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arXiv · 2512.00154

Cosmology of Gravi-Axions

Stephon Alexander·Gregory Gabadadze·Leah Jenks·Nicolás Yunes
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Abstract

We show how a mass term for gravitational axions (''gravi-axions'') with a Chern-Simons coupling to gravity can naturally arise due to non-perturbative contributions from Euclidean wormholes, breaking the continuous shift symmetry of the standard theory. The induced mass can be generated in a cosmologically relevant range to be the dark matter or dark energy of the universe for a reasonable and well-motivated range of the symmetry breaking scale. Upon generating the gravi-axion mass term, we discuss the cosmology of the theory. We find that the gravi-axion can be produced to be the dominant dark matter component via misalignment or gravitational particle production, and that in a different regime, the gravi-axion can act as dynamical dark energy. We discuss gravi-axion decay into gravitons as a potential observational window for this theory. Finally, we find that, for late-time, astrophysical compact objects, cosmologically relevant gravi-axions behave as minimally-coupled, massive scalar fields.

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Stephon Alexander, Gregory Gabadadze, Leah Jenks, Nicolás Yunes. 2025-11-28. Cosmology of Gravi-Axions. https://doi.org/10.1103/yst4-cr4c

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