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Peter Tinyakov

Publications and source records attributed to Peter Tinyakov.

At least 37 records · Page 2Linked to original sources
arXiv2014

Cosmic Rays from the Ankle to the Cut-Off

Recent advances in measuring and interpreting cosmic rays from the spectral ankle to the highest energies are briefly reviewed. The prime question at the highest energies is about the origin of the flux suppression observed at E ~ 4x10^{19} eV. Is this the long awaited GZK-effect or the exhaustion of sources? The key to answering this question will be provided by the largely unknown mass composition at the highest energies. The high level of isotropy observed even at the highest energies challenges models of a proton dominated composition if extragalactic magnetic fields are on the order of a few nG or less. We shall discuss the experimental and theoretical progress in the field and the prospects for the next decade.

astro-ph.HE↗
arXiv2013

Growth of Black Holes in the interior of Rotating Neutron Stars

Mini-black holes made of dark matter that can potentially form in the interior of neutron stars have been always thought to grow by accreting the matter of the core of the star via a spherical Bondi accretion. However, neutron stars have sometimes significant angulal velocities that can in principle stall the spherical accretion and potentially change the conclusions derived about the time it takes for black holes to destroy a star. We study the effect of the star rotation on the growth of such black holes and the evolution of the black hole spin. Assuming no mechanisms of angular momentum evacuation, we find that even moderate rotation rates can in fact destroy spherical accretion at the early stages of the black hole growth. However, we demonstrate that the viscosity of nuclear matter can alleviate the effect of rotation, making it possible for the black hole to maintain spherical accretion while impeding the black hole from becoming maximally rotating.

astro-ph.SR↗
arXiv2013

Constraints on primordial black holes as dark matter candidates from capture by neutron stars

We investigate constraints on primordial black holes (PBHs) as dark matter candidates that arise from their capture by neutron stars (NSs). If a PBH is captured by a NS, the star is accreted onto the PBH and gets destroyed in a very short time. Thus, mere observations of NSs put limits on the abundance of PBHs. High DM densities and low velocities are required to constrain the fraction of PBHs in DM. Such conditions may be realized in the cores of globular clusters if the latter are of a primordial origin. Assuming that cores of globular clusters possess the DM densities exceeding several hundred GeV/cm$^3$ would imply that PBHs are excluded as comprising all of the dark matter in the mass range $3\times 10^{18} \text{g} \lesssim m_\text{BH}\lesssim 10^{24} \text{g}$. At the DM density of $2\times 10^3$ GeV/cm$^3$ that has been found in simulations in the corresponding models, less than 5% of the DM may consist of PBH for these PBH masses.

astro-ph.CO↗
arXiv2013

Constraints on primordial black holes as dark matter candidates from star formation

By considering adiabatic contraction of the dark matter (DM) during star formation, we estimate the amount of DM trapped in stars at their birth. If the DM consists partly of primordial black holes (PBHs), they will be trapped together with the rest of the DM and will be finally inherited by a star compact remnant --- a white dwarf (WD) or a neutron star (NS), which they will destroy in a short time. Observations of WDs and NSs thus impose constraints on the abundance of PBH. We show that the best constraints come from WDs and NSs in globular clusters which exclude the DM consisting entirely of PBH in the mass range $10^{16}{\rm g} - 3\times 10^{22}{\rm g}$, with the strongest constraint on the fraction $Ω_{\rm PBH} /Ω_{\rm DM}\lesssim 10^{-2}$ being in the range of PBH masses $10^{17}{\rm g} - 10^{18}$ g.

