# Strong Coupling Universality at Large N for Pure CFT Thermodynamics in 2+1 dimensions

## TL;DR

This paper demonstrates a universal ratio in the entropy density of large N pure CFTs in 2+1 dimensions at strong coupling, revealing a universal thermodynamic behavior across various models.

## Contribution

It analytically computes the entropy density at strong coupling for the O(N) Wess-Zumino model and shows its universality across a broad class of theories with equal fermion and boson numbers.

## Key findings

- Entropy density at strong coupling is 31/35 of Stefan-Boltzmann result.
- Universal ratio applies to a wide class of theories with equal fermion and boson numbers.
- Boundaries for the thermodynamic ratio are established for unequal fermion and boson numbers.

## Abstract

Pure CFTs have vanishing $\beta$-function at any value of the coupling. One example of a pure CFT is the O(N) Wess-Zumino model in 2+1 dimensions in the large N limit. This model can be analytically solved at finite temperature for any value of the coupling, and we find that its entropy density at strong coupling is exactly equal to 31/35 of the non-interacting Stefan-Boltzmann result. We show that a large class of theories with equal numbers of N-component fermions and bosons, supersymmetric or not, for a large class of interactions, exhibit the same universal ratio. For unequal numbers of fermions and bosons we find that the strong-weak thermodynamic ratio is bounded to lie in between 4/5 and 1.