New Early Dark Energy as a solution to the $H_0$ and $S_8$ tensions

TL;DR

New Early Dark Energy proposes a phase transition mechanism around matter-radiation equality to address the H_0 and S_8 tensions, extending the standard cosmological model with a natural, trigger-based approach.

Contribution

It introduces a novel phase transition triggered by an ultralight scalar or dark sector temperature, providing a new framework to resolve key cosmological tensions.

Findings

Potential to reconcile H_0 tension

Addresses S_8 discrepancy

Links phase transition to neutrino mass generation

Abstract

New Early Dark Energy introduces a new phase of dark energy that decays in a fast-triggered phase transition around matter-radiation equality. The presence of a trigger mechanism sets it apart from other early dark energy models. Here, we will argue that New Early Dark Energy offers a simple and natural framework to extend $\Lambda$CDM while also providing a pathway to resolving the $H_0$ tension alongside its smaller cousin, the $S_8$ tension. At the microscopic level, we discuss the possibility that the trigger is either given by an ultralight scalar field or a dark sector temperature. In both cases, it prompts the transition of an $\mathrm{eV}$-mass scalar field from its false to its true minimum. Furthermore, we argue that the same phase transition could give rise to a dynamic process for generating neutrino masses.