Würzburg Seminar on Quantum Field Theory and Gravity

In recent years, condensed matter systems have emerged as a probe of high-energy phenomena. While high-energy theory suggests the (perhaps anomalous) conservation of the system's energy-momentum and electric charges, in condensed matter they are forced to relax to environment-selected values. The associated relaxation times must respect microscopic, i.e. high energy, time-reversal invariance, which renders them inconsistent with condensed matter phenomenology. In this talk, I will resolve this inconsistency by introducing generalized relaxation times. Working mainly in a hydrodynamic setting, I will show there are several families of relaxation times consistent with time-reversal invariance and condensed matter phenomenology. For concreteness, I will focus on Weyl semimetals, which enjoy a conserved energy-momentum and electric charge, but an anomalous chiral charge. The distinct families of relaxations lead to distinct expressions for Weyl semimetal conductivities, establishing a clear link between experimental observation and theoretical input. I will supplement the hydrodynamic calculations via minimal kinetic theory models realizing these families of relaxations.