Some findings on the minus-sign problem for the Hubbard model in the projector quantum Monte Carlo method

The quantum Monte Carlo method for tile Hubbard model using the Hubbard-Str atonovich transformation is reexamined. It is observed that the value of th e ground state energy for a 3 x 2 and 4 x 4 system is estimated correctly b y ignoring the minus-sign of the negative sampling weight appearing in the simulation using the projector method. It is also observed that the average of sign is positive and the correlation between the energy and the sign is weak for these systems. The reasons why the ground state energy is estimat ed correctly is given on a phenomenological base.