PQ Axiverse
Mehmet Demirtas, Naomi Gendler, Cody Long, Liam McAllister, Jakob, Moritz

TL;DR
This paper demonstrates that the strong CP problem can be resolved within a broad class of string theory compactifications by analyzing quantum gravitational effects, instanton contributions, and cosmological constraints, highlighting the role of large N effects.
Contribution
It provides a detailed analysis of how flux compactifications and large N effects suppress CP-violating contributions, offering a string-theoretic solution to the strong CP problem.
Findings
D-brane instanton contributions to neutron EDM are negligible for N>17.
Large N effects create hierarchies that suppress instanton actions and ultraviolet cutoff.
A significant fraction of models satisfy cosmological and astrophysical constraints.
Abstract
We show that the strong CP problem is solved in a large class of compactifications of string theory. The Peccei-Quinn mechanism solves the strong CP problem if the CP-breaking effects of the ultraviolet completion of gravity and of QCD are small compared to the CP-preserving axion potential generated by low-energy QCD instantons. We characterize both classes of effects. To understand quantum gravitational effects, we consider an ensemble of flux compactifications of type IIB string theory on orientifolds of Calabi-Yau hypersurfaces in the geometric regime, taking a simple model of QCD on D7-branes. We show that the D-brane instanton contribution to the neutron electric dipole moment falls exponentially in , with the number of axions. In particular, this contribution is negligible in all models in our ensemble with . We interpret this result as a consequence of large …
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Taxonomy
TopicsBlack Holes and Theoretical Physics · Cosmology and Gravitation Theories · Particle physics theoretical and experimental studies
