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A. D. Dolgov

Publications and source records attributed to A. D. Dolgov.

At least 55 records · Page 3Linked to original sources
arXiv2017

Primordial Black Holes and Cosmological Problems

It is argued that the bulk of black holes (BH) in the universe are primordial (PBH). This assertion is strongly supported by the recent astronomical observations, which allow to conclude that supermassive BHs with $M= (10^6 - 10^9) M_\odot$ "work" as seeds for galaxy formation, intermediate mass BHs, $ M = (10^3 - 10^4) M_\odot$, do the same job for globular clusters and dwarf galaxies, while black holes of a few solar masses are the constituents of dark matter of the universe. The mechanism of PBH formation, suggested in 1993, which predicted such features of the universe, is described. The model leads to the log-normal mass spectrum of PBHs, which is determined by three constant parameters. With proper adjustment of these parameters the above mentioned features are quantitatively explained. In particular, the calculated density of numerous superheavy BHs in the young universe, $ z = 5 - 10$, nicely fits the data. The puzzling properties of the sources of the LIGO-discovered gravitational waves are also naturally explained assuming that these sources are PBHs.

astro-ph.CO↗
arXiv2017

Problems of spontaneous and gravitational baryogenesis

Spontaneous and closely related to it gravitational baryogenesis are critically analyzed. It is shown that the coupling of the curvature scalar to baryonic current, which induces nonzero baryonic asymmetry of the universe, simultaneously leads to higher order gravitational equations, which have exponentially unstable solutions. It is shown that this instability endangers the standard cosmology.

hep-ph↗
arXiv2017

Instability of gravitational baryogenesis with fermions

The derivative coupling of baryonic current to the curvature scalar in gravitational baryogenesis scenarios leads to higher order equations for gravitational field. It is shown that these equations are strongly unstable and destroy standard cosmology. This is a generalization of our earlier results obtained for scalar baryons to realistic fermions.

gr-qc↗
arXiv2017

Massive and supermassive black holes in the contemporary and early universe and the new problems of cosmology and astrophysics

This is the translation into English of the introduction, conclusion, and the list of references of the review on massive primordial black holes, which is submitted in Russian to Uspekhi Fizicheskikh Nauk (Physics-Uspekhi). If accepted, this review is translated into English by the Journal and published in Russian and a little later in English. The review concerns the recent astronomical data which show that massive primordial black holes play much more significant role in the universe than it was previously believed. This is true both for the the contemporary and the early universe at the red-shifts about 10. The mechanism, proposed in 1993, of primordial creation of heavy and superheavy black holes in the very early universe is discussed. This mechanism predicts the log-normal mass spectrum of the primordial black holes, which became very popular during the last couple of years. The proposed mechanism presents a natural explanation of a large amount of the recent observational data, which do not fit the standard cosmology and astrophysics.

astro-ph.CO↗
arXiv2017

Relic abundance of MeV millicharged particles

The relic abundance of light millicharged particles (MCPs) with the electric charge $e' = 5\cdot 10^{-5} e$ and with the mass slightly below or above the electron mass is calculated. The abundance depends on the mass ratio $η=m_X/m_e$ and for $η<1$ can be high enough to allow MCPs to be the cosmological dark matter or to make a noticeable contribution to it. On the other hand, for $η\gtrsim 1$ the cosmological energy density of MCPs can be quite low, $Ω_X h_0^2 \approx 0.02$ for scalar MCPs, and $Ω_X h_0^2 \approx 0.001$ for spin 1/2 fermions. But even the lowest value of $Ω_X h_0^2$ is in tension with several existing limits on the MCP abundances and parameters. However, these limits have been derived under some natural or reasonable assumptions on the properties of MCPs. If these assumptions are relaxed, a patch in the mass-charge plot of MCPs may appear, permitting them to be dark matter particles.

hep-ph↗
arXiv2017

New Old Mechanism of Dark Matter Burning

Recently several papers have been published, where "a new mechanism" of dark matter burning and freezing is suggested. The usual two-body annihilation process is generalized to multi-body initial states, mostly three-body. These processes have quite a few interesting cosmological implications. I want to indicate here that such a process was studied in 1980 to determine the cosmological number density of the so called theta-particles. The file of the translated into English original paper and the reference to the published English version are attached.

hep-ph↗
arXiv2017

Intrinsic problems of gravitational baryogenesis

Modification of gravity due to the curvature dependent term in the gravitational baryogenesis scenario is considered. It is shown that this term leads to the fourth order differential equation of motion for the curvature scalar instead of the algebraic one of General Relativity (GR). The fourth order gravitational equations are generically unstable with respect to small perturbations. Non-linear in curvature terms may stabilize the solution but the magnitude of the stabilized curvature scalar would be much larger than that dictated by GR, so the standard cosmology would be strongly distorted.

gr-qc↗
arXiv2017

Problems with the sources of the observed gravitational waves and their resolution

Recent direct registration of gravitational waves by LIGO and astronomical observations of the universe at redshifts 5-10 demonstrate that the standard astrophysics and cosmology are in tension with the data. The origin of the source of the GW150914 event, which presumably is a binary of coalescing black holes with masses about 30 solar masses, each with zero spin, as well as the densely populated universe at z= 5-10 by superheavy black holes, blight galaxies, supernovae, and dust does not fit the standard astrophysical picture. It is shown here that the model of primordial black hole (PBH) formation, suggested in 1993, nicely explains all these and more puzzles, including those in contemporary universe, such as MACHOs and the mass spectrum of the observed solar mass black holes.. The mass spectrum and density of PBH is predicted. The scenario may possibly lead to abundant antimatter in the universe and even in the Galaxy.

