Thraxions: Towards Full String Models

TL;DR

This paper investigates the physics of thraxions, ultra-light axions in string theory compactifications, analyzing their stabilization, mass suppression, backreaction effects, and challenges in constructing global models with multiple thraxions.

Contribution

It provides a detailed study of thraxion stabilization in KKLT and LVS setups, explores their mass suppression depending on throat configurations, and introduces a new database of Calabi-Yau orientifolds suitable for thraxions.

Findings

Thraxion mass squared is suppressed by the warp factor, with different factors for minimal and non-minimal throats.

Backreaction of thraxions can break the Calabi-Yau structure to a complex manifold.

A new database of Calabi-Yau orientifolds without frozen conifolds is proposed for model building.

Abstract

We elucidate various aspects of the physics of thraxions, ultra-light axions arising at Klebanov-Strassler multi-throats in the compactification space of IIB superstring theory. We study the combined stabilization of K\"ahler moduli and thraxions, showing that under reasonable assumptions, one can solve the combined problem both in a KKLT and a LVS setup. We find that for non-minimal multi-throats, the thraxion mass squared is three-times suppressed by the throat warp factor. However, the minimal case of a double-throat can preserve the six-times suppression as originally found. We also discuss the backreaction of a non-vanishing thraxion vacuum expectation value on the geometry, showing that it induces a breaking of the imaginary self-duality condition for $3$-form fluxes. This in turn breaks the Calabi-Yau structure to a complex manifold one. Finally, we extensively search for global models which can accommodate the presence of multiple thraxions within the database of Complete Intersection Calabi-Yau orientifolds. We find that each multi-throat system holds a single thraxion. We further point out difficulties in constructing a full-fledged global model, due to the generic presence of frozen-conifold singularities in a Calabi-Yau orientifold. For this reason, we propose a new database (https://www.desy.de/~westphal/orientifold_webpage/cicy_thraxions.html) of CICY orientifolds that do not have frozen conifolds but that admit thraxions.