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.