Abstract
In the framework where the strong coupling is dynamical, the QCD sector may confine at a much higher temperature than it would in the Standard Model, and the temperature-dependent mass of the QCD axion evolves in a non-trivial way. We find that, depending on the evolution of ΛQCD, the axion field may undergo multiple distinct phases of damping and oscillation leading generically to a suppression of its relic abundance. Such a suppression could therefore open up a wide range of parameter space, resurrecting in particular axion dark-matter models with a large Peccei-Quinn scale fa ≫ 1012 GeV, i.e., with a lighter mass than the standard QCD axion.
Highlights
Axion field typically evolves into a complex network of global strings, domain walls, and oscillons [15, 16], which must be simulated numerically (e.g. [17])
The quark condensate generates a tadpole term for the Higgs via the SM Yukawa interactions, which shifts the minimum of its potential and deforms the usual SM electroweak symmetry breaking (EWSB), and causes it to occur earlier than in the SM, if QCD confines before the SM electroweak phase transition
We restrict ourselves to cases where initially ΛQCD > Λ0QCD, and assume the de-confinement transition is such that ΛQCD can be approximated as instantaneously decreasingly to Λ0QCD at Td ≡ (Td− + Td+)/2
Summary
We outline a simple module which promotes the strong coupling constant to a dynamical quantity capable of triggering early confinement, and its impact on the mass of the QCD axion during this phase. Where gs0 is the value of the effective strong coupling constant at φ = 0. Corrections lead to a larger effective coupling during some early epoch, it may result in QCD confining earlier than it would under a standard cosmology. We will assume throughout the paper that the potential is such that φ tracks an approximately constant value corresponding to a meta-stable vacuum at φ = φ1 < 0 before transitioning into the true minimum at φ0 = 0 (see figure 1). Later on when φ transitions to the true minimum at φ = 0, the confinement scale quickly relaxes to Λ0QCD. If this happens at Td Λ0QCD, a period of deconfinement can result, until QCD reconfines as in the SM case
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