Extra-dimensional axion patterns

TL;DR

This paper explores the full parameter space of bulk axions in extra dimensions, identifying regimes with multiple axions solving the strong CP problem and analyzing their phenomenological constraints.

Contribution

It characterizes the parameter space of bulk axions in flat and warped extra dimensions, revealing conditions for multiple axion solutions and their phenomenological viability.

Findings

Multiple axion solutions are constrained by phenomenology.

KK canonical patterns are the most viable solutions.

Generalized eigenvalue equations for axions in extra dimensions.

Abstract

We study the $\textit{complete}$ parameter space of a bulk axion in flat and warped extra spacetime dimensions. We characterize in detail the regimes where no single KK mode is produced along the canonical QCD axion line, and instead, it is maximally deviated along with several other axions that constitute a multiple solution to the strong CP problem. In both flat and Randall-Sundrum scenarios, and assuming that all Peccei-Quinn breaking comes from QCD, we find that these solutions are however subject to tight phenomenological constraints. In light of these results, we expect that only KK canonical patterns (with the zero-mode close to the standard QCD line) can emerge from a bulk axion in one or more extra spacetime dimensions. As a byproduct, we generalize the axions eigenvalue and eigenvector equations for an arbitrary number of spacetime dimensions and compactifications.