equivalent to a cosmological model with decay law Λ(H)=3βH2.

  16. Substitutional 4d and 5d impurities in graphene.

    PubMed

    Alonso-Lanza, Tomás; Ayuela, Andrés; Aguilera-Granja, Faustino

    2016-08-21

    We describe the structural and electronic properties of graphene doped with substitutional impurities of 4d and 5d transition metals. The adsorption energies and distances for 4d and 5d metals in graphene show similar trends for the later groups in the periodic table, which are also well-known characteristics of 3d elements. However, along earlier groups the 4d impurities in graphene show very similar adsorption energies, distances and magnetic moments to the 5d ones, which can be related to the influence of the 4d and 5d lanthanide contraction. Surprisingly, within the manganese group, the total magnetic moment of 3 μB for manganese is reduced to 1 μB for technetium and rhenium. We find that compared with 3d elements, the larger size of the 4d and 5d elements causes a high degree of hybridization with the neighbouring carbon atoms, reducing spin splitting in the d levels. It seems that the magnetic adjustment of graphene could be significantly different if 4d or 5d impurities are used instead of 3d impurities.

  17. Substitutional 4d and 5d impurities in graphene.

    PubMed

    Alonso-Lanza, Tomás; Ayuela, Andrés; Aguilera-Granja, Faustino

    2016-08-21

    We describe the structural and electronic properties of graphene doped with substitutional impurities of 4d and 5d transition metals. The adsorption energies and distances for 4d and 5d metals in graphene show similar trends for the later groups in the periodic table, which are also well-known characteristics of 3d elements. However, along earlier groups the 4d impurities in graphene show very similar adsorption energies, distances and magnetic moments to the 5d ones, which can be related to the influence of the 4d and 5d lanthanide contraction. Surprisingly, within the manganese group, the total magnetic moment of 3 μB for manganese is reduced to 1 μB for technetium and rhenium. We find that compared with 3d elements, the larger size of the 4d and 5d elements causes a high degree of hybridization with the neighbouring carbon atoms, reducing spin splitting in the d levels. It seems that the magnetic adjustment of graphene could be significantly different if 4d or 5d impurities are used instead of 3d impurities. PMID:27439363

  18. Cosmological perturbations in warm-tachyon inflationary universe model with viscous pressure on the brane

    NASA Astrophysics Data System (ADS)

    Setare, M. R.; Kamali, V.

    2013-03-01

    We study warm-viscous inflationary universe model on the brane, in a tachyon field theory. We obtain the general conditions which are required for this model to be realizable. In longitudinal gauge, the primoradial perturbation parameters are found in great details, using slow-roll and quasi-stable approximations. The general expressions of the tensor-to-scalar ratio, scalar spectral index and its running are found. We derive the characteristics of the inflationary universe model by using an effective exponential potential in two cases: 1 — dissipative parameter Γ and bulk viscous parameter ζ are constant parameters. 2 — dissipative parameter as a function of tachyon field ϕ and bulk viscous parameter as a function of radiation-matter mixture energy density ρ. The parameters of the model are restricted by recent observational data from the seven-year Wilkinson microwave anisotropy probe (WMAP7).

  19. Cosmological Imprints of a Generalized Chaplygin Gas Model for the Early Universe

    SciTech Connect

    Bouhmadi-Lopez, Mariam; Chen, Pisin; Liu, Yen-Wei; /Taiwan, Natl. Taiwan U.

    2012-06-06

    We propose a phenomenological model for the early universe where there is a smooth transition between an early quintessence phase and a radiation-dominated era. The matter content is modeled by an appropriately modified Chaplygin gas for the early universe. We constrain the model observationally by mapping the primordial power spectrum of the scalar perturbations to the latest data of WMAP7. We compute as well the spectrum of the primordial gravitational waves as would be measured today. We show that the high frequencies region of the spectrum depends on the free parameter of the model and most importantly this region of the spectrum can be within the reach of future gravitational waves detectors.

  20. Five dimensional spherically symmetric cosmological model in Brans-Dicke theory of gravitation

    NASA Astrophysics Data System (ADS)

    Rao, V. U. M.; Jaysudha, V.

    2015-08-01

    In this paper, we consider the spherically symmetric space-time in five dimensions in Brans-Dicke (Phys. Rev. 124:925, 1961) theory of gravitation in the presence of perfect fluid distribution. A determinate solution of the highly non-linear field equations is presented using (i) relation between metric potentials and (ii) an equation of state which represents disordered radiation in five dimensional universe. The solution obtained describes five dimensional radiating model in Brans-Dicke theory. Some physical and kinematical properties of the model are also discussed.

  1. WMAP normalization of inflationary cosmologies

    SciTech Connect

    Liddle, Andrew R.; Parkinson, David; Mukherjee, Pia; Leach, Samuel M.

    2006-10-15

    We use the three-year WMAP observations to determine the normalization of the matter power spectrum in inflationary cosmologies. In this context, the quantity of interest is not the normalization marginalized over all parameters, but rather the normalization as a function of the inflationary parameters n{sub S} and r with marginalization over the remaining cosmological parameters. We compute this normalization and provide an accurate fitting function. The statistical uncertainty in the normalization is 3%, roughly half that achieved by COBE. We use the k-l relation for the standard cosmological model to identify the pivot scale for the WMAP normalization. We also quote the inflationary energy scale corresponding to the WMAP normalization.

  2. Double field theory inspired cosmology

    SciTech Connect

    Wu, Houwen; Yang, Haitang E-mail: hyanga@scu.edu.cn

    2014-07-01

    Double field theory proposes a generalized spacetime action possessing manifest T-duality on the level of component fields. We calculate the cosmological solutions of double field theory with vanishing Kalb-Ramond field. It turns out that double field theory provides a more consistent way to construct cosmological solutions than the standard string cosmology. We construct solutions for vanishing and non-vanishing symmetry preserving dilaton potentials. The solutions assemble the pre- and post-big bang evolutions in one single line element. Our results show a smooth evolution from an anisotropic early stage to an isotropic phase without any special initial conditions in contrast to previous models. In addition, we demonstrate that the contraction of the dual space automatically leads to both an inflation phase and a decelerated expansion of the ordinary space during different evolution stages.

