Time filter

Source Type

Nojiri S.,Nagoya University | Odintsov S.D.,Institute Of Ciencies Of Lespai Ieec Csic
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

We consider the diffeomorphism invariant gravity coupled with the ideal fluid in the nonstandard way. The Lorentz invariance of the graviton propagator in such a theory considered as perturbation over flat background turns out to be broken due to the nonstandard coupling with the ideal fluid. As a result the behavior of the propagator in the ultraviolet/infrared region indicates that some versions of such theory are (super-)renormalizable ones (with appearance of only physical transverse modes). The Friedmann-Robertson-Walker cosmology in some cases may be different from the one in general relativity with the possible power law inflationary stage. © 2010 The American Physical Society.


Odintsov S.D.,Institute Of Ciencies Of Lespai Ieec Csic | Odintsov S.D.,Tomsk State Pedagogical University | Oikonomou V.K.,Aristotle University of Thessaloniki | Oikonomou V.K.,Tomsk State Pedagogical University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We investigate which Jordan frame F(R) gravity can describe a type IV singular bouncing cosmological evolution, with special emphasis given near the point at which the type IV singularity occurs. The cosmological bounce is chosen in such a way that the bouncing point coincides exactly with the type IV singularity point. The stability of the resulting F(R) gravity is examined and in addition, we study the Einstein frame scalar-tensor theory counterpart of the resulting Jordan frame F(R) gravity. Also, by assuming that the Jordan frame metric is chosen in such a way so that, when conformally transformed in the Einstein frame, it yields a quasi-de Sitter or de Sitter-Friedmann-Robertson-Walker metric, we study the observational indexes which turn out to be consistent with Planck 2015 data in the case of the Einstein frame scalar theory. Finally, we study the behavior of the effective equation of state corresponding to the type IV singular bounce and after we compare the resulting picture with other bouncing cosmologies, we critically discuss the implications of our analysis. © 2015 American Physical Society.


Odintsov S.D.,Institute Of Ciencies Of Lespai Ieec Csic | Odintsov S.D.,Catalan Institution for Research and Advanced Studies | Oikonomou V.K.,Aristotle University of Thessaloniki
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Using the reconstruction method, we investigate which F(R) theories, with or without the presence of matter fluids, can produce the matter bounce scenario of holonomy corrected loop quantum cosmology. We focus our study in two limits of the cosmic time, the large cosmic time limit and the small cosmic time limit. For the former, we find that, in the presence of noninteracting and nonrelativistic matter, the F(R) gravity that reproduces the late time limit of the matter bounce solution is actually the Einstein-Hilbert gravity plus a power law term. In the early time limit, since it corresponds to large spacetime curvatures, assuming that the Jordan frame is described by a general metric that, when it is conformally transformed to the Einstein frame, produces an accelerating Friedmann-Robertson-Walker metric, we find explicitly the scalar field dependence on time. After demonstrating that the solution in the Einstein frame is indeed accelerating, we calculate the spectral index derived from the Einstein frame scalar-tensor counterpart theory of the F(R) theory and compare it with the Planck experiment data. In order to implement the resulting picture, we embed the F(R) gravity explicitly in a loop quantum cosmology framework by introducing holonomy corrections to the F(R) gravity. In this way, the resulting inflation picture corresponding to the F(R) gravity can be corrected in order that it coincides to some extent with the current experimental data. © 2014 American Physical Society.


Schneider A.,University of Sussex | Smith R.E.,Max Planck Institute for Astrophysics | Reed D.,Institute Of Ciencies Of Lespai Ieec Csic
Monthly Notices of the Royal Astronomical Society | Year: 2013

