436 research outputs found
Examples of Semiclassical Instanton-Like Scattering: Massless and SU(2) Gauge Theories
Two-parameter sets of solutions to the classical field equations in the
massless model and SU(2) gauge theory are found, each solution
presumably describing a multi-particle instanton-like transition at high
energy. In the limit of small number of initial particles, the probability of
the transition is suppressed by , where is the instanton
action.Comment: 18pp., LaTeX, to be published in Nucl. Phys.
Ultra-High Energy Cosmic Rays and Diffuse Photon Spectrum
It is argued that if extragalactic magnetic fields are smaller than
2x10^{-12} G the flux of ultra-high energy photons of (a few)x10^{-1} eV
cm^{-2}s^{-1}sr^{-1} predicted in the top-down models of UHE CR implies similar
flux of the diffuse photons in the energy range 10^{15}-10^{17} eV, which is
close to the existing experimental limit.Comment: Talk given at XI Rencontres de Blois. 3 pages, no figure
On the offset of the DM cusp and the interpretation of the 130 GeV line as a DM signal
We show that the cusp in the dark matter (DM) distribution required to
explain the recently found excess in the gamma-ray spectrum at energies ~130
GeV in terms of the DM annihilations cannot survive the tidal forces if it is
offset by ~1.5^\circ from the Galactic centre as suggested by observations.Comment: 3 pages, replaced with journal versio
Correlations and Charge Composition of UHECR without Knowledge of Galactic Magnetic Field
We develop a formalism which allows to study correlations of charged UHECR
with potential sources without using any Galactic Magnetic Field (GMF) model.
The method is free of subjective chose of parameters on which the significance
of correlations depends strongly. We show that correlations of the AGASA
dataset with BL Lacs (found previously after reconstruction of particle
trajectories in a specific GMF) are present intrinsically and can be detected
without reference to a particular model of magnetic field.Comment: To be published in the Proceedings of the 28th International Cosmic
Ray Conferenc
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.Comment: 9 page
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 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
Sources of sub-GZK cosmic rays
We analyze the existing evidence that BL Lacertae objects (BL Lacs) are
sources of the highest-energy cosmic rays. We argue that three independent
signatures observed in the real data -- (1) improvement of correlations with
corrections of trajectories for the Galactic magnetic field; (2) connection
between gamma-ray and UHECR emissions; (3) non-uniform distribution of
correlating rays over the sky -- are consistent with the hypothesis that a
substantial fraction of cosmic rays in the energy range 40-60 EeV are protons
accelerated in BL Lacs.Comment: Talk at the International Workshop on Extremely High Energy Cosmic
Rays, November 5-6, 2002, RIKEN, Japa
Extra dimensions as an alternative to Higgs mechanism?
We show that a pure gauge theory in higher dimensions may lead to an
effective lower-dimensional theory with massive vector field, broken gauge
symmetry and no fundamental Higgs boson. The mechanism we propose employs the
localization of a vector field on a lower-dimensional defect. No non-zero
expectation values of the vector field components along extra dimensions are
required. New possibilities for the solution to the gauge hierarchy problem are
discussed.Comment: Latex, 7 pages, 1 fig. Few references added. Final version to appear
in Phys.Lett.
Cuts and penalties: comment on "The clustering of ultra-high energy cosmic rays and their sources"
In a series of papers we have found statistically significant correlations
between arrival directions of ultra-high energy cosmic rays and BL Lacertae
objects. Recently, our calculations were partly repeated by Evans, Ferrer and
Sarkar with different conclusions. We demonstrate that the criticism of Evans,
Ferrer and Sarkar is incorrect. We also present the details of our method.Comment: Replaced with version accepted for publication in Phys. Rev.
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.Comment: Invited review prepared for Comptes Rendus Physique (2014), in pres
- …