Hot New Early Dark Energy

TL;DR

This paper introduces hot NEDE, a new early dark energy model triggered by thermal effects in a dark sector, which improves cosmological fits and offers solutions to the Hubble tension, LSS tension, and neutrino mass generation.

Contribution

It proposes a novel hot NEDE mechanism based on thermal corrections and explores its phenomenology, microscopic embeddings, and implications for dark matter, neutrino masses, and cosmological tensions.

Findings

Hot NEDE naturally explains the decay of dark energy via a vacuum phase transition.

The strong supercooled regime is favored phenomenologically.

Models include non-Abelian dark matter and neutrino mass generation mechanisms.

Abstract

New early dark energy (NEDE) makes the cosmic microwave background consistent with a higher value of the Hubble constant inferred from supernovae observations. It is an improvement over the old early dark energy model (EDE) because it explains naturally the decay of the extra energy component in terms of a vacuum first-order phase transition that is triggered by a subdominant scalar field at zero temperature. With hot NEDE, we introduce a new mechanism to trigger the phase transition. It relies on thermal corrections that subside as a subdominant radiation fluid in a dark gauge sector cools. We explore the phenomenology of hot NEDE and identify the strong supercooled regime as the scenario favored by phenomenology. In a second step, we propose different microscopic embeddings of hot NEDE. This includes the (non-)Abelian dark matter model, which has the potential to also resolve the LSS tension through interactions with the dark radiation fluid. We also address the coincidence problem generically present in EDE models by relating NEDE to the mass generation of neutrinos via the inverse seesaw mechanism. We finally propose a more complete dark sector model, which embeds the NEDE field in a larger symmetry group and discuss the possibility that the hot NEDE field is central for spontaneously breaking lepton number symmetry.