The nature of structure formation around the particle free streaming scale is still far from understood. Many attempts to simulate hot, warm and cold dark matter cosmologies with a free streaming cut-offhave been performed with cosmological particle-based simulations, but they all suffer from spurious structure formation at scales below their respective free streaming scales - i.e. where the physics of halo formation ismost affected by free streaming. We perform a series of high-resolution numerical simulations of different warm dark matter (WDM) models, and develop an approximate method to subtract artificial structures in the measured halo mass function. The corrected measurements are then used to construct and calibrate an extended Press-Schechter (EPS) model with sharp-k window function and adequate mass assignment. The EPS model gives accurate predictions for the low-redshift halo mass function of cold dark matter (CDM) and WDM models, but it significantly underpredicts the halo abundance at high redshifts. By taking into account the ellipticity of the initial patches and connecting the characteristic filter scale to the smallest ellipsoidal axis, we are able to eliminate this inconsistency and obtain an accurate mass function over all redshifts and all dark matter particle masses covered by the simulations. As an additional application we use our model to predict the microhalo abundance of the standard neutralino-CDM scenario and we give the first quantitative prediction of the mass function over the full range of scales of CDM structure formation. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Nojiri S.,Nagoya University | Odintsov S.D.,Institute Of Ciencies Of Lespai Ieec Csic | Odintsov S.D.,Catalan Institution for Research and Advanced Studies | Odintsov S.D.,Tomsk State Pedagogical University | And 2 more authors.
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

We study models with a generalized inhomogeneous equation of state fluids, in the context of singular inflation, focusing to so-called Type IV singular evolution. In the simplest case, this cosmological fluid is described by an equation of state with constant w, and therefore a direct modification of this constant w fluid is achieved by using a generalized form of an equation of state. We investigate from which models with generalized phenomenological equation of state, a Type IV singular inflation can be generated and what the phenomenological implications of this singularity would be. We support our results with illustrative examples and we also study the impact of the Type IV singularities on the slow-roll parameters and on the observational inflationary indices, showing the consistency with Planck mission results. The unification of singular inflation with singular dark energy era for specific generalized fluids is also proposed. © 2015 The Authors.


Kluson J.,Masaryk University | Nojiri S.,Nagoya University | Odintsov S.D.,Catalan Institution for Research and Advanced Studies | Odintsov S.D.,Institute Of Ciencies Of Lespai Ieec Csic | Odintsov S.D.,Tomsk State Pedagogical University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

We propose new version of massive F(R) gravity which is natural generalization of convenient massive ghost-free gravity. Its Hamiltonian formulation in scalar-tensor frame is developed. We show that such F(R) theory is ghost-free. The cosmological evolution of such theory is investigated. Despite the strong Bianchi identity constraint the possibility of cosmic acceleration (especially, in the presence of cold dark matter) is established. Ghost-free massive F(R, T) gravity is also proposed. © 2013 Elsevier B.V.


Casas R.,Institute Of Ciencies Of Lespai Ieec Csic | Vaquero J.M.,University of Extremadura
Solar Physics | Year: 2014

In the 19th century, several astronomers made observations of sunspots, recording their positions and sometimes their areas. These observations were published in the form of extensive tables, but have been unhelpful until now. Three of these observers were Richard C. Carrington, Christian H.F. Peters and Warren de la Rue (and their respective collaborators). They published, in various articles, the data corresponding to 26 641 sunspot positions (Carrington, Peters and de la Rue registered 4900, 14040 and 7701 sunspot positions, respectively). In this paper we present a translation of more than 400 pages of their printed numerical tables into a machine readable format, including an initial analysis targeted at detecting possible mistakes in the reading or in the original transcription. The observations carried out by these three astronomers have been made available at the Centre de Donées Astronomiques de Strasbourg (http://cdsarc.u-strasbg.fr/cgi-bin/VizieR?-source=VI/138). © 2013 Springer Science+Business Media Dordrecht.


