arXiv subjects

D. Polarski

Publications and source records attributed to D. Polarski.

27 records · Page 2Linked to original sources

arXiv2000

Reconstruction of a scalar-tensor theory of gravity in an accelerating universe

The present acceleration of the Universe strongly indicated by recent observational data can be modeled in the scope of a scalar-tensor theory of gravity. We show that it is possible to determine the structure of this theory (the scalar field potential and the functional form of the scalar-gravity coupling) along with the present density of dustlike matter from the following two observable cosmological functions: the luminosity distance and the linear density perturbation in the dustlike matter component as functions of redshift. Explicit results are presented in the first order in the small inverse Brans-Dicke parameter 1/omega.

gr-qc↗

arXiv1999

Direct Detection of Primordial Gravitational Waves in a BSI Inflationary Model

We investigate the possibility for a direct detection by future space interferometers of the stochastic gravitational wave (GW) background generated during the inflationary stage in a class of viable $Λ$CDM BSI models. At frequencies around $10^{-3}$Hz, maximal values $Ω_{gw}(ν)\sim 3\times 10^{-15}$ are found, an improvement of about one order of magnitude compared to single-field, slow-roll inflationary models. This is presumably not sufficient in order to be probed in the near future.

gr-qc↗

arXiv1999

Parameter extraction by Planck for a CDM model with broken scale invariance and cosmological constant

We consider a class of spatially flat cold dark matter (CDM) models, with a cosmological constant and a broken-scale-invariant (BSI) steplike primordial spectrum of adiabatic perturbations, previously found to be in very good agreement with observations. Performing a Fisher matrix analysis, we show that in case of a large gravitational waves (GW) contribution some free parameters (defining the step) of our BSI model can be extracted with remarkable accuracy by the Planck satellite, thanks to the polarisation anisotropy measurements. Further, cosmological parameters can still be found with very good precision, despite a larger number of free parameters than in the simplest inflationary models.

astro-ph↗

arXiv1999

Large primordial gravitational wave background in a class of BSI Lambda-CDM models

We consider the primordial gravitational wave (GW) background in a class of spatially-flat inflationary cosmological models with cold dark matter (CDM), a cosmological constant, and a broken-scale-invariant (BSI) steplike primordial (initial) spectrum of adiabatic perturbations produced in an exactly solvable inflationary model where the inflaton potential has a rapid change of its first derivative at some point. In contrast to inflationary models with a scale-free initial spectrum, these models may have a GW power spectrum whose amplitude (though not its shape) is arbitrary for fixed amplitude and shape of the adiabatic perturbations power spectrum. In the presence of a positive cosmological constant, the models investigated here possess the striking property that a significant part of the large-angle CMB temperature anisotropy observed in the COBE experiment is due to primordial GW. Confronting them with existing observational data on CMB angular temperature fluctuations, galaxy clustering and peculiar velocities of galaxies, we find that for the best parameter values Omega_Lambda=0.7 and h=0.7, the GW contribution to the CMB anisotropy can be as large as that of the scalar fluctuations.

astro-ph↗

arXiv1998

Emergence of classicality for primordial fluctuations: Concepts and analogies

We clarify the way in which cosmological perturbations of quantum origin, produced during inflation, assume classical properties. Two features play an important role in this process: First, the dynamics of fluctuations which are presently on large cosmological scales leads to a very peculiar state (highly squeezed) that is indistinguishable, in a precise sense, from a classical stochastic process. This holds for almost all initial quantum states. Second, the process of decoherence by interaction with the environment distinguishes the field amplitude basis as a robust pointer basis. We discuss in detail the interplay between these features and use simple analogies such as the free quantum particle to illustrate the main conceptual issues.

gr-qc↗

arXiv1998

Quantum-to-classical transition for fluctuations in the early Universe

According to the inflationary scenario for the very early Universe, all inhomogeneities in the Universe are of genuine quantum origin. On the other hand, looking at these inhomogeneities and measuring them, clearly no specific quantum mechanical properties are observed. We show how the transition from their inherent quantum gravitational nature to classical behaviour comes about -- a transition whereby none of the successful quantitative predictions of the inflationary scenario for the present-day universe is changed. This is made possible by two properties. First, the quantum state for the spacetime metric perturbations produced by quantum gravitational effects in the early Universe becomes very special (highly squeezed) as a result of the expansion of the Universe (as long as the wavelength of the perturbations exceeds the Hubble radius). Second, decoherence through the environment distinguishes the field amplitude basis as being the pointer basis. This renders the perturbations presently indistinguishable from stochastic classical inhomogeneities.

gr-qc↗

arXiv1997

CDM models with a BSI steplike primordial spectrum and a cosmological constant

A class of spatially-flat models with cold dark matter (CDM), a cosmological constant and a broken-scale-invariant (BSI) steplike primordial (initial) spectrum of adiabatic perturbations, generated in an exactly solvable inflationary model where the inflaton potential has a rapid change of its first derivative at some point, is confronted with existing observational data on angular fluctuations of the CMB temperature, galaxy clustering and peculiar velocities of galaxies. If we locate the step in the initial spectrum at k=0.05 h/Mpc, where some feature in the spectrum of Abell clusters of galaxies was found that could reflect a property of the initial spectrum, and if the large scales flat plateau of the spectrum is normalized according to the COBE data, the only remaining parameter of the spectrum is p - the ratio of amplitudes of the metric perturbations between the small scales and large scales flat plateaux. Allowed regions in the plane of parameters (Omega=1-Omega_Lambda, H_0) satisfying all data have been found for p lying in the region (0.8-1.7). Especially good agreement of the form of the present power spectrum in this model with the form of the cluster power spectrum is obtained for the inverted step (p<1, p=0.7-0.8), when the initial spectrum has slightly more power on small scales.

astro-ph↗

arXiv1994

Isocurvature Perturbations in Multiple Inflationary Models

Dynamics of long-wave isocurvature perturbations during an inflationary stage in multiple (multi-component) inflationary models is calculated analytically for the case where scalar fields producing this stage interact between themselves through gravity only. This enables to determine correct amplitudes of such perturbations produced by vacuum quantum fluctuations of the scalar fields during the multiple inflationary stage. Exact matching to a post-inflationary evolution that gives the amplitude of isocurvature perturbations in the cold dark matter model with radiation is performed in the case where a massive inflaton field remains uncoupled from usual matter up to the present time. For this model, isocurvature perturbations are smaller than adiabatic ones in the region of the break in the perturbation spectrum which arises due to a transition between the two phases of inflation, but they may be much bigger and have a maximum at much shorter scales. The case of an inflaton with a quartic coupling which remains uncoupled after inflation is considered, too.

astro-ph↗

arXiv1994

Confrontation of Double-Inflationary Models with Observations

We consider double-inflationary models with two noninteracting scalar fields, a light scalar field $ϕ_l$ with potential $\frac{1}{2}m_l^2ϕ_l^2$ and a heavy scalar field $ϕ_h$ with potential $\fracλ{n}ϕ_h^n$ with $n=2,4$. CDM with the initial spectrum of adiabatic perturbations produced in these models is compared with observations. These models contain two more free parameters than the standard CDM model with an initial scale-invariant spectrum. We normalize our spectra to COBE DMR and compare the predictions with observations on the biasing factor, large-scale peculiar velocities, quasar and galaxy formation and the Stromlo-APM counts-in-cells analysis. The model with $n=4$ is excluded by the data while for the $n=2$ model, taking cosmic variance into account, a small window of parameters compatible with observations is found.

astro-ph↗