Abstract.
The New Early Dark Energy (NEDE) model introduces a scalar field that undergoes a phase transition at the eV scale. It provides a promising framework for addressing the Hubble tension in terms of simple new physics. Its crucial ingredient is the scalar field's false vacuum energy, which plays the role of a new phase of dark energy and decays in a first-order phase transition when a subdomiant trigger removes the potential barrier. I will first argue that the presence of a trigger is a crucial element to remain compatible with observations of the CMB. I will then discuss the prospects of two microscopic realizations. While cold NEDE introduces an ultralight axion to trigger the phase transition, hot NEDE relies on a dark sector temperature to achieve the same. I will argue that both scenarios come with unique signatures that can be looked for in the CMB, the large-scale-structure of the Universe, and gravitational wave experiments.
(The slides will be available here)