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Register a new userMuon Flavor Violation in Two Higgs Doublet Model with Extra Yukawa Couplings
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The new round of experiments, MEG II, COMET/Mu2e, and Mu3e, would soon start to push the $mu to egamma$, $mu N to eN$ conversion, and $mu to 3e$ frontier, while Belle II would probe $tau to mugamma$ and $tau to 3mu$. In the general two Higgs doublet model with extra Yukawa couplings, we show that all these processes probe the lepton flavor violating (LFV) dipole transition that arises from the two loop mechanism, with scalar-induced contact terms subdominant. This is because existing data suggest the extra Yukawa couplings $rho_{mu e},, rho_{ee} lesssim lambda_e$, while $rho_{taumu},, rho_{tautau} lesssim lambda_tau$ and $rho_{tt} lesssim lambda_t$, with $lambda_i$ the usual Yukawa coupling of the Standard Model (SM), where $rho_{mu e}rho_{tt}$ and $rho_{taumu}rho_{tt}$ enter the $mu egamma$ and $taumugamma$ two loop amplitudes, respectively. With the $B_s to mumu$ decay rate basically consistent with SM expectation, together with the $B_s$ mixing constraint, we show that $B_s to tautau$ would also be consistent with SM, while $B_s to taumu$ and $B to Ktaumu$ decays would be out of reach of projected sensitivities, in strong contrast with some models motivated by the B anomalies.
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With discovery of the 125 GeV boson $h^0$, the existence of a second doublet is very plausible. We show that the alignment phenomenon, that $h^0$ is found to resemble closely the Standard Model Higgs boson, may correspond to Higgs quartic couplings $eta_i$ that are ${cal O}(1)$ in strength. If the exotic bosons of the second doublet possess extra top Yukawa couplings, which are the least constrained by data, such a two Higgs doublet model could drive electroweak baryogenesis, as well as further protect the apparent alignment. The exotic Higgs bosons can be sub-TeV in mass while remaining well hidden so far, with broad parameter space for search at the Large Hadron Collider.
We carry out a detailed analysis of the general two Higgs doublet model with CP violation. We describe two different parametrizations of this model, and then study the Higgs boson masses and the trilinear Higgs couplings for these two parametrizations. Within a rather general model, we find that the trilinear Higgs couplings have a significant dependence on the details of the model, even when the lightest Higgs boson mass is taken to be a fixed parameter. We include radiative corrections in the one-loop effective potential approximation in our analysis of the Higgs boson masses and the Higgs trilinear couplings. The one-loop corrections to the trilinear couplings of the two Higgs doublet model also depend significantly on the details of the model, and can be rather large. We study quantitatively the trilinear Higgs couplings, and show that these couplings are typically several times larger than the corresponding Standard Model trilinear Higgs coupling in some regions of the parameter space. We also briefly discuss the decoupling limit of the two Higgs doublet model.
We discuss two Higgs doublet models with a softly-broken discrete $mathbb{S}_3$ symmery, where the mass matrix for charged-leptons is predicted as the diagonal form in the weak eigenbasis of lepton fields. Similar to an introduction of $mathbb{Z}_2$ symmetry, the tree level flavor changing neutral current can be forbidden by imposing the $mathbb{S}_3$ symmetry to the model. Under the $mathbb{S}_3$ symmetry, there are four types of Yukawa interactions depending on the $mathbb{S}_3$ charge assignment to right-handed fermions. We find that extra Higgs bosons can be muon and electron specific in one of four types of the Yukawa interaction. This property does not appear in any other two Higgs doublet models with a softly-broken ${mathbb Z}_2$ symmetry. We discuss the phenomenology of the muon and electron specific Higgs bosons at the Large Hadron Collider; namely we evaluate allowed parameter regions from the current Higgs boson search data and discovery potential of such a Higgs boson at the 14 TeV run.
We consider two Higgs doublet models with a softly broken U(1) symmetry, for various limiting values of the scalar mixing angles $alpha$ and $beta$. These correspond to the Standard Model Higgs particle being the lighter CP-even scalar (alignment) or the heavier CP-even scalar (reverse alignment), and also the limit in which some of the Yukawa couplings of this particle are of the opposite sign from the vector boson couplings (wrong sign). In these limits we impose a criterion for naturalness by demanding that quadratic divergences cancel at one loop. We plot the allowed masses of the remaining physical scalars based on naturalness, stability, perturbative unitarity and constraints coming from the $rho$ parameter. We also calculate the $hto gammagamma$ decay rate in the wrong sign limit.
We study flavor violating processes in the production or decay of a neutral pseudoscalar meson $P^0$ in the framework of a general two Higgs Doublet Model type III (2HDM-III). We use a version of the model where Yukawa interactions of neutral Higgs bosons allow for flavor change at the tree-level, but conserves CP symmetry. We focus on all possible $tau^{pm} to l^{pm}P^0 $ and $P^0 to l^+l^-$ decay channels, where $l,l$ are charged leptons. We find that these processes provide complementary information on quark and lepton FCNC Yukawa couplings. In particular flavor violating parameters in the quark sector, $chi_{sb}$ and $chi_{db}$, are significantly constrained by present experimental data, whereas the corresponding parameters in the leptonic sector are less constrained.
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