Crocce M.,Institute Of Ciencies Of Lespai Ieec Csic | Scoccimarro R.,New York University | Bernardeau F.,CEA Saclay Nuclear Research Center
Monthly Notices of the Royal Astronomical Society | Year: 2012

We put forward and test a simple description of multipoint propagators (MP), which serve as building blocks to calculate the non-linear matter power spectrum. On large scales these propagators reduce to the well-known kernels in standard perturbation theory, while at smaller scales they are suppressed due to non-linear couplings. Through extensive testing with numerical simulations we find that this decay is characterized by the same damping scale for both two- and three-point propagators. In turn this transition can be well modelled with resummation results that exponentiate one-loop computations. For the first time, we measure the four components of the non-linear (two-point) propagator using dedicated simulations started from two independent random Gaussian fields for positions and velocities, verifying in detail the fundamentals of propagator resummation. We use these results to develop an implementation of the MP expansion for the non-linear power spectrum that only requires seconds to evaluate at baryon acoustic oscillations (BAO) scales. To test it we construct six suites of large numerical simulations with different cosmologies. From these and LasDamas runs we show that the non-linear power spectrum can be described at the ≲ 2 per cent level at BAO scales for redshifts in the range [0-2.5]. We make a public release of the MPTbreeze code with the hope that it can be useful to the community. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Bonvin C.,Kavli Institute for Cosmology Cambridge | Bonvin C.,University of Cambridge | Hui L.,Columbia University | Gaztanaga E.,Institute Of Ciencies Of Lespai Ieec Csic
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We study the two-point cross-correlation function between two populations of galaxies: for instance, a bright population and a faint population. We show that this cross-correlation is asymmetric under the exchange of the line-of-sight coordinate of the galaxies, i.e. that the correlation is different if the bright galaxy is in front of, or behind, the faint galaxy. We give an intuitive, quasi-Newtonian derivation of all the effects that contribute to such an asymmetry in large-scale structure: gravitational redshift, Doppler shift, lensing, light-cone, evolution and Alcock-Paczynski effects; interestingly, the gravitational redshift term is exactly canceled by some of the others, assuming geodesic motion. Most of these effects are captured by previous calculations of general relativistic corrections to the observed galaxy density fluctuation; the asymmetry arises from terms that are suppressed by the ratio (H/k) - H is the Hubble constant and k is the wave number - which are more readily observable than the terms suppressed by (H/k)2. Some of the contributions to the asymmetry, however, arise from terms that are generally considered "Newtonian" - the lensing and evolution - and thus represent a contaminant in the search for general relativistic corrections. We propose methods to disentangle these different contributions. A simple method reduces the contamination to a level of 10% for redshifts z1. We also clarify the relation to recent work on measuring gravitational redshifts by stacking clusters. © 2014 American Physical Society.


Nojiri S.,Nagoya University | Odintsov S.D.,Catalan Institution for Research and Advanced Studies | Odintsov S.D.,Institute Of Ciencies Of Lespai Ieec Csic | Odintsov S.D.,Tomsk State Pedagogical University
Physics Reports | Year: 2011

The classical generalization of general relativity is considered as the gravitational alternative for a unified description of the early-time inflation with late-time cosmic acceleration. The structure and cosmological properties of a number of modified theories, including traditional F(R) and Hořava-Lifshitz F(R) gravity, scalar-tensor theory, string-inspired and Gauss-Bonnet theory, non-local gravity, non-minimally coupled models, and power-counting renormalizable covariant gravity are discussed. Different representations of and relations between such theories are investigated. It is shown that some versions of the above theories may be consistent with local tests and may provide a qualitatively reasonable unified description of inflation with the dark energy epoch. The cosmological reconstruction of different modified gravities is provided in great detail. It is demonstrated that eventually any given universe evolution may be reconstructed for the theories under consideration, and the explicit reconstruction is applied to an accelerating spatially flat Friedmann-Robertson-Walker (FRW) universe. Special attention is paid to Lagrange multiplier constrained and conventional F(R) gravities, for latter F(R) theory, the effective ΛCDM era and phantom divide crossing acceleration are obtained. The occurrences of the Big Rip and other finite-time future singularities in modified gravity are reviewed along with their solutions via the addition of higher-derivative gravitational invariants. © 2011 Elsevier B.V.

Loading Institute Of Ciencies Of Lespai Ieec Csic collaborators
Loading Institute Of Ciencies Of Lespai Ieec Csic collaborators