Non-decoupling scalars at future colliders

TL;DR

This paper explores non-decoupling scalar electroweak multiplets in BSM models, showing future lepton colliders can probe their parameter space and shed light on electroweak symmetry breaking mechanisms.

Contribution

It demonstrates that future precision lepton colliders can effectively probe all non-decoupling scalar electroweak multiplet parameter space, revealing insights into electroweak symmetry breaking.

Findings

Future colliders can test non-decoupling scalar models at TeV scale.

Distinct low-energy effects from these scalars differ from SMEFT predictions.

Electroweak phase transition can be significantly altered by these scalars.

Abstract

We consider a class of BSM models where a generic scalar electroweak multiplet obtains a significant fraction of its mass from a coupling to the Higgs. Such models are non-decoupling: their new states are necessarily at the TeV scale or below, they can significantly alter the electroweak phase transition, and they have a pattern of low energy effects that are distinct from those predicted by SMEFT. Using their minimal gauge and Higgs couplings, we show that a future precision lepton collider (such as FCC-ee, CEPC, ILC, or CLIC) can probe all the non-decoupling parameter space of scalar electroweak multiplets, providing fundamental information on the mechanism of electroweak symmetry breaking.