Hot New Early Dark Energy: Towards a Unified Dark Sector of Neutrinos,
  Dark Energy and Dark Matter
  We propose that a first-order phase transition of a sub-eV scalar field in
the dark sector, triggered by the decreasing temperature as the universe
expands, can simultaneously relieve the Hubble tension and explain neutrino
masses. Here, the supercooled vacuum of the scalar field gives rise to a
sizable fraction of an early dark energy component that boosts the expansion
before recombination and subsequently decays. The neutrino masses are generated
through the inverse seesaw mechanism by making a set of sterile Majorana
fermions massive when the scalar field picks up its vacuum expectation value.
We embed this low-energy theory in a larger gauge group that is partially
broken above the TeV scale. This novel theory, which could even be motivated
independently of the Hubble tension, completes the high-energy corner of the
inverse seesaw mechanism and explains the mass of a dark matter candidate that
can be produced through gravitational interactions at high energies. An
approximate global lepton symmetry that is spontaneously broken during the
low-energy phase transition protects the neutrino masses against loop
corrections.
