Accions

TL;DR

This paper explores how accions, axion-like particles arising from accidental U(1) symmetries in string theory, can have decay constants compatible with cosmological bounds, especially within Z_6-II orbifold models.

Contribution

It demonstrates that accions can have adjustable decay constants depending on vacuum configurations, and can be embedded in realistic string compactifications.

Findings

Accions' decay constants depend on vacuum configurations.

Accions with suitable decay constants can be embedded in Z_6-II orbifold models.

The study provides a pathway to reconcile axion models with cosmological constraints.

Abstract

Axion fields provide the most elegant solution to the strong CP problem. In string compactifications it is difficult to obtain an axion whose decay constant is consistent with current cosmological bounds. We examine this question in theories with accidental U(1) symmetries that appear as low energy remnants of discrete symmetries. We refer to the axion-like particles from the spontaneous breakdown of these symmetries as accions. In such systems, the accion decay constant depends on the vacuum configuration and can be lowered to fit the bounds. Furthermore, we find that such accions with consistent decay constant can be embedded in special vacua of Z_6-II orbifold models with realistic features.