Fermion number conservation and two-Higgs-doublet models without tree-level flavor-changing neutral currents

Abstract

The charged fermion mass matrices are always invariant under U (1) 3 symmetry linked to the fermion number transformation. A class of two Higgs doublet models (2HDM) can be identified by requiring that the definition of this symmetry in an arbitrary weak basis be independent of Higgs parameters such as the ratio of the Higgs vacuum expectation values. The tree level flavour changing neutral currents normally present in 2HDM are absent in this class of models but unlike the type I or type II Higgs doublet models, the charged Higgs couplings in these models contain additional flavour dependent CP violating phases. These phases can account for the recent hints of the beyond standard model CP violation in the B d and B s mixing. In particular, there is a range of parameters in which new phases do not contribute to the K meson CP violation but give identical new physics contribution to the B d and B s meson mixing. Specific model realizations of the above scenario are briefly discussed. * anjan@prl.res.in † bhavik@prl.res.in

Charged-Higgs phenomenology in the aligned two-Higgs-doublet model

“…This more general scenario can be formally described by the Lagrangian (2.10) with the substitution ς f M f → Y f . One could still use nine dimensionless parameters ς f ≡ y f /m f , one for each charged fermion [151], but in this case this is just a redefinition of the Yukawa couplings y f because a priori nothing relates them to the fermion masses [152]. The hierarchy of couplings characteristic of the A2HDM ansatz is lost and one can no longer justify that the leading charged-scalar effects originate in the heavier fermion couplings (it becomes an assumption).…”

Theory and phenomenology of two-Higgs-doublet models

“…eq. (222). Under a CP transformation, besides the change in the sign of the space coordinates, H 1 transforms to its complex conjugate 24 while H 2 transforms to its complex conjugate apart from an arbitrary phase:…”

“…For example, the processes B s → µ + µ − , with tree-level pseudoscalar exchange, and B → Kµ + µ − , with tree-level scalar exchange, will bound the product λ bs λ µµ ; it has been shown [107,222] that data will be obtained at the Tevatron and LHC which will bound the product to approximately 0.6 (for scalar or pseudoscalar masses of 120 GeV). One of the most interesting decays, since it vanishes in the SM, is B → Kµτ .…”

Flavor conservation in two-Higgs-doublet models

“…On a different line of thought, suppression (rather than the absence) of FCNCs in other "natural" manners has also attracted significant interest, including suppression given by masses like in the Cheng-Sher ansatz [54], suppression obtained from broken/approximate flavor symmetries [55][56][57][58], and symmetry controlled FCNC scenarios [59][60][61][62][63]. Among the latter, Branco-Grimus-Lavoura models are worth mentioning in particular, since this suppression is simply given by products of CKM matrix elements [64,65] (see also related extensions [66][67][68]).…”