arXiv subjects

Veniamin Berezinsky

Publications and source records attributed to Veniamin Berezinsky.

15 recordsLinked to original sources

arXiv2015

SUSY dark matter annihilation in the Galactic halo

Neutralino annihilation in the Galactic halo is the most definite observational signature proposed for indirect registration of the SUSY Dark Matter (DM) candidate particles. The corresponding annihilation signal (in the form of gamma-rays, positrons and antiprotons) may be boosted for one or three orders of magnitude due to the clustering of cold DM particles into the small-scale and very dense self-gravitating clumps. We discuss the formation of these clumps from the initial density perturbations and their successive fate in the Galactic halo. Only a small fraction of these clumps, $\sim0.1$%, in each logarithmic mass interval $Δ\log M\sim1$ survives the stage of hierarchical clustering. We calculate the probability of surviving the remnants of dark matter clumps in the Galaxy by modelling the tidal destruction of the small-scale clumps by the Galactic disk and stars. It is demonstrated that a substantial fraction of clump remnants may survive through the tidal destruction during the lifetime of the Galaxy. The resulting mass spectrum of survived clumps is extended down to the mass of the core of the cosmologically produced clumps with a minimal mass. The survived dense remnants of tidally destructed clumps provide an amplification (boosting) of the annihilation signal with respect to the diffuse DM in the Galactic halo. We describe the anisotropy of clump distribution caused by the tidal destruction of clumps in the Galactic disk.

astro-ph.HE↗

arXiv2011

Extremely High Energy Neutrinos from Cosmic Strings

Superstring theory and other supersymmetric theories predict the existence of relatively light, weakly interacting scalar particles, called moduli, with a universal form of coupling to matter. Such particles can be emitted from cusps of cosmic strings, where extremely large Lorentz factors are achieved momentarily. Highly boosted modulus bursts emanating from cusps subsequently decay into gluons, they generate parton cascades which in turn produce large numbers of pions and then neutrinos. Due to very large Lorentz factors, extremely high energy neutrinos, up to the Planck scale and above, are produced. For some model parameters, the predicted flux of neutrinos with energies $\gtrsim 10^{21}$ eV is observable by JEM-EUSO and by the future large radio detectors LOFAR and SKA.

astro-ph.CO↗

arXiv2010

UHE neutrinos from superconducting cosmic strings

Superconducting cosmic strings naturally emit highly boosted charge carriers from cusps. This occurs when a cosmic string or a loop moves through a magnetic field and develops an electric current. The charge carriers and the products of their decay, including protons, photons and neutrinos, are emitted as a narrow jets with opening angle $θ\sim 1/γ_c$, where $γ_c$ is the Lorentz factor of the cusp. The excitation of electric currents in strings occurs mostly in clusters of galaxies, which are characterized by magnetic fields $B \sim 10^{-6}$ G and a filling factor $f_B \sim 10^{-3}$. Two string parameters determine the emission of the particles: the symmetry breaking scale $η$, which for successful applications should be of order $10^9$--$10^{12}$ GeV, and the dimensionless parameter $i_c$, which determines the maximum induced current as $J_{max} =i_c e η$ and the energy of emitted charge carriers as $ε_x \sim i_c γ_c η$, where $e$ is the electric charge of a particle. For the parameters $η$ and $B$ mentioned above, the Lorentz factor reaches $γ_c \sim 10^{12}$ and the maximum particle energy can be as high as $γ_cη\sim 10^{22}$ GeV. The diffuse fluxes of UHE neutrinos are close to the cascade upper limit, and can be detected by future neutrino observatories. The signatures of this model are: very high energies of neutrinos, in excess of $10^{20}$ eV, correlation of neutrinos with clusters of galaxies, simultaneous appearance of several neutrino-produced showers in the field of view of very large detectors, such as JEM-EUSO, and 10 TeV gamma radiation from the Virgo cluster. The flux of UHE protons from cusps may account for a large fraction of the observed events at the highest energies.

astro-ph.HE↗

arXiv2008

Remnants of dark matter clumps

What happened to the central cores of tidally destructed dark matter clumps in the Galactic halo? We calculate the probability of surviving of the remnants of dark matter clumps in the Galaxy by modelling the tidal destruction of the small-scale clumps. It is demonstrated that a substantial fraction of clump remnants may survive through the tidal destruction during the lifetime of the Galaxy if the radius of a core is rather small. The resulting mass spectrum of survived clumps is extended down to the mass of the core of the cosmologically produced clumps with a minimal mass. Since the annihilation signal is dominated by the dense part of the core, destruction of the outer part of the clump affects the annihilation rate relatively weakly and the survived dense remnants of tidally destructed clumps provide a large contribution to the annihilation signal in the Galaxy. The uncertainties in minimal clump mass resulting from the uncertainties in neutralino models are discussed.

