Abstract
We compute one-loop induced trilinear vertices with physical charged Higgs bosons H± and ordinary gauge bosons, i.e., H±W∓Z and H±W∓γ, in the model with two active plus one inert scalar doublet fields under a Z2(unbroken) × $$ {\tilde{Z}}_2 $$ (softly-broken) symmetry. The Z2 and $$ {\tilde{Z}}_2 $$ symmetries are introduced to guarantee the stability of a dark matter candidate and to forbid the flavour changing neutral current at the tree level, respectively. The dominant form factor F Z of the H±W∓Z vertex can be enhanced by effects of extra scalar boson loop contributions. We find that, in such a model, |F Z |2 can be one order of magnitude larger than that predicted in two Higgs doublet models, under the constraints from vacuum stability, perturbative unitarity and the electroweak precision observables. In addition, the branching fraction of the H± → W±Z (H± → W±γ) mode can be of order 10 (1)% level when the mass of H± is below the top quark mass. Such a light H± is allowed by the so-called Type-I and Type-X Yukawa interactions which appear under the classification of the $$ \tilde{Z} $$ charge assignment of the quarks and leptons. We also calculate the cross sections for the processes H± → W±Z and H± → W±γ onset by the top quark decay t → H±b and electroweak H± production at the LHC.
Highlights
Properties of H± states strongly depend on the structure of the Higgs sector, e.g., the symmetries of the model, the actual number of doublets, the mass spectrum, etc
It has been known that the H±W ∓Z vertex does not appear at the tree level1 in multi-doublet models [10], because of an approximate global SU(2) symmetry known as the custodial symmetry2 in the kinetic terms for the doublet fields
The H±W ∓Z vertex is loop induced, its magnitude can be enhanced by effects of particles running in the loop, especially for the case where they come from the sector which breaks the custodial symmetry
Summary
This too can be understood, as the trilinear H±SS (S and S being extra scalar bosons) couplings can be rewritten by squared masses of extra scalar bosons Another important reason for the appearance of a Mi2 dependence in FZ is in relation to a violation of the custodial SU(2)V symmetry. Where XV1PI and δXV are respectively the 1PI and the counter term contributions to the form factor XV (X = F, G and H) Their analytic expressions are given in appendix A. We here note that the parameter M 2 defined in eq (2.5) appearing in the second term in eq (3.20) is not relevant to the Higgs VEV, and if M 2 < v2, the masses of extra active scalar bosons are mainly given from v2. The quadratic dependence of FZ on m2A and m2ηA disappears, there still remains their logarithmic dependence
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