Hybrid Monte Carlo and topological modes of full QCD
  We investigate the performance of the hybrid Monte Carlo algorithm, the standard algorithm used for lattice QCD simulations involving fermions, in updating non-trivial global topological structures. We find that the hybrid Monte Carlo algorithm has serious problems decorrelating the global topological charge at the values of $\beta$ and $m$ currently simulated, where continuum physics should be approximately realized. This represents a warning which must be seriously considered when simulating full QCD by hybrid Monte Carlo. 
B. All\'es, G. Boyd, M. D'Elia, A. Di Giacomo and E. Vicari