Boltzmann’s mean entropy formula for unbounded spin systems
Abstract
In this paper, we rigorously prove Boltzmann’s entropy formula S=kS=k log WW in classical unbounded spin systems. By restricting our consideration to negatively interacting super-stable potentials, we prove the existence of pressure and the concavity of micro-canonical entropy corresponding to log WW. Notably, the lattice φ4νφ4ν model becomes a feasible example through the exploitation of the physical equivalence of potentials. Our proof is mostly based on a cut-off technique for configuration spaces that enables us to lift-up the results for bounded systems. This approach is independent of the existence of Gibbs states and, moreover, holds a clear mathematical conciseness.