Exploring the HMC trajectory-length dependence of autocorrelation times   in lattice QCD
  We study autocorrelation times of physical observables in lattice QCD as a function of the molecular dynamics trajectory length in the hybrid Monte-Carlo algorithm. In an interval of trajectory lengths where energy and reversibility violations can be kept under control, we find a variation of the integrated autocorrelation times by a factor of about two in the quantities of interest. Trajectories longer than conventionally used are found to be superior both in the Nf=0 and Nf=2 examples considered here. We also provide evidence that they lead to faster thermalization of systems with light quarks. 
Harvey B. Meyer, Hubert Simma, Rainer Sommer, Michele Della Morte,   Oliver Witzel, Ulli Wolff