Implications of Conformal Invariance in Field Theories for General Dimensions

TL;DR

This paper investigates conformal invariance constraints on two and three point functions in general dimensions, providing a group theoretic construction and calculating coefficients for free theories, with implications for trace anomalies.

Contribution

It introduces a compact group theoretic method for constructing three point functions of arbitrary spin fields in any dimension and analyzes their properties under conservation laws.

Findings

Identifies three independent conformal invariant forms for the energy momentum tensor three point function in general dimensions.

Calculates coefficients for free scalar, fermion, and abelian vector theories in various dimensions.

Shows simplifications of three point functions when points are collinear and relates coefficients to trace anomalies.

Abstract

The requirements of conformal invariance for two and three point functions for general dimension $d$ on flat space are investigated. A compact group theoretic construction of the three point function for arbitrary spin fields is presented and it is applied to various cases involving conserved vector operators and the energy momentum tensor. The restrictions arising from the associated conservation equations are investigated. It is shown that there are, for general $d$, three linearly independent conformal invariant forms for the three point function of the energy momentum tensor, although for $d=3$ there are two and for $d=2$ only one. The form of the three point function is also demonstrated to simplify considerably when all three points lie on a straight line. Using this the coefficients of the conformal invariant point functions are calculated for free scalar and fermion theories in general dimensions and for abelian vector fields when $d=4$. Ward identities relating three and two point functions are also discussed. This requires careful analysis of the singularities in the short distance expansion and the method of differential regularisation is found convenient. For $d=4$ the coefficients appearing in the energy momentum tensor three point function are related to the coefficients of the two possible terms in the trace anomaly for a conformal theory on a curved space background.