On $C_J$ and $C_T$ in the Gross-Neveu and $O(N)$ Models

TL;DR

This paper uses diagrammatic techniques to compute and verify the leading large N corrections to the coefficients of conserved current and stress-energy tensor two-point functions in the $O(N)$ and Gross-Neveu models across various dimensions, confirming known results and providing new estimates.

Contribution

It applies large N diagrammatic methods to calculate corrections to $C_J$ and $C_T$ in conformal models, including new explicit formulas for the Gross-Neveu model and cross-checks with perturbation theory.

Findings

Diagrammatic approach reproduces known large N results for $O(N)$ model.

Provides explicit formulas for $C_J$ and $C_T$ corrections in the Gross-Neveu model.

Estimates $C_J$ and $C_T$ in 3D using Pade approximants, aligning with bootstrap results.

Abstract

We apply large $N$ diagrammatic techniques for theories with double-trace interactions to the leading corrections to $C_J$, the coefficient of a conserved current two-point function, and $C_T$, the coefficient of the stress-energy tensor two-point function. We study in detail two famous conformal field theories in continuous dimensions, the scalar $O(N)$ model and the Gross-Neveu model. For the $O(N)$ model, where the answers for the leading large $N$ corrections to $C_J$ and $C_T$ were derived long ago using analytic bootstrap, we show that the diagrammatic approach reproduces them correctly. We also carry out a new perturbative test of these results using the $O(N)$ symmetric cubic scalar theory in $6-\epsilon$ dimensions. We go on to apply the diagrammatic method to the Gross-Neveu model, finding explicit formulae for the leading corrections to $C_J$ and $C_T$ as a function of dimension. We check these large $N$ results using regular perturbation theory for the Gross-Neveu model in $2+\epsilon$ dimensions and the Gross-Neveu-Yukawa model in $4-\epsilon$ dimensions. For small values of $N$, we use Pade approximants based on the $4-\epsilon$ and $2+\epsilon$ expansions to estimate the values of $C_J$ and $C_T$ in $d=3$. For the $O(N)$ model our estimates are close to those found using the conformal bootstrap. For the GN model, our estimates suggest that, even when $N$ is small, $C_T$ differs by no more than $2\%$ from that in the theory of free fermions. We find that the inequality $C_T^{\textrm{UV}} > C_T^{\textrm{IR}}$ applies both to the GN and the scalar $O(N)$ models in $d=3$.