A brief review of "little string theories"

TL;DR

This article surveys six-dimensional little string theories (LSTs), non-gravitational theories with string-like properties arising from gs→0 limits of NS5-branes. It reviews foundational definitions and properties, DLCQ constructions, holographic duals in linear-dilaton backgrounds, and the finite-energy-density behavior that signals non-locality and a Hagedorn-like spectrum. The authors discuss how LSTs exhibit dualities, BPS strings, and a continuum of states in holography, and highlight open questions about high-energy limits, intermediate regimes, and compactifications. They also outline future directions, including potential perturbative holographic calculations in special moduli, and the broader relevance of LSTs to non-local field theories and holography.

Abstract

This is a brief review of the current state of knowledge on "little string theories", which are non-gravitational theories having several string-like properties. We focus on the six dimensional maximally supersymmetric "little string theories" and describe their definition, some of their simple properties, the motivations for studying them, the DLCQ and holographic constructions of these theories and their behaviour at finite energy density. (Contribution to the proceedings of Strings '99 in Potsdam, Germany.)