astro-ph.CO↗
arXiv2012

On (Not)-Constraining Heavy Asymmetric Bosonic Dark Matter

Recently, constraints on bosonic asymmetric dark matter have been imposed based on the existence of old neutron stars excluding the dark matter masses in the range from $\sim 2$ keV up to several GeV. The constraints are based on the star destruction scenario where the dark matter particles captured by the star collapse forming a black hole that eventually consumes the host star. In addition, there were claims in the literature that similar constraints can be obtained for dark matter masses heavier than a few TeV. Here we argue that it is not possible to extend to these constraints. We show that in the case of heavy dark matter, instead of forming a single large black hole that consumes the star, the collapsing dark matter particles form a series of small black holes that evaporate fast without leading to the destruction of the star. Thus, no constraints arise for bosonic asymmetric dark matter particles with masses of a few TeV or higher.

astro-ph.HE↗
arXiv2011

Enhancement of dark matter capture by neutron stars in binary systems

We study the capture of dark matter particles by neutron stars in close binary systems. By performing a direct numerical simulation, we find that there is a sizable amplification of the rate of dark matter capture by each of the companions. In case of the binary pulsar PSR J1906+0746 with the orbital period of 4 hours the amplification factor is 3.5. This amplification can be attributed to the energy loss by dark matter particles resulting from their gravitational scattering off moving companions.

astro-ph.CO↗
arXiv2011

Excluding Light Asymmetric Bosonic Dark Matter

We argue that current neutron star observations exclude asymmetric bosonic non-interacting dark matter in the range from 2 keV to 16 GeV, including the 5-15 GeV range favored by DAMA and CoGeNT. If bosonic WIMPs are composite of fermions, the same limits apply provided the compositeness scale is higher than ~10^12 GeV (for WIMP mass ~1 GeV). In case of repulsive self-interactions, we exclude large range of WIMP masses and interaction cross sections which complements the constraints imposed by observations of the Bullet Cluster.

astro-ph.CO↗
arXiv2010

Constraining Asymmetric Dark Matter through observations of compact stars

We put constraints on asymmetric dark matter candidates with spin-dependent interactions based on the simple existence of white dwarfs and neutron stars in globular clusters. For a wide range of the parameters (WIMP mass and WIMP-nucleon cross section), WIMPs can be trapped in progenitors in large numbers and once the original star collapses to a white dwarf or a neutron star, these WIMPs might self-gravitate and eventually collapse forming a mini-black hole that eventually destroys the star. We impose constraints competitive to direct dark matter search experiments, for WIMPs with masses down to the TeV scale.

astro-ph.HE↗
arXiv2010

Can Neutron stars constrain Dark Matter?

We argue that observations of old neutron stars can impose constraints on dark matter candidates even with very small elastic or inelastic cross section, and self-annihilation cross section. We find that old neutron stars close to the galactic center or in globular clusters can maintain a surface temperature that could in principle be detected. Due to their compactness, neutron stars can acrete WIMPs efficiently even if the WIMP-to-nucleon cross section obeys the current limits from direct dark matter searches, and therefore they could constrain a wide range of dark matter candidates.

astro-ph.GA↗
arXiv2009

Note on galaxy catalogues in UHECR flux modelling

We consider the dependence of ultra-high energy cosmic ray (UHECR) flux predictions on the choice of galaxy catalogue. We demonstrate that model predictions by Koers & Tinyakov (2009b), based on the so-called KKKST catalogue, are in good agreement with predictions based on the XSCz catalogue, a recently compiled catalogue that contains spectroscopic redshifts for a large fraction of galaxies. This agreement refutes the claim by Kashti (2009) that the KKKST catalogue is not suited for studies of UHECR anisotropy due to its dependence on photometric redshift estimates. In order to quantify the effect of galaxy catalogues on flux predictions, we develop a measure of anisotropies associated with model flux maps. This measure offers a general criterion to study the effect of model parameters and assumptions on the predicted strength of UHECR anisotropies.

astro-ph.CO↗
arXiv2009

Flux calculations in an inhomogeneous Universe: weighting a flux-limited galaxy sample

