Gonzalo Villa (DAMTP, University of Cambridge)

String Thermodynamics In and Out of Equilibrium: Boltzmann Equations and Random Walks

In this talk, we explore the Bolzmann equation approach to string thermodynamics and explore its inherent capability of studying out-of-equilibrium physics, with cosmological applications in mind. More concretely, after a short description of the phase space of string theory in a flat background, we consider the leading contribution to the decay and absorption rates of typical highly excited strings in a thermal ensemble, in an arbitrary number d of effectively non-compact dimensions (which we define in the talk). Using the random walk interpretation of these rates, which should apply in more general backgrounds, we infer more complicated contributions which at the moment lack a worldsheet computation.  All these are then used to write down Boltzmann equations in such a way that the principle of detailed balance becomes manifest, and we use this principle to find equilibrium configurations and test our inferred rates. We conclude by studying perturbations out-of-equilibrium by computing equilibration rates and fully solve for the behaviour of the perturbations in simple cases. Time permitting, potential implications in cosmology will be outlined.