Tensionless Strings from Worldsheet Symmetries

TL;DR

This work develops a comprehensive framework for tensionless strings by exploiting the Galilean conformal symmetry that remains on the tensionless worldsheet. It shows that tensionless strings arise from a worldsheet contraction of the tensile theory, yielding a 2D GCFT with generators L_n and M_n, and introduces a fundamentally new tensionless vacuum related to tensile excitations by Bogoliubov transformations. The authors demonstrate that tensionless closed strings exhibit open-string-like behavior under a chiral truncation of the GCFT and connect these degrees of freedom to high-temperature Hagedorn physics, where a long string dominates and a thermal-like worldsheet vacuum emerges from entanglement between left- and right-moving sectors. They also outline broader implications for flat holography, higher-spin physics, and potential extensions to open strings, D-branes, and supersymmetric theories, highlighting rich avenues for future exploration.

Abstract

We revisit the construction of the tensionless limit of closed bosonic string theory in the covariant formulation in the light of Galilean conformal symmetry that rises as the residual gauge symmetry on the tensionless worldsheet. We relate the analysis of the fundamentally tensionless theory to the tensionless limit that is viewed as a contraction of worldsheet coordinates. Analysis of the quantum regime uncovers interesting physics. The degrees of freedom that appear in the tensionless string are fundamentally different from the usual string states. Through a Bogoliubov transformation on the worldsheet, we link the tensionless vacuum to the usual tensile vacuum. As an application, we show that our analysis can be used to understand physics of strings at very high temperatures and propose that these new degrees of freedom are naturally connected with the long-string picture of the Hagedorn phase of free string theory. We also show that tensionless closed strings behave like open strings.