5,749 research outputs found
Overdamping Phenomena near the Critical Point in O() Model
We consider the dynamic critical behavior of the propagating mode for the
order parameter fluctuation of the O() Ginzburg-Landau theory, involving the
canonical momentum as a degree of freedom. We reexamine the renormalization
group analysis of the Langevin equation for the propagating mode. We find the
fixed point for the propagating mode as well as that for the diffusive one, the
former of which is unstable to the latter. This indicates that the propagating
mode becomes overdamped near the critical point. We thus can have a sufficient
understanding of the phonon mode in the structural phase transition of solids.
We also discuss the implication for the chiral phase transition.Comment: 5 pages, 1 figure;v3 modification for correcting a misleading
description, conclusion unchange
Derivation of Covariant Dissipative Fluid Dynamics in the Renormalization-group Method
We derive generic relativistic hydrodynamical equations with dissipative
effects from the underlying Boltzmann equation in a mechanical and systematic
way on the basis of so called the renormalization-group (RG) method. A
macroscopic frame vector is introduced to specify the frame on which the
macroscopic dynamics is described. Our method is so mechanical with only few
ansatz that our method give a microscopic foundation of the available
hydrodynamical equations, and also can be applied to make a reduction of the
kinetic equations other than the simple Boltzmann equation.Comment: Serious typos and a minor one are corrected in p.6 and 7, and in p.1,
respectivel
The g-mode Excitation in the Proto Neutron Star by the Standing Accretion Shock Instability
The so-called "acoustic revival mechanism" of core-collapse supernova
proposed recently by the Arizona group is an interesting new possibility.
Aiming to understand the elementary processes involved in the mechanism, we
have calculated the eigen frequencies and eigen functions for the g-mode
oscillations of a non-rotating proto neutron star. The possible excitation of
these modes by the standing accretion shock instability, or SASI, is discussed
based on these eigen functions. We have formulated the forced oscillations of
-modes by the external pressure perturbations exerted on the proto neutron
star surface. The driving pressure fluctuations have been adopted from our
previous computations of the axisymmetric SASI in the non-linear regime. We
have paid particular attention to low l modes, since these are the modes that
are dominant in SASI and that the Arizona group claimed played an important
role in their acoustic revival scenario. Here l is the index of the spherical
harmonic functions, . Although the frequency spectrum of the non-linear
SASI is broadened substantially by non-linear couplings, the typical frequency
is still much smaller than those of g-modes, the fact leading to a severe
impedance mismatch. As a result, the excitations of various -modes are
rather inefficient and the energy of the saturated g-modes is erg
or smaller, with the g_2-mode being the largest in our model. Here the g_2-mode
has two radial nodes and is confined to the interior of the convection region.
The energy transfer rate from the g-modes to out-going sound waves is estimated
from the growth of the g-modes and found to be erg/s in the model
studied in this paper.Comment: 24 pages, 6 figure
Entropy production and isotropization in Yang-Mills theory with use of quantum distribution function
We investigate thermalization process in relativistic heavy ion collisions in
terms of the Husimi-Wehrl (HW) entropy defined with the Husimi function, a
quantum distribution function in a phase space. We calculate the semiclassical
time evolution of the HW entropy in Yang-Mills field theory with the
phenomenological initial field configuration known as the McLerran-Venugopalan
model in a non-expanding geometry, which has instabilty triggered by initial
field fluctuations. HW-entropy production implies the thermalization of the
system and it reflects the underlying dynamics such as chaoticity and
instability. By comparing the production rate with the Kolmogorov-Sina\"i rate,
we find that the HW entropy production rate is significantly larger than that
expected from chaoticity. We also show that the HW entropy is finally saturated
when the system reaches a quasi-stationary state. The saturation time of the HW
entropy is comparable with that of pressure isotropization, which is around
fm/c in the present calculation in the non-expanding geometry.Comment: 17 pages, 5 figure
Belle II iTOP Optics: Design, Construction and Performance
The imaging-Time-of-Propogation (iTOP) counter is a new type of ring-imaging
Cherenkov counter developed for particle identification at the Belle II
experiment. It consists of 16 modules arranged azimuthally around the beam
line. Each module consists of one mirror, one prism and two quartz bar
radiators. Here we describe the design, acceptance test, alignment, gluing and
assembly of the optical components. All iTOP modules have been successfully
assembled and installed in the Belle II detector by the middle of 2016. After
installation, laser and cosmic ray data have been taken to test the performance
of the modules. First results from these tests are presented.Comment: Proceedings of TIPP 2017, May 22 - 26, Beijing, China, 2017;
University of Cincinnati preprint UCHEP-17-07. arXiv admin note: text overlap
with arXiv:1709.0993
Study of entropy production in Yang-Mills theory with use of Husimi function
Understanding the thermalization process in a pure quantum system is a
challenge in theoretical physics. In this work, we explore possible
thermalization mechanism in Yang-Mills(YM) theory by using a positive
semi-definite quantum distribution function called a Husimi function which is
given by a coarse graining of the Wigner function within the minimum
uncertainty. Then entropy is defined in terms of the Husimi function, which is
called the Husimi-Wehrl(HW) entropy. We propose two numerical methods to
calculate the HW entropy. We find that it is feasible to apply the
semi-classical approximation with the use of classical YM equation. It should
be noted that the semi-classical approximation is valid in the systems of
physical interest including the early stage of heavy-ion collisions. Using a
product ansatz for the Husimi function, which is confirmed to reproduce the HW
entropy within 20% error (overestimate) for a few-body quantum system, we
succeed in a numerical evaluation of HW entropy of YM fields and show that it
surely has a finite value and increases in time.Comment: 7 pages, 5 figures, Proceeding of the 33rd International Symposium on
Lattice Field Theory (Lattice 2015), 14-18 July 2015, Kobe International
Conference Center, Kobe, Japa
Entropy production in quantum Yang-Mills mechanics in semi-classical approximation
We discuss thermalization of isolated quantum systems by using the
Husimi-Wehrl entropy evaluated in the semiclassical treatment. The Husimi-Wehrl
entropy is the Wehrl entropy obtained by using the Husimi function for the
phase space distribution. The time evolution of the Husimi function is given by
smearing the Wigner function, whose time evolution is obtained in the
semiclassical approximation. We show the efficiency and usefullness of this
semiclassical treatment in describing entropy production of a couple of quantum
mechanical systems, whose classical counter systems are known to be chaotic. We
propose two methods to evaluate the time evolution of the Husimi-Wehrl entropy,
the test-particle method and the two-step Monte-Carlo method. We demonstrate
the characteristics of the two methods by numerical calculations, and show that
the simultaneous application of the two methods ensures the reliability of the
results of the Husimi-Wehrl entropy at a given time.Comment: 11 pages, 8 figure
Jet-fluid string formation and decay in high-energy heavy-ion collisions
We propose a new hadronization mechanism, jet-fluid string (JFS) formation
and decay, to understand observables in intermediate to high- regions
comprehensively. In the JFS model, hard partons produced in jet lose their
energy in traversing the QGP fluid, which is described by fully
three-dimensional hydrodynamic simulations. When a jet parton escapes from the
QGP fluid, it picks up a partner parton from a fluid and forms a color singlet
string, then it decays to hadrons. We find that high- values in JFS
are about two times larger than in the independent fragmentation model.Comment: 6 pages, 2 figures; Proceeding for poster sessions at Quark Matter
2006, Shanghai, China, 14-20 November 2006; to appear in Int. J. of Mod.
Phys.
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