Cosmological Signals of a Mirror Twin Higgs

TL;DR

This paper explores how cosmological observations can test the mirror Twin Higgs model, proposing mechanisms like scalar decay and Twinflation to reconcile the model with dark radiation constraints, and predicting observable signatures in CMB data.

Contribution

It introduces new scenarios that modify energy densities in the twin sectors, making the mirror Twin Higgs cosmologically viable and providing testable predictions for future CMB experiments.

Findings

Dilution mechanisms can reconcile mirror Twin Higgs with BBN and CMB constraints.

Predicted contributions to cosmological observables are within reach of current and future experiments.

Cosmological signatures offer a new avenue to test neutral naturalness models.

Abstract

We investigate the cosmology of the minimal model of neutral naturalness, the mirror Twin Higgs. The softly-broken mirror symmetry relating the Standard Model to its twin counterpart leads to significant dark radiation in tension with BBN and CMB observations. We quantify this tension and illustrate how it can be mitigated in several simple scenarios that alter the relative energy densities of the two sectors while respecting the softly-broken mirror symmetry. In particular, we consider both the out-of-equilibrium decay of a new scalar as well as reheating in a toy model of twinned inflation, Twinflation. In both cases the dilution of energy density in the twin sector does not merely reconcile the existence of a mirror Twin Higgs with cosmological constraints, but predicts contributions to cosmological observables that may be probed in current and future CMB experiments. This raises the prospect of discovering evidence of neutral naturalness through cosmology rather than colliders.