Cosmologically safe QCD axion as a present from extra dimension
Masahiro Kawasaki, Masaki Yamada, and Tsutomu T. Yanagida
TL;DR
This paper introduces a novel QCD axion model utilizing extra dimensions to naturally suppress isocurvature perturbations and PQ symmetry breaking, addressing key cosmological constraints.
Contribution
It presents a new extra-dimensional framework where the PQ symmetry and axion suppression are achieved through brane separation and dynamic extra dimension size.
Findings
PQ symmetry can be temporarily broken during inflation
Extra dimension dynamics suppress axion isocurvature fluctuations
Model provides a cosmologically safe axion scenario
Abstract
We propose a QCD axion model where the origin of PQ symmetry and suppression of axion isocurvature perturbations are explained by introducing an extra dimension. Each extra quark-antiquark pair lives on branes separately to suppress PQ breaking operators. The size of the extra dimension changes after inflation due to an interaction between inflaton and a bulk scalar field, which implies that the PQ symmetry can be drastically broken during inflation to suppress undesirable axion isocurvature fluctuations.
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