The meso-inflationary QCD axion

Abstract

We study the possibility that the axion Peccei-Quinn symmetry is spontaneously broken after the beginning of inflation. This scenario interpolates between pre-inflationary and post-inflationary axion cosmology with significant phenomenological differences from both. Since the axion is not present at the early stages of inflation large inflationary fluctuations are produced only at scales not constrained by CMB, avoiding the strongest isocurvature constraints. The energy density in isocurvature perturbations at short scales however can be comparable with the adiabatic contribution from misalignment. These large overdensities can lead to the formation of axion mini-clusters and also to constraints from Lyman-$\alpha$ forest and future CMB spectral distortion measurements. If Peccei-Quinn symmetry is broken during the first O(25) e-foldings of inflation no axions are produced from the string network but contributions from the annihilation of domain walls can further boost the abundance. This scenario is minimally realized if the Hubble scale during inflation drops below the Peccei-Quinn symmetry breaking scale but other realizations are possible.

arXiv comment7 pages, 3 figures. v2) figures improved, minor changes, version to appear on PRD

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• Constraints on Dark Matter from Dynamical Heating of Stars in Ultrafaint Dwarfs. Part 2: Substructure and the Primordial Power Spectrum
• Detecting Dark Matter Substructures on Small Scales with Fast Radio Bursts
• Induced Domain Walls of QCD Axion, and Gravitational Waves
• Searching for blue in the dark
• The Quality/Cosmology Tension for a Post-Inflation QCD Axion
• New mechanism for primordial black hole formation from the QCD axion
• Revisiting Isocurvature Bounds on the Minimal QCD Axion
• Stochastic gravitational wave background: birth from string-wall death
• Minimal solution to the axion isocurvature problem from a nonminimal coupling
• Imperfect Axion Precludes the Domain Wall Problem
• Meso-inflationary Peccei-Quinn symmetry breaking with non-minimal coupling
• Ultimate light-shining-through-a-wall experiments to establish QCD axions as the dominant form of dark matter
• Resolving the QCD Axion Domain Wall Problem with a Light Axion
• Crescendo Beyond the Horizon: More Gravitational Waves from Domain Walls Bounded by Inflated Cosmic Strings
• Structure Formation with Warm White Noise: Effects of Finite Number Density and Velocity Dispersion in Particle and Wave Dark Matter