MONTE-CARLO SIMULATION WITH FLUCTUATING BOUNDARY-CONDITIONS

I study the finite size behavior of the ratio of partition functions w ith periodic and antiperiodic boundary conditions in the vicinity of t he critical coupling of the 3D Ising model. This ratio is obtained as a simple expectation value in an ensemble where I average over both ki nds of boundary conditions. Based on such simulations I obtain beta(c) = 0.221650(5) and nu = 0.630(2). These results are compared with four th order cumulant results obtained in the same Monte Carlo simulations .