846 research outputs found
The influence of corporate governance on bank risk during a financial crisis
Using agency theory, we explore the relationship between corporate
governance mechanisms and bank risk. We employ panel data analysis
to study the 97 largest European listed banks between 2006 and 2010,
thereby covering the most recent international financial crisis. The
results show that corporate governance mechanisms influence bank
risk. During the financial crisis, different governance mechanisms can
minimise or accentuate the agency conflict between shareholders and
managers. In our model, bank size and G.D.P. per capita also exert a
considerable influence.info:eu-repo/semantics/publishedVersio
Bose-Einstein Condensation in a CO_2-laser Optical Dipole Trap
We report on the achieving of Bose-Einstein condensation of a dilute atomic
gas based on trapping atoms in tightly confining CO_2-laser dipole potentials.
Quantum degeneracy of rubidium atoms is reached by direct evaporative cooling
in both crossed and single beam trapping geometries. At the heart of these
all-optical condensation experiments is the ability to obtain high initial
atomic densities in quasistatic dipole traps by laser cooling techniques.
Finally, we demonstrate the formation of a condensate in a field insensitive
m_F=0 spin projection only. This suppresses fluctuations of the chemical
potential from stray magnetic fields.Comment: 8 pages, 5 figure
Pixel Detectors for Charged Particles
Pixel Detectors, as the current technology of choice for the innermost vertex
detection, have reached a stage at which large detectors have been built for
the LHC experiments and a new era of developments, both for hybrid and for
monolithic or semi-monolithic pixel detectors is in full swing. This is largely
driven by the requirements of the upgrade programme for the superLHC and by
other collider experiments which plan to use monolithic pixel detectors for the
first time. A review on current pixel detector developments for particle
tracking and vertexing is given, comprising hybrid pixel detectors for superLHC
with its own challenges in radiation and rate, as well as on monolithic,
so-called active pixel detectors, including MAPS and DEPFET pixels for RHIC and
superBelle.Comment: 19 pages, 23 drawings in 14 figure
Quantum phase transition for the BEC--BCS crossover in condensed matter physics and CPT violation in elementary particle physics
We discuss the quantum phase transition that separates a vacuum state with
fully-gapped fermion spectrum from a vacuum state with topologically-protected
Fermi points (gap nodes). In the context of condensed-matter physics, such a
quantum phase transition with Fermi point splitting may occur for a system of
ultracold fermionic atoms in the region of the BEC-BCS crossover, provided
Cooper pairing occurs in the non-s-wave channel. For elementary particle
physics, the splitting of Fermi points may lead to CPT violation, neutrino
oscillations, and other phenomena.Comment: 13 pages, 1 figure, v3: published versio
Anomalies in low-energy Gamma-Ray Burst spectra with the Fermi Gamma-Ray Burst Monitor
A Band function has become the standard spectral function used to describe
the prompt emission spectra of gamma-ray bursts (GRBs). However, deviations
from this function have previously been observed in GRBs detected by BATSE and
in individual GRBs from the \textit{Fermi} era. We present a systematic and
rigorous search for spectral deviations from a Band function at low energies in
a sample of the first two years of high fluence, long bursts detected by the
\textit{Fermi} Gamma-Ray Burst Monitor (GBM). The sample contains 45 bursts
with a fluence greater than 2 erg / cm (10 - 1000 keV). An
extrapolated fit method is used to search for low-energy spectral anomalies,
whereby a Band function is fit above a variable low-energy threshold and then
the best fit function is extrapolated to lower energy data. Deviations are
quantified by examining residuals derived from the extrapolated function and
the data and their significance is determined via comprehensive simulations
which account for the instrument response. This method was employed for both
time-integrated burst spectra and time-resolved bins defined by a signal to
noise ratio of 25 and 50 . Significant deviations are evident
in 3 bursts (GRB\,081215A, GRB\,090424 and GRB\,090902B) in the time-integrated
sample ( 7%) and 5 bursts (GRB\,090323, GRB\,090424, GRB\,090820,
GRB\,090902B and GRB\,090926A) in the time-resolved sample ( 11%).} The
advantage of the systematic, blind search analysis is that it can demonstrate
the requirement for an additional spectral component without any prior
knowledge of the nature of that extra component. Deviations are found in a
large fraction of high fluence GRBs; fainter GRBs may not have sufficient
statistics for deviations to be found using this method
Synchrotron Cooling in Energetic Gamma-Ray Bursts Observed by the Fermi Gamma-Ray Burst Monitor
We study the time-resolved spectra of eight GRBs observed by Fermi GBM in its
first five years of mission, with 1 keV - 1 MeV fluence
erg cm and signal-to-noise level above 900 keV. We
aim to constrain in detail the spectral properties of GRB prompt emission on a
time-resolved basis and to discuss the theoretical implications of the fitting
results in the context of various prompt emission models. We perform
time-resolved spectral analysis using a variable temporal binning technique
according to optimal S/N criteria, resulting in a total of 299 time-resolved
spectra. We fit the Band function to all spectra and obtain the distributions
for the low-energy power-law index , the high-energy power-law index
, the peak energy in the observed spectrum , and
the difference between the low- and high-energy power-law indices . Using the distributions of and , the
electron population index is found to be consistent with the "moderately
fast" scenario which fast- and slow-cooling scenarios cannot be distinguished.
We also apply a physically motivated synchrotron model, which is a triple
power-law with constrained power-law indices and a blackbody component, to test
for consistency with a synchrotron origin for the prompt emission and obtain
the distributions for the two break energies and ,
the middle segment power-law index , and the Planck function temperature
. A synchrotron model is found consistent with the majority of
time-resolved spectra for these eight energetic Fermi GBM bursts with good
high-energy photon statistics, as long as both the cooling and injection break
are included and the leftmost spectral slope is lifted either by inclusion of a
thermal component or when an evolving magnetic field is accounted for.Comment: 20 pages, 7 figures, 8 tables, accepted for publication in A&
Quasiparticle excitations in relativistic quantum field theory
We analyze the particle-like excitations arising in relativistic field
theories in states different than the vacuum. The basic properties
characterizing the quasiparticle propagation are studied using two different
complementary methods. First we introduce a frequency-based approach, wherein
the quasiparticle properties are deduced from the spectral analysis of the
two-point propagators. Second, we put forward a real-time approach, wherein the
quantum state corresponding to the quasiparticle excitation is explicitly
constructed, and the time-evolution is followed. Both methods lead to the same
result: the energy and decay rate of the quasiparticles are determined by the
real and imaginary parts of the retarded self-energy respectively. Both
approaches are compared, on the one hand, with the standard field-theoretic
analysis of particles in the vacuum and, on the other hand, with the
mean-field-based techniques in general backgrounds.Comment: 53 pages, 4 figures. Version accepted for publication in Ann. Phy
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