  3. Timelike information broadcasting in cosmology

    NASA Astrophysics Data System (ADS)

    Blasco, Ana; Garay, Luis J.; Martín-Benito, Mercedes; Martín-Martínez, Eduardo

    2016-01-01

    We study the transmission of information and correlations through quantum fields in cosmological backgrounds. With this aim, we make use of quantum information tools to quantify the classical and quantum correlations induced by a quantum massless scalar field in two particle detectors, one located in the early universe (Alice's) and the other located at a later time (Bob's). In particular, we focus on two phenomena: (a) the consequences on the transmission of information of the violations of the strong Huygens principle for quantum fields, and (b) the analysis of the field vacuum correlations via correlation harvesting from Alice to Bob. We will study a standard cosmological model first and then assess whether these results also hold if we use other than the general relativistic dynamics. As a particular example, we will study the transmission of information through the big bounce, that replaces the big bang, in the effective dynamics of loop quantum cosmology.

  4. Viable cosmology in bimetric theory

    SciTech Connect

    Felice, Antonio De; Gümrükçüoğlu, A. Emir; Mukohyama, Shinji; Tanahashi, Norihiro; Tanaka, Takahiro E-mail: Emir.Gumrukcuoglu@nottingham.ac.uk E-mail: norihiro.tanahashi@ipmu.jp

    2014-06-01

    We study cosmological perturbations in bimetric theory with two fluids each of which is coupled to one of the two metrics. Focusing on a healthy branch of background solutions, we clarify the stability of the cosmological perturbations. For this purpose, we extend the condition for the absence of the so-called Higuchi ghost, and show that the condition is guaranteed to be satisfied on the healthy branch. We also calculate the squared propagation speeds of perturbations and derive the conditions for the absence of the gradient instability. To avoid the gradient instability, we find that the model parameters are weakly constrained.

  5. Cosmologies with variable gravitational constant

    SciTech Connect

    Narkikar, J.V.

    1983-03-01

    In 1937 Dirac presented an argument, based on the socalled large dimensionless numbers, which led him to the conclusion that the Newtonian gravitational constant G changes with epoch. Towards the end of the last century Ernst Mach had given plausible arguments to link the property of inertia of matter to the large scale structure of the universe. Mach's principle also leads to cosmological models with a variable gravitational constant. Three cosmologies which predict a variable G are discussed in this paper both from theoretical and observational points of view.

  6. Singularities in loop quantum cosmology.

    PubMed

    Cailleteau, Thomas; Cardoso, Antonio; Vandersloot, Kevin; Wands, David

    2008-12-19

    We show that simple scalar field models can give rise to curvature singularities in the effective Friedmann dynamics of loop quantum cosmology (LQC). We find singular solutions for spatially flat Friedmann-Robertson-Walker cosmologies with a canonical scalar field and a negative exponential potential, or with a phantom scalar field and a positive potential. While LQC avoids big bang or big rip type singularities, we find sudden singularities where the Hubble rate is bounded, but the Ricci curvature scalar diverges. We conclude that the effective equations of LQC are not in themselves sufficient to avoid the occurrence of curvature singularities.

  7. Cosmological constraints on generalized Chaplygin gas model: Markov Chain Monte Carlo approach

    SciTech Connect

    Xu, Lixin; Lu, Jianbo E-mail: lvjianbo819@163.com

    2010-03-01

    We use the Markov Chain Monte Carlo method to investigate a global constraints on the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy from the latest observational data: the Constitution dataset of type supernovae Ia (SNIa), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. In a non-flat universe, the constraint results for GCG model are, Ω{sub b}h{sup 2} = 0.0235{sup +0.0021}{sub −0.0018} (1σ) {sup +0.0028}{sub −0.0022} (2σ), Ω{sub k} = 0.0035{sup +0.0172}{sub −0.0182} (1σ) {sup +0.0226}{sub −0.0204} (2σ), A{sub s} = 0.753{sup +0.037}{sub −0.035} (1σ) {sup +0.045}{sub −0.044} (2σ), α = 0.043{sup +0.102}{sub −0.106} (1σ) {sup +0.134}{sub −0.117} (2σ), and H{sub 0} = 70.00{sup +3.25}{sub −2.92} (1σ) {sup +3.77}{sub −3.67} (2σ), which is more stringent than the previous results for constraint on GCG model parameters. Furthermore, according to the information criterion, it seems that the current observations much support ΛCDM model relative to the GCG model.

  8. 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

  9. Energy of homogeneous cosmologies

    SciTech Connect

    Nester, James M.; So, L.L.; Vargas, T.

    2008-08-15

    An energy for the homogeneous cosmological models is presented. More specifically, using an appropriate natural prescription, we find the energy within any region with any gravitational source for a large class of gravity theories--namely, those with a tetrad description--for all nine Bianchi types. Our energy is given by the value of the Hamiltonian with homogeneous boundary conditions; this value vanishes for all regions in all Bianchi class A models, and it does not vanish for any class B model. This is so not only for Einstein's general relativity but, moreover, for the whole three-parameter class of tetrad-teleparallel theories. For the physically favored one-parameter subclass, which includes the teleparallel equivalent of Einstein's theory as an important special case, the energy for all class B models is, contrary to expectation, negative.

  10. 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.

  11. Cosmological constant in scale-invariant theories

    SciTech Connect

    Foot, Robert; Kobakhidze, Archil; Volkas, Raymond R.

    2011-10-01

    The incorporation of a small cosmological constant within radiatively broken scale-invariant models is discussed. We show that phenomenologically consistent scale-invariant models can be constructed which allow a small positive cosmological constant, providing certain relation between the particle masses is satisfied. As a result, the mass of the dilaton is generated at two-loop level. Another interesting consequence is that the electroweak symmetry-breaking vacuum in such models is necessarily a metastable ''false'' vacuum which, fortunately, is not expected to decay on cosmological time scales.

  12. Bianchi Type VI1 Viscous Fluid Cosmological Model in Wesson´s Theory of Gravitation

    NASA Astrophysics Data System (ADS)

    Khadekar, G. S.; Avachar, G. R.

