Scanning the Topological Sectors of the QCD Vacuum with Hybrid Monte   Carlo
  We address a long standing issue and determine the decorrelation efficiency of the Hybrid Monte Carlo algorithm (HMC), for full QCD with Wilson fermions, with respect to vacuum topology. On the basis of five state-of-the art QCD vacuum field ensembles (with 3000 to 5000 trajectories each and m_pi/m_rho-ratios in the regime >0.56, for two sea quark flavours) we are able to establish, for the first time, that HMC provides sufficient tunneling between the different topological sectors of QCD. This will have an important bearing on the prospect to determine, by lattice techniques, the topological susceptibility of the vacuum, and topology sensitive quantities like the spin content of the proton, or the eta' mass. 
B. Alles, G. Bali, M. D'Elia, A. Di Giacomo, N. Eicker, S. Guesken, H.   Hoeber, Th. Lippert, K. Schilling, A. Spitz, T. Str...