On higher spins and the tensionless limit of String Theory

TL;DR

The paper analyzes the tensionless limit of string theory to reveal triplet structures for both bosonic and fermionic higher-spin fields, and develops their unconstrained, compensator-based formulations using BRST methods. It presents explicit bosonic triplets (including mixed-symmetry generalizations) and extends them to (A)dS, supported by direct constructions and AdS BRST analysis, along with compensator Lagrangians in flat space. It then extends the framework to fermions via open superstrings, deriving fermionic triplets and their compensator forms, while highlighting obstacles to fermionic AdS deformations. Overall, the work clarifies how unconstrained gauge symmetry and compensator fields can yield local higher-spin dynamics in tensionless/stringy regimes and illuminates the interplay with (A)dS and Vasiliev-type structures.

Abstract

We discuss string spectra in the low-tension limit using the BRST formalism, with emphasis on the role of triplets of totally symmetric tensors and spinor-tensors and their generalizations to cases with mixed symmetry and to (A)dS backgrounds. We also present simple compensator forms of the field equations for individual higher-spin gauge fields that display the {unconstrained} gauge symmetry of a previous non-local construction and reduce upon partial gauge fixing to the (Fang-)Fronsdal equations. For Bose fields we also show how a local Lagrangian formulation with {unconstrained} gauge symmetry is determined by a previous BRST construction.