16,648 research outputs found
Constraining the viscous freeze-out distribution function with data obtained at the BNL Relativistic Heavy Ion Collider (RHIC)
We investigate the form of the viscous correction to the equilibrium
distribution function in the context of a Cooper-Frye freeze out prescription
for viscous hydrodynamic simulations of relativistic heavy ion collisions. The
standard quadratic ansatz used by all groups for the case of shear viscosity is
found to be disfavored by experimental data for v4/(v2)^2 at the Relativistic
Heavy Ion Collider, and is unlikely to be correct for the hadron resonance gas
present at freeze out. Instead, data for v2(pt) along with v4/(v2)^2 favor a
momentum dependence between linear and quadratic.Comment: 5 pages, 4 figures; v2: version accepted for publication (minor
changes
Quantifying Nonequilibrium Behavior with Varying Cooling Rates
We investigate nonequilibrium behavior in (1+1)-dimensional stochastic field
theories in the context of Ginzburg-Landau models at varying cooling rates. We
argue that a reliable measure of the departure from thermal equilibrium can be
obtained from the absolute value of the rate of change of the
momentum-integrated structure function, . We show that the
peak of scales with the cooling, or quench, time-scale,
, in agreement with the prediction by Laguna and Zurek for the scaling
of freeze-out time in both over and under-damped regimes. Furthermore, we show
that the amplitude of the peak scales as independent of the
viscosity.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Sensornet checkpointing: enabling repeatability in testbeds and realism in simulations
When developing sensor network applications, the shift from
simulation to testbed causes application failures, resulting in additional
time-consuming iterations between simulation and testbed. We propose
transferring sensor network checkpoints between simulation and testbed
to reduce the gap between simulation and testbed. Sensornet checkpointing
combines the best of both simulation and testbeds: the nonintrusiveness
and repeatability of simulation, and the realism of testbeds
Cluster update and recognition
We present a fast and robust cluster update algorithm that is especially
efficient in implementing the task of image segmentation using the method of
superparamagnetic clustering. We apply it to a Potts model with spin
interactions that are are defined by gray-scale differences within the image.
Motivated by biological systems, we introduce the concept of neural inhibition
to the Potts model realization of the segmentation problem. Including the
inhibition term in the Hamiltonian results in enhanced contrast and thereby
significantly improves segmentation quality. As a second benefit we can - after
equilibration - directly identify the image segments as the clusters formed by
the clustering algorithm. To construct a new spin configuration the algorithm
performs the standard steps of (1) forming clusters and of (2) updating the
spins in a cluster simultaneously. As opposed to standard algorithms, however,
we share the interaction energy between the two steps. Thus the update
probabilities are not independent of the interaction energies. As a
consequence, we observe an acceleration of the relaxation by a factor of 10
compared to the Swendson and Wang procedure.Comment: 4 pages, 2 figure
Impact of Nucleon Mass Shift on the Freeze Out Process
The freeze out of a massive nucleon gas through a finite layer with time-like
normal is studied. The impact of in-medium nucleon mass shift on the freeze out
process is investigated. A considerable modification of the thermodynamical
variables temperature, flow-velocity, energy density and particle density has
been found. Due to the nucleon mass shift the freeze out particle distribution
functions are changed noticeably in comparison with evaluations, which use
vacuum nucleon mass.Comment: submitted to Physical Review
The Federal Emergency Employment Act of 1971: An Appraisal of Texas\u27 Experience
An assessment of the first few years of the Federal Emergency Employment Act’s implementation in the state of Texas, with focuses on various perspectives including the federal, state, and city levels
QCD phase transitions via a refined truncation of Dyson-Schwinger equations
We investigate both the chiral and deconfinement phase transitions of QCD
matter in a refined scheme of Dyson-Schwinger equations, which have been shown
to be successful in giving the meson mass spectrum and matching the interaction
with the results from ab initio computation. We verify the equivalence of the
chiral susceptibility criterion with different definitions for the
susceptibility and confirm that the chiral susceptibility criterion is
efficient to fix not only the chiral phase boundary but also the critical end
point (CEP), especially when one could not have the effective thermodynamical
potential. We propose a generalized Schwinger function criterion for the
confinement. We give the phase diagram of both phase transitions and show that
in the refined scheme the position of the CEP shifts to lower chemical
potential and higher temperature. Based on our calculation and previous results
of the chemical freeze out conditions, we propose that the CEP locates in the
states of the matter generated by the Au--Au collisions with
GeV.Comment: 12 pages, 6 figures, 1 tabl
A Non-thermal WIMP Miracle
Light scalar fields with only gravitational strength couplings are typically
present in UV complete theories of physics beyond the Standard Model. In the
early universe it is natural for these fields to dominate the energy density,
and their subsequent decay, if prior to BBN, will typically yield some dark
matter particles in their decay products. In this paper we make the observation
that a Non-thermal WIMP `Miracle' may result: that is, in the simplest solution
to the cosmological moduli problem, non-thermally produced WIMPs can naturally
account for the observed dark matter relic density. Such a solution may be
generic in string theory compactifications.Comment: 6 pages, no figures, References added, minor errors correcte
- …