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Register a new userFlavor-changing neutral current in production and decay of pseudoscalar mesons in a type III two-Higgs-doublet-model with four-texture Yukawa couplings
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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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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.
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