Improved harmonic approximation and the 2D Ising model at T not equal T-c and h not equal 0

摘要

We propose a new method to determine the unknown parameter associated with a self-consistent harmonic approximation. We check the validity of our technique in the context of the sine-Gordon model. As a non-trivial application we consider the scaling regime of the 2D Ising model away from the critical point and in the presence of a magnetic field h. We derive an expression that relates the approximate correlation length epsilon, T - T-c and h. [References: 35]