Gert Aarts
Swansea University

Mikko Laine
Bern University

Guy Moore
McGill University

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Laura Lee
(206) 685-3509

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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.


  • 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.