arXiv subjects

A. D. Dolgov

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

At least 19 recordsLinked to original sources

arXiv2026

Vacuum energy problem in anti-de Sitter space

We investigate the cosmological evolution of a universe with an initially large negative vacuum energy, corresponding to an anti-de Sitter (AdS) space-time. Such a universe inevitably contracts and collapses into a singularity. To prevent this collapse, we propose a dynamical mechanism of vacuum energy compensation based on a scalar field non-minimally coupled to the curvature scalar. Numerical and analytical calculations demonstrate that the suggested mechanism completely compensates the gravitational impact of the vacuum energy, successfully driving the curvature to zero. As a result, the universe avoids the singularity and evolves into a power-law expansion, typical for a radiation-dominated cosmology.

gr-qc↗

arXiv2026

Antimatter in the universe and Milky Way

Theoretical model leading to a significant Galaxy population by primordial antimatter is described. Observational data confirming this "crazy" prediction are presented.

astro-ph.GA↗

arXiv2026

Possible explanation of primordial $^7$Li deficit

A reduction mechanism of the theoretically predicted excessive abundance of $^7$Li via baryons evaporated by primordial black holes is suggested. It is shown that the fraction of $^7$Li with respect to the number density of baryons can be diminished down to the observed value via the process of $^7$Li transformation by neutron capture. The created in this process $^8$Li or $^8$Be quickly decay into a pair of $^4$He nuclei.

astro-ph.CO↗

arXiv2026

Progress in Particle Physics and Modern Cosmology

This is the translation into English of my paper published in Russian at the paper collection on cosmology at \\ 1981. The content of the book is presented in the Appendix. This is the first paper where the dynamical mechanism of phoenix universe was worked out. The notion of phoenix universe was first mentioned in the paper by Lemaitre in 1933, where he assumed that a repetition of successive phases of expansion and contraction was possible. Lemaitre called such model of the universe, that is born, dies and is reborn, the phoenix model, named after the mythical bird able to reborn from the ashes. According to the author, there could be an infinite number of such cycles in the past and future. In this model, however, a possible solution to the fundamental question was unclear, what was the mechanism for the rebirth of the universe. This mechanism was worked out in my paper, published in 1980 in Russian. Moreover, in our recent paper with E. Arbuzova a mechanism of dynamical cancellation of vacuum energy was proposed, that permits to eliminate vacuum energy locally down to zero and permits universe to jump to a lower hot level, leading to rebirth of a hot universe.

astro-ph.CO↗

arXiv2025

Tension between HST/JWST and $Λ$CDM Cosmology, PBH, and Antimatter in the Galaxy

Recent data released by James Webb Space Telescope (JWST) and, somewhat earlier, the data presented by Hubble Space Telescope (HST) are commonly understood as a strong indication for breaking of the canonical $Λ$CDM cosmology. It is argued in the presented work that massive primordial black holes (PBH) could seed galaxy and quasar formation in the very young universe as it has been conjectured in our paper of 1993 and resolve the tension induced by the JWST and the HST data with the standard cosmology. This point of view is presently supported by several recent works. The proposed mechanism of PBH formation leads to the log-normal mass spectrum of PBHs and predicts abundant antimatter population of our Galaxy, Milky Way. Both these predictions are in excellent agreement with astronomical observations.

astro-ph.CO↗

arXiv2025

Dynamical mechanism of vacuum energy compensation

The model of vacuum energy compensation due to interaction of a scalar field $ϕ$ with curvature scalar of the form $βR ϕ^2 f(ϕ) $ is proposed. It is shown that with a simple power form of $f(ϕ)$ the exponential expansion, induced by vacuum energy (or what is the same by cosmological constant), is transformed into canonical cosmological evolution of the universe dominated by relativistic matter.

