Amnesia in the Axion Misalignment Landscape

2026/08/04 by Kierthika Chathirathas, Cem Eröncel, Mathieu Kaltschmidt +2
Physics and Astronomy · #hep-ph #astro-ph.CO #hep-th

paper · pdf

Main letter: 5 pages, 5 figures. SupM: 26 pages, 14 additional figures. Comments welcome!

arxiv created 2026/08/04 · arxiv updated 2026/08/06

Abstract

Pre-inflationary axion cosmologies admit a broad range of initial velocities and angles that generate a landscape of misalignment histories, whose nonlinear fate and small-scale structure remain uncertain. We use lattice simulations to follow the QCD axion in the kinetic misalignment scenario through the QCD crossover into the non-relativistic regime, towards matter-radiation equality. In the meV mass range, this landscape contains a continuum of ''summit-landing" solutions sensitive to both the initial angle and velocity. Nonlinear fragmentation reduces the comoving axion number and modifies the relation between the misalignment history and present relic abundance. For sufficiently large axion masses, strong self-interactions drive the small-scale spectrum towards the attractor found for post-inflationary axions, so that distinct early histories can lead to similar late-time structures.

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