16,556 research outputs found
The Epeak-Eiso plane of long Gamma Ray Bursts and selection effects
We study the distribution of long Gamma Ray Bursts in the Ep-Eiso and in the
Ep,obs-Fluence planes through an updated sample of 76 bursts, with measured
redshift and spectral parameters, detected up to September 2007. We confirm the
existence of a strong rest frame correlation Ep ~ Eiso^0.54+-0.01. Contrary to
previous studies, no sign of evolution with redshift of the Ep-Eiso correlation
(either its slope and normalisation) is found. The 76 bursts define a strong
Ep,obs-Fluence correlation in the observer frame (Ep,obs ~ F^0.32+-0.05) with
redshifts evenly distributed along this correlation. We study possible
instrumental selection effects in the observer frame Ep,obs-Fluence plane. In
particular, we concentrate on the minimum peak flux necessary to trigger a
given GRB detector (trigger threshold) and the minimum fluence a burst must
have to determine the value of Ep,obs (spectral analysis threshold). We find
that the latter dominates in the Ep,obs-Fluence plane over the former. Our
analysis shows, however, that these instrumental selection effects do not
dominate for bursts detected before the launch of the Swift satellite, while
the spectral analysis threshold is the dominant truncation effect of the Swift
GRB sample (27 out of 76 events). This suggests that the Ep,obs-Fluence
correlation defined by the pre--Swift sample could be affected by other, still
not understood, selection effects. Besides we caution about the conclusions on
the existence of the Ep,obs-Fluence correlation based on our Swift sample
alone.Comment: To appear in MNRA
"Quasi-particle breakdown" in the quasi-one-dimensional Ising ferromagnet CoNbO
We present experimental and theoretical evidence that an interesting quantum
many-body effect -- quasi-particle breakdown -- occurs in the
quasi-one-dimensional spin-1/2 Ising-like ferromagnet CoNbO in its
paramagnetic phase at high transverse field as a result of explicit breaking of
spin inversion symmetry. We propose a quantum spin Hamiltonian capturing the
essential one-dimensional physics of CoNbO and determine the exchange
parameters of this model by fitting the calculated single particle dispersion
to the one observed experimentally in applied transverse magnetic fields. We
present high-resolution inelastic neutron scattering measurements of the single
particle dispersion which observe "anomalous broadening" effects over a narrow
energy range at intermediate energies. We propose that this effect originates
from the decay of the one particle mode into two-particle states. This decay
arises from (i) a finite overlap between the one-particle dispersion and the
two-particle continuum in a narrow energy-momentum range and (ii) a small
misalignment of the applied field away from the direction perpendicular to the
Ising axis in the experiments, which allows for non-zero matrix elements for
decay by breaking the spin inversion symmetry of the
Hamiltonian.Comment: v1: 15 pages, 10 figures. v2: 16 pages, 10 figures, minor changes, as
accepted to PR
Evaluation of flexible barrier and sabo dam to control effects of debris flow in Santo Domingo Ravine
Coast of Peru is characterized for the presence of ephemeral creeks which drain water only on wet season. The extremely dry soil and pebble combined with precipitation produce debris flow in a seasonal geodynamic. This is the case of Santo Domingo ravine which is located at eastern Lima, and drains their water to Rimac River. In this article the vulnerability of villages near to Santo Domingo ravine by debris flow and use of flexible barrier and sabo dams are analyzed. In a first stage, the liquid hydrograph to a 100 years return period was built and a solid hydrograph, a relationship between volume concentration and time, was essayed. Then, both the liquid and the solid hydrograph are calibrated in a debris flow numerical model and the vulnerability map is built. Finally, this model is coupled to the Rimac River to analyze the possible damming effect. Calibration of numerical model was done in base to previous estimated volumes by Japanese International Cooperation Agency (JICA). These first results permit to define high vulnerability zones which will be a reference to evaluate efficiency of control measures. In a second stage, mitigation effects of flexible barriers application is simulated in base to Debris Flow Barrier from Geobrugg®. Also, application of sabo dams was evaluated to by using “Kanako” debris flow simulator from Laboratory of Erosion Control, Division of Forest Science, Graduate School of Agriculture, Kyoto University, & SABO Technical Center. Results permit to evaluate efficiency and select the more economical option
Energy weighted sum rules for mesons in hot and dense matter
We study energy weighted sum rules of the pion and kaon propagator in nuclear
matter at finite temperature. The sum rules are obtained from matching the
Dyson form of the meson propagator with its spectral Lehmann representation at
low and high energies. We calculate the sum rules for specific models of the
kaon and pion self-energy. The in-medium spectral densities of the K and anti-K
mesons are obtained from a chiral unitary approach in coupled channels which
incorporates the S- and P-waves of the kaon-nucleon interaction. The pion
self-energy is determined from the P-wave coupling to particle-hole and
Delta-hole excitations, modified by short range correlations. The sum rules for
the lower energy weights are fulfilled satisfactorily and reflect the
contributions from the different quasi-particle and collective modes of the
meson spectral function. We discuss the sensitivity of the sum rules to the
distribution of spectral strength and their usefulness as quality tests of
model calculations.Comment: 19 pages, 6 figures; one figure added, enhanced discussion, version
to appear in PR
Spectral analysis of Swift long GRBs with known redshift
We study the spectral and energetics properties of 47 long-duration gamma-ray
bursts (GRBs) with known redshift, all of them detected by the Swift satellite.
