Supersymmetry and finite-temperature strings

TL;DR

This paper models finite-temperature N=4 superstrings using effective supergravity, finding stable BPS solutions that preserve supersymmetry and avoid tachyonic instabilities, suggesting a new stable phase relevant for early universe cosmology.

Contribution

It introduces exact BPS solutions in finite-temperature superstring theory that maintain supersymmetry and stability across all temperatures, unlike standard perturbative approaches.

Findings

No tachyonic instabilities in the solutions

Existence of a stable BPS phase at all temperatures

Preservation of half of the supersymmetries

Abstract

We describe finite temperature N=4 superstrings in D=5 by an effective four-dimensional supergravity of the thermal winding modes that can become tachyonic and trigger the instabilities at the Hagedorn temperature. Using a domain-wall ansatz, exact solutions to special BPS-type first order equations are found. They preserve half of the supersymmetries, contrary to the standard perturbative superstring at finite temperature that breaks all supersymmetries. Our solutions show no indication of any tachyonic instability and provide evidence for a new BPS phase of finite temperature superstrings that is stable for all temperatures. This would have important consequences for a stringy description of the early universe.