Many astrophysical problems arising within the context of ultra-high energy cosmic rays, very-high energy gamma rays or neutrinos, require calculation of the flux produced by sources tracing the distribution of galaxies in the Universe. We discuss a simple weighting scheme, an application of the method introduced by Lynden-Bell in 1971, that allows the calculation of the flux sky map directly from a flux-limited galaxy catalog without cutting a volume-limited subsample. Using this scheme, the galaxy distribution can be modeled up to large scales while representing the distribution in the nearby Universe with maximum accuracy. We consider fluctuations in the flux map arising from the finiteness of the galaxy sample. We show how these fluctuations are reduced by the weighting scheme and discuss how the remaining fluctuations limit the applicability of the method.

astro-ph.CO↗
arXiv2009

Testing large-scale (an)isotropy of ultra-high energy cosmic rays

We present a simple yet powerful method to test models of cosmic-ray (CR) origin using the distribution of CR arrival directions. The method is statistically unambiguous in the sense that it is binless and does not invoke scanning over unknown parameters, and general in the sense that it can be applied to any model that predicts a continuous distribution of CRs over the sky. We show that it provides a powerful discrimination between an isotropic distribution and predictions from the "matter tracer" model, a benchmark model that assumes small CR deflections and a continuous distribution of sources tracing the distribution of matter in the Universe. Our method is competitive or superior in statistical power to existing methods, and is especially sensitive in the case of relatively few high-energy events. Applying the method to the present data we find that neither an isotropic distribution nor the matter tracer model can be excluded. Based on estimates of its statistical power, we expect that the proposed test will lead to meaningful constraints on models of CR origin with the data that will be accumulated within the next few years by the Pierre Auger Observatory and the Telescope Array.

astro-ph↗
arXiv2008

On the relation between the neutrino flux from Centaurus A and the associated diffuse neutrino flux

Based on recent results obtained by the Pierre Auger Observatory (PAO), it has been hypothesized that Centaurus A (Cen A) is a source of ultra-high-energy cosmic rays (UHECRs) and associated neutrinos. We point out that the diffuse neutrino flux may be used to constrain the source model if one assumes that the ratio between the UHECR and neutrino fluxes outputted by Cen A is representative for other sources. Under this assumption we investigate the relation between the neutrino flux from Cen A and the diffuse neutrino flux. Assuming furthermore that Cen A is the source of two UHECR events observed by PAO, we estimate the all-sky diffuse neutrino flux to be ~200-5000 times larger than the neutrino flux from Cen A. As a result, the diffuse neutrino fluxes associated with some of the recently proposed models of UHECR-related neutrino production in Cen A are above existing limits. Regardless of the underlying source model, our results indicate that the detection of neutrinos from Cen A without the accompanying diffuse flux would mean that Cen A is an exceptionally efficient neutrino source.

astro-ph↗
arXiv2007

Bumpy black holes from spontaneous Lorentz violation

We consider black holes in Lorentz violating theories of massive gravity. We argue that in these theories black hole solutions are no longer universal and exhibit a large number of hairs. If they exist, these hairs probe the singularity inside the black hole providing a window into quantum gravity. The existence of these hairs can be tested by future gravitational wave observatories. We generically expect that the effects we discuss will be larger for the more massive black holes. In the simplest models the strength of the hairs is controlled by the same parameter that sets the mass of the graviton (tensor modes). Then the upper limit on this mass coming from the inferred gravitational radiation emitted by binary pulsars implies that hairs are likely to be suppressed for almost the entire mass range of the super-massive black holes in the centers of galaxies.

hep-th↗
arXiv2003

Constraining superheavy dark matter model of UHECR with SUGAR data

Models which associate the origin of the ultra-high energy cosmic rays (UHECR) with decays of relic superheavy particles predict the anisotropy of UHECR flux toward the Galactic center. We use the existing SUGAR data, which covered the Galactic center best so far, to look for such a signal and limit the fraction of UHECR produced by this mechanism. The absence of anisotropy toward the Galactic center in the SUGAR data implies at 95% confidence level that the fraction of SHDM-related cosmic rays should be less than 20% at $E>1\times10^{19}$ eV and less than 50% at $E>4\times10^{19}$ eV.

astro-ph↗