Topological Defects and nano-Hz Gravitational Waves in Aligned Axion Models
Abstract
We study the formation and evolution of topological defects in an aligned axion model with multiple Peccei-Quinn scalars, where the QCD axion is realized by a certain combination of the axions with decay constants much smaller than the conventional Peccei-Quinn breaking scale. When the underlying U(1) symmetries are spontaneously broken, the aligned structure in the axion field space exhibits itself as a complicated string-wall network in the real space. We find that the string-wall network likely survives until the QCD phase transition if the number of the Peccei-Quinn scalars is greater than two. The string-wall system collapses during the QCD phase transition, producing a significant amount of gravitational waves in the nano-Hz range at present. The typical decay constant is constrained to be below O(100) TeV by the pulsar timing observations, and the constraint will be improved by a factor of 2 in the future SKA observations.
Keywords
Cite
@article{arxiv.1606.05552,
title = {Topological Defects and nano-Hz Gravitational Waves in Aligned Axion Models},
author = {Tetsutaro Higaki and Kwang Sik Jeong and Naoya Kitajima and Toyokazu Sekiguchi and Fuminobu Takahashi},
journal= {arXiv preprint arXiv:1606.05552},
year = {2016}
}
Comments
23 pages, 7 figures