    2007-03-01

    Field equations of a scale invariant theory of gravitation proposed by Wesson [1, 2] are obtained in the presence of viscous fluid with the aid of Bianchi type VIh space-time with the time dependent gauge function (Dirac gauge). It is found that Bianchi type VIh (h = 1) space-time with viscous fluid is feasible in this theory, whereas Bianchi type VIh (h = -1, 0) space-times are not feasible in this theory, even in the presence of viscosity. For the feasible case, by assuming a relation connecting viscosity and metric coefficient, we have obtained a nonsingular-radiating model. We have discussed some physical and kinematical properties of the models.

  13. Techniques for the modelling of QUBIC: a next-generation quasi-optical bolometric interferometer for cosmology

    NASA Astrophysics Data System (ADS)

    Scully, S.; Gayer, D.; Bennet, D.; O'Sullivan, C.; Gradziel, M. L.

    2014-03-01

    The expansion of the universe has red-shifted remnant radiation, called the Cosmic Microwave Background (CMB) radiation, to the terahertz band, one of the last areas of the electromagnetic spectrum to be explored. The CMB has imprinted upon it extremely faint temperature and polarisation features that were present in the early universe. The next ambitious goal in CMB astronomy is to map the polarisation characteristics but their detection will require a telescope with unprecedented levels of sensitivity and systematic error control. The QUBIC (Q&U Bolometric Interferometer for Cosmology) instrument has been specifically designed for this task, combining the sensitivity of a large array of wideband bolometers with the accuracy of interferometry. QUBIC will observe the sky through an array of horns whose signals will be added using a quasi-optical beam combiner (an off-axis Gregorian dual reflector designed to have low aberrations). Fringes will be formed on two focal planes separated by a polarising grid. MODAL (our in house simulation package) has been used to great effect in achieving a detailed level of understanding of the QUBIC combiner. Using a combination of scalar (GBM) and vector (PO) analysis, MODAL is capable of high speed and accuracy in the simulation of quasi-optical systems. There are several technical challenges to overcome but the development of MODAL and simulation techniques have gone a long way to solving these in the design and analysis phase. In this paper I outline the quasi-optical modelling of the QUBIC beam combiner and work envisaged for the future.

  14. Quantum cosmological Friedman models with a Yang-Mills field and positive energy levels

    NASA Astrophysics Data System (ADS)

    Gerhardt, Claus

    2010-02-01

    We prove the existence of a spectral resolution of the Wheeler-DeWitt equation when the matter field is provided by a Yang-Mills field, with or without mass term, if the spatial geometry of the underlying spacetime is homothetic to {\\bb R}^{3} . The energy levels of the resulting quantum model, i.e. the eigenvalues of the corresponding self-adjoint Hamiltonian with a pure point spectrum, are strictly positive. This work has been supported by the DFG.

  15. Evolution of perturbations and cosmological constraints in decaying dark matter models with arbitrary decay mass products

    SciTech Connect

    Aoyama, Shohei; Sekiguchi, Toyokazu; Sugiyama, Naoshi; Ichiki, Kiyotomo E-mail: toyokazu.sekiguchi@nagoya-u.jp E-mail: naoshi@nagoya-u.jp

    2014-07-01

    Decaying dark matter (DDM) is a candidate which can solve the discrepancies between predictions of the concordance ΛCDM model and observations at small scales such as the number counts of companion galaxies of the Milky Way and the density profile at the center of galaxies. Previous studies are limited to the cases where the decay particles are massless and/or have almost degenerate masses with that of mother particles. Here we expand the DDM models so that one can consider the DDM with arbitrary lifetime and the decay products with arbitrary masses. We calculate the time evolutions of perturbed phase-space distribution functions of decay products for the first time and study effects of DDM on the temperature anisotropy in the cosmic microwave background and the matter power spectrum at present. From a recent observational estimate of σ{sub 8}, we derive constraints on the lifetime of DDM and the mass ratio between the decay products and DDM. We also discuss implications of the DDM model for the discrepancy in the measurements of σ{sub 8} recently claimed by the Planck satellite collaboration.

  16. The Higgs boson and cosmology

    PubMed Central

    Shaposhnikov, Mikhail

    2015-01-01

    I will discuss how the Higgs field of the Standard Model may have played an important role in cosmology, leading to the homogeneity, isotropy and flatness of the Universe; producing the quantum fluctuations that seed structure formation; triggering the radiation-dominated era of the hot Big Bang; and contributing to the processes of baryogenesis and dark matter production.

  17. Averaging inhomogeneous cosmologies - a dialogue.

    NASA Astrophysics Data System (ADS)

    Buchert, T.

    The averaging problem for inhomogeneous cosmologies is discussed in the form of a disputation between two cosmologists, one of them (RED) advocating the standard model, the other (GREEN) advancing some arguments against it. Technical explanations of these arguments as well as the conclusions of this debate are given by BLUE.

  18. Averaging inhomogenous cosmologies - a dialogue

    NASA Astrophysics Data System (ADS)

    Buchert, T.

    The averaging problem for inhomogeneous cosmologies is discussed in the form of a disputation between two cosmologists, one of them (RED) advocating the standard model, the other (GREEN) advancing some arguments against it. Technical explanations of these arguments as well as the conclusions of this debate are given by BLUE.

  19. The Higgs boson and cosmology.

    PubMed

    Shaposhnikov, Mikhail

    2015-01-13

    I will discuss how the Higgs field of the Standard Model may have played an important role in cosmology, leading to the homogeneity, isotropy and flatness of the Universe; producing the quantum fluctuations that seed structure formation; triggering the radiation-dominated era of the hot Big Bang; and contributing to the processes of baryogenesis and dark matter production. PMID:26949807

  20. The Higgs boson and cosmology.

    PubMed

    Shaposhnikov, Mikhail

    2015-01-13

    I will discuss how the Higgs field of the Standard Model may have played an important role in cosmology, leading to the homogeneity, isotropy and flatness of the Universe; producing the quantum fluctuations that seed structure formation; triggering the radiation-dominated era of the hot Big Bang; and contributing to the processes of baryogenesis and dark matter production.

  1. Cosmology with decaying particles

    SciTech Connect

    Turner, M.S.

