arXiv subjects

A. A. Starobinsky

Publications and source records attributed to A. A. Starobinsky.

At least 73 records · Page 4Linked to original sources

arXiv1999

Future and Origin of our Universe: Modern View

The existence of a positive and possibly varying Lambda-term opens a much wider field of possibilities for the future of our Universe than it was usually thought before. Definite predictions may be made for finite (though very large) intervals of time only, as well as in other branches of science. In particular, our Universe will continue to expand as far as the Lambda-term remains positive and does not decay to other forms of matter, even if the Universe is closed. Two new effects due to the presence of a constant Lambda-term are discussed: reversal of a sign of the redshift change with time for sufficiently close objects and inaccessibility of sufficiently distant objects in the Universe for us. A number of more distant and speculative possibilities for the future evolution of the Universe is listed including hitting a space-time singularity during an expansion phase. Finally, in fantastically remote future, a part of our Universe surrounding us can become supercurved and superdense due to various quantum-gravitational effects. This returns us to the past, to the origin of our Universe from a superdense state about 14 Gy ago. According to the inflationary scenario, this state was almost maximally symmetric (de Sitter-like). Though this scenario seems to be sufficient for the explanation of observable properties of the present Universe, and its predictions have been confirmed by observations, the question of the origin of the initial de Sitter (inflationary) state itself remains open. A number of conjectures regarding the very origin of our Universe, ranging from "creation from nothing" to "creation from anything", are discussed.

astro-ph↗

arXiv1999

The supercluster-void network V. Alternative evidence for its regularity

The distribution of Abell clusters of galaxies is analysed to study the regularity of the supercluster-void network. A new geometric method sensitive to the regularity of the location of clusters is applied. We find that the supercluster-void network resembles a cubical lattice over the whole space investigated. The distribution of rich superclusters is not isotropic: along the main axis of the network it is periodic with a step of length about 130 Mpc (for Hubble constant h=1), whereas along the diagonal of the network the period is larger. This large-scale inhomogeneity is compatible with recent CMB data.

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

Steps toward the power spectrum of matter. I.The mean spectrum of galaxies

We calculate the mean power spectrum of galaxies using published power spectra of galaxies and clusters of galaxies. On small scales we use the power spectrum derived from the 2-dimensional distribution of APM galaxies, on large scales we use power spectra derived from 3-dimensional data for galaxy and cluster samples. Spectra are reduced to real space and to the amplitude of the power spectrum of APM galaxies. Available data indicate the presence of two different populations in the nearby Universe. Clusters of galaxies sample a relatively large region in the Universe where rich, medium and poor superclusters are well represented. Their mean power spectrum has a spike on scale 120 h^{-1}Mpc, followed by an approximate power-law spectrum of index n = -1.9 towards small scales. The power spectrum found from LCRS and IRAS 1.2 Jy surveys is flatter around the maximum, which may represent regions of the Universe with medium-rich and poor superclusters.

astro-ph↗

arXiv1998

Steps toward the power spectrum of matter. II. The biasing correction with sigma_8 normalization

A new method to determine the bias parameter of galaxies relative to matter is suggested. The method is based on the assumption that gravity is the dominating force which determines the formation of the structure in the Universe. Due to gravitational instability the galaxy formation is a threshold process: in low-density environments galaxies do not form and matter remains in primordial form. We investigate the influence of the presence of void and clustered populations to the power spectrum of matter and galaxies. The power spectrum of galaxies is similar to the power spectrum of matter; the fraction of total matter in the clustered population determines the difference between amplitudes of fluctuations of matter and galaxies, i.e. the bias factor. To determine the fraction of matter in voids and clustered population we perform numerical simulations. The fraction of matter in galaxies at the present epoch is found using a calibration through the sigma_8 parameter.

astro-ph↗

arXiv1998

Steps toward the power spectrum of matter. III. The primordial spectrum

Observed power spectrum of matter found in Papers I and II is compared with analytical power spectra. Spatially flat cold and mixed dark matter models with cosmological constant and open models are considered. The primordial power spectrum of matter is determined using the power spectrum of matter and the transfer functions of analytical models. The primordial power spectrum has a break in amplitude. We conclude that a scale-free primordial power spectrum is excluded if presently available data on the distribution of clusters and galaxies represent the true mass distribution of the Universe.

astro-ph↗

arXiv1998

Beyond the Simplest Inflationary Cosmological Models

Though predictions of the simplest inflationary cosmological models with cold dark matter, flat space and approximately flat initial spectrum of adiabatic perturbations are remarkably close to observational data, we have to go beyond them and to introduce new physics not yet discovered in laboratories to account for all data. Two extensions of these models which seem to be the most actual at present time are discussed. The first one is the possibility that we are living at the beginning of a new inflation-like era. Then classical cosmological tests, like the luminosity distance or the angular size of distant objects as functions of redshift, as well as the behaviour of density perturbations in a dustlike matter component including baryons as a function of redshift, can provide information sufficient for the unambiguous determination of an effective potential of a corresponding present inflaton scalar field. The second, unrelated extension is a possibility of broken-scale-invariant cosmological models which have localized steps or spikes in the primordial perturbation spectrum. These features can be produced by fast phase transitions in physical fields other than an inflaton field in the early Universe during inflation and not far from the end of it. At present, it seems that the only scale in the spectrum around which we might see something of this type is $k=0.05 h Mpc^{-1}$.

