A second-quantized red herring in full configuration-interaction Monte   Carlo
  This paper deals with the sign problem in full configuration-interaction quantum Monte Carlo.   After putting this article on the arxiv, it was pointed out to us that our argument applies to a number of model Hamiltonians we considered numerically but not to the most generic case. Please see arxiv: 1209.3044, where we have a corrected comprehensive discussion of the necessary and sufficient conditions for when the sign problem for a given Hamiltonian (and basis) differ between first and second quantization. 
Michael Kolodrubetz and Bryan K. Clark
physics.comp-ph