4,471 research outputs found

### Real-time gauge theory simulations from stochastic quantization using optimized updating

Stochastic quantisation is applied to the problem of calculating real-time
evolution on a Minkowskian space-time lattice. We employ optimized updating
using reweighting, or gauge fixing, respectively. These procedures do not
affect the underlying theory, but strongly improve the stability properties of
the stochastic dynamics.Comment: 4 pages, 3 figures, contributed talk to SEWM 2008, Amsterda

### Turbulent spectra in real-time gauge field evolution

We investigate ultraviolet fixed points in the real-time evolution of
non-Abelian gauge fields. Classical-statistical lattice simulations reveal
equal-time correlation functions with a spectral index 3/2. Analytical
understanding of this result is achieved by employing a 2PI- loop expansion for
the quantum theory.Comment: 4 pages, 2 figures. Talk presented at SEWM 2008, August 26-29,
Amsterda

### QCD at high Baryon Density and Temperature: Competing Condensates and the Tricritical Point

The phase diagram of strongly interacting matter is explored as a function of
temperature and baryon number density. We investigate the possible simultaneous
formation of condensates in the conventional quark--anti-quark channel
(breaking chiral symmetry) and in a quark--quark channel leading to color
superconductivity: the spontaneous breaking of color symmetry via the formation
of quark Cooper pairs. We point out that for two massless quark flavors a
tricritical point in the phase diagram separates a chiral symmetry restoring
first order transition at high densities from the second order transition at
high temperatures. Away from the chiral limit this tricritical point becomes a
second order phase transition with Ising model exponents, suggesting that a
long correlation length may develop in heavy ion collisions in which the phase
transition is traversed at the appropriate density.Comment: Talk given at the Workshop on QCD at Finite Baryon Density: A Complex
System with a Complex Action, Bielefeld, Germany, 27-30 Apr 1998; 7 pages;
references adde

### Introduction to the nonequilibrium functional renormalization group

In these lectures we introduce the functional renormalization group out of
equilibrium. While in thermal equilibrium typically a Euclidean formulation is
adequate, nonequilibrium properties require real-time descriptions. For quantum
systems specified by a given density matrix at initial time, a generating
functional for real-time correlation functions can be written down using the
Schwinger-Keldysh closed time path. This can be used to construct a
nonequilibrium functional renormalization group along similar lines as for
Euclidean field theories in thermal equilibrium. Important differences include
the absence of a fluctuation-dissipation relation for general
out-of-equilibrium situations. The nonequilibrium renormalization group takes
on a particularly simple form at a fixed point, where the corresponding
scale-invariant system becomes independent of the details of the initial
density matrix. We discuss some basic examples, for which we derive a hierarchy
of fixed point solutions with increasing complexity from vacuum and thermal
equilibrium to nonequilibrium. The latter solutions are then associated to the
phenomenon of turbulence in quantum field theory.Comment: Lectures given at the 49th Schladming Winter School `Physics at all
scales: The Renormalization Group' (to appear in the proceedings); 24 pages,
3 figure

### Isotropization far from equilibrium

Isotropization occurs on time scales much shorter than the thermal
equilibration time. This is a crucial ingredient for the understanding of
collision experiments of heavy nuclei or other nonequilibrium phenomena in
complex many body systems. We discuss in detail the limitations of estimates
based on standard ``linear'' or relaxation-time approximations, where
isotropization and thermal equilibration rates agree. For a weak-coupling
$\phi^4$-model the relaxation-time approximation underestimates the thermal
equilibration time by orders of magnitude, in contrast to the isotropization
time. The characteristic nonequilibrium isotropization rate can be enhanced as
compared to the close-to-equilibrium value. Our results are obtained from the
two-particle irreducible effective action, which includes off-shell and memory
effects and does not involve a gradient expansion. This allows us to determine
the range of validity of a description to lowest-order in gradients, which is
typically employed in kinetic equations.Comment: 27 pages, 7 figures, NPB version, minor text change

### The Joint COntrols Project Framework

The Framework is one of the subprojects of the Joint COntrols Project (JCOP),
which is collaboration between the four LHC experiments and CERN. By sharing
development, this will reduce the overall effort required to build and maintain
the experiment control systems. As such, the main aim of the Framework is to
deliver a common set of software components, tools and guidelines that can be
used by the four LHC experiments to build their control systems. Although
commercial components are used wherever possible, further added value is
obtained by customisation for HEP-specific applications. The supervisory layer
of the Framework is based on the SCADA tool PVSS, which was selected after a
detailed evaluation. This is integrated with the front-end layer via both OPC
(OLE for Process Control), an industrial standard, and the CERN-developed DIM
(Distributed Information Management System) protocol. Several components are
already in production and being used by running fixed-target experiments at
CERN as well as for the LHC experiment test beams. The paper will give an
overview of the key concepts behind the project as well as the state of the
current development and future plans.Comment: Paper from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 4 pages, PDF. PSN THGT00

### Unlocking Color and Flavor in Superconducting Strange Quark Matter

We explore the phase diagram of strongly interacting matter with massless u
and d quarks as a function of the strange quark mass m_s and the chemical
potential mu for baryon number. Neglecting electromagnetism, we describe the
different baryonic and quark matter phases at zero temperature. For quark
matter, we support our model-independent arguments with a quantitative analysis
of a model which uses a four-fermion interaction abstracted from single-gluon
exchange. For any finite m_s, at sufficiently large mu we find quark matter in
a color-flavor locked state which leaves a global vector-like SU(2)_{color+L+R}
symmetry unbroken. As a consequence, chiral symmetry is always broken in
sufficiently dense quark matter. As the density is reduced, for sufficiently
large m_s we observe a first order transition from the color-flavor locked
phase to a color superconducting phase analogous to that in two flavor QCD. At
this unlocking transition chiral symmetry is restored. For realistic values of
m_s our analysis indicates that chiral symmetry breaking may be present for all
densities down to those characteristic of baryonic matter. This supports the
idea that quark matter and baryonic matter may be continuously connected in
nature. We map the gaps at the quark Fermi surfaces in the high density
color-flavor locked phase onto gaps at the baryon Fermi surfaces at low
densities.Comment: Latex with eps figures, 28 pages, minor corrections, references
update

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