Random Walks and the Correlation Length Critical Exponent in Scalar Quantum Field Theory

Abstract

The distance scale for a quantum field theory is the correlation length $\xi$, which diverges with exponent $\nu$ as the bare mass approaches a critical value. If $t=m^2-m_c^2$, then $\xi =m_P^{-1}\sim t^{-\nu }$ as $t\to 0$. The two-point function of a scalar field has a random walk representation. The walk takes place in a background of fluctuations (closed walks) of the field itself. We describe the connection between properties of the walk and of the two-point function. Using the known behavior of the two point function, we deduce that the dimension of the walk is $d_w=\varphi /\nu$ and that there is a singular relation between $t$ and the energy per unit length of the walk $\theta \sim t^{\varphi }$ that is due to the singular behavior of the background at $t=0$. ($\varphi$ is a computable crossover exponent.)