Cosmological Perturbations of Axion with a Dynamical Decay Constant

Abstract

A QCD axion with a time-dependent decay constant has been known to be able to accommodate high-scale inflation without producing topological defects or too large isocurvature perturbations on CMB scales. We point out that a dynamical decay constant also has the effect of enhancing the small-scale axion isocurvature perturbations. The enhanced axion perturbations can even exceed the periodicity of the axion potential, and thus lead to the formation of axionic domain walls. Unlike the well-studied axionic walls, the walls produced from the enhanced perturbations are not bounded by cosmic strings, and thus would overclose the universe independently of the number of degenerate vacua along the axion potential.

19 pages, 1 figure, v2: published in JCAP

References in corpus (4)

• Axion isocurvature fluctuations with extremely blue spectrum
• Unifying inflation and dark matter with the Peccei-Quinn field: observable axions and observable tensors
• Resonant conversions of QCD axions into hidden axions and suppressed isocurvature perturbations
• Axion Dark Matter with High-Scale Inflation

Cited by in corpus (5)

• Lyman-alpha Constraints on Ultralight Scalar Dark Matter: Implications for the Early and Late Universe
• Kilobyte Cosmic Birefringence from ALP Domain Walls
• Gravitational production of dark photon dark matter with mass generated by the Higgs mechanism
• Revisiting Isocurvature Bounds on the Minimal QCD Axion
• Ultraviolet Sensitivity of Peccei-Quinn Inflation