Carving Out the Space of 4D CFTs

TL;DR

This paper presents a new numerical semidefinite programming algorithm to compute bounds on operator dimensions, central charges, and OPE coefficients in 4D conformal and superconformal field theories, significantly improving previous results.

Contribution

Introduction of a novel semidefinite programming algorithm for bounding key CFT quantities, especially in theories with global symmetries and N=1 supersymmetry.

Findings

Tighter bounds on operator dimensions in 4D CFTs.

Strong constraints on models of conformal technicolor.

Bounds on OPE coefficients and central charges close to known theories.

Abstract

We introduce a new numerical algorithm based on semidefinite programming to efficiently compute bounds on operator dimensions, central charges, and OPE coefficients in 4D conformal and N=1 superconformal field theories. Using our algorithm, we dramatically improve previous bounds on a number of CFT quantities, particularly for theories with global symmetries. In the case of SO(4) or SU(2) symmetry, our bounds severely constrain models of conformal technicolor. In N=1 superconformal theories, we place strong bounds on dim(Phi*Phi), where Phi is a chiral operator. These bounds asymptote to the line dim(Phi*Phi) <= 2 dim(Phi) near dim(Phi) ~ 1, forbidding positive anomalous dimensions in this region. We also place novel upper and lower bounds on OPE coefficients of protected operators in the Phi x Phi OPE. Finally, we find examples of lower bounds on central charges and flavor current two-point functions that scale with the size of global symmetry representations. In the case of N=1 theories with an SU(N) flavor symmetry, our bounds on current two-point functions lie within an O(1) factor of the values realized in supersymmetric QCD in the conformal window.