    1984-09-01

    We consider a cosmological model in which an unstable massive relic particle species (denoted by X) has an initial mass density relative to baryons ..beta../sup -1/ identically equal rho/sub X//rho/sub B/ >> 1, and then decays recently (redshift z less than or equal to 1000) into particles which are still relativistic today (denoted by R). We write down and solve the coupled equations for the cosmic scale factor a(t), the energy density in the various components (rho/sub X/, rho/sub R/, rho/sub B/), and the growth of linear density perturbations (delta rho/rho). The solutions form a one parameter (..beta..) family of solutions; physically ..beta../sup -1/ approx. = (..cap omega../sub R//..cap omega../sub NR/) x (1 + z/sub D/) = (ratio today of energy density of relativistic to nonrelativistic particles) x (1 + redshift of (decay)). We discuss the observational implications of such a cosmological model and compare our results to earlier results computed in the simultaneous decay approximation. In an appendix we briefly consider the case where one of the decay products of the X is massive and becomes nonrelativistic by the present epoch. 21 references.

  2. Primordial SdS universe from a 5D vacuum: scalar field fluctuations on Schwarzschild and Hubble horizons

    SciTech Connect

    Aguilar, José Edgar Madriz; Bellini, Mauricio E-mail: mbellini@mdp.edu.ar

    2010-11-01

    We study scalar field fluctuations of the inflaton field in an early inflationary universe on an effective 4D Schwarzschild-de Sitter (SdS) metric, which is obtained after make a planar coordinate transformation on a 5D Ricci-flat Schwarzschild-de Sitter (SdS) static metric. We obtain the important result that the spectrum of fluctuations at zeroth order is independent of the scalar field mass M on Schwarzschild scales, while on cosmological scales it exhibits a mass dependence. However, in the first-order expansion, the spectrum depends of the inflaton mass and the amplitude is linear with the Black-Hole (BH) mass m.

  3. Variable cosmological term \\varLambda(t)

    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 \\varLambda(t). The main idea arises by proposing that as in the cosmological constant case, the scalar potential is identified as V(φ)=2\\varLambda, with \\varLambda a constant, this identification should be kept even when the cosmological term has a temporal dependence, i.e., V(φ(t))=2\\varLambda(t). We use the Lagrangian formalism for a scalar field φ with standard kinetic energy and arbitrary potential V(φ) and apply this model to the Friedmann-Robertson-Walker (FRW) cosmology. Exact solutions of the field equations are obtained by a special ansatz 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.

  4. Particle physics and cosmology with high-scale SUSY breaking in five-dimensional supergravity models

    NASA Astrophysics Data System (ADS)

    Otsuka, Hajime

    2015-10-01

    We discuss a high-scale SUSY breaking scenario with the wino dark matter in the five-dimensional supergravity model on S 1 /Z 2. The extra U(1) symmetries broken by the orbifold projection control the flavor structure of soft SUSY-breaking parameters as well as the Yukawa couplings, and a scalar component of the one of moduli multiplets, which arise from extra-dimensional components of the U(1) vector multiplets, induces the slow-roll inflation. Because of the supersymmetric moduli stabilization as well as the moduli inflation, it is found that the correct dark matter relic abundance is non-thermally generated by the gravitino decaying into the wino.

  5. Loop quantum cosmology in 2 +1 dimension

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangdong

    2014-12-01

    As a first step to generalize the structure of loop quantum cosmology to the theories with the spacetime dimension other than four, the isotropic model of loop quantum cosmology in 2 +1 dimension is studied in this paper. We find that the classical big bang singularity is again replaced by a quantum bounce in the model. The similarities and differences between the (2 +1 )-dimensional model and the (3 +1 )-dimensional one are also discussed.

  6. Average observational quantities in the timescape cosmology

    SciTech Connect

    Wiltshire, David L.

    2009-12-15

    We examine the properties of a recently proposed observationally viable alternative to homogeneous cosmology with smooth dark energy, the timescape cosmology. In the timescape model cosmic acceleration is realized as an apparent effect related to the calibration of clocks and rods of observers in bound systems relative to volume-average observers in an inhomogeneous geometry in ordinary general relativity. The model is based on an exact solution to a Buchert average of the Einstein equations with backreaction. The present paper examines a number of observational tests which will enable the timescape model to be distinguished from homogeneous cosmologies with a cosmological constant or other smooth dark energy, in current and future generations of dark energy experiments. Predictions are presented for comoving distance measures; H(z); the equivalent of the dark energy equation of state, w(z); the Om(z) measure of Sahni, Shafieloo, and Starobinsky; the Alcock-Paczynski test; the baryon acoustic oscillation measure, D{sub V}; the inhomogeneity test of Clarkson, Bassett, and Lu; and the time drift of cosmological redshifts. Where possible, the predictions are compared to recent independent studies of similar measures in homogeneous cosmologies with dark energy. Three separate tests with indications of results in possible tension with the {lambda}CDM model are found to be consistent with the expectations of the timescape cosmology.

  7. 5D Tempest simulations of kinetic edge turbulence

    NASA Astrophysics Data System (ADS)

    Xu, X. Q.; Xiong, Z.; Cohen, B. I.; Cohen, R. H.; Dorr, M. R.; Hittinger, J. A.; Kerbel, G. D.; Nevins, W. M.; Rognlien, T. D.; Umansky, M. V.; Qin, H.

    2006-10-01

    Results are presented from the development and application of TEMPEST, a nonlinear five dimensional (3d2v) gyrokinetic continuum code. The simulation results and theoretical analysis include studies of H-mode edge plasma neoclassical transport and turbulence in real divertor geometry and its relationship to plasma flow generation with zero external momentum input, including the important orbit-squeezing effect due to the large electric field flow-shear in the edge. In order to extend the code to 5D, we have formulated a set of fully nonlinear electrostatic gyrokinetic equations and a fully nonlinear gyrokinetic Poisson's equation which is valid for both neoclassical and turbulence simulations. Our 5D gyrokinetic code is built on 4D version of Tempest neoclassical code with extension to a fifth dimension in binormal direction. The code is able to simulate either a full torus or a toroidal segment. Progress on performing 5D turbulence simulations will be reported.

