Lefschetz thimble Monte Carlo for many body theories: application to the   repulsive Hubbard model away from half filling
  Recently, a new method, based on stochastic integration on the surfaces of steepest descent of the action, was introduced to tackle the sign problem in quantum field theories. We show how this method can be used in many body theories to perform fully non-perturbative calculations of quantum corrections about mean field solutions. We discuss an explicit algorithm for implementing our method, and present results for the repulsive Hubbard model away from half-filling at intermediate temperatures. Our results are consistent with those from the recent state of the art cluster dynamical mean field theory calculations. 
Abhishek Mukherjee and Marco Cristoforetti
cond-mat.str-el cond-mat.quant-gas hep-lat nucl-th physics.comp-ph