74,244 research outputs found
Primordial Black Holes: Observational Characteristics of The Final Evaporation
Many early universe theories predict the creation of Primordial Black Holes
(PBHs). PBHs could have masses ranging from the Planck mass to 10^5 solar
masses or higher depending on the size of the universe at formation. A Black
Hole (BH) has a Hawking temperature which is inversely proportional to its
mass. Hence a sufficiently small BH will quasi-thermally radiate particles at
an ever-increasing rate as emission lowers its mass and raises its temperature.
The final moments of this evaporation phase should be explosive and its
description is dependent on the particle physics model. In this work we
investigate the final few seconds of BH evaporation, using the Standard Model
and incorporating the most recent Large Hadron Collider (LHC) results, and
provide a new parameterization for the instantaneous emission spectrum. We
calculate for the first time energy-dependent PBH burst light curves in the
GeV/TeV energy range. Moreover, we explore PBH burst search methods and
potential observational PBH burst signatures. We have found a unique signature
in the PBH burst light curves that may be detectable by GeV/TeV gamma-ray
observatories such as the High Altitude Water Cerenkov (HAWC) observatory. The
implications of beyond the Standard Model theories on the PBH burst
observational characteristics are also discussed, including potential
sensitivity of the instantaneous photon detection rate to a squark threshold in
the 5 -10 TeV range.Comment: Accepted to Astroparticle Physics Journal (71 Pages, 22 Figures
Robust graphical modeling of gene networks using classical and alternative T-distributions
Graphical Gaussian models have proven to be useful tools for exploring
network structures based on multivariate data. Applications to studies of gene
expression have generated substantial interest in these models, and resulting
recent progress includes the development of fitting methodology involving
penalization of the likelihood function. In this paper we advocate the use of
multivariate -distributions for more robust inference of graphs. In
particular, we demonstrate that penalized likelihood inference combined with an
application of the EM algorithm provides a computationally efficient approach
to model selection in the -distribution case. We consider two versions of
multivariate -distributions, one of which requires the use of approximation
techniques. For this distribution, we describe a Markov chain Monte Carlo EM
algorithm based on a Gibbs sampler as well as a simple variational
approximation that makes the resulting method feasible in large problems.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS410 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
High-energy astroparticle physics
In these three lectures I discuss the present status of high-energy
astroparticle physics including Ultra-High-Energy Cosmic Rays (UHECR),
high-energy gamma rays, and neutrinos. The first lecture is devoted to
ultra-high-energy cosmic rays. After a brief introduction to UHECR I discuss
the acceleration of charged particles to highest energies in the astrophysical
objects, their propagation in the intergalactic space, recent observational
results by the Auger and HiRes experiments, anisotropies of UHECR arrival
directions, and secondary gamma rays produced by UHECR. In the second lecture I
review recent results on TeV gamma rays. After a short introduction to
detection techniques, I discuss recent exciting results of the H.E.S.S., MAGIC,
and Milagro experiments on the point-like and diffuse sources of TeV gamma
rays. A special section is devoted to the detection of extragalactic magnetic
fields with TeV gamma-ray measurements. Finally, in the third lecture I discuss
Ultra-High-Energy (UHE) neutrinos. I review three different UHE neutrino
detection techniques and show the present status of searches for diffuse
neutrino flux and point sources of neutrinos.Comment: 29 pages, Lectures given at the 5th CERN-Latin-American School of
High-Energy Physics, Recinto Quirama, Colombia, 15 - 28 Mar 200
Massive Stars as Major Factories of Galactic Cosmic Rays
The identification of major contributors to the locally observed fluxes of
Cosmic Rays (CRs) is a prime objective towards the resolution of the
long-standing enigma of CRs. We report on a compelling similarity of the energy
and radial distributions of multi-TeV CRs extracted from observations of very
high energy (VHE) -rays towards the Galactic Center (GC) and two
prominent clusters of young massive stars, Cyg~OB2 and Westerlund~1. This
resemblance we interpret as a hint that CRs responsible for the diffuse VHE
-ray emission from the GC are accelerated by the ultracompact stellar
clusters located in the heart of GC. The derived decrement of the CR
density with the distance from a star cluster is a distinct signature of
continuous, over a few million years, CR injection into the interstellar
medium. The lack of brightening of the -ray images toward the stellar
clusters excludes the leptonic origin of -radiation. The hard, type power-law energy spectra of parent protons continues up to
1 PeV. The efficiency of conversion of kinetic energy of stellar winds
to CRs can be as high as 10 percent implying that the young massive stars may
operate as proton PeVatrons with a dominant contribution to the flux of highest
energy galactic CRs.Comment: minor revisions have been applied to address the referees' comments,
conclusion unchange
Statistical distributions in the folding of elastic structures
The behaviour of elastic structures undergoing large deformations is the
result of the competition between confining conditions, self-avoidance and
elasticity. This combination of multiple phenomena creates a geometrical
frustration that leads to complex fold patterns. By studying the case of a rod
confined isotropically into a disk, we show that the emergence of the
complexity is associated with a well defined underlying statistical measure
that determines the energy distribution of sub-elements,``branches'', of the
rod. This result suggests that branches act as the ``microscopic'' degrees of
freedom laying the foundations for a statistical mechanical theory of this
athermal and amorphous system
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