The Cap in the Hat: Unoriented 2D Strings and Matrix(-Vector) Models

TL;DR

This paper classifies unoriented 2D bosonic and Type 0 string theories and identifies their dual matrix models, analyzing their consistency and tachyon tadpole conditions to find stable vacua.

Contribution

It provides a comprehensive classification of unoriented 2D string theories and their dual matrix models, including solutions to tadpole cancellation conditions.

Findings

No RP^2 R-R tadpoles in any models

Many models have a massless tachyon tadpole

Some models are tachyon tadpole-free and consistent

Abstract

We classify the possible bosonic and Type 0 unoriented string theories in two dimensions, and find their dual matrix(-vector) models. There are no RP^2 R-R tadpoles in any of the models, but many of them possess a massless tachyon tadpole. Thus all the models we find are consistent two-dimensional string vacua, but some get quantum corrections to their classical tachyon background. Where possible, we solve the tadpole cancellation condition, and find all the tachyon tadpole-free theories.