(deadline August 31)
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INT Program INT-12-1|
Gauge Field Dynamics In and Out of Equilibrium
March 5 - April 13, 2012
The many-body physics of relativistic non-Abelian gauge theories plays an
important role in current heavy ion collision experiments as well as in the
astrophysics of compact stars. Similar conceptual problems are also met in
certain dark matter and leptogenesis computations in cosmology (the gauge
group being then that of weak interactions); in upcoming laser physics
experiments in the MeV range (the gauge group being then Abelian); and
even in a number of condensed matter systems (despite the fact that
these are non-relativistic). A plethora of methods have been developed for
addressing such problems, ranging from analytic effective field theory
techniques, through numerical lattice Monte Carlo simulations, all the
way to string-theory inspired dualities applicable for idealized limits.
The goal of this program is to bring together experts from a range of
fields, expert in a range of methods, both in order to discuss the latest
specific developments and to establish links between the various fronts.
Although there will be no thematically fixed schedule, we have
nominated a "responsible organizer" for various periods, which
may naturally lead to some shift in the focal point of the
activities. The responsible organizers are:
Weeks 1-2 (March 5 - 16): Gert Aarts.
Weeks 3-4 (March 19 - 30): Guy Moore.
Weeks 5-6 (April 2 - 13): Mikko Laine.
SELECTED SCIENTIFIC OBJECTIVES
Non-perturbative transport coefficients and spectral functions
The dynamical properties of a many-body system are encoded in various
gauge-invariant spectral functions and, in particular, their
zero-frequency limits, known as transport coefficients. It would
be of utmost importance to develop controlled non-perturbative
methods for the determination of these quantities, starting from
Euclidean correlators computed via Monte Carlo simulations.
Moreover, effective field theory techniques or computations
in idealized but related theories may help to develop a generic
understanding of the qualitative shape of the spectral functions.
Hydrodynamics and its limitations
Given some values for thermodynamic potentials and transport coefficients,
the macroscopic evolution of a system and the propagation of various probe
particles can be studied via hydrodynamics. It would be important to
understand, on one hand, the qualitative nature of the hydrodynamic solutions
relevant for heavy ion collisions and for astrophysics. On the other
hand, the finite size of the system implies particularly in the former
context that the hydrodynamic description may lose its validity
under some circumstances, when a gradient expansion is no longer
justifiable. Perhaps examples from gauge/gravity duality or from
condensed matter systems may provide valuable insights on this matter.
QCD phase diagram at finite density
As is well known, the Boltzmann weight in the QCD path integral
is complex at non-zero chemical potential, which poses a formidable
challenge for practical simulations. There are ongoing efforts
to evade this problem, via the use of imaginary chemical potential,
the strong coupling expansion, or the density of states method.
A relatively recent alternative uses complex Langevin dynamics.
It is hoped that studies in simplified systems, some of them
of academic nature but others actually relevant for
condensed matter physics, help to suggest avenues for progress.
Connection to weakly coupled methods
Thanks to asymptotic freedom, strongly interacting systems do become
analytically tractable in the limit of a very large temperature or
density, although even in these limits naive perturbative computations
need to be resummed via effective field theory techniques. On the other
hand, some cosmological problems (leptogenesis, dark matter production)
as well as forthcoming laser physics experiments are weakly coupled
to start with. It seems pertinent to develop systematic techniques for
these limits, and confront the results with those of the strongly coupled
systems. For instance, the few dynamical quantities which have been
computed beyond leading perturbative order in nonabelian gauge theories
show surprisingly large second-order corrections. It is essential
to understand the origin of these corrections and whether there
is a resummation method which can capture them.