Thermal properties of a string bit model at large N

TL;DR

This paper investigates the finite temperature behavior of a string bit model at large N, revealing a Hagedorn transition where string degrees of freedom become dominant and the system undergoes a phase change.

Contribution

The study provides a detailed analysis of the thermodynamics and phase structure of a string bit model, including an algorithm for density profile determination at infinite N.

Findings

Identification of a Hagedorn transition at finite temperature.

Development of an algorithm for density profile calculation at N=∞.

Analytical characterization of the transition and high-temperature phases.

Abstract

We study the finite temperature properties of a recently introduced string bit model designed to capture some features of the emergent string in the tensionless limit. The model consists of a pair of bosonic and fermionic bit operators transforming in the adjoint representation of the color group SU(N). Color confinement is not achieved as a dynamical effect, but instead is enforced by an explicit singlet projection. At large N and finite temperature, the model has a non trivial thermodynamics. In particular, there is a Hagedorn type transition at a finite temperature $T=T_H$ where the string degrees of freedom are liberated and the free energy gets a large contribution $\sim N^{2}$ that plays the role of an order parameter. For $T>T_H$, the low temperature phase becomes unstable. In the new phase, the thermodynamically favoured configurations are characterized by a non-trivial gapped density of the SU(N) angles associated with the singlet projection. We present an accurate algorithm for the determination of the density profile at $N=\infty$. In particular, we determine the gap endpoint at generic temperature and analytical expansions valid near the Hagedorn transition as well as at high temperature. The leading order corrections are characterized by non-trivial exponents that are determined analytically and compared with explicit numerical calculations.