Axionic Wormholes in Metric-Affine Gravity
Abstract
The axion is a promising candidate for solving the strong CP problem. To solve this problem, the global U(1) symmetry must be preserved to a high degree of accuracy. However, it is well known that global symmetries are explicitly violated by quantum gravity effects, giving rise to what is referred to as the axion quality problem. In this paper, we investigate axionic wormholes as a source of explicit U(1) violation in Metric-Affine Gravity. This framework allows for spacetime torsion and non-metricity, which accommodate additional curvature-like and topological terms, such as the Holst and Nieh--Yan terms, that are absent from the metric and Palatini formalisms. We show that non-minimal couplings to these terms modify the wormhole dynamics and enhance the Euclidean wormhole action, thereby alleviating the axion quality problem. We also find that the viable parameter space is enlarged when two of these couplings are simultaneously present. We further identify representative parameter regions where the alleviation of the axion quality problem is compatible with inflationary constraints.
Related
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- A principal-symbol obstruction in metric-affine Gauss--Bonnet gravity
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- Projective Symmetry and Its Breaking in Quadratic Metric-Affine Gravity
- Inflationary attractors in metric-affine gravity
BibTeX
@misc{takeshita2026axionic,
title = {{Axionic Wormholes in Metric-Affine Gravity}},
author = {Shonosuke Takeshita and Naoki Yoshioka},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.11010},
eprint = {2609.11010},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.11010},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Axionic Wormholes in Metric-Affine Gravity
AU - Shonosuke Takeshita
AU - Naoki Yoshioka
PY - 2026
DA - 2026/09/16
PB - arXiv
DO - 10.48550/arxiv.2609.11010
UR - https://arxiv.org/abs/2609.11010
AB - The axion is a promising candidate for solving the strong CP problem. To solve this problem, the global U(1) symmetry must be preserved to a high degree of accuracy. However, it is well known that global symmetries are explicitly violated by quantum gravity effects, giving rise to what is referred to as the axion quality problem. In this paper, we investigate axionic wormholes as a source of explicit U(1) violation in Metric-Affine Gravity. This framework allows for spacetime torsion and non-metricity, which accommodate additional curvature-like and topological terms, such as the Holst and Nieh--Yan terms, that are absent from the metric and Palatini formalisms. We show that non-minimal couplings to these terms modify the wormhole dynamics and enhance the Euclidean wormhole action, thereby alleviating the axion quality problem. We also find that the viable parameter space is enlarged when two of these couplings are simultaneously present. We further identify representative parameter regions where the alleviation of the axion quality problem is compatible with inflationary constraints.
ER -