2,656 research outputs found
Non-Standard Time Reversal for Particle Multiplets and the Spin-Flavor Structure of Hadrons
We show that a system of quarks interacting with chiral fields provides a
physical representation of a ``non-standard'' time reversal for particle
multiplets proposed by Weinberg. As an application, we argue that, if the
internal structure of hadrons is described by a chiral lagrangian, the
so-called time-reversal-odd quark distribution functions might not be forbidden
by time-reversal invariance.Comment: 2 pages, proceedings of "The Spin Structure of the Proton", ECT -
Trento, July 2001. Eds. S Bass, A De Roeck and A Deshpand
Synchrotron oscillation damping due to beam-beam collisions
In DA{\Phi}NE, the Frascati e+/e- collider, the crab waist collision scheme
has been successfully implemented in 2008 and 2009. During the collision
operations for Siddharta experiment, an unusual synchrotron damping effect has
been observed. Indeed, with the longitudinal feedback switched off, the
positron beam becomes unstable with beam currents in the order of 200-300 mA.
The longitudinal instability is damped by bringing the positron beam in
collision with a high current electron beam (~2A). Besides, we have observed a
shift of \approx 600Hz in the residual synchrotron sidebands. Precise
measurements have been performed by using both a commercial spectrum analyzer
and the diagnostics capabilities of the DA{\Phi}NE longitudinal bunch-by-bunch
feedback. This damping effect has been observed in DA{\Phi}NE for the first
time during collisions with the crab waist scheme. Our explanation is that beam
collisions with a large crossing angle produce a longitudinal tune shift and a
longitudinal tune spread, providing Landau damping of synchrotron oscillations.Comment: 3 pages, 5 figures, talk presented to IPAC'10 - Kyoto - May 24-28
201
Dynamics of Phase Transitions in Asymmetric Nuclear Matter
We present several possibilities offered by the reaction dynamics of
dissipative heavy ion collisions to study in detail the symmetry term of the
nuclear equation of state, . In particular we discuss isospin effects on
the nuclear liquid-gas phase transition, {\it Isospin Distillation}, and on
collective flows. We stress the importance of a microscopic relativistic
structure of the effective interaction in the isovector channel. The
possibility of an {\it early} transition to deconfined matter in high isospin
density regions is also suggested. We finally select {\it Eleven} observables,
in different beam energy regions, that appear rather sensitive to the isovector
part of the nuclear , in particular in more exclusive experiments.Comment: 8 pages, 7 figures, ISPUN02 Conference, Halong-Vietnam, Nov.20-25
2002, to appear in Nucl.Phys.A. Elsevier Proceedings Styl
Prospects for intermediate mass black hole binary searches with advanced gravitational-wave detectors
We estimated the sensitivity of the upcoming advanced, ground-based
gravitational-wave observatories (the upgraded LIGO and Virgo and the KAGRA
interferometers) to coalescing intermediate mass black hole binaries (IMBHB).
We added waveforms modeling the gravitational radiation emitted by IMBHBs to
detectors' simulated data and searched for the injected signals with the
coherent WaveBurst algorithm. The tested binary's parameter space covers
non-spinning IMBHBs with source-frame total masses between 50 and 1050
and mass ratios between and 1. We found that
advanced detectors could be sensitive to these systems up to a range of a few
Gpc. A theoretical model was adopted to estimate the expected observation
rates, yielding up to a few tens of events per year. Thus, our results indicate
that advanced detectors will have a reasonable chance to collect the first
direct evidence for intermediate mass black holes and open a new, intriguing
channel for probing the Universe over cosmological scales.Comment: 9 pages, 4 figures, corrected the name of one author (previously
misspelled
Testing Deconfinement at High Isospin Density
We study the transition from hadronic matter to a mixed phase of quarks and
hadrons at high baryon and isospin densities reached in heavy ion collisions.
We focus our attention on the role played by the nucleon symmetry energy at
high density.In this respect the inclusion of a scalar isovector meson, the
\delta-coupling, in the Hadron Lagrangian appears rather important. We study in
detail the formation of a drop of quark matter in the mixed phase, and we
discuss the effects on the quark drop nucleation probability of the finite size
and finite time duration of the high density region. We find that, if the
parameters of quark models are fixed so that the existence of quark stars is
allowed, then the density at which a mixed phase starts forming drops
dramatically in the range Z/A \sim 0.3--0.4. This opens the possibility to
verify the Witten-Bodmer hypothesis on absolute stability of quark matter using
ground-based experiments in which neutron-rich nuclei are employed. These
experiments can also provide rather stringent constraints on the Equation of
State (EoS) to be used for describing the pre-Supernova gravitational collapse.
Consistent simulations of neutron rich heavy ion collisions are performed in
order to show that even at relatively low energies, in the few AGeV range, the
system can enter such unstable mixed phase. Some precursor observables are
suggested, in particular a ``neutron trapping'' effect.Comment: 32 pages, 14 figures, elsart late
Quiescent times in Gamma-Ray-Bursts: hints of a dormant inner engine
We perform a statistical analysis of the temporal structure of long
Gamma-Ray-Bursts (GRBs). First we consider a sample of bursts in which a long
quiescent time is present. Comparing the pre-quiescence with the
post-quiescence emission we show that they display similar temporal structures,
hardness ratios and emitted powers, but, on the average, the post-quiescence
emission is roughly twice as long as the pre-quiescence emission. We then
consider a sample of long and bright GRBs. We show that the duration of each
emission period is compatible with the duration of an active period computed in
various inner engine models. At the contrary, if the inner engine is assumed to
be always active, i.e. also during the quiescent times, in several cases the
total duration of the burst largely exceeds the theoretical durations. Our
analysis therefore does not support the interpretation of long quiescent times
in terms of stochastic modulation of a continuous wind. Instead the quiescent
times can be interpreted as dormancy periods of the inner engine. Before and
after a dormancy period the inner engine produces similar emissions.Comment: 17 pages, 7 figures. New version after referee's comments. Two
figures adde
Enhancing the significance of gravitational wave bursts through signal classification
The quest to observe gravitational waves challenges our ability to
discriminate signals from detector noise. This issue is especially relevant for
transient gravitational waves searches with a robust eyes wide open approach,
the so called all- sky burst searches. Here we show how signal classification
methods inspired by broad astrophysical characteristics can be implemented in
all-sky burst searches preserving their generality. In our case study, we apply
a multivariate analyses based on artificial neural networks to classify waves
emitted in compact binary coalescences. We enhance by orders of magnitude the
significance of signals belonging to this broad astrophysical class against the
noise background. Alternatively, at a given level of mis-classification of
noise events, we can detect about 1/4 more of the total signal population. We
also show that a more general strategy of signal classification can actually be
performed, by testing the ability of artificial neural networks in
discriminating different signal classes. The possible impact on future
observations by the LIGO-Virgo network of detectors is discussed by analysing
recoloured noise from previous LIGO-Virgo data with coherent WaveBurst, one of
the flagship pipelines dedicated to all-sky searches for transient
gravitational waves
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