gr-qc↗

arXiv2024

Conversion of protons to positrons by a black hole

The conversion of protons to positrons at the horizon of a black hole (BH) is considered. It is shown that the process may efficiently proceed for BHs with masses in the range $\sim 10^{18}$ -- $10^{21}$ g. It is argued that the electric charge of BH acquired by the proton accretion to BH could create electric field near BH horizon close to the critical Schwinger one. It leads to efficient electron-positron pair production, when electrons are back captured by the BH while positrons are emitted into outer space. Annihilation of these positrons with electrons in the interstellar medium may at least partially explain the origin of the observed 511 keV line.

hep-ph↗

arXiv2024

Cosmic rays from annihilation of heavy dark matter particles

The origin of the ultra high energy cosmic rays via annihilation of heavy stable, fermions "f", of the cosmological dark matter (DM) is studied. The particles in question are supposed to be created by the scalaron decays in $R^2$ modified gravity. Novel part of our approach is the assumption that the mass of these carriers of DM is slightly below than a half of the scalaron mass. In such a case the phase space volume becomes tiny. It leads to sufficiently low probability of "f" production, so their average cosmological energy density could be equal to the observed energy density of dark matter. Several regions of the universe, where the annihilation could take place, are studied. They include the whole universe under assumption of homogeneous energy density, the high density DM clump in the galactic centre, the cloud of DM in the Galaxy with realistic density distribution, and high density clusters of DM in the Galaxy. Possible resonance annihilation of $f \bar f$ into energetic light particle is considered. We have shown that the proposed scenario can successfully explain the origin of the ultrahigh energy flux of cosmic rays where the canonical astrophysical mechanisms are not operative.

hep-ph↗

arXiv2024

Solution of JWST and HST problems by primordial black holes

Observations of the early universe at redshifts of order 10, collected during the last several years presented by the Hubble Space Telescope (HST) and recent data by the James Webb Space telescope (JWST) created strong doubts on the validity of the conventional $Λ$CDM cosmology. It is argued here that the 30 year old conjecture by A.Dolgov \& J.Silk~\cite{DS} of galaxy and quasar seeding by supermassive primordial black holes (SMBHs) naturally solves the problem of the observed dense early population of the universe, as well as the problem of the formation of SMBH in the contemporary universe. The idea of seeding of cosmic structures by SMBH is supported by a good agreement of the predicted log-normal mass spectrum of primordial black holes (PBH) with observations and by a noticeable antimatter population of the Milky Way.

astro-ph.CO↗

arXiv2023

Graviton to photon conversion in curved space-time and external magnetic field

The suppression of relic gravitational waves due to their conversion into electromagnetic radiation in a cosmological magnetic field is studied. The coupled system of equations describing gravitational and electromagnetic wave propagation in an arbitrary curved space-time and in external magnetic field is derived. The subsequent elimination of photons from the beam due to their interaction with the primary plasma is taken into account. The resulting system of equations is solved numerically in Friedman-LeMaitre-Robertson-Walker metric for the upper limit of the intergalactic magnetic field strength of 1 nGs. We conclude that the gravitational wave conversion into photons in the intergalactic magnetic field cannot significantly change the amplitude of the relic gravitational wave and their frequency spectrum.

gr-qc↗

arXiv2023

Cosmic rays from heavy particle decays

Multidimensional modification of gravity with a smaller mass scale of the gravitational interaction is considered. Stable by assumption dark matter particles could decay via interactions with virtual black holes. The decay rates of such processes are estimated. It is shown that with the proper fixation of the parameters the decays of these ultra-massive particles can give noticeable contribution to the flux of high energy cosmic rays in particular, near the Greisen-Zatsepin-Kuzmin limit. Such particles can also create neutrinos of very high energies observed in the existing huge underwater or ice-cube detectors.

hep-ph↗

arXiv2023

Calculations of scalaron decay probabilities

The particle production through the scalaron decays are considered for several different channels. The central part of the work is dedicated to a study of the decay probability into two complex minimally coupled massless scalars. The calculations are performed by two different independent methods. In addition we calculated the decay probability into real minimally coupled massless scalars, conformally coupled massive scalars, massive fermions, and gauge bosons. The results are compared with the published papers which in some cases disagree with each other.

