A strong electroweak phase transition in the 2HDM after LHC8

Abstract

The nature of the electroweak phase transition in two-Higgs-doublet models is revisited in light of the recent LHC results. A scan over an extensive region of their parameter space is performed, showing that a strongly first-order phase transition favours a light neutral scalar with SM-like properties, together with a heavy pseudo-scalar (m_A^0 > 400 GeV) and a mass hierarchy in the scalar sector, m_H^+ < m_H^0 < m_A^0. We also investigate the h^0 -> gamma gamma decay channel and find that an enhancement in the branching ratio is allowed, and in some cases even preferred, when a strongly first-order phase transition is required

Strong first order electroweak phase transition in the CP-conserving 2HDM revisited

“…The latter corresponds to the alignment limit where only one of the physical Higgs bosons has a VEV [111]. Previous investigations suggest that a firstorder PT prefers a scalar spectrum, which is not too heavy [46,47,50], or else a large mass splitting between the heavy scalars [47,51]. In the type II 2HDM the requirement of a light Higgs spectrum puts some tension on the model, as compatibility with the EW precision tests requires one of the non-SM-like neutral Higgs bosons to be close to m H ± .…”

“…H, which acquires a VEV, should be light, so that the strength of JHEP02 (2017) the PT is not reduced by a heavy H. Consequently m 2 12 is small, 14 which means that the strength of the phase transition is governed by the quartic couplings λ 4 and λ 5 , cf. also [46]. The next important mass configuration is given by scenarios where again the mass gap between A and H is large, but now overall pushed to higher mass values, i.e.…”

“…Their contributions to the effective Higgs potential can strengthen the PT and in addition introduce new sources of CP violation. Previous studies have shown that 2HDMs provide a good framework for successful baryogenesis [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] (see [48][49][50][51][52] for studies in the CP-violating 2HDM).…”

“…7 Previous works included only the VEVs and (subsets of) the masses in the renormalisation conditions and required them to be equal to their tree-level values [46][47][48][49][50]. In models with extended Higgs sectors, the mixing angles, which enter all Higgs boson observables through the Higgs couplings, are crucial for the interpretation of the results.…”

“…It is a well-known problem that this derivative leads to infrared divergences for the Goldstone bosons in the Landau gauge [46,48,50,[72][73][74]. In order to circumvent this problem, in [48] the logarithm is redefined to capture on-shell effects regularising the divergence while in [46,47,50] a non-vanishing infrared mass for the Goldstones is employed to regulate the divergence. In the effective potential approach itself, which is the approximation of the full theory at vanishing external momenta, it is not possible to cancel these divergences.…”