B -> D^(*) tau nu and B -> tau nu in chiral U(1)' models with flavored multi Higgs doublets

We discuss semileptonic and leptonic B decays, B to D^{(*)} tau nu and B to tau nu, in the chiral U(1)' models which were proposed by the present authors in the context of the top forward-backward asymmetry (A^t_FB) observed at the Tevatron. In these models, extra Higgs doublets with nonzero U(1)' charges are required in order to make the realistic mass matrix for up-type quarks. Then the extra (pseudo)scalars contribute to A^t_FB with large flavor-changing Yukawa couplings involving top quark. The contribution of the charged Higgs to A^t_FB is negligible, but it may significantly affect B decays: especially, B to D^(*) tau nu and B to tau nu. We investigate constraints on the B decays, based on the recent results in BaBar and Belle experiments, and discuss the possibility that the allowed parameter region in the B decays can achieve large A^t_ FB.Comment: 19 pages, 8 figures, version published in JHE

Top Forward-backward asymmetry at the Tevatron vs. Charge asymmetry at the LHC in chiral U(1)′U(1)' models with flavored Higgs fields

An extra $U(1)'$ model with $Z'$ coupled only to the right-handed (RH) up-type quarks has been one of the popular models for the Tevatron top forward-backward asymmetry (FBA), and has been excluded by the same-sign top-pair productions at the LHC. However, the original $Z'$ model is not physical, since the up-type quarks are massless including the top quark. This disaster can be evaded if the Higgs sector is extended by including new Higgs doublets with nonzero $U(1)'$ charges. We find that some parameter regions could achieve not only the top FBA at the Tevatron, but also the charge asymmetry at the LHC without exceeding the upper limit of the same-sign top-quark pair production at the LHC. The lesson is that it is mandatory to extend the Higgs sector whenever one considers chiral gauge symmetries beyond the SM gauge group. Otherwise some fermions remain massless, and thus it is meaningless to work on phenomenology without the extra Higgs doublets with new chiral gauge charges.Comment: Contribution to HCP2012 Proceedin

Multi-Higgs doublet models with local U(1)HU(1)_H gauge symmetry and neutrino physics therein

Multi-Higgs doublet models appear in many interesting extensions of the standard model (SM). But they suffer from Higgs-mediated flavor changing neutral current (FCNC) problem which is very generic. In this talk, I describe that this problem can be resolved or mitigated if we introduce local $U(1)_H$ Higgs flavor gauge symmetry. As examples, I describe chiral $U(1)_{H}$ models where the right-handed up-type quarks also carry $U(1)_H$ charges and discuss the top forward-backward asymmetry (FBA) and $B\rightarrow D^{(*)} \tau \nu$ puzzle. Next I describe the two-Higgs doublet models where the usual $Z_2$ symmetry is implemented to $U(1)_H$ and show how the Type-I and Type-II models are extended. One possible extension of Type-II has the same fermion contents with the leptophobic $E_6$ $Z^{'}$ model by Rosner, and I discuss the neutrino sector in this model briefly.Comment: Contribution to the proceeding for the 2013 CETUP* Workshop on Neutrino and Astrophysics. arXiv admin note: text overlap with arXiv:1302.2195, arXiv:1204.458

Top forward-backward asymmetry in chiral U(1)' models

We construct flavor-dependent chiral U(1)' models with a Z' boson which couples to the right-handed up-type quarks in the standard model (SM). To make the models have realistic renormalizable Yukawa couplings, we introduce new Higgs doublets with nonzero U(1)' charges. Anomaly-free condition can be satisfied by adding extra chiral fermions. We show that these models could analyze the discrepancy between the SM prediction and empirical data in the top forward-backward asymmetry at the Tevatron.Comment: 4 pages, 2 figures, Submitted to proceedings of TOP2011 - 4th International Workshop on Top Quark Physics, 25-30th September 2011, Sant Feliu de Guixols, Spai

Dark Matter and Dark Force in the Type-I Inert 2HDM with Local U(1)_H Gauge Symmetry

We discuss dark matter (DM) physics in the Type-I inert two-Higgs-doublet model (2HDM) with local U(1)_H Higgs gauge symmetry. The local U(1)_H gauge symmetry is assigned to the extra Higgs doublet in order to avoid the Higgs-mediated flavor problems, and it spontaneously breaks down to its discrete subgroup. The lightest neutral scalar component H of the U(1)_H-charged Higgs doublet, which does not have Yukawa couplings with the Standard-Model (SM) fermions, is stable because of the remnant discrete symmetry, and it interacts with the SM particles through the U(1)_H gauge boson (Z_H) exchange as well as the SM boson exchange. We first investigate the constraint on the U(1)_H gauge interaction, especially through the kinetic and mass mixing between the SM gauge bosons and the extra gauge boson. Then we discuss dark matter physics in our 2HDM: thermal relic density, and direct/indirect detections of dark matter. The additional U(1)_H gauge interaction plays a crucial role in reducing the DM thermal relic density. The most important result within the inert DM model with local U(1)_H symmetry is that ~ O(10) GeV dark matter scenario, which is strongly disfavored in the usual Inert Doublet Model (IDM) with Z_2 symmetry, is revived in our model because of newly open channels, H H -> Z_H Z_H , Z_H Z. Exotic Higgs decays, h -> Z_H Z_H, Z Z_H, would be distinctive signatures of the inert 2HDM with local U(1)_H symmetry.Comment: 24 pages, 6 figures, version published in JHE