astro-ph↗

arXiv2007

Anisotropy of dark matter annihilation with respect to the Galactic plane

We describe the anisotropy of dark matter clump distribution caused by tidal destruction of clumps in the Galactic disk. A tidal destruction of clumps with orbit planes near the disk plane occurs more efficiently as compared with destruction of clumps at near-polar orbits. A corresponding annihilation of dark matter particles in small-scale clumps produces the anisotropic gamma-ray signal with respect to the Galactic disk. This anisotropy is rather small, 9%, and superimposed on that due to off-centering position of the Sun in the Galaxy. The anisotropy of annihilation signal with respect to the Galactic disk provides a possibility to discriminate dark matter annihilation from the diffuse gamma-ray backgrounds of other origin.

astro-ph↗

arXiv2007

Phenomenological constraints on low-scale gravity

We study the constraints on gravity scale $M_P$ in extra-dimension gravitational theory, obtained from gravity-induced processes. The obtained constraints are subdivided into strong (though not robust) and reliable (though less strong). The strong constraints can be in principle relaxed due to some broken gauge symmetries, e.g. family symmetry. The strongest constraint is given by neutrino oscillations. For different assumptions the lower bound on $M_P$ is $10^{15} - 10^{18}$ GeV. However, it can be, in principle, reduced by broken family symmetry. More reliable bounds are due to flavor-conserved operators or those which change the flavors within one family. These bounds, obtained using the electron mass and width of $π\to eν$ decay, are $1\times 10^5$ GeV and $5\times 10^5$ GeV, for these two cases, respectively.

hep-ph↗

arXiv2006

Destruction of small-scale dark matter clumps in the hierarchical structures and galaxies

A mass function of small-scale dark matter clumps is calculated in the standard cosmological scenario with an inflationary-produced primordial fluctuation spectrum and with a hierarchical clustering. We take into account the tidal destruction of clumps at early stages of structure formation starting from a time of clump detachment from the Universe expansion. Only a small fraction of these clumps, ~0.1-0.5%, in each logarithmic mass interval $Δ\log M\sim1$ survives the stage of hierarchical clustering. The surviving clumps can be disrupted further in the galaxies by tidal interactions with stars. We performed the detailed calculations of the tidal destruction of clumps by stars in the Galactic bulge and halo and by the Galactic disk itself. It is shown that the Galactic disc provides the dominant contribution to the tidal destruction of small-scale clumps outside the bulge. The results obtained are crucial for calculations of the dark matter annihilation signal in the Galaxy.

astro-ph↗

arXiv2005

Dip in UHECR and Transition from Galactic to Extragalactic Cosmic Rays

The dip is a feature in the diffuse spectrum of UHE protons in energy range $1\times 10^{18} - 4\times 10^{19}$ eV, which is caused by electron-positron pair production on CMB photons. Calculated for power-law generation spectrum with index $γ_g=2.7$, the shape of the dip is confirmed with high accuracy by data of Akeno - AGASA, HiRes, Yakutsk and Fly's Eye detectors. The predicted shape of the dip is robust: it is valid for the rectilinear and diffusive propagation, for different discretenesses in the source distribution, for local source overdensity and deficit, for source inhomogeneities on scale $\ell \lsim 100$ Mpc etc. Below the characteristic energy $E_c \approx 1\times 10^{18}$ eV the spectrum of the dip flattens for both diffusive and rectilinear propagation, and more steep galactic spectrum becomes dominant at $E < E_c$. The energy of transition $E_{\rm tr} < E_c$ approximately coincides with the position of the second knee $E_{2kn}$ observed in the cosmic ray spectrum. The critical energy $E_c$ is determined by the energy $E_{\rm eq} = 2.3\times 10^{18}$ eV, where adiabatic and pair-production energy losses are equal. Thus, position of the second knee is explained by proton energy losses on CMB photons.

astro-ph↗

arXiv2005

Low scale gravity as the source of neutrino masses?

We address the question whether low-scale gravity alone can generate the neutrino mass matrix needed to accommodate the observed phenomenology. In low-scale gravity the neutrino mass matrix in the flavor basis is characterized by one parameter (the gravity scale M_X) and by an exact or approximate flavor blindness (namely, all elements of the mass matrix are of comparable size). Neutrino masses and mixings are consistent with the observational data for certain values of the matrix elements, but only when the spectrum of mass is inverted or degenerate. For the latter type of spectra the parameter M_{ee} probed in double beta experiments and the mass parameter probed by cosmology are close to existing upper limits.

