Abstract
Light new physics weakly coupled to the Higgs can induce a strong first-order electroweak phase transition (EWPT). Here, we argue that scenarios in which the EWPT is driven first-order by a light scalar with mass between $\sim 10$ GeV - $m_h/2$ and small mixing with the Higgs will be conclusively probed by the high-luminosity LHC and future Higgs factories. Our arguments are based on analytic and numerical studies of the finite-temperature effective potential and provide a well-motivated target for exotic Higgs decay searches at the LHC and future lepton colliders.
Highlights
Determining the thermal history of electroweak symmetry breaking (EWSB) in the early Universe is an important challenge for particle physics and cosmology
In summary we find that successful completion of the phase transition is the dominant factor in determining the lower boundary of this parameter space for successful strongly first-order EWPT (SFOEWPT); the conditions on the depth of minima at zero and finite temperature, Eqs. (23) and (29), do not by themselves lead to a nontrivial lower bound on a2
We have explored scenarios in which the interaction between the Standard Model (SM) Higgs boson and a light scalar field catalyzes a first order electroweak phase transition, and have demonstrated that there remains viable, albeit potentially fine-tuned, parameter space for SFOEWPTs featuring a new scalar state with mass lighter than half the Higgs mass
Summary
Determining the thermal history of electroweak symmetry breaking (EWSB) in the early Universe is an important challenge for particle physics and cosmology. Alternate possibility is that light BSM particles (with masses e.g., below mZ) coupled to the Higgs could result in a strongly first-order EWPT (SFOEWPT) These scenarios are appealing experimentally, though they provide qualitatively distinct challenges compared to the case where all BSM particles are heavier than the SM Higgs. (iii) The high luminosity LHC (HL-LHC) and prospective future lepton colliders will be able to improve this sensitivity down to ∼10 GeV in the channels we consider, and potentially further While these results come with certain caveats (discussed below), the work presented here provides an important physics target for current and future exotic Higgs decay searches. V we discuss some caveats to our arguments, and conclude
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