Thermal Perturbations from Cosmological Constant Relaxation

Abstract

We probe the cosmological consequences of a recently proposed class of solutions to the cosmological constant problem. In these models, the universe undergoes a long period of inflation followed by a contraction and a bounce that sets the stage for the hot big bang era. A requirement of any successful early universe model is that it must reproduce the observed scale-invariant density perturbations at CMB scales. While these class of models involve a long period of inflation, the inflationary Hubble scale during their observationally relevant stages is at or below the current Hubble scale, rendering the de Sitter fluctuations too weak to seed the CMB anisotropies. We show that sufficiently strong perturbations can still be sourced thermally if the relaxion field serving as the inflaton interacts with a thermal bath, which can be generated and maintained by the same interaction. We present a simple model where the relaxion field is derivatively (i.e. technically naturally) coupled to a non-abelian gauge sector, which gets excited tachyonically and subsequently thermalizes due to its nonlinear self-interactions. This model explains both the smallness of the cosmological constant and the amplitude of CMB anisotropies.

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Cited by in corpus (5)

• Gravitational wave background from non-Abelian reheating after axion-like inflation
• Microphysical manifestations of viscosity and consequences for anisotropies in the very early universe
• Axion dark matter from frictional misalignment
• Swampland Bounds on Dark Sectors
• Constraints on the Sharpness of the Curvature Power Spectrum