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 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.