hep-ph↗

arXiv2004

Cosmological Origin of Small-Scale Clumps and DM Annihilation Signal

We study the cosmological origin of small-scale DM clumps in the hierarchical scenario with the most conservative assumption of adiabatic Gaussian fluctuations. The mass spectrum of small-scale clumps with M<10^3Msun 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. The mass distribution of clumps has a cutoff at Mmin due to diffusion of DM particles out of a fluctuation and free streaming at later stage. Mmin is a model dependent quantity. In the case the neutralino DM, considered as a pure bino, Mmin~10^-8 Msun. 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 ~0.1R, 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 global annihilation signal in most cases is dominated by clumps, with major contribution given by small clumps. The enhancement due to large clumps with M>10^6 Msun is very small.

astro-ph↗

arXiv2003

U(e3) from physics above the GUT scale

We consider non-renormalizable 1/M_X interaction terms as a perturbation of the conventional neutrino mass matrix. Particular attention is given to the gravitational interaction with M_X=M_Pl. We find that for the degenerate neutrino mass spectrum, the considered perturbation generates a non-zero U(e3) which is within reach of the high performance neutrino factories and just on the borderline to be of interest for supernova physics. For the hierarchical mass spectrum this effect is small. For 1/M_X interaction terms with M_X about the GUT scale, a detectable U(e3) term is induced for the hierarchical mass spectra also. Numerical estimates are given for all the above mentioned cases and renormalization effects are considered.

hep-ph↗

arXiv2003

Mirror model for sterile neutrinos

Sterile neutrinos are studied as subdominant contribution to solar neutrino physics. The mirror-matter neutrinos are considered as sterile neutrinos. We use the symmetric mirror model with gravitational communication between mirror and visible sectors. This communication term provides mixing between visible and mirror neutrinos with the basic scale mu=v^2/M_Pl=5*10^-6 eV, where v=174 GeV is the vacuum expectation value of the standard electroweak group and M_Pl is the Planckian mass. It is demonstrated that each mass eigenstate of active neutrinos splits into two states separated by small Delta m^2. Unsuppressed oscillations between active and sterile neutrinos nu_a --> nu_s occur only in transitions between each of these close pairs (``windows''). These oscillations are characterized by very small Delta m^2 and can suppress the flux and distort spectrum of pp-neutrinos in detectable way. The other observable effect is anomalous seasonal variation of neutrino flux, which appears in LMA solution. The considered subdominant neutrino oscillations nu_a <--> nu_s can reveal itself as big effects in observations of supernova neutrinos and high energy (HE) neutrinos. In the case of HE neutrinos they can provide a very large diffuse flux of active neutrinos unconstrained by the e-m cascade upper limit.

hep-ph↗

arXiv2003

SuperGZK neutrinos: testing physics beyond the Standard Model

The sources and fluxes of superGZK neutrinos, $E>10^{20}$ eV, are discussed. The most promising sources are reionization bright phase, topological defects, superheavy dark matter and mirror matter. The energy of neutrinos can be above the GUT scale ($\sim 10^{16}$ GeV). The predicted fluxes are observable by future space detectors EUSO and OWL.

hep-ph↗

arXiv1997

Cosmic Necklaces and Ultrahigh Energy Cosmic Rays

Cosmic necklaces are hybrid topological defects consisting of monopoles and strings, with two strings attached to each monopole. We argue that the cosmological evolution of necklaces may significantly differ from that of cosmic strings. The typical velocity of necklaces can be much smaller than the speed of light, and the characteristic scale of the network much smaller than the horizon. We estimate the flux of high-energy protons produced by monopole annihilation in the decaying closed loops. For some reasonable values of the parameters it is comparable to the observed flux of ultrahigh-energy cosmic rays.

astro-ph↗

arXiv1997

High Energy Particles from Monopoles Connected by Strings

Monopole-antimonopole pairs connected by strings and monopole-string networks with $N>2$ strings attached to each monopole can be formed at phase transitions in the early universe. In such hybrid defects, monopoles accelerate under the string tension and can reach ultrarelativistic Lorentz factors, $γ\gg 1$. We study the radiation of gauge quanta by accelerating monopoles. For monopoles with a chromomagnetic charge, we also discuss the high-energy hadron production through emission of virtual gluons and their subsequent fragmentation into hadrons. The relevant parameter for gauge boson radiation is $M/a$, where $M$ is the boson mass and $a$ is the proper acceleration of the monopole. For $M\ll a$, the gauge bosons can be considered as massless and the typical energy of the emitted quanta is $E\simγa$. In the opposite limit, $M\gg a$, the radiation power is exponentially suppressed and gauge quanta are emitted with a typical energy $E\simγM$ in a narrow range $ΔE/E\sim (a/M)^{1/2}$. Cosmological monopole-string networks can produce photons and hadrons of extremely high energies. For a wide range of parameters these energies can be much greater than the Planck scale.

astro-ph↗