# Viable Twin Cosmology from Neutrino Mixing

## TL;DR

This paper proposes a cosmological solution for Twin Higgs models involving neutrino mixing, which reduces the radiation density contribution and is testable in current experiments, providing a natural UV completion.

## Contribution

It introduces a novel mechanism where SM and twin neutrino mixing thermalizes sectors, addressing cosmological constraints in Twin Higgs models with a warped UV completion.

## Key findings

- Neutrino mixing reduces twin sector radiation density.
- Twin neutrino masses of 1-20 GeV are viable and testable.
- Warped UV models naturally realize the required neutrino parameters.

## Abstract

Twin Higgs models solve the little hierarchy problem without introducing new colored particles, however they are often in tension with measurements of the radiation density at late times. Here we explore viable cosmological histories for Twin Higgs models. In particular, we show that mixing between the SM and twin neutrinos can thermalize the two sectors below the twin QCD phase transition, significantly reducing the twin sector's contribution to the radiation density. The requisite twin neutrino masses of order 1-20 GeV and mixing angle with SM neutrinos of 10^{-3} - 10^{-5} can be probed in a variety of current and planned experiments. We further find that these parameters can be naturally accessed in a warped UV completion, where the neutrino sector can also generate the Z2-breaking Higgs mass term needed to produce the hierarchy between the symmetry breaking scales f and v.