# Dualities in CHL-Models

## TL;DR

This paper introduces a broad class of CHL-models in string theory, analyzing their T-dualities and revealing the presence of Atkin-Lehner symmetries, extending previous specific cases to a more general framework.

## Contribution

It generalizes the understanding of CHL-models by defining a broad class associated with any string theory compactification and analyzing their T-duality symmetries, including Atkin-Lehner types.

## Key findings

- Models exhibit Atkin-Lehner type symmetries in T-duality.
- Generalization of previous N=4 and monstrous CHL-models.
- Framework applies to both bosonic and supersymmetric string theories.

## Abstract

We define a very general class of CHL-models associated with any string theory (bosonic or supersymmetric) compactified on an internal CFT C x T^d. We take the orbifold by a pair (g,\delta), where g is a (possibly non-geometric) symmetry of C and \delta is a translation along T^d. We analyze the T-dualities of these models and show that in general they contain Atkin-Lehner type symmetries. This generalizes our previous work on N=4 CHL-models based on heterotic string theory on T^6 or type II on K3 x T^2, as well as the `monstrous' CHL-models based on a compactification of heterotic string theory on the Frenkel-Lepowsky-Meurman CFT V^{\natural}.