30,269 research outputs found
Chiral Symmetry Breaking and Stability of the Magnetized Vacuum
The recent claim [arXiv:hep-th/0603070, arXiv:hep-th/0605020] that there
exists in QED a maximum magnetic field of 10^{42} G, above which the magnetized
vacuum becomes unstable with respect to the so-called "positronium collapse" is
critically examined and unequivocally refuted.Comment: Contribution to Proceedings of Quantum Field Theory Under the
Influence of External Conditions (QFEXT09), Norman, OK, September 21-25, 200
Real-time Nonequilibrium Dynamics in Hot QED Plasmas
The quantum kinetics of photons is studied directly in real time by
implementing the dynamical renormalization group. In contrast to conventional
approach, the dynamical renormalization group method consistently includes
off-shell (energy non-conserving) effects and accounts for time-dependent
collisional kernel. To lowest order we find that in the relaxation time
approximation the semihard photon distribution function relaxes with a power
law.Comment: LaTeX, 3 pages, talk presented at DPF2000, August 10, 2000, revised
versio
Analysis and control of a scalar conservation law modeling a highly re-entrant manufacturing system
In this paper, we study a scalar conservation law that models a highly
re-entrant manufacturing system as encountered in semi-conductor production. As
a generalization of \cite{CKWang}, the velocity function possesses both the
local and nonlocal character. We prove the existence and uniqueness of the weak
solution to the Cauchy problem with initial and boundary data in .
We also obtain the stability (continuous dependence) of both the solution and
the out-flux with respect to the initial and boundary data. Finally, we prove
the existence of an optimal control that minimizes, in the -sense with
, the difference between the actual out-flux and a forecast
demand over a fixed time period.Comment: 32 pages, 12 figure
Holographic study on the jet quenching parameter in anisotropic systems
We first calculate the jet quenching parameter of an anisotropic plasma with
a U(1) chemical potential via the AdS/CFT duality. The effects of charge,
anisotropy parameter and quark motion direction on the jet quenching parameter
are investigated. We then discuss the situation of anisotropic black brane in
the IR region. We study both the jet quenching parameters along the
longitudinal direction and transverse plane
Direct photons: a nonequilibrium signal of the expanding quark-gluon plasma
Direct photon production from a longitudinally expanding quark-gluon plasma
(QGP) at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC)
energies is studied with a real-time kinetic description that is consistently
incorporated with hydrodynamics. Within Bjorken's hydrodynamical model, energy
nonconserving (anti)quark bremsstrahlung q(\bar{q})\to q(\bar{q})\gamma and
quark-antiquark annihilation q\bar{q}\to \gamma are shown to be the dominant
nonequilibrium effects during the transient lifetime of the QGP. For central
collisions we find a significant excess of direct photons in the range of
transverse momentum 1-2 \lesssim p_T \lesssim 5 GeV/c as compared to
equilibrium results. The photon rapidity distribution exhibits a central
plateau. The transverse momentum distribution at midrapidity falls off with a
{\em power law} p^{-\nu}_T with 2.5 \lesssim \nu \lesssim 3 as a consequence of
these energy nonconserving processes, providing a distinct experimental {\em
nonequilibrium signature}. The power law exponent \nu increases with the
initial temperature of the QGP and hence with the total multiplicity rapidity
distribution dN_\pi/dy.Comment: LaTeX (elsart.cls), 33 pages, 4 eps figures, updated with data for
LHC, to appear in Nucl. Phys.
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