# Non-resonant Collider Signatures of a Singlet-Driven Electroweak Phase Transition

## TL;DR

This paper explores collider signatures of a singlet extension of the Standard Model that can produce a strong first-order electroweak phase transition, focusing on non-resonant scalar pair production at current and future colliders.

## Contribution

It identifies the correlation between phase transition strength and non-resonant scalar pair production, proposing collider strategies to probe this connection.

## Key findings

- Non-resonant singlet scalar pair production is a key signature.
- Future 100 TeV colliders can effectively probe the phase transition.
- Correlations exist between phase transition strength and collider observables.

## Abstract

We analyze the collider signatures of the real singlet extension of the Standard Model in regions consistent with a strong first-order electroweak phase transition and a singlet-like scalar heavier than the Standard Model-like Higgs. A definitive correlation exists between the strength of the phase transition and the trilinear coupling of the Higgs to two singlet-like scalars, and hence between the phase transition and non-resonant scalar pair production involving the singlet at colliders. We study the prospects for observing these processes at the LHC and a future 100 TeV $pp$ collider, focusing particularly on double singlet production. We also discuss correlations between the strength of the electroweak phase transition and other observables at hadron and future lepton colliders. Searches for non-resonant singlet-like scalar pair production at 100 TeV would provide a sensitive probe of the electroweak phase transition in this model, complementing resonant di-Higgs searches and precision measurements. Our study illustrates a strategy for systematically exploring the phenomenologically viable parameter space of this model, which we hope will be useful for future work.