  8. Cosmological implications of a viable non-analytical f(R) model

    NASA Astrophysics Data System (ADS)

    Capozziello, S.; Carlevaro, N.; De Laurentis, M.; Lattanzi, M.; Montani, G.

    2013-12-01

    Power-law corrections (having the exponent strictly between 2 and 3) to the Einstein-Hilbert action yield an extended theory of gravity which is consistent with Solar-System tests and properly reproduces the main phases of the Universe thermal history. We find two distinct constraints for the characteristic length scale of the model: a lower bound from the Solar-System test and an upper bound by requiring the existence of the matter-dominated era. We also show how the extended framework can accommodate the existence of an early de Sitter phase. Within the allowed range of characteristic length scales, the relation between the expansion rate and the energy scale of inflation is modified, yielding a value of the rate several orders of magnitude smaller than in the standard picture. The observational implication of this fact is that a tiny value of the tensor-to-scalar ratio is expected in the extended framework. The suppression of primordial tensor modes also implies that the inflationary scale can be made arbitrarily close to the Planck one according to the current limits. Finally, an analysis of the propagation of gravitational waves on a Robertson-Walker background is addressed.

  9. Effects of Inlet Modification and Rocket-Rack Extension on the Longitudinal Trim and Low-Lift Drag of the Douglas F5D-1 Airplane as Obtained with a 0.125-Scale Rocket-Boosted Model between Mach Numbers of 0.81 and 1.64, TED No. NACA AD 399

    NASA Technical Reports Server (NTRS)

    Hastings, Earl C., Jr.; Dickens, Waldo L.

    1957-01-01

    A flight investigation was conducted to determine the effects of an inlet modification and rocket-rack extension on the longitudinal trim and low-lift drag of the Douglas F5D-1 airplane. The investigation was conducted with a 0.125-scale rocket-boosted model which was flight tested at the Langley Pilotless Aircraft Research Station at Wallops Island, Va. Results indicate that the combined effects of the modified inlet and fully extended rocket racks on the trim lift coefficient and trim angle of attack were small between Mach numbers of 0.94 and 1.57. Between Mach numbers of 1.10 and 1.57 there was an average increase in drag coefficient of about o,005 for the model with modified inlet and extended rocket racks. The change in drag coefficient due to the inlet modification alone is small between Mach numbers of 1.59 and 1.64

  10. Gravitino problem in f (R) cosmology

    NASA Astrophysics Data System (ADS)

    Lambiase, G.

    2016-09-01

    The gravitino problem is investigated in the framework of f ( R) cosmology. Since in f ( R) cosmology the expansion laws of the Universe are modified, as compared to the standard cosmology, it follows that also the thermal history of particles gets modified. We show that f ( R) models allow to avoid the late abundance of gravitinos. In particular, we found that for an appropriate choice of the parameters characterizing the f ( R) model, the gravitino abundance turns out to be independent of the reheating temperature.

  11. Quantum Cosmology

    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. 1.Lachieze-Rey, M., Luminet, J.P.: Phys. Rept. 254,135 (1995), gr-qc/9605010 2.BSDeWitt1967Phys. Rev.160511131967PhRv..160.1113D0158.4650410.1103/PhysRev.160.1113DeWitt, B.S.: Phys. Rev. 160(5), 1113 (1967) 3.Wiltshire, D.L.: In: Robson B., Visvanathan N., Woolcock W.S. (eds.) Cosmology: The Physics of the Universe, pp. 473-531. World Scientific, Singapore (1996

  12. Nonlinear growing neutrino cosmology

    NASA Astrophysics Data System (ADS)

    Ayaita, Youness; Baldi, Marco; Führer, Florian; Puchwein, Ewald; Wetterich, Christof

    2016-03-01

    The energy scale of dark energy, ˜2 ×10-3 eV , is a long way off compared to all known fundamental scales—except for the neutrino masses. If dark energy is dynamical and couples to neutrinos, this is no longer a coincidence. The time at which dark energy starts to behave as an effective cosmological constant can be linked to the time at which the cosmic neutrinos become nonrelativistic. This naturally places the onset of the Universe's accelerated expansion in recent cosmic history, addressing the why-now problem of dark energy. We show that these mechanisms indeed work in the growing neutrino quintessence model—even if the fully nonlinear structure formation and backreaction are taken into account, which were previously suspected of spoiling the cosmological evolution. The attractive force between neutrinos arising from their coupling to dark energy grows as large as 106 times the gravitational strength. This induces very rapid dynamics of neutrino fluctuations which are nonlinear at redshift z ≈2 . Nevertheless, a nonlinear stabilization phenomenon ensures only mildly nonlinear oscillating neutrino overdensities with a large-scale gravitational potential substantially smaller than that of cold dark matter perturbations. Depending on model parameters, the signals of large-scale neutrino lumps may render the cosmic neutrino background observable.

  13. 5d Higgs branch localization, Seiberg-Witten equations and contact geometry

    NASA Astrophysics Data System (ADS)

    Pan, Yiwen

    2015-01-01

    In this paper we apply the idea of Higgs branch localization to 5d supersymmetric theories of vector multiplet and hypermultiplets, obtained as the rigid limit of = 1 supergravity with all auxiliary fields. On supersymmetric K-contact/Sasakian background, the Higgs branch BPS equations can be interpreted as 5d generalizations of the Seiberg-Witten equations. We discuss the properties and local behavior of the solutions near closed Reeb orbits. For U(1) gauge theories, which can be straight-forwardly generalized to theories whose gauge group can be completely broken, we show the suppression of the deformed Coulomb branch, and the partition function is dominated by 5d Seiberg-Witten solutions. For squashed S 5 and Y pq manifolds, we show the matching between poles in the perturbative Coulomb branch matrix model, and the bound on local winding numbers of the BPS solutions.

  14. Dark D-brane cosmology

    SciTech Connect

    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.

