Non-Universal Finite Size Effects with Universal Infinite-Size Free Energy for the α-XY model

We study finite size effects in a family of systems in which a parameter controls interaction-range. In the long-range regime where the infinite-size free energy is universal, we show that the finite size effects are not universal but depend on the interaction-range. The finite size effects are observed through discrepancies between time-averages of macroscopic variables in Hamiltonian dynamics and canonical averages of ones with infinite degrees of freedom. For a high energy regime, the relation to a pair of the discrepancies is theoretically predicted and numerically confirmed. We also numerically show that the finite-size effects of macroscopic variables in the canonical ensemble are close to ones in the dynamical systems.