Tensionless Strings, WZW Models at Critical Level and Massless Higher Spin Fields

TL;DR

This paper explores the tensionless limit of quantum bosonic string theory across various backgrounds, revealing a critical level where the theory gains enhanced symmetry and massless higher spin states.

Contribution

It identifies the critical level in curved spaces where string tension vanishes, leading to new symmetries and the emergence of massless higher spin fields.

Findings

Critical level corresponds to tensionless string limit.

Enhanced symmetry appears at the critical level.

Massless higher spin states emerge at the critical level.

Abstract

We discuss the notion of tensionless limit in quantum bosonic string theory, especially in flat Minkowski space, noncompact group manifolds (e.g., SL(2,R)) and coset manifolds (e.g., AdS). We show that in curved space typically there exists a critical value of the tension which is related to the critical value of the level of the corresponding affine algebra. We argue that at the critical level the sring theory becomes tensionless and that there exists a huge new symmetry of the theory. We dicuss the appearence of the higher spin massless states at the critical level.