Quantum Monte Carlo study of quasiparticles in the Hubbard model

We present an improved version of the projector quantum Monte Carlo method, which has recently been proposed by Sorella et al. This scheme allows a very precise computation of the ground-state energy of fermionic models. The ‘‘minus sign’’ has been treated without further approximations and does not influence the accuracy. In this paper we focus on the question of the existence of quasiparticles in the Hubbard model in one dimension and resolve the controversy concerning the discontinuity in the momentum distribution function between recent quantum Monte Carlo and weak-coupling renormalization-group techniques.