arXiv subjects

Yuji Omura

Publications and source records attributed to Yuji Omura.

At least 73 records · Page 4Linked to original sources

arXiv2014

Multi-Higgs doublet models with local $U(1)_H$ 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 $B\rightarrow D^{(*)} τν$ 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.

hep-ph↗

arXiv2013

Higgs phenomenology in Type-I 2HDM with U(1)_H Higgs gauge symmetry

It is well known that generic two-Higgs-doublet models (2HDMs) suffer from potentially large Higgs-mediated flavor-changing neutral current (FCNC) problem, unless additional symmetries are imposed on the Higgs fields thereby respecting the Natural Flavor Conservation Criterion (NFC) by Glashow and Weinberg. A common way to respect the NFC is to impose Z_2 symmetry which is softly broken by a dim-2 operator. Another new way is to introduce local U(1)_H Higgs flavor symmetry that distinguishes one Higgs doublet from the other. In this paper, we consider the Higgs phenomenology in Type-I 2HDMs with the U(1)_H symmetry with the simplest U(1)_H assignments that the SM fermions are all neutral under U(1)_H, and we make detailed comparison with the ordinary Type-I 2HDM. After imposing various constraints such as vacuum stability and perturbativity as well as the electroweak precision observables and collider search bounds on charged Higgs boson, we find that the allowed Higgs signal strengths in our model are much broader than those in the ordinary Type-I 2HDM, because of newly introduced U(1)_H-charged singlet scalar and U(1)_H gauge boson. Still the ATLAS data on gg to h to gamma gamma cannot be accommodated. Our model could be distinguished from the ordinary 2HDM with the Z_2 symmetry in a certain parameter region and some channels. If the couplings of the new boson turn out to be close to those in the SM, it would be essential to search for extra U(1)_H gauge boson and/or one more neutral scalar boson to distinguish two models.

hep-ph↗

arXiv2013

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.

hep-ph↗

arXiv2013

Predictivity of models with spontaneously broken non-Abelian discrete flavor symmetries

In a class of supersymmetric flavor models predictions are based on residual symmetries of some subsectors of the theory such as those of the charged leptons and neutrinos. However, the vacuum expectation values of the so-called flavon fields generally modify the Kähler potential of the setting, thus changing the predictions. We derive simple analytic formulae that allow us to understand the impact of these corrections on the predictions for the masses and mixing parameters. Furthermore, we discuss the effects on the vacuum alignment and on flavor changing neutral currents. Our results can also be applied to non--supersymmetric flavor models.

hep-ph↗

arXiv2013

Top FB asymmetry vs. (semi)leptonic B decays in multi-Higgs-doublet models

We investigate the semileptonic and leptonic B decays, B to D^{(*)} tau nu and B to tau nu in our multi-Higgs-doublet models, while keeping in mind the enhancement of the top forward-backward (FB) asymmetry (A^t_{FB}) at the Tevatron. In these models, the extra (pseudo)scalar bosons contribute to A^t_{FB} with large flavor-changing Yukawa couplings involving the top quark, but the contribution of the charged Higgs boson to A^t_{FB} is negligible. However, it may significantly affect B decays: especially, B to D^{(*)} tau nu and B to tau nu. We investigate the 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}.

hep-ph↗

arXiv2013

Top Forward-backward asymmetry at the Tevatron vs. Charge asymmetry at the LHC in chiral $U(1)'$ 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.

hep-ph↗

arXiv2012

Top A_FB at the Tevatron vs. charge asymmetry at the LHC in chiral U(1) flavor models with flavored Higgs doublets

We consider the top forward-backward (FB) asymmetry at the Tevatron and top charge asymmetry at the LHC within chiral U(1)^\prime models with flavor-dependent U(1)^\prime charges and flavored Higgs fields, which were introduced in the ref. [65]. The models could enhance not only the top forward-backward asymmetry at Tevatron, but also the top charge asymmetry at LHC, without too large same-sign top pair production rates. We identify parameter spaces for the U(1)^\prime gauge boson and (pseudo)scalar Higgs bosons where all the experimental data could be accommodated, including the case with about 125 GeV Higgs boson, as suggested recently by ATLAS and CMS.

hep-ph↗

arXiv2012

A Resolution of the Flavor Problem of Two Higgs Doublet Models with an Extra U(1)_H Symmetry for Higgs Flavor

