Capture of the free-floating planets and primordial black holes into protostellar clouds

The capture of the free-floating planets and primordial black holes into a collapsing protostellar cloud is considered. Although the last stage of rapid contraction leading to the star formation lasts for a relatively short time $\sim 10^5$ years, during this time there is a strong change in the gravitational potential created by the movement of the entire cloud's mass ($\sim M_\odot$). As a result, the probability of capturing an object into a contracting cloud is comparable to the probability of capturing into an already formed planetary system. Taking into account the collapse of the cloud increases by 70% the full probability of the planets capture at the orbits with large semi-axis $a<10^3$ au. Capture in the cloud can explain the wide inclined orbit of the supposed 9th planet in the solar system. At the same time, the probability of primordial black holes capturing from the galactic halo into a contracting cloud is extremely small.Comment: 5 pages, 3 figure

Escape from a black hole with spherical warp drive

In this paper, a class of the warp drive (WD) type metrics is proposed in the form of spherical and plane waves or shells. In particular, these metrics can describe the passage of spherical WD through the horizon of a black hole from the inside out. In this metrics, non-singular evolution of physical fields is possible, which is demonstrated by examples of scalar, vector and fermion fields. The passage of a warp-wave through the fields is accompanied by soliton-like configurations (kinks). The limiting case of Planck-scale WD can lead to the evaporation of singularities inside black holes with the escape of particles and information into outer space, and the EPR=WD conjecture can also be proposed.Comment: 7 pages, 2 figures, misprints correcte

Looking at the NANOGrav Signal Through the Anthropic Window of Axion-Like Particles

We explore the inflationary dynamics leading to formation of closed domain walls in course of evolution of an axion like particle (ALP) field whose Peccei-Quinn-like phase transition occurred well before inflationary epoch. Evolving after inflation, the domain walls may leave their imprint in stochastic gravitational waves background, in the frequency range accessible for the pulsar timing array measurements. We derive the characteristic strain power spectrum produced by the distribution of the closed domain walls and relate it with the recently reported NANOGrav signal excess. We found that the slope of the frequency dependence of the characteristic strain spectrum generated by the domain walls is very well centered inside the range of the slopes in the signal reported by the NANOGrav. Analyzing the inflationary dynamics of the ALP field, in consistency with the isocurvature constraint, we revealed those combinations of the parameters where the signal from the inflationary induced ALPs domain walls could saturate the amplitude of the NANOGrav excess. The evolution of big enough closed domain walls may incur in formation of wormholes with the walls escaping into baby universes. We studied the conditions, when closed walls escaped into baby universes could leave a detectable imprint in the stochastic gravitational waves background.Comment: 39 pages, 3 figures, the version accepted for publication in Physical Review

Accretion with back reaction

We calculate analytically a back reaction of the stationary spherical accretion flow near the event horizon and near the inner Cauchy horizon of the charged black hole. It is shown that corresponding back-reaction corrections to the black hole metric depend only on the fluid accretion rate and diverge in the case of an extremely charged black hole. In result, the test fluid approximation for stationary accretion is violated for extreme black holes. This behavior of the accreting black hole is in accordance with the third law of black hole thermodynamics, forbidding the practical attainability of the extreme state.Comment: 5 pages, 2 figures; new figure and references adde

Clusters of primordial black holes

The Primordial Black Holes (PBHs) are gradually involved into consideration as the phenomenon having reliable basis. We discuss here the possibility of their agglomeration into clusters that may have several prominent observable features. The clusters can form due to closed domain walls appearance in the natural and the hybrid inflation with subsequent evolution and gravitational collapse. Early dustlike stages of dominance of heavy metastable dissipative particles, at which star-like objects are formed, can also naturally lead to formation of black hole clusters, remaining in the Universe after decay of particles, from which they have originated. The dynamical evolution of such clusters discussed here is of the crucial importance. Such a model inherits all the advantages of the single PBHs like possible explanation of existence of supermassive black holes (origin of the early quasars), binary BH merges registered by LIGO/Virgo through gravitational waves, contribution to reionization of the Universe, but also has additional benefits. The cluster could alleviate or completely avoid existing constraints on the single PBH abundance making PBHs a real dark matter candidate. The most of existing constraints on (single) PBH density should be re-considered as applied to the clusters. Also unidentified cosmic gamma-ray point-like sources could be (partially) accounted for by them. One can conclude, that it seems really to be much more viable model with respect to the single PBHs.Comment: v2: both the text and bibliography are essentially extended, coincides with EPJC versio

Small-scale clumps in the galactic halo and dark matter annihilation

Production of small-scale DM clumps is studied in the standard cosmological scenario with an inflation-produced primeval fluctuation spectrum. Special attention is given to three following problems: (i) The mass spectrum of small-scale clumps with $M \lesssim 10^3 M_{\odot}$ is calculated with tidal destruction of the clumps taken into account within the hierarchical model of clump structure. Only 0.1 - 0.5% of small clumps survive the stage of tidal destruction in each logarithmic mass interval $\Delta\ln M\sim1$. (ii) The mass distribution of clumps has a cutoff at $M_{\rm min}$ due to diffusion of DM particles out of a fluctuation and free streaming at later stage. $M_{\rm min}$ is a model dependent quantity. In the case the neutralino, considered as a pure bino, is a DM particle, $M_{\rm min} \sim 10^{-8} M_{\odot}$. (iii) The evolution of density profile in a DM clump does not result in the singularity because of formation of the core under influence of tidal interaction. The radius of the core is $R_c \sim 0.1 R$, where $R$ is radius of the clump. The applications for annihilation of DM particles in the Galactic halo are studied. The number density of clumps as a function of their mass, radius and distance to the Galactic center is presented. The enhancement of annihilation signal due to clumpiness, valid for arbitrary DM particles, is calculated. In spite of small survival probability, the annihilation signal in most cases is dominated by clumps. For observationally preferable value of index or primeval fluctuation spectrum $n_p \approx 1$, the enhancement of annihilation signal is described by factor 2 - 5 for different density profiles in a clump.Comment: inor changes in text and 2 references adde

Production and evaporation of micro black holes as a link between mirror universes

International audienceIt is shown that the equalization of temperatures between our and mirror sectors occurs during one Hubble time due to microscopic black hole production and evaporation in particle collisions if the temperature of the Universe is near the multidimensional Plank mass. This effect excludes multidimensional Planck masses smaller than the reheating temperature of the Universe (∼1013  GeV) in the mirror matter models, because the primordial nucleosynthesis theory requires that the temperature of the mirror world should be lower than ours. In particular, the birth of microscopic black holes in the LHC is impossible if the dark matter of our Universe is represented by baryons of mirror matter. It excludes some of the possible coexisting options in particle physics and cosmology. Multidimensional models with flat additional dimensions are already strongly constrained in maximum temperature due to the effect of Kaluza-Klein mode (KK-mode) overproduction. In these models, the reheating temperature should be significantly less than the multidimensional Planck mass, so our restrictions in this case are not paramount. The new constraints play a role in multidimensional models in which the spectrum of KK modes does not lead to their overproduction in the early Universe, for example, in theories with hyperbolic additional space