A. A. Kirillov

SIGNATURES OF PRIMORDIAL BLACK HOLE DARK MATTER

The nonbaryonic dark matter of the Universe is assumed to consist of new stable forms of matter. Their stability reflects symmetry of micro world and mechanisms of its symmetry breaking. In the early Universe heavy metastable particles can dominate, leaving primordial black holes (PBHs) after their decay, as well as the structure of particle symmetry breaking gives rise to cosmological phase transitions, from which massive black holes and/or their clusters can originate. PBHs can be formed in such transitions within a narrow interval of masses about

Black hole clusters in our Galaxy

10^{17}

Fermi-LAT kills dark matter interpretations of AMS-02 data. Or not?

g and, avoiding severe observational constraints on PBHs, can be a candidate for the dominant form of dark matter. PBHs in this range of mass can give solution of the problem of reionization in the Universe at the redshift

On the classical description of the recombination of dark matter particles with a Coulomb-like interaction

z\sim 5... 10

Clusters of Primordial Black Holes and Reionization Problem

. Clusters of massive PBHs can serve as a nonlinear seeds for galaxy formation, while PBHs evaporating in such clusters can provide an interesting interpretation for the observations of point-like gamma-ray sources. Analysis of possible PBH signatures represents a universal probe for super-high energy physics in the early Universe in studies of indirect effects of the dark matter.

Gamma-ray evidence for dark matter clumps

We discuss a way of observing intermediate-mass black holes which may exist in the Galaxy. We show that these black holes form clusters which could be identified as gamma-ray sources.

Classical transitions with the topological number changing in the early Universe

A number of papers attempt to explain the positron anomaly in cosmic rays, observed by PAMELA and AMS-02, in terms of dark matter (DM) decays or annihilations. However, the recent progress in cosmic gamma-ray studies challenges these attempts. Indeed, as we show, any rational DM model explaining the positron anomaly abundantly produces final state radiation and Inverse Compton gamma rays, which inevitably leads to a contradiction with Fermi-LAT isotropic diffuse gamma-ray background measurements. Furthermore, the Fermi-LAT observation of Milky Way dwarf satellites, supposed to be rich in DM, revealed no significant signal in gamma rays. We propose a generic approach in which the major contribution to cosmic rays comes from the dark matter disc and prove that the tension between the DM origin of the positron anomaly and the cosmic gamma-ray observations can be relieved. We consider both a simple model, in which DM decay/annihilate into charged leptons, and a model-independent minimal case of particle production, and we estimate the optimal thickness of DM disk. Possible mechanisms of formation and its properties are briefly discussed.

Transitions between topologically non-trivial configurations

Abstract Cold dark matter (DM) scenario may be cured of several problems by involving self-interaction of dark matter. Viability of the models of long-range interacting DM crucially depends on the effectiveness of recombination of the DM particles, making thereby their interaction short-range. Usually in numeric calculations, recombination is described by cross section obtained on a feasible quantum level. However in a wide range of parameter values, a classical treatment, where the particles are bound due to dipole radiation, is applicable. The cross sections, obtained in both approaches, are very different and lead to diverse consequences. Classical cross section has a steeper dependence on relative velocity, what leads to the fact that, after decoupling of DM particles from thermal background of “dark photons” (carriers of DM long-range interaction), recombination process does not “freeze out”, diminishing gradually density of unbound DM particles. Our simplified estimates show, that at the taken parameter values (the mass of DM particle is 100 GeV, interaction constant is 100 − 1 , and quite natural assumptions on initial conditions, from which the result is very weakly dependent) the difference in residual density reaches about 5 orders of magnitude on pre-galactic stage. This estimate takes into account thermal effects induced by dipole radiation and recombination, which resulted in the increase of both temperature and density of DM particles by a half order of magnitude.

High-energy cosmic antiparticle excess vs. isotropic gamma-ray background problem in decaying dark matter Universe

Clusters of primordial black holes may cause the formation of quasars in the early Universe. In turn, radiation from these quasars may lead to the reionization of the Universe. However, the evaporation of primordial black holes via Hawking’s mechanism may also contribute to the ionization of matter. The possibility of matter ionization via the evaporation of primordial black holes with allowance for existing constraints on their density is discussed. The contribution to ionization from the evaporation of primordial black holes characterized by their preset mass spectrum can roughly be estimated at about 10−3.

Astrophysical manifestations of clumps of cold dark matter

We discuss the possibility of identification of point-like gamma-ray sources (PGS) with small-scale dark matter (DM) clumps in our Galaxy. Gamma rays are supposed to originate from annihilation of DM particles in the clumps, where the annihilation rate is supposed to be enhanced, besides higher density, due to smaller relative velocities v of DM particles. We parametrized the annihilation cross section σann(v) in the form of an arbitrary power-law dependence on the relative velocity v with/without the Sommerfeld-Gamow-Sakharov factor, implying the existence of a new Coulomb-like interaction. Adopting different parameters of the cross-section and the clump, satisfying the condition Ω ≲ 0.2 on the density of DM particles, they are constrained by comparison with the Fermi/LAT data on unidentified PGS as well as on diffuse γ radiation; the results are applied to concrete DM candidates. This analysis is found to be sensitive enough to the existing uncertainty in the DM density profiles in the clump, which can provide a tool for their test. We also discuss the possibilities where a gamma-radiating clump changes visibly its position on the celestial sphere and it is seen as a spatially extended gamma source (EGS), which can be probed in future experiments like Gamma-400.