Power-law correction in the probability density function of the critical Ising magnetization

At the critical point, the probability density function of the Ising magnetization is believed to decay like $\exp{(-x^{δ+1})}$, where $δ$ is the Ising critical exponent that controls the decay to zero of the magnetization in a vanishing external field. In this paper, we discuss the presence of a power-law correction $x^{\frac{δ-1}{2}}$, which has been debated in the physics literature. We argue that whether such a correction is present or not is related to the asymptotic behavior of a function that measures the extent to which the average magnetization of a finite system with an external field is influenced by the boundary conditions. Our discussion is informed by a mixture of heuristic calculations and rigorous results. Along the way, we review some recent results on the critical Ising model and prove properties of the average magnetization in two dimensions which are of independent interest.