  15. Cosmological immortality: how to eliminate aging on a universal scale.

    PubMed

    Vidal, Clement

    2014-01-01

    The death of our universe is as certain as our individual death. Some cosmologists have elaborated models which would make the cosmos immortal. In this paper, I examine them as cosmological extrapolations of immortality narratives that civilizations have developed to face death anxiety. I first show why cosmological death should be a worry, then I briefly examine scenarios involving the notion of soul or resurrection on a cosmological scale. I discuss in how far an intelligent civilization could stay alive by engaging in stellar, galactic and universal rejuvenation. Finally, I argue that leaving a cosmological legacy via universe making is an inspiring and promising narrative to achieve cosmological immortality. PMID:24852011

  16. Cosmological immortality: how to eliminate aging on a universal scale.

    PubMed

    Vidal, Clement

    2014-01-01

    The death of our universe is as certain as our individual death. Some cosmologists have elaborated models which would make the cosmos immortal. In this paper, I examine them as cosmological extrapolations of immortality narratives that civilizations have developed to face death anxiety. I first show why cosmological death should be a worry, then I briefly examine scenarios involving the notion of soul or resurrection on a cosmological scale. I discuss in how far an intelligent civilization could stay alive by engaging in stellar, galactic and universal rejuvenation. Finally, I argue that leaving a cosmological legacy via universe making is an inspiring and promising narrative to achieve cosmological immortality.

  17. Alcock-paczynski cosmological test

    SciTech Connect

    López-Corredoira, M.

    2014-02-01

    In order to test the expansion of the universe and its geometry, we carry out an Alcock-Paczyński cosmological test, that is, an evaluation of the ratio of observed angular size to radial/redshift size. The main advantage of this test is that it does not depend on the evolution of the galaxies but only on the geometry of the universe. However, the redshift distortions produced by the peculiar velocities of the gravitational infall also have an influence, which should be separated from the cosmological effect. We derive the anisotropic correlation function of sources in three surveys within the Sloan Digital Sky Survey (SDSS): galaxies from SDSS-III/Baryon Oscillation Spectroscopic Survey Data Release 10 (BOSS-DR10) and QSOs from SDSS-II and SDSS-III/BOSS-DR10. From these, we are able to disentangle the dynamic and geometric distortions and thus derive the ratio of observed angular size to radial/redshift size at different redshifts. We also add some other values available in the literature. Then we use the data to evaluate which cosmological model fits them. We used six different models: concordance ΛCDM, Einstein-de Sitter, open-Friedman cosmology without dark energy, flat quasi-steady state cosmology, a static universe with a linear Hubble law, and a static universe with tired-light redshift. Only two of the six models above fit the data of the Alcock-Paczyński test: concordance ΛCDM and static universe with tired-light redshift, whereas the rest of them are excluded at a >95% confidence level. If we assume that ΛCDM is the correct one, the best fit with a free Ω {sub m} is produced for Ω{sub m}=0.24{sub −0.07}{sup +0.10}.

  18. Generalized Swiss-cheese cosmologies: Mass scales

    SciTech Connect

    Grenon, Cedric; Lake, Kayll

    2010-01-15

    We generalize the Swiss-cheese cosmologies so as to include nonzero linear momenta of the associated boundary surfaces. The evolution of mass scales in these generalized cosmologies is studied for a variety of models for the background without having to specify any details within the local inhomogeneities. We find that the final effective gravitational mass and size of the evolving inhomogeneities depends on their linear momenta but these properties are essentially unaffected by the details of the background model.

  19. Generalized Swiss-cheese cosmologies: Mass scales

    NASA Astrophysics Data System (ADS)

    Grenon, Cédric; Lake, Kayll

    2010-01-01

    We generalize the Swiss-cheese cosmologies so as to include nonzero linear momenta of the associated boundary surfaces. The evolution of mass scales in these generalized cosmologies is studied for a variety of models for the background without having to specify any details within the local inhomogeneities. We find that the final effective gravitational mass and size of the evolving inhomogeneities depends on their linear momenta but these properties are essentially unaffected by the details of the background model.

  20. Onset of inflation in loop quantum cosmology

    SciTech Connect

    Germani, Cristiano; Nelson, William; Sakellariadou, Mairi

    2007-08-15

    Using a Liouville measure, similar to the one proposed recently by Gibbons and Turok, we investigate the probability that single-field inflation with a polynomial potential can last long enough to solve the shortcomings of the standard hot big bang model, within the semiclassical regime of loop quantum cosmology. We conclude that, for such a class of inflationary models and for natural values of the loop quantum cosmology parameters, a successful inflationary scenario is highly improbable.

  1. Is there a flatness problem in classical cosmology?

    NASA Astrophysics Data System (ADS)

    Helbig, Phillip

    2012-03-01

    I briefly review the flatness problem within the context of classical cosmology and examine some of the debate in the literature with regard to its definition and even the question whether it exists. I then present some new calculations for cosmological models which will collapse in the future; together with previous work by others for models which will expand forever, this allows one to examine the flatness problem quantitatively for all cosmological models. This leads to the conclusion that the flatness problem does not exist, not only for the cosmological models corresponding to the currently popular values of λ0 and Ω0 but indeed for all Friedmann-Lemaître models.

  2. Neutrinos in Cosmology

    SciTech Connect

    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.

  3. Hamiltonian cosmology of bigravity

    NASA Astrophysics Data System (ADS)

    Soloviev, V. O.

    The purpose of this talk is to give an introduction both to the Hamiltonian formalism and to the cosmological equations of bigravity. In the Hamiltonian language we provide a study of flat-space cosmology in bigravity and massive gravity constructed mostly with de Rham, Gabadadze, Tolley (dRGT) potential. It is demonstrated that the Hamiltonian methods are powerful not only in proving the absence of the Boulware-Deser ghost, but also in addressing cosmological problems.

  4. The cosmological constant

    NASA Technical Reports Server (NTRS)

    Carroll, Sean M.; Press, William H.; Turner, Edwin L.

    1992-01-01

    The cosmological constant problem is examined in the context of both astronomy and physics. Effects of a nonzero cosmological constant are discussed with reference to expansion dynamics, the age of the universe, distance measures, comoving density of objects, growth of linear perturbations, and gravitational lens probabilities. The observational status of the cosmological constant is reviewed, with attention given to the existence of high-redshift objects, age derivation from globular clusters and cosmic nuclear data, dynamical tests of Omega sub Lambda, quasar absorption line statistics, gravitational lensing, and astrophysics of distant objects. Finally, possible solutions to the physicist's cosmological constant problem are examined.

