Leptonic decays of the B charged meson and B → Xsγ in the Two Higgs Doublet Model type III

Abstract

We consider the Two Higgs Doublet Model (2HDM) of type III which leads to Flavour Changing Neutral Currents (FCNC) at tree level. In the framework of this model we calculate the NLO contribution for b → sγ and the branchings for the meson decays B + → l + ν. We examine the limits on the new parameters λ bb and M H ± . We take into account the relationship between λ tt and λ bb coming from the validness of perturbation theory.Keywords: B Meson decay; 2HDM type III; Charged Higgs mass The Standard Model (SM) of particle physics based on the gauge group SU(3) c × SU(2) L × U(1) Y makes fit the symmetry breaking by including a fundamental weak doublet of scalar Higgs bosons φ with a scalar potential V (φ) = λ(φ † φ − 1 2 v 2 ) 2 . However, the SM does not explain the dynamics responsible for the generation of masses. Between the models beyond the SM, many of them include more than one scalar Higgs doublet; for instance, the case of the minimal supersymmetric standard model (MSSM)). We consider one of these extensions which has a richer scalar sector, called generically as the Two Higgs Doublet Model (2HDM). There are several kinds of such 2HDM models. In the model called type I, one Higgs doublet provides masses to the up and down quarks, simultaneously. In the model type II, one Higgs doublet gives masses to the up type quarks and the other one to the down type quarks. These two models include a discrete symmetry to avoid flavour changing neutral currents (FCNC) at tree level [1]. However, the addition of these discrete symmetries is not compulsory and in this case both doublets are contributing to generate the masses for up-type and down-type quarks. In the literature, such a model is known as the 2HDM type III [2]. It has been used to search for physics beyond the SM and specifically for FCNC at tree level [3][4][5]. In general, both doublets can acquire a vacuum expectation value (VEV), but one of them can be absorbed redefining the Higgs boson fields properly. Nevertheless, other studies on 2HDM-III using different basis have been done and there is a case where both doublets get VEVs that allows to study the models type I and II in a specific limit [5,6].In the 2HDM models, the two complex Higgs doublets correspond to eigth scalar states. Spontanoues Symmetry breaking procedure leads to five Higgs fields: two neutral CP-even scalars h 0 and H 0 , a neutral CP-odd scalar A 0 , and two charged scalars H ± . While the neutral Higgs bosons may be difficult to distinguish from the one of the SM, the charged Higgs bosons would have a distinctive signal for physics beyond the SM. Therefore the direct or indirect evidence of a charged Higgs boson would play an important role in the discovery of an extended Higgs sector. Direct searches have carried out by LEP collaborations and they reported a combined lower limit on M H ± of 78.6 GeV [7] assuming H + → τ + ν τ (cs). At the Tevatron, the direct searches for charged Higgs boson are based on pp → tt where at least one top quark decay can be used in order to look for the...

Theory and phenomenology of two-Higgs-doublet models

“…Other bounds on the λ ij do not involve flavour-changing neutral currents. If one assumes that only λ tt and λ bb are nonzero, then neutral scalars play no role, and one can bound λ tt and λ bb by considering the charged-Higgs contributions to b → sγ [232,233,234]; one obtains a bound on λ tt of approximately 1.7, for a charged-Higgs mass below 300 GeV. More recently, Mahmoudi and Stal [46] analysed b → sγ and ∆m B d as well as B, K, and D s decays, and obtained bounds on all the second-and third-generation diagonal λ ij (including for the leptons).…”

“…Of course, if additional λ ij are taken to be non-zero the parameter space becomes quite large. Some recent analyses that discuss other λ ij include the work of Diaz et al [367], in which the effects of non-zero λ sb and λ tc were discussed (λ sb was found to be unbounded, λ tc was found to be smaller than 1), and of Idarraga et al [368], who also considered bounds from leptonic B decays but chose very large λ µµ and λ τ τ . Also note that, if neutral fields are allowed in the loop, one could get an effect proportional to λ 2 bs , which is, however, negligible.…”

QCD corrections in two-Higgs-doublet extensions of the standard model with minimal flavor violation

“…[11,12,13]) used various combinations of flavor and electroweak observables to constrain the parameter space of the type-II 2HDM, which garnered most of the attention because of its property of having the same Higgs-sector realization as the Minimal Supersymmetric Standard Model (MSSM). Other studies [14,15,16] explored the parameter space of 2HDMs unconstrained by a Z 2 symmetry, with the second Higgs doublet still in the (1, 2) 1/2 representation.…”

Constraints on two-Higgs-doublet model parameters in light of rare B decays

“…The purpose of the present study is to look for the constraints on all physical Higgs masses and coupling parameters in the light of the rare B-meson decays. In the framework of the 2HDM type III Yukawa interaction, the Cheng-Sher-Yuan (CSY) parameterization [39,40] for the couplings ε ij = m i m j v 2 λ ij is useful and among these, the third family couplings λ bb and λ tt are constrained, along-with charged Higgs boson mass, from the branching ratios of b → sγ and B + → l + ν [41]. They have shown that the most stringent constraints are coming from b → sγ and the pure leptonic decays can only exclude regions with small λ bb and small m H ± .…”

“…parameterization [39,40] for the couplings ε ij = m i m j v 2 λ ij is useful and among these, the third family couplings λ bb and λ tt are constrained, along-with charged Higgs boson mass, from the branching ratios of b → sγ and B + → l + ν [41]. They have shown that the most stringent constraints are coming from b → sγ and the pure leptonic decays can only exclude regions with small λ bb and small m H ± .…”