hep-ph↗

arXiv2023

Mixing of scalar and tensor metric perturbations

Metric perturbations in General Relativity are usually separated into three distinct classes: scalar, vector, and tensor. In many cases these modes are separable, i.e. they satisfy independent equations of motion for each mode. However, in the present paper we argue that in many cases tensor and scalar modes are not separable, no matter what gauge conditions are chosen. The propagation of any of these mode depends on the other. A realistic example providing such mixing is presented.

gr-qc↗

arXiv2023

James Webb Space Telescope: data, problems, and resolution

It is argued that the data presented by Hubble Space Telescope and James Webb Space Telescope, that seem to be at odds with the canonical big bang cosmology, find simple explanation if galaxy formation is seeded by massive primordial black holes (PBH), as anticipated in 1993 (A. Dolgov and J. Silk, later DS). The statement that the galaxy formation might be seeded by PBH is now rediscovered in several works. The predicted by DS log-normal mass spectrum of PBHs very well agrees with astronomical data. Abundant BH population of the Galaxy with masses of the order of tens solar masses is predicted. Extended mass spectrum of PBH together with their possible clustering allows them to make 100\% contribution into the cosmological dark matter. Another prediction of DS mechanism on noticeable amount of antimatter in the Milky Way also seems to be confirmed by the data.

astro-ph.CO↗

arXiv2022

Rates of particle production in $R^2$ gravity and supersymmetry-kind dark matter

Universe heating in $R^2$-modified gravity is considered. The rates of particle production by the scalaron are calculated for different decay channels. Freezing of massive stable relics with the interaction strength typical for supersymmetry is studied. It is shown that the bounds on masses of supersymmetry-kind particles allowing them to form the cosmological dark matter (DM)depend upon the dominant decay mode of the scalaron. In any case the results presented open much wider mass window for DM with the interaction strength typical for supersymmetry.

astro-ph.CO↗

arXiv2022

Anti-stars in the Milky Way and primordial black holes

Astronomical data of the several recent years, which present an evidence in favour of abundant antimatter population in our Galaxy, Milky Way, are analysed. The data include: registration of gamma-rays with energy 0.511 MeV, which surely originate from electron-positron annihilation at rest, very large flux of anti-helium nuclei, discovered at AMS, and 14 stars which produce excessive gamma-rays with energies of several hundred MeV which may be interpreted as indication that these stars consist of antimatter. Theoretical predictions of these phenomena, made much earlier ago are described

astro-ph.GA↗

arXiv2022

On graviton propagation in curved space-time background

Equation describing propagation of gravitational waves (GW) over arbitrary curved space-time background is analyzed. New terms, which are absent in the conventional homogeneous and isotropic Friedmann cosmology, are found. Some examples of realistic metric, where these new terms manifest themselves, are presented. Possible implications to very low frequency GW are briefly discussed.

gr-qc↗

arXiv2022

X-ray signature of antistars in the Galaxy

The existence of macroscopic objects from antimatter (antistars) is envisaged in some models of baryogenesis. Searches for antistars has been usually carried out in gamma-rays through hadronic annihilation of matter. In astrophysically plausible cases of the interaction of neutral atmospheres or winds from antistars with ionized interstellar gas, the hadronic annihilation will be preceded by the formation of excited $p\bar p$ and He$\bar p$ atoms. These atoms rapidly cascade down to low levels prior to annihilation giving rise to a series of narrow lines which can be associated with the hadronic annihilation gamma-ray emission. The most significant are L (3p-2p) 1.73 keV line (yield more than 90\%) from $p\bar p$ atoms, and M (4-3) 4.86 keV (yield $\sim 60\% $) and L (3-2) 11.13 keV (yield about 25\%) lines from $^4$He$\bar p$ atoms. These lines can be probed in dedicated observations by forthcoming sensitive X-ray spectroscopic missions XRISM, \textit{Athena, \textit{Lynx}and in wide-field X-ray surveys like SRG/\textit{eROSITA} all-sky survey.

astro-ph.HE↗