  5. Asymptotic dynamics of the exceptional Bianchi cosmologies

    NASA Astrophysics Data System (ADS)

    Hewitt, C. G.; Horwood, J. T.; Wainwright, J.

    2003-05-01

    In this paper we give, for the first time, a qualitative description of the asymptotic dynamics of a class of non-tilted spatially homogeneous (SH) cosmologies, the so-called exceptional Bianchi cosmologies, which are of Bianchi type VI$_{-1/9}$. This class is of interest for two reasons. Firstly, it is generic within the class of non-tilted SH cosmologies, being of the same generality as the models of Bianchi types VIII and IX. Secondly, it is the SH limit of a generic class of spatially inhomogeneous $G_{2}$ cosmologies. Using the orthonormal frame formalism and Hubble-normalized variables, we show that the exceptional Bianchi cosmologies differ from the non-exceptional Bianchi cosmologies of type VI$_{h}$ in two significant ways. Firstly, the models exhibit an oscillatory approach to the initial singularity and hence are not asymptotically self-similar. Secondly, at late times, although the models are asymptotically self-similar, the future attractor for the vacuum-dominated models is the so-called Robinson-Trautman SH model instead of the vacuum SH plane wave models.

  6. Comparison between 2.5D and 3D simulations of coronal mass ejections

    NASA Astrophysics Data System (ADS)

    Jacobs, C.; van der Holst, B.; Poedts, S.

    2007-07-01

    Context: The shocks and magnetic clouds related to Coronal Mass Ejections (CMEs) in the solar corona and interplanetary space (IP) play an important role in the study of space weather. In order to study the evolution of these IP shocks, numerical simulations of a simplified CME model were performed. Aims: In an earlier study, the effect of the background wind on the evolution of interplanetary shock waves was investigated, where the computations were carried out under the assumption of axial symmetry. The assumption of axial symmetry might be a good approach for the solar corona under conditions of solar minimum, but for the study of CMEs this assumption is definitely no longer valid as CMEs possess clearly a fully three dimensional (3D) structure. From this perspective, the previous simulations were repeated, but now in a three dimensional set-up in order to point out the differences between the 2.5D and 3D simulations and to check the quality and reliability of the 2.5D simulations. Methods: The computations were performed in the framework of ideal magnetohydrodynamics (MHD) and to advance the ideal MHD equations in time a parallel finite volume code with explicit upwind solver was used. The shock waves are generated in a similar way in both the 3D and 2.5D simulations, namely by a simple density-blob model. The 3D and 2.5D simulations are all performed with the same numerical methods and on comparable grids, such that the differences between the simulations are purely due to the dimensionality of the problem, and/or the initial parameters for the CME generation. Results: Three different axisymmetric simulations of CME propagation are compared with the fully three dimensional computation. The 2.5D simulations differ from each other in the parameters used for CME initiation. In a first simulation, the same initial parameters as for the 3D case were taken, in a second simulation the initial amount of mass in the 2.5D and 3D CME was the same, and in a third

  7. 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.

  8. Cosmological solutions of emergent noncommutative gravity.

    PubMed

    Klammer, Daniela; Steinacker, Harold

    2009-06-01

    Matrix models of the Yang-Mills type lead to an emergent gravity theory, which does not require fine-tuning of a cosmological constant. We find cosmological solutions of the Friedmann-Robertson-Walker type. They generically have a big bounce, and an early inflationlike phase with graceful exit. The mechanism is purely geometrical; no ad hoc scalar fields are introduced. The solutions are stabilized through vacuum fluctuations and are thus compatible with quantum mechanics. This leads to a Milne-like universe after inflation, which appears to be in remarkably good agreement with observation and may provide an alternative to standard cosmology.

  9. Cosmological Solutions of Emergent Noncommutative Gravity

    SciTech Connect

    Klammer, Daniela; Steinacker, Harold

    2009-06-05

    Matrix models of the Yang-Mills type lead to an emergent gravity theory, which does not require fine-tuning of a cosmological constant. We find cosmological solutions of the Friedmann-Robertson-Walker type. They generically have a big bounce, and an early inflationlike phase with graceful exit. The mechanism is purely geometrical; no ad hoc scalar fields are introduced. The solutions are stabilized through vacuum fluctuations and are thus compatible with quantum mechanics. This leads to a Milne-like universe after inflation, which appears to be in remarkably good agreement with observation and may provide an alternative to standard cosmology.

  10. Cosmological solutions of emergent noncommutative gravity.

    PubMed

    Klammer, Daniela; Steinacker, Harold

    2009-06-01

    Matrix models of the Yang-Mills type lead to an emergent gravity theory, which does not require fine-tuning of a cosmological constant. We find cosmological solutions of the Friedmann-Robertson-Walker type. They generically have a big bounce, and an early inflationlike phase with graceful exit. The mechanism is purely geometrical; no ad hoc scalar fields are introduced. The solutions are stabilized through vacuum fluctuations and are thus compatible with quantum mechanics. This leads to a Milne-like universe after inflation, which appears to be in remarkably good agreement with observation and may provide an alternative to standard cosmology. PMID:19658852

  11. A Comparison of the Performance of the EQ-5D and the EQ-5D-Y Health-Related Quality of Life Instruments in South African Children

    ERIC Educational Resources Information Center

    Jelsma, Jennifer

    2010-01-01

    The aim of this study was to investigate the performance of the recent EQ-5D-Y instrument compared with the standard EQ-5D in assessing the health-related quality of life of high school children in Cape Town. Either the EQ-5D or the EQ-5D-Y was given to high school children. The sample consisted of 521 respondents. The EQ-5D-Y was found to be…

  12. New coupled quintessence cosmology

    SciTech Connect

    Jesus, J. F.; Santos, R. C.; Lima, J. A. S.; Alcaniz, J. S.

