Coloured gravitational instantons, the strong CP problem and the companion axion solution

Abstract

Quantum gravity introduces a new source of the combined parity (CP) violation in gauge theories. We argue that this new CP violation gets bundled with the strong CP violation through the coloured gravitational instantons. Consequently, the standard axion solution to the strong CP problem is compromised. Further, we argue that the ultimate solution to the strong CP problem must involve at least one additional axion particle.

5 pages; v2: expanded discussion, to appear in EPJC

References in corpus (3)

• Three-Form Gauging of axion Symmetries and Gravity
• A Holographic Perspective on the Axion Quality Problem
• Phenomenology of the companion-axion model: photon couplings

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• Hint to Supersymmetry from GR Vacuum
• Gravitational instantons and the quality problem of the QCD axion: Facts, speculations, and statements in between
• $\mathcal{H}$olographic $\mathcal{N}$aturalness and Information See-Saw Mechanism for Neutrinos
• Perturbative Quantum Gravity Induced Scalar Coupling to Electromagnetism
• Cosmology of the companion-axion model: dark matter, gravitational waves, and primordial black holes