Fusing Vectors into Scalars at High Energy Lepton Colliders

TL;DR

This paper investigates the potential of high energy lepton colliders to detect new scalar singlets produced via vector boson fusion, highlighting their sensitivity compared to the LHC and future hadron colliders, with implications for models like Twin Higgs and NMSSM.

Contribution

It provides a detailed analysis of scalar singlet production at lepton colliders and compares sensitivities with other collider types, emphasizing the importance of pair production for probing phase transitions.

Findings

CLIC can test cross-sections of a few tens of attobarns.

High-energy muon colliders outperform future hadron colliders in sensitivity.

Pair production of scalars is a key probe for electroweak phase transition models.

Abstract

We study vector boson fusion production of new scalar singlets at high energy lepton colliders. We find that CLIC has the potential to test single production cross-sections of a few tens of attobarns in di-Higgs and di-boson final states. In models with a sizeable singlet-Higgs mixing, these values correspond to a precision in Higgs couplings of order 0.1% or better. We compare our sensitivities with those of the LHC and interpret our results in well-motivated models like the Twin Higgs, the NMSSM and axion-like particles. Looking forward to even higher energy machines, we show that the reach of muon colliders like LEMMA or MAP overcomes the one of future hadron machines like FCC-hh. We finally study the pair production of the new scalar singlets via an off-shell Higgs. This process does not vanish for small mixings and will constitute a crucial probe of models generating a first order electro-weak phase transition.