astro-ph.CO↗
arXiv2016

Evolution of thick domain walls in de Sitter universe

We consider thick domain walls in a de Sitter universe following paper by Basu and Vilenkin. However, we are interested not only in stationary solutions found therein, but also investigate the general case of domain wall evolution with time. When the wall thickness parameter, $δ_0$, is smaller than $H^{-1}/\sqrt{2}$, where $H$ is the Hubble parameter in de Sitter space-time, then the stationary solutions exist, and initial field configurations tend with time to the stationary ones. However, there are no stationary solutions for $δ_0 \geq H^{-1}/\sqrt{2}$. We have calculated numerically the rate of the wall expansion in this case and have found that the width of the wall grows exponentially fast for $δ_0 \gg H^{-1}$. An explanation for the critical value $δ_{0c} = H^{-1}/\sqrt{2}$ is also proposed.

gr-qc↗
arXiv2016

General properties and kinetics of spontaneous baryogenesis

General features of spontaneous baryogenesis are studied. The relation between the time derivative of the (pseudo)goldstone field and the baryonic chemical potential is revisited. It is shown that this relation essentially depends upon the representation chosen for the fermionic fields with non-zero baryonic number (quarks). The calculations of the cosmological baryon asymmetry are based on the kinetic equation generalized to the case of non-stationary background. The effects of the finite interval of the integration over time are also included into consideration. All these effects combined lead to a noticeable deviation of the magnitude of the baryon asymmetry from the canonical results.

astro-ph.CO↗
arXiv2016

Beasts in Lambda-CDM Zoo

Recent astronomical discoveries of supermassive black holes (quasars), gamma-bursters, supernovae, and dust at high redshifts, z = (5 --10), are reviewed. Such a dense population of the early universe is at odds with the conventional mechanisms of its possible origin. Similar data from the contemporary universe, which are also in conflict with natural expectations, are considered too. Two possible mechanisms are suggested, at least one of which can potentially solve all these problems. As a by-product of the last model, an abundant cosmological antimatter may be created.

astro-ph.CO↗
arXiv2015

Separated matter and antimatter domains with vanishing domain walls

We present a model of spontaneous (or dynamical) C and CP violation where it is possible to generate domains of matter and antimatter separated by cosmologically large distances. Such C(CP) violation existed only in the early universe and later it disappeared with the only trace of generated baryonic and/or antibaryonic domains. So the problem of domain walls in this model does not exist. These features are achieved through a postulated form of interaction between inflaton and a new scalar field, realizing short time C(CP) violation.

astro-ph.CO↗
arXiv2015

Shape of the inflaton potential and the efficiency of the universe heating

It is shown that the efficiency of the universe heating by an inflaton field depends not only on the possible presence of parametric resonance in the production of scalar particles but also strongly depends on the character of the inflaton approach to its mechanical equilibrium point. In particular, when the inflaton oscillations deviate from pure harmonic ones toward a succession of step functions, the production probability rises by several orders of magnitude. This in turn leads to a much higher temperature of the universe after the inflaton decay, in comparison to the harmonic case. An example of the inflaton potential is presented which creates a proper modification of the evolution of the inflaton toward equilibrium and does not destroy the nice features of inflation.

astro-ph.CO↗
arXiv2015

Reconciling Planck results with low redshift astronomical measurements

We show that emerging tension between the direct astronomical measurements at low redshifts and cosmological parameters deduced from the Planck measurements of the CMB anisotropies can be alleviated if the dark matter consists of two fractions, stable part being dominant and a smaller unstable fraction. The latter constitutes $\sim 10$ per cent at the recombination epoch if decays by now.

astro-ph.CO↗
arXiv2015

Early formed astrophysical objects and cosmological antimatter

Astronomical observations of recent years show that the universe at high redshifts about ten is densely populated by the early formed objects: bright galaxies, quasars, gamma-bursters, and contains a lot of metals and dust. Such rich early formed varieties have not been expected in the standard model of formation of astrophysical objects. There is serious tension between the standard theory and observations.We describe the model which naturally relaxes this tension and nicely fits the data. The model naturally leads to creation of cosmologically significant antimatter which may be abundant even in the Galaxy. Phenomenological consequences of our scenario and possibility of distant registration of antimatter are discussed.

astro-ph.CO↗
arXiv2015

Gravitational instability in oscillating background

Evolution of density and metric perturbations in the background of high frequency oscillations of curvature in F(R) gravity is considered. In addition to the usual Jeans-like instability new effects of amplification of perturbations, associated with parametric resonance and antifriction phenomena, are found.

gr-qc↗
arXiv2015

Study of Supernovae Important for Cosmology

The dense shell method for the determination of distances to type IIn supernovae has been briefly reviewed. Applying our method to SN 2006gy, SN 2009ip, and SN 2010jl supernovae, we have obtained distances in excellent agreement with the previously known distances to the parent galaxies. The dense shell method is based on the radiation hydrodynamic model of a supernova. The method of the blackbody model, as well as the correctness of its application for simple estimates of distances from observation data, has been justified.

astro-ph.CO↗