Short-time Dynamic Behaviour of Critical XY Systems
  Using Monte Carlo methods, the short-time dynamic scaling behaviour of two-dimensional critical XY systems is investigated. Our results for the XY model show that there exists universal scaling behaviour already in the short-time regime, but the values of the dynamic exponent $z$ differ for different initial conditions. For the fully frustrated XY model, power law scaling behaviour is also observed in the short-time regime.   However, a violation of the standard scaling relation between the exponents is detected. 
H.J. Luo, M. Schulz, L. Schuelke, S. Trimper, B. Zheng