New Proposal for Numerical Simulations ofθ-Vacuum-like Systems

We propose a new approach to perform numerical simulations of $\theta$-vacuum-like systems, test it in two analytically solvable models, and apply it to $C{P}^3$. The main new ingredient in our approach is the method used to compute the probability distribution function of the topological charge at $\theta =0$. We do not get unphysical phase transitions (flattening behavior of the free energy density) and reproduce the exact analytical results for the order parameter in the whole $\theta$ range within a few percent.