Gravitational wave background from vacuum and thermal fluctuations during axion-like inflation. Issue 12 (1st December 2022)

• Record Type: Journal Article
• Authors: Klose, P.; Laine, M.; Procacci, S.
• Is Part Of: Journal of cosmology and astroparticle physics. Volume 2022:Issue 12(2022)
• Publication Date: 2022-12-01
• Subjects: particle physics - cosmology connection -- primordial gravitational waves (theory) -- inflation -- axions; Cosmology -- Periodicals; Astrophysics -- Periodicals; 523.0105
• DOI: 10.1088/1475-7516/2022/12/020
• Languages: English
• ISSNs: 1475-7516

Abstract

Abstract: We revisit the framework of axion-like inflation in view of the possibility that the coupling of the inflaton to a non-Abelian topological charge density could lead to the generation of a rapidly thermalizing heat bath. Both dispersive (mass) and absorptive (friction) effects are included. For phenomenologically viable parameters, the system remains in a weak regime of warm inflation (thermal friction ≪ Hubble rate). For tensor perturbations we derive an interpolating formula that incorporates both vacuum and thermal production. The latter yields a model-independent frequency shape ∼ f 0 3 in the LISA window, whose coefficient allows to measure the maximal shear viscosity of the thermal epoch. It is a challenge, however, to find models where the coefficient is large enough to be observable.