Hot new early dark energy

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 a better alternative to the old EDE model 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.

Automated summary

New Early Dark Energy (NEDE) can explain the consistency between the cosmic microwave background and the higher value of the Hubble constant inferred from supernova observations. It is a better alternative to the old EDE model as it naturally explains the decay of the extra energy component through a vacuum first-order phase transition triggered by a subdominant scalar field at zero temperature. With hot NEDE, a new mechanism to trigger the phase transition is introduced, relying on thermal corrections that subside with cooling in a dark gauge sector. The phenomenology of hot NEDE is explored, and the supercooled regime is identified as the favored scenario. Different microscopic embeddings of hot NEDE, including the (non-)Abelian dark matter model, are proposed, which can potentially resolve the LSS tension through interactions with the dark radiation fluid. The coincidence problem present in EDE models is addressed by relating NEDE to the mass generation of neutrinos via the inverse seesaw mechanism. Finally, a more complete dark sector model is proposed, embedding the NEDE field in a larger symmetry group and discussing the central role of the hot NEDE field in spontaneously breaking lepton number symmetry.