    2008-09-15

    A component of dark energy has been recently proposed to explain the current acceleration of the Universe. Unless some unknown symmetry in Nature prevents or suppresses it, such a field may interact with the pressureless component of dark matter, giving rise to the so-called models of coupled quintessence. In this paper we propose a new cosmological scenario where radiation and baryons are conserved, while the dark energy component is decaying into cold dark matter. The dilution of cold dark matter particles, attenuated with respect to the usual a{sup -3} scaling due to the interacting process, is characterized by a positive parameter {epsilon}, whereas the dark energy satisfies the equation of state p{sub x}={omega}{rho}{sub x} ({omega}<0). We carry out a joint statistical analysis involving recent observations from type Ia supernovae, baryon acoustic oscillation peak, and cosmic microwave background shift parameter to check the observational viability of the coupled quintessence scenario here proposed.

  13. Problems of applicability of statistical methods in cosmology

    SciTech Connect

    Levin, S. F.

    2015-12-15

    The problems arising from the incorrect formulation of measuring problems of identification for cosmological models and violations of conditions of applicability of statistical methods are considered.

  14. 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.

  15. Cosmological and supernova neutrinos

    SciTech Connect

    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.

  16. Modular properties of full 5D SYM partition function

    NASA Astrophysics Data System (ADS)

    Qiu, Jian; Tizzano, Luigi; Winding, Jacob; Zabzine, Maxim

    2016-03-01

    We study properties of the full partition function for the U(1) 5D N = {2}^{ast } gauge theory with adjoint hypermultiplet of mass M . This theory is ultimately related to abelian 6D (2,0) theory. We construct the full non-perturbative partition function on toric Sasaki-Einstein manifolds by gluing flat copies of the Nekrasov partition function and we express the full partition function in terms of the generalized double elliptic gamma function G 2 C associated with a certain moment map cone C. The answer exhibits a curious SL(4 , ℤ) modular property. Finally, we propose a set of rules to construct the partition function that resembles the calculation of 5d supersymmetric partition function with the insert ion of defects of various co-dimensions.

  17. 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.

  18. Ecological and cosmological coexistence thinking in a hypervariable environment: causal models of economic success and failure among farmers, foragers, and fishermen of southwestern Madagascar.

    PubMed

    Tucker, Bram; Tsiazonera; Tombo, Jaovola; Hajasoa, Patricia; Nagnisaha, Charlotte

    2015-01-01

    A fact of life for farmers, hunter-gatherers, and fishermen in the rural parts of the world are that crops fail, wild resources become scarce, and winds discourage fishing. In this article we approach subsistence risk from the perspective of "coexistence thinking," the simultaneous application of natural and supernatural causal models to explain subsistence success and failure. In southwestern Madagascar, the ecological world is characterized by extreme variability and unpredictability, and the cosmological world is characterized by anxiety about supernatural dangers. Ecological and cosmological causes seem to point to different risk minimizing strategies: to avoid losses from drought, flood, or heavy winds, one should diversify activities and be flexible; but to avoid losses caused by disrespected spirits one should narrow one's range of behaviors to follow the code of taboos and offerings. We address this paradox by investigating whether southwestern Malagasy understand natural and supernatural causes as occupying separate, contradictory explanatory systems (target dependence), whether they make no categorical distinction between natural and supernatural forces and combine them within a single explanatory system (synthetic thinking), or whether they have separate natural and supernatural categories of causes that are integrated into one explanatory system so that supernatural forces drive natural forces (integrative thinking). Results from three field studies suggest that (a) informants explain why crops, prey, and market activities succeed or fail with reference to natural causal forces like rainfall and pests, (b) they explain why individual persons experience success or failure primarily with supernatural factors like God and ancestors, and (c) they understand supernatural forces as driving natural forces, so that ecology and cosmology represent distinct sets of causes within a single explanatory framework. We expect that future cross-cultural analyses may

  19. Ecological and cosmological coexistence thinking in a hypervariable environment: causal models of economic success and failure among farmers, foragers, and fishermen of southwestern Madagascar

    PubMed Central

    Tucker, Bram; Tsiazonera; Tombo, Jaovola; Hajasoa, Patricia; Nagnisaha, Charlotte

    2015-01-01

    A fact of life for farmers, hunter-gatherers, and fishermen in the rural parts of the world are that crops fail, wild resources become scarce, and winds discourage fishing. In this article we approach subsistence risk from the perspective of “coexistence thinking,” the simultaneous application of natural and supernatural causal models to explain subsistence success and failure. In southwestern Madagascar, the ecological world is characterized by extreme variability and unpredictability, and the cosmological world is characterized by anxiety about supernatural dangers. Ecological and cosmological causes seem to point to different risk minimizing strategies: to avoid losses from drought, flood, or heavy winds, one should diversify activities and be flexible; but to avoid losses caused by disrespected spirits one should narrow one’s range of behaviors to follow the code of taboos and offerings. We address this paradox by investigating whether southwestern Malagasy understand natural and supernatural causes as occupying separate, contradictory explanatory systems (target dependence), whether they make no categorical distinction between natural and supernatural forces and combine them within a single explanatory system (synthetic thinking), or whether they have separate natural and supernatural categories of causes that are integrated into one explanatory system so that supernatural forces drive natural forces (integrative thinking). Results from three field studies suggest that (a) informants explain why crops, prey, and market activities succeed or fail with reference to natural causal forces like rainfall and pests, (b) they explain why individual persons experience success or failure primarily with supernatural factors like God and ancestors, and (c) they understand supernatural forces as driving natural forces, so that ecology and cosmology represent distinct sets of causes within a single explanatory framework. We expect that future cross-cultural analyses

  20. Primordial nucleosynthesis: A cosmological point of view

    SciTech Connect

    Mathews, G. J.; Kusakabe, M.; Cheoun, M.-K.

    2014-05-09

    Primordial nucleosynthesis remains as one of the pillars of modern cosmology. It is the test-ing ground upon which all cosmological models must ultimately rest. It is our only probe of the universe during the first few minutes of cosmic expansion and in particular during the important radiation-dominated epoch. These lectures review the basic equations of space-time, cosmology, and big bang nucleosynthesis. We will then review the current state of observational constraints on primordial abundances along with the key nuclear reactions and their uncertainties. We summarize which nuclear measure-ments are most crucial during the big bang. We also review various cosmological models and their constraints. In particular, we summarize the constraints that big bang nucleosynthesis places upon the possible time variation of fundamental constants, along with constraints on the nature and origin of dark matter and dark energy, long-lived supersymmetric particles, gravity waves, and the primordial magnetic field.