48 research outputs found
Antiproton constraints on dark matter annihilations from internal electroweak bremsstrahlung
If the dark matter particle is a Majorana fermion, annihilations into two
fermions and one gauge boson could have, for some choices of the parameters of
the model, a non-negligible cross-section. Using a toy model of leptophilic
dark matter, we calculate the constraints on the annihilation cross-section
into two electrons and one weak gauge boson from the PAMELA measurements of the
cosmic antiproton-to-proton flux ratio. Furthermore, we calculate the maximal
astrophysical boost factor allowed in the Milky Way under the assumption that
the leptophilic dark matter particle is the dominant component of dark matter
in our Universe. These constraints constitute very conservative estimates on
the boost factor for more realistic models where the dark matter particle also
couples to quarks and weak gauge bosons, such as the lightest neutralino which
we also analyze for some concrete benchmark points. The limits on the
astrophysical boost factors presented here could be used to evaluate the
prospects to detect a gamma-ray signal from dark matter annihilations at
currently operating IACTs as well as in the projected CTA.Comment: 32 pages; 13 figure
Astrophysical Uncertainties in the Cosmic Ray Electron and Positron Spectrum From Annihilating Dark Matter
In recent years, a number of experiments have been conducted with the goal of
studying cosmic rays at GeV to TeV energies. This is a particularly interesting
regime from the perspective of indirect dark matter detection. To draw reliable
conclusions regarding dark matter from cosmic ray measurements, however, it is
important to first understand the propagation of cosmic rays through the
magnetic and radiation fields of the Milky Way. In this paper, we constrain the
characteristics of the cosmic ray propagation model through comparison with
observational inputs, including recent data from the CREAM experiment, and use
these constraints to estimate the corresponding uncertainties in the spectrum
of cosmic ray electrons and positrons from dark matter particles annihilating
in the halo of the Milky Way.Comment: 21 pages, 9 figure
Neutrino signatures of the supernova - gamma ray burst relationship
We calculate the TeV-PeV neutrino fluxes of gamma-ray bursts associated with
supernovae, based on the observed association between GRB 030329 and supernova
SN 2003dh. The neutrino spectral flux distributions can test for possible
delays between the supernova and the gamma-ray burst events down to much
shorter timescales than what can be resolved with photons. As an illustrative
example, we calculate the probability of neutrino induced muon and electron
cascade events in a km scale under-ice detector at the South Pole, from the GRB
030329. Our calculations demonstrate that km scale neutrino telescopes are
expected to detect signals that will allow to constrain supernova-GRB models.Comment: 7 pages, 2 figures. Accepted for publication in Phys. Rev.
Resolving Fermi, PAMELA and ATIC anomalies in split supersymmetry without R-parity
A long-lived decaying dark matter as a resolution to Fermi, PAMELA and ATIC
anomalies is investigated in the framework of split supersymmetry (SUSY)
without R-parity, where the neutralino is regarded as the dark matter and the
extreme fine-tuned couplings for the long-lived neutralino are naturally evaded
in the usual approach.Comment: 14 pages, 6 figures. Erroneous results concerning the cascade
processes removed. Main results unchange
Extensive Air Showers from Ultra High Energy Gluinos
We study the proposal that the cosmic ray primaries above the
Greisen-Zatsepin-Kuzmin (GZK) cutoff are gluino-containing hadrons (-hadrons). We describe the interaction of -hadrons with nucleons in
the framework of the Gribov-Regge approach using a modified version of the
hadronic interaction model QGSJET for the generations of Extensive Air Showers
(EAS). There are two mass windows marginally allowed for gluinos: m_{\tilde
g}\lsim 3 GeV and 25\lsim m_{\tilde g}\lsim 35 GeV. Gluino-containing
hadrons corresponding to the second window produce EAS very different from the
observed ones. Light -hadrons corresponding to the first gluino
window produce EAS similar to those initiated by protons, and only future
detectors can marginally distinguish them. We propose a beam-dump accelerator
experiment to search for -hadrons in this mass window. We emphasize
the importance of this experiment: it can discover (or exclude) the light
gluino and its role as a cosmic ray primary at ultra high energies.Comment: 27 pages latex, 13 eps figure
Relativistic Laser-Matter Interaction and Relativistic Laboratory Astrophysics
The paper is devoted to the prospects of using the laser radiation
interaction with plasmas in the laboratory relativistic astrophysics context.
We discuss the dimensionless parameters characterizing the processes in the
laser and astrophysical plasmas and emphasize a similarity between the laser
and astrophysical plasmas in the ultrarelativistic energy limit. In particular,
we address basic mechanisms of the charged particle acceleration, the
collisionless shock wave and magnetic reconnection and vortex dynamics
properties relevant to the problem of ultrarelativistic particle acceleration.Comment: 58 pages, 19 figure
Particle acceleration mechanisms
We review the possible mechanisms for production of non-thermal electrons
which are responsible for non-thermal radiation in clusters of galaxies. Our
primary focus is on non-thermal Bremsstrahlung and inverse Compton scattering,
that produce hard X-ray emission. We briefly review acceleration mechanisms and
point out that in most astrophysical situations, and in particular for the
intracluster medium, shocks, turbulence and plasma waves play a crucial role.
We consider two scenarios for production of non-thermal radiation. The first is
hard X-ray emission due to non-thermal Bremsstrahlung by nonrelativistic
particles. Non-thermal tails are produced by accelerating electrons from the
background plasma with an initial Maxwellian distribution. However, these tails
are accompanied by significant heating and they are present for a short time of
<10^6 yr, which is also the time that the tail will be thermalised. Such
non-thermal tails, even if possible, can only explain the hard X-ray but not
the radio emission which needs GeV or higher energy electrons. For these and
for production of hard X-rays by the inverse Compton model, we need the second
scenario where there is injection and subsequent acceleration of relativistic
electrons. It is shown that a steady state situation, for example arising from
secondary electrons produced from cosmic ray proton scattering by background
protons, will most likely lead to flatter than required electron spectra or it
requires a short escape time of the electrons from the cluster. An episodic
injection of relativistic electrons, presumably from galaxies or AGN, and/or
episodic generation of turbulence and shocks by mergers can result in an
electron spectrum consistent with observations but for only a short period of
less than one billion years.Comment: 22 pages, 5 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 11; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Pulsar Wind Nebulae with Bow Shocks: Non-thermal Radiation and Cosmic Ray Leptons
Pulsars with high spin-down power produce relativistic winds radiating a non-negligible fraction of this power over the whole electromagnetic range from radio to gamma-rays in the pulsar wind nebulae (PWNe). The rest of the power is dissipated in the interactions of the PWNe with the ambient interstellar medium (ISM). Some of the PWNe are moving relative to the ambient ISM with supersonic speeds producing bow shocks. In this case, the ultrarelativistic particles accelerated at the termination surface of the pulsar wind may undergo reacceleration in the converging flow system formed by the plasma outflowing from the wind termination shock and the plasma inflowing from the bow shock. The presence of magnetic perturbations in the flow, produced by instabilities induced by the accelerated particles themselves, is essential for the process to work. A generic outcome of this type of reacceleration is the creation of particle distributions with very hard spectra, such as are indeed required to explain the observed spectra of synchrotron radiation with photon indices Γ≲ 1.5. The presence of this hard spectral component is specific to PWNe with bow shocks (BSPWNe). The accelerated particles, mainly electrons and positrons, may end up containing a substantial fraction of the shock ram pressure. In addition, for typical ISM and pulsar parameters, the e+ released by these systems in the Galaxy are numerous enough to contribute a substantial fraction of the positrons detected as cosmic ray (CR) particles above few tens of GeV and up to several hundred GeV. The escape of ultrarelativistic particles from a BSPWN—and hence, its appearance in the far-UV and X-ray bands—is determined by the relative directions of the interstellar magnetic field, the velocity of the astrosphere and the pulsar rotation axis. In this respect we review the observed appearance and multiwavelength spectra of three different types of BSPWNe: PSR J0437-4715, the Guitar and Lighthouse nebulae, and Vela-like objects. We argue that high resolution imaging of such objects provides unique information both on pulsar winds and on the ISM. We discuss the interpretation of imaging observations in the context of the model outlined above and estimate the BSPWN contribution to the positron flux observed at the Earth