Correlation Functions of a Conformal Field Theory in Three Dimensions

TL;DR

This paper derives explicit two-point correlation functions for the $O(N)$ non-linear sigma model at criticality in three dimensions, analyzing their behavior on various curved manifolds and revealing geometry-dependent correlation decay.

Contribution

It provides explicit forms of the two-point correlation functions in the large N limit on different three-dimensional manifolds of constant curvature, highlighting the influence of geometry on correlation decay.

Findings

Correlation functions decay exponentially on curved manifolds.

Correlation length scale is determined by the manifold's geometry.

On flat space, decay follows a power law.

Abstract

We derive explicit forms of the two--point correlation functions of the $O(N)$ non-linear sigma model at the critical point, in the large $N$ limit, on various three dimensional manifolds of constant curvature. The two--point correlation function, $G(x, y)$, is the only $n$-point correlation function which survives in this limit. We analyze the short distance and long distance behaviour of $G(x, y)$. It is shown that $G(x, y)$ decays exponentially with the Riemannian distance on the spaces $R^2 \times S^1,~S^1 \times S^1 \times R, ~S^2 \times R,~H^2 \times R$. The decay on $R^3$ is of course a power law. We show that the scale for the correlation length is given by the geometry of the space and therefore the long distance behaviour of the critical correlation function is not necessarily a power law even though the manifold is of infinite extent in all directions; this is the case of the hyperbolic space where the radius of curvature plays the role of a scale parameter. We also verify that the scalar field in this theory is a primary field with weight $\delta=-{1 \over 2}$; we illustrate this using the example of the manifold $S^2 \times R$ whose metric is conformally equivalent to that of $R^3-\{0\}$ up to a reparametrization.