A scaling non-compact QCD axion

Georgios K. Karananas; Mikhail Shaposhnikov

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arXiv · 2606.17019

A scaling non-compact QCD axion

Georgios K. Karananas·Mikhail Shaposhnikov

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Abstract

We present a dynamical mechanism for the erasure of inflationary isocurvature perturbations of the non-compact QCD axion. The key ingredient is an early-time runaway exponential potential, which drives the axion onto the well-known scaling cosmological attractor after inflation. Once on the attractor, the axion tracks the dominant component of the Universe, radiation, and isocurvature modes are erased even if the field is effectively massless during inflation. When the QCD potential turns on, the axion carries nonzero velocity, and kinetic misalignment can become operative. The exponential potential induces residual CP violation, potentially accessible to future electric dipole moment searches. This mechanism requires that the axion be effectively non-compact over the field range relevant for its post-inflationary evolution.

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Georgios K. Karananas, Mikhail Shaposhnikov. 2026-06-15. A scaling non-compact QCD axion. https://arxiv.org/abs/2606.17019

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