SU(2)-spin Invariant Auxiliary Field Quantum Monte Carlo Algorithm for Hubbard models

Auxiliary field quantum Monte Carlo methods for Hubbard models are generally based on a Hubbard-Stratonovitch transformation where the field couples to the z-component of the spin. This transformation breaks SU(2) spin invariance. The symmetry is restored only after summation over the auxiliary fields. Here, we analyze an alternative decomposition, which conserves SU(2) spin invariance, but requires the use of complex numbers. We show that this algorithm gets rid of the very large fluctuations observed in imaginary time displaced correlation functions of quantities which do not commute with the z-component of the total spin. The algorithm prooves to be efficient for the study of spin dynamics.
Comment: 5 pages including 2 figures in encapsulated postscript format