Towards the F-Theorem: N=2 Field Theories on the Three-Sphere

TL;DR

This paper investigates the free energy of 3D N=2 supersymmetric field theories on the three-sphere, proposing an F-theorem analogous to the c-theorem, supported by calculations matching M-theory duals and volume minimization principles.

Contribution

It introduces the F-theorem for 3D N=2 theories, linking free energy minimization to geometric volume minimization and providing large N calculations that match dual supergravity backgrounds.

Findings

F maximization yields N^{3/2} scaling in superconformal cases.

F decreases along RG flows and is stationary at fixed points.

In certain Chern-Simons theories, free energy scales as N^{5/3}, matching string theory predictions.

Abstract

For 3-dimensional field theories with {\cal N}=2 supersymmetry the Euclidean path integrals on the three-sphere can be calculated using the method of localization; they reduce to certain matrix integrals that depend on the R-charges of the matter fields. We solve a number of such large N matrix models and calculate the free energy F as a function of the trial R-charges consistent with the marginality of the superpotential. In all our {\cal N}=2 superconformal examples, the local maximization of F yields answers that scale as N^{3/2} and agree with the dual M-theory backgrounds AdS_4 x Y, where Y are 7-dimensional Sasaki-Einstein spaces. We also find in toric examples that local F-maximization is equivalent to the minimization of the volume of Y over the space of Sasakian metrics, a procedure also referred to as Z-minimization. Moreover, we find that the functions F and Z are related for any trial R-charges. In the models we study F is positive and decreases along RG flows. We therefore propose the "F-theorem" that we hope applies to all 3-d field theories: the finite part of the free energy on the three-sphere decreases along RG trajectories and is stationary at RG fixed points. We also show that in an infinite class of Chern-Simons-matter gauge theories where the Chern-Simons levels do not sum to zero, the free energy grows as N^{5/3} at large N. This non-trivial scaling matches that of the free energy of the gravity duals in type IIA string theory with Romans mass.