Universal short-time dynamics: boundary functional renormalization group for a temperature quench

We present a method to calculate short-time non-equilibrium universal exponents within the functional renormalization-group scheme. As an example, we consider the classical critical dynamics of the relaxational model A after a quench of the temperature of the system and calculate the initial slip exponent which characterizes the non-equilibrium universal short-time behaviour of both the order parameter and correlation functions. The value of this exponent is found to be consistent with the result of a perturbative dimensional expansion and of Monte Carlo simulations in three spatial dimensions.