Phenomenology of the new light Higgs bosons in Gildener-Weinberg models

Abstract

Gildener-Weinberg (GW) models of electroweak symmetry breaking are especially interesting because the low mass and nearly Standard Model couplings of the 125 GeV Higgs boson H are protected by approximate scale symmetry. Another important but so far underappreciated feature of these models is that a sum rule bounds the masses of the new charged and neutral Higgs bosons appearing in all these models to be below about 500 GeV. Therefore, they are within reach of LHC data currently or soon to be in hand. Also so far unnoticed of these models, certain cubic and quartic Higgs scalar couplings vanish at the classical level. This is due to spontaneous breaking of the scale symmetry. These couplings become nonzero from explicit scale breaking in the Coleman-Weinberg loop expansion of the effective potential. In a two-Higgs doublet GW model, we calculate λ HHH ≃ 2ðλ HHH Þ SM ¼ 64 GeV. This corresponds to σðpp → HHÞ ≅ 15-20 fb, its minimum value for ffiffi ffi s p ¼ 13-14 TeV at the LHC. It will require at least the 27 TeV HE-LHC to observe this cross section. We also find λ HHHH ≃ 4ðλ HHHH Þ SM ¼ 0.129, whose observation in pp → HHH requires a 100 TeV collider. Because of the above-mentioned sum rule, these results apply to all GW models. In view of this unpromising forecast, we stress that LHC searches for the new relatively light Higgs bosons of GW models are by far the surest way to test them in this decade.

Two-loop analysis of classically scale-invariant models with extended Higgs sectors

“…[24] to the "scalon" direction along which EWSB is radiatively realised, is automatically aligned at tree level -as pointed out in ref. [32] for a CSI variant of the Two-Higgs-Doublet Model (2HDM) -thereby explaining current experimental results.…”

“…Indeed, we should recall that due to the relation among masses in CSI models, the new BSM states cannot be arbitrarily heavy (even in non-degenerate scenarios) and will be within reach of experiments in a foreseeable future (see for instance the discussions for the CSI-2HDM in refs. [32,79]). In the eventuality that a new scalar state is found in direct searches, determining the value of the Higgs trilinear coupling and verifying whether the relation among masses is fulfilled or not can potentially provide clear evidence of the CSI nature of the underlying theory.…”

“…Once one considers specific scenarios for the particle contents of BSM CSI theories, it becomes possible to obtain constraints on the masses of the new states -as studied for example in refs. [32,50,79]. We will return to this type of relations among masses in the following, when we consider particular BSM models.…”

“…Such effects have been studied for instance in ref. [32] in the CSI 2HDM (see also ref. [106] for the usual 2HDM) and were found to be relatively small for most of the parameter space, so that we consider them subleading before the two-loop corrections from the BSM scalar states.…”

Two-loop corrections to the Higgs trilinear coupling in models with extended scalar sectors

“…We consider now a specific model, namely the classically scale-invariant version of the Two-Higgs-Doublet Model, devised in Ref [16] (and studied also in Refs. [17][18][19]). Although it shares many similarities to the usual 2HDM (see e.g.…”