astro-ph↗

arXiv1998

How to determine an effective potential for a variable cosmological term

It is shown that if a variable cosmological term in the present Universe is described by a scalar field with minimal coupling to gravity and with some phenomenological self-interaction potential $V(φ)$, then this potential can be unambiguously determined from the following observational data: either from the behaviour of density perturbations in dustlike matter component as a function of redshift (given the Hubble constant additionally), or from the luminosity distance as a function of redshift (given the present density of dustlike matter in terms of the critical one).

astro-ph↗

arXiv1998

Inflation for Large Scale Structure

Two extensions of ideas lying in the basis of the inflationary scenario of the early Universe and their effect on the large scale structure of the present-day Universe are discussed. The first of them is the possibility of fast phase transitions in physical fields other than an inflaton scalar field during inflation and nor far from the end of it. This results in the appearance of specific features in the inflaton effective potential which, in turn, lead to the generation of localized spikes in the primordial perturbation spectrum. At present, there seems to exist one scale in the spectrum, $k=0.05h$ Mpc$^{-1}$, around which we might see something of this type. The second one is the possibility that we are living at the beginning of a new inflation-like era now. Then observations of clustering of high-redshift objects can provide information sufficient for the unambiguous determination of the effective potential of a corresponding present inflaton scalar field.

astro-ph↗

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↗

arXiv1997

A built-in scale in the initial spectrum of density perturbations: evidence from cluster and CMB data

We calculate temperature anisotropies of the cosmic microwave background (CMB) for several initial power spectra of density perturbations with a built-in scale suggested by recent optical data on the spatial distribution of rich clusters of galaxies. Using cosmological models with different values of spectral index, baryon fraction, Hubble constant and cosmological constant, we compare the calculated radiation power spectrum with the CMB temperature anisotropies measured by the Saskatoon experiment. We show that spectra with a sharp peak at 120 h^{-1} Mpc are in agreement with the Saskatoon data. The combined evidence from cluster and CMB data favours the presence of a peak and a subsequent break in the initial matter power spectrum. Such feature is similar to the prediction of an inflationary model where an inflaton field is evolving through a kink in the potential.

astro-ph↗

arXiv1997

The supercluster--void network II. An oscillating cluster correlation function

We use rich clusters of galaxies in the Northern and Southern Galactic hemispheres up to a redshift z=0.12 to determine the cluster correlation function. We show that superclusters of galaxies and voids between them form a moderately regular network. As a result the correlation function determined for clusters located in rich superclusters oscillates: it has a series of regularly spaced secondary maxima and minima. The scale of the supercluster-void network, determined from the period of oscillations, is P=115 Mpc. The amplitude of oscillations is about 3 times larger than the estimated error. We compare the observed cluster correlation function with similar functions derived for popular models of structure formation. We find that the production of the observed cluster correlation function in any model with a smooth transition of the power spectrum from a Harrison-Zeldovich regime with positive spectral index on long wavelengths to a negative spectral index on short wavelengths is highly unlikely. The power spectrum must have an extra peak located at the wavelength equal to the period of oscillations of the correlation function.

astro-ph↗

arXiv1997

The supercluster--void network III. The correlation function as a geometrical statistic

We investigate properties of the correlation function of clusters of galaxies using geometrical models. On small scales the correlation function depends on the shape and the size of superclusters. On large scales it describes the geometry of the distribution of superclusters. If superclusters are distributed randomly then the correlation function on large scales is featureless. If superclusters and voids have a tendency to form a regular lattice then the correlation function on large scales has quasi-regularly spaced maxima and minima of decaying amplitude; i.e., it is oscillating. The period of oscillations is equal to the step size of the grid of the lattice. We calculate the power spectrum for our models and compare the geometrical information of the correlation function with other statistics. We find that geometric properties (the regularity of the distribution of clusters on large scales) are better quantified by the correlation function. We also analyse errors in the correlation function and the power spectrum by generating random realizations of models and finding the scatter of these realizations.

astro-ph↗

arXiv1997

A 120-Mpc Periodicity in the Three-Dimensional Distribution of Galaxy Superclusters

Using a new compilation of available data on galaxy clusters and superclusters we present evidence for a quasiregular three-dimensional network of rich superclusters and voids, with the regions of high density separated by about 120 Mpc. We calculate the power spectrum for clusters of galaxies; it has a peak on the wavelength equal to the step of the network; the excess in the amplitude of the spectrum over that of the cold dark matter model is by a factor of 1.4. The probability that the spectrum can be formed within the framework of the standard cosmogony is very small. If the cluster distribution reflects the distribution of all matter (luminous and dark), then there must exists some hithero unknown process that produces regular structure on large scales.

astro-ph↗

arXiv1996

Modern Cosmological Models with Dark Matter and Their Confrontation with Observational Data

New systematic classification of cosmological models of the present Universe is introduced. After making the comparison of these models with all existing observational data three viable models remain: the cold dark matter model with the cosmological constant (which becomes the most reasonable one if the Hubble constant $H_0>60$ km/s/Mpc); the mixed cold-hot dark matter model (models with two and especially three types of neutrinos with equal masses are in a slightly better agreement with observational data than the model with one massive neutrino); the pure cold dark matter model with a step-like initial spectrum of perturbations. The two latter models require $H_0\leq 60$ km/s/Mpc.

astro-ph↗

arXiv1996

Spectrum of Initial Perturbations in Open and Closed Inflationary Models

Spectrum of initial scalar and tensor perturbations created during an inflationary stage producing a closed or open FRW universe now is discussed. In the closed case, the CMB temperature anisotropy ${ΔT/T}$ generated by scalar perturbations is enhanced for low multipoles. It is argued that in the open case there is no suppression of low multipoles. A possibility of the existence of a preferred space direction in the open case is noted.

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↗