We propose to implement the Natural Flavor Conservation criterion in the two Higgs doublet model (2HDM) to an extra U(1)_H gauge symmetry for Higgs flavor, assuming two Higgs doublets carry different U(1)_H charges. Then one can easily avoid the tree level FCNC from neutral Higgs mediations using local gauge symmetries, instead of softly broken ad hoc Z_2 symmetry, and the pseudoscalar boson could be eaten by extra Z_H boson. Imposing the anomaly cancellation, we find that the U(1)_H in the Type-II and Type-IV 2HDM's become leptophobic and leptophilic, respectively. For the Type-I case, U(1)_H depends on two parameters, and some simple cases include U(1)_H = U(1)_{B-L}, U(1)_R, or U(1)_Y. We sketch qualitative phenomenology of these models.

hep-ph↗

arXiv2012

Top A_{FB} and charge asymmetry in flavor-dependent chiral U(1)' model

We study the flavor-dependent chiral U(1)' model where only the right-handed up-type quarks are charged under U(1)$^\prime$ and additional Higgs doublets charged with U(1)' charges are introduced to give proper Yukawa interactions. We find that in some parameter regions, this model is not accommodated only with the top forward-backward asymmetry at the Tevatron, but also with the charge asymmetry at the LHC. At the same time, the cross section for the same-sign top-quark pair production in this model could be below the upper limit at the LHC.

hep-ph↗

arXiv2012

Top forward-backward asymmetry and the CDF Wjj excess in leptophobic U(1)' flavor models

We construct anomaly-free leptophobic U(1)' flavor models with light Z'(~ 145 GeV). In order to allow renormalizable Yukawa interactions for the standard model chiral fermions, new Higgs doublets with nonzero U(1)' charges are introduced. Then the neutral (pseudo)scalar Higgs bosons as well as Z' contribute to the t\bar{t} and the same sign top pair productions [σ(t\bar{t}]) and σ(tt)], and one can evade the strong constraint from σ(tt). The top forward-backward asymmetry (A_{FB}) and Wjj excess at CDF could be accommodated by A_{FB}^{New} = 0.084 ~ 0.12 and σ(W j j) \lesssim O(10) pb \times \sin^2 2 β.

hep-ph↗

arXiv2012

Cold Dark Matters in U(1)' Models

We consider models with extra U(1)' gauge symmetry that is broken spontaneously. In the models, there are cold dark matter candidates which are charged under U(1)' symmetry. Depending on the charge assignment, we can evade the strong bound from the Drell-Yang process, and consider the scenario that the dark matters strongly interact with the fermions in the Standard Model through the extra gauge boson exchanging. As an illustrative example, we discuss a supersymmetric gauged U(1)_B \times U(1)_L model and see that not only correct relic density but also the DAMA/CoGeNT excess can be achieved by the dark matters.

hep-ph↗

arXiv2012

Chiral U(1) flavor models and flavored Higgs doublets: the top FB asymmetry and the Wjj

We present U(1) flavor models for leptophobic Z' with flavor dependent couplings to the right-handed up-type quarks in the Standard Model, which can accommodate the recent data on the top forward-backward (FB) asymmetry and the dijet resonance associated with a W boson reported by CDF Collaboration. Such flavor-dependent leptophobic charge assignments generally require extra chiral fermions for anomaly cancellation. Also the chiral nature of U(1)' flavor symmetry calls for new U(1)'-charged Higgs doublets in order for the SM fermions to have realistic renormalizable Yukawa couplings. The stringent constraints from the top FB asymmetry at the Tevatron and the same sign top pair production at the LHC can be evaded due to contributions of the extra Higgs doublets. We also show that the extension could realize cold dark matter candidates.

hep-ph↗

arXiv2012

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.

hep-ph↗

arXiv2011

Supersymmetric U(1)B x U(1)L model with leptophilic and leptophobic cold dark matters

We consider a supersymmetric model with extra $U(1)_B \times U(1)_L$ gauge symmetry that are broken spontaneously. Salient features of this model are that there are three different types of cold dark matter (CDM) candidates, and neutral scalar sector has a rich structure. Light CDM with $σ_{\rm SI} \sim 10^{-3\pm 1}$ pb can be easily accommodated by leptophobic dark matter ($χ_B$) with correct relic density, if the $U(1)_B$ gauge boson mass is around $2 m_{χ_B}$. Also the PAMELA and Fermi/LAT data can be fit by leptophilic CDM with mass $\sim 1$ TeV