arXiv subjects

V. S. Berezinsky

Publications and source records attributed to V. S. Berezinsky.

12 recordsLinked to original sources

arXiv2014

Small-scale clumps of dark matter

Small-scale clumps of dark matter are gravitationally bounded structures that have masses comparable to or lower than stellar masses and consist of noninteracting or weakly interacting dark matter particles. In this paper, the current knowledge about the formation and evolution of such structures is reviewed, various types of spectra of primordial cosmological perturbations are considered, and various dark matter models are discussed. Depending on the particular spectrum type, dark matter clumps may differ considerably in their formation processes and ultimate characteristics. The role of clumps in experiments on indirect detection of dark matter particles via their annihilation products is discussed. A number of astrophysical problems and phenomena that are related to dark matter clumps are examined.

astro-ph.HE↗

arXiv2013

Formation and internal structure of superdense dark matter clumps and ultracompact minihaloes

We discuss the formation mechanisms and structure of the superdense dark matter clumps (SDMC) and ultracompact minihaloes (UCMH), outlining the differences between these types of DM objects. We define as SDMC the gravitationally bounded DM objects which have come into virial equilibrium at the radiation-dominated (RD) stage of the universe evolution. Such objects can be formed from the isocurvature (entropy) density perturbations or from the peaks in the spectrum of curvature (adiabatic) perturbation. The axion miniclusters (Kolb and Tkachev 1994) are the example of the former model. The system of central compact mass (e. g. in the form of SDMC or primordial black hole (PBH)) with the outer DM envelope formed in the process of secondary accretion we refer to as UCMH. Therefore, the SDMC can serve as the seed for the UCMH in some scenarios. Recently, the SDMC and UCMH were considered in the many works, and we try to systematize them here. We consider also the effect of asphericity of the initial density perturbation in the gravitational evolution, which decreases the SDMC amount and, as the result, suppresses the gamma-ray signal from DM annihilation.

astro-ph.CO↗

arXiv2011

Dense DM clumps seeded by cosmic string loops and DM annihilation

We develop a model of production of the very dense clumps of DM in RD epoch due to the accretion of DM on the loops of cosmic strings as the seeds. At some time the loops disappear, for example due to the gravitational radiation, and the remaining dense clumps produce the enhancement of the annihilation signal. We take into account the velocity distribution of the strings, and consider the two extreme regimes of DM annihilation: fast decay and continuous evaporation. The produced annihilation flux of gamma radiation is detectable, and for some parameters of DM particles and the strings can exceed the extragalactic flux of the gamma-radiation observed by Fermi. For the fixed parameters of DM particles (e.g. neutralino with fixed masses and cross-section of annihilation) one can obtain the limits on the basic string parameter, tension μ, which is stronger than (more general) limits obtained from WMAP observations, cosmological nucleosynthesis and gravitational lensing. In particular for the neutralino with 100 GeV mass we exclude the interval 5\times10^{-10}<Gμ/c^2<5.1\times10^{-9}.

astro-ph.HE↗

arXiv2005

Anti-GZK effect in UHECR spectrum

In this paper we discuss the anti-GZK effect that arises in the framework of the diffusive propagation of Ultra High Energy (UHE) protons. This effect consists in a jump-like increase of the maximum distance from which UHE protons can reach the observer. The position of the jump is independent of the Intergalactic Magnetic Field (IMF) strength and depends only on the energy losses of protons, namely on the transition energy from adiabatic and pair-production energy losses. The Ultra High Energy Cosmic Rays (UHECR) spectrum presents a low-energy steepening approximately at this energy, which is very close to the position of the observed second knee. The dip, seen in the universal spectrum as a signature of the proton interaction with the Cosmic Microwave Background (CMB) radiation, is also present in the case of diffusive propagation in magnetic fields.

astro-ph↗

arXiv2005

Anti-GZK effect in Ultra High Energy Cosmic Rays diffusive propagation

We discuss the antiGZK effect in the diffusive propagation of ultra high energy protons in intergalactic magnetic fields, which consists in a jump-like increase of the maximum distance from which ultra high energy protons can reach an observer. The position of this jump, $E_j \approx 2\times 10^{18}$ eV, is determined exclusively by energy losses (transition from adiabatic to pair-production energy losses) and it is independent of the diffusion parameters. The diffuse spectrum presents a low-energy steepening approximately at this energy, which is very close to the position of the second knee observed in the cosmic ray spectrum. The dip, seen in the universal spectrum as a signature of the interaction with the cosmic microwave background radiation, is also present in the case of diffusive propagation in magnetic fields.

astro-ph↗

arXiv2004

Extragalactic UHE proton spectrum and prediction for iron-nuclei flux at 10^8 - 10^9 GeV

We investigate the problem of transition from Galactic cosmic rays to extragalactic ultra high energy cosmic rays. Using the model for extragalactic ultra high energy cosmic rays and observed all-particle cosmic ray spectrum, we calculate the galactic spectrum of iron nuclei in the energy range $10^8 - 10^9$ GeV. The flux and spectrum predicted at lower energies agree well with the KASCADE data. The transition from Galactic to extragalactic cosmic rays is distinctly seen in spectra of protons and iron nuclei, when they are measured separately. The shape of predicted iron spectrum agrees with the Hall diffusion.

astro-ph↗

arXiv2000

Hidden source of high-energy neutrinos in collapsing galactic nucleus

We propose the model of a short-lived very powerful source of high energy neutrinos. It is formed as a result of the dynamical evolution of a galactic nucleus prior to its collapse into a massive black hole and formation of high-luminosity AGN. This stage can be referred to as ``pre-AGN''. A dense central stellar cluster in the galactic nucleus on the late stage of evolution consists of compact stars (neutron stars and stellar mass black holes). This cluster is sunk deep into massive gas envelope produced by destructive collisions of a primary stellar population. Frequent collisions of neutron stars in a central stellar cluster are accompanied by the generation of ultrarelativistic fireballs and shock waves. These repeating fireballs result in a formation of the expanding rarefied cavity inside the envelope. The charged particles are effectively accelerated in the cavity and, due to pp-collisions in the gas envelope, they produce high energy neutrinos. All high energy particles, except neutrinos, are absorbed in the thick envelope. Duration of this pre-AGN phase is about 10 yr, the number of the sources can be \~ 10 per cosmological horizon. High energy neutrino signal can be detected by underground neutrino telescope with effective area ~1 km^2.

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arXiv1998

Signatures of Topological Defects

We argue that due to various restrictions cosmic strings and monopole-string networks are not likely to produce the observed flux of ultra-high energy cosmic rays (UHECR). Among the topological defects studied so far, the most promising UHECR sources are necklaces and monopolonia. Other viable sources which are similar to topological defects are relic superheavy particles. All these sources have an excess of pions (and thus photons) over nucleons at production. We demonstrate that in the case of necklaces the diffuse proton flux can be larger than photon flux, due to absorption of the latter on radiobackground, while monopolonia and relic particles are concentrated in the Galactic halo, and the photon flux dominates. Another signature of the latter sources is anisotropy imposed by asymmetric position of the sun in the Galactic halo. In all cases considered so far, including necklaces, photons must be present in ultra-high energy radiation observed from topological defects, and experimental discrimination between photon-induced and proton-induced extensive air showers can give a clue to the origin of ultra-high energy cosmic rays.

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arXiv1997

Clusters of Galaxies as a Storage Room for Cosmic Rays

It is demonstrated that clusters of galaxies are able to keep cosmic rays for a time exceeding the age of the Universe. This phenomenon reveals itself by the production of the diffuse flux of high energy gamma and neutrino radiation due to the interaction of the cosmic rays with the intracluster gas. The produced flux is determined by the cosmological density of baryons, $Ω_b$, if a large part of this density is provided by the intracluster gas. The signal from relic cosmic rays has to be compared with the flux produced by the late sources, which can be considered as a background in the search for cosmic ray production in the past. We calculate this flux considering the normal galaxies and AGN in the clusters as the sources of cosmic rays. Another potential cosmic ray source is the shock in the gas accreting to a cluster. We found that this background is relatively high: the diffuse fluxes produced by relic cosmic rays are of the same order of magnitude which can be expected from AGN in the clusters. In all cases the predicted diffuse gamma-ray flux is smaller than the observed one and the diffuse neutrino flux can be seen as the small bump at $E\sim 10^6~GeV$ over the atmospheric neutrino flux. A bright phase in the galaxy evolution can be a source of the relic cosmic rays in clusters, revealing itself by diffuse gamma and neutrino radiations. We found that the observation of a signal from the bright phase is better for an individual cluster.

astro-ph↗

arXiv1995

SNI: a new mechanism for gamma ray burst. I.Weak magnetic field

We propose a new mechanism for high energy gamma ray burst in Supernova type I (SNI) explosion. Presupernova is assumed to be a binary system comprised of a red giant and a white dwarf with a wind accretion. The accretion flow terminates by the accretion shock in the vicinity of the white dwarf at the distance of the order of the accretion radius. The gas inside the accretion radius constitutes the main body of a target for gamma ray production by $pp$ collisions.\par The supernova explosion and the shock propagation in the white dwarf result in the hydrodynamical acceleration of the outer layers of the star. The spectrum of accelerated particles is steep and the maximum energy does not exceed $1000$ $GeV$.\par The gamma ray burst is produced due to interaction of the accelerated particles with the gas in the binary system. Most of the photons have energies about $100$ $MeV$, the total number of the emitted photons is between $10^{46}$ and $10^{47}$. The gamma ray burst might have one or two precursors. The first one is produced during the shock breakout when the shock approaches the star surface and crosses it.\par The calculations are valid in the case of a weak magnetic field. The case of strong magnetic field will be considered in part II (in preparation).

astro-ph↗

arXiv1995

HELIUM PHOTODISINTEGRATION AND NUCLEOSYNTHESIS: IMPLICATIONS FOR TOPOLOGICAL DEFECTS, HIGH ENERGY COSMIC RAYS, AND MASSIVE BLACK HOLES

We consider the production of $^3$He and $^2$H by $^4$He photodisintegration initiated by non-thermal energy releases during early cosmic epochs. We find that this process cannot be the predominant source of primordial $^2$H since it would result in anomalously high $^3$He/D ratios in conflict with standard chemical evolution assumptions. We apply this fact to constrain topological defect models of highest energy cosmic ray (HECR) production. Such models have been proposed as possible sources of ultrahigh energy particles and gamma-rays with energies above $10^{20}$eV. The constraints on these models derived from $^4$He-photodisintegration are compared to corresponding limits from spectral distortions of the cosmic microwave background radiation (CMBR) and from the observed diffuse gamma-ray background. It is shown that for reasonable primary particle injection spectra superconducting cosmic strings, unlike ordinary strings or annihilating monopoles, cannot produce the HECR flux at the present epoch without violating at least the $^4$He-photodisintegration bound. The constraint from the diffuse gamma-ray background rules out the dominant production of HECR by the decay of Grand Unification particles in models with cosmological evolution assuming standard fragmentation functions. Constraints on massive black hole induced photodisintegration are also discussed.

astro-ph↗

arXiv1995

Electromagnetic Cascades and Cascade Nucleosynthesis in the Early Universe

We describe a calculation of electromagnetic cascading in radiation and matter in the early universe initiated by the decay of massive particles or by some other process. We have used a combination of Monte Carlo and numerical techniques which enables us to use exact cross sections, where known, for all the relevant processes. In cascades initiated after the epoch of big bang nucleosynthesis $γ$-rays in the cascades will photodisintegrate $^4$He, producing $^3$He and deuterium. Using the observed $^3$He and deuterium abundances we are able to place constraints on the cascade energy deposition as a function of cosmic time. In the case of the decay of massive primordial particles, we place limits on the density of massive primordial particles as a function of their mean decay time, and on the expected intensity of decay neutrinos.

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