Due to the narrow energy range (15-150 keV) of the Swift-BAT detector, the
spectral fitting is reliable only for fitting models with 2 or 3 parameters. As
high uncertainty and correlation among the errors is expected, a careful
analysis of the errors is necessary. We fit both the power law (PL, 2
parameters) and cut--off power law (CPL, 3 parameters) models to the
time-integrated spectra of the 47 bursts, and present the corresponding
parameters, their uncertainties, and the correlations among the uncertainties.
The CPL model is reliable only for 29 bursts for which we estimate the nuf_nu
peak energy Epk. For these GRBs, we calculate the energy fluence and the rest-
frame isotropic-equivalent radiated energy, Eiso, as well as the propagated
uncertainties and correlations among them. We explore the distribution of our
homogeneous sample of GRBs on the rest-frame diagram E'pk vs Eiso. We confirm a
significant correlation between these two quantities (the "Amati" relation) and
we verify that, within the uncertainty limits, no outliers are present. We also
fit the spectra to a Band model with the high energy power law index frozen to
-2.3, obtaining a rather good agreement with the "Amati" relation of non-Swift
GRBs.Comment: 16 pages. To appear in MNRAS. Minor changes were introduced in this
last versio
Heavy flavor in relativistic heavy-ion collisions
We study charm production in ultra-relativistic heavy-ion collisions by using
the Parton-Hadron-String Dynamics (PHSD) transport approach. The initial charm
quarks are produced by the PYTHIA event generator tuned to fit the transverse
momentum spectrum and rapidity distribution of charm quarks from Fixed-Order
Next-to-Leading Logarithm (FONLL) calculations. The produced charm quarks
scatter in the quark-gluon plasma (QGP) with the off-shell partons whose masses
and widths are given by the Dynamical Quasi-Particle Model (DQPM), which
reproduces the lattice QCD equation-of-state in thermal equilibrium. The
relevant cross sections are calculated in a consistent way by employing the
effective propagators and couplings from the DQPM. Close to the critical energy
density of the phase transition, the charm quarks are hadronized into
mesons through coalescence and/or fragmentation. The hadronized mesons then
interact with the various hadrons in the hadronic phase with cross sections
calculated in an effective lagrangian approach with heavy-quark spin symmetry.
The nuclear modification factor and the elliptic flow of
mesons from PHSD are compared with the experimental data from the STAR
Collaboration for Au+Au collisions at =200 GeV and to the ALICE
data for Pb+Pb collisions at =2.76 TeV. We find that in the
PHSD the energy loss of mesons at high can be dominantly attributed
to partonic scattering while the actual shape of versus reflects
the heavy-quark hadronization scenario, i.e. coalescence versus fragmentation.
Also the hadronic rescattering is important for the at low and
enhances the -meson elliptic flow .Comment: 8 pages, 3 figures, to be published in the Proceedings of the 15th
International Conference on Strangeness in Quark Matter (SQM2015), 6-11 July
2015, JINR, Dubna, Russi
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