ANOMALOUS DECOUPLINGS AND THE FERMION SIGN PROBLEM

In expressing the partition function for a system of interacting electrons as a path integral, the effective Boltzmann weight is not sign definite. This limits our ability to reach very low temperatures in numerical simulations. While magnetic phase transitions are well studied, superconducting instabilities are much more elusive. In this paper we study the properties of the sign in a novel formulation of the path integral within the finite-temperature grand-canonical determinantal Monte Carlo method. The approach decouples the interaction into pair creation and annihilation operators rather than the particle number density operators previously used. We find that the average sign depends on the particular path-integral formulation and hence does not correspond to any physical observable. The asymptotic exponential behavior of with previously reported holds here as well but with a different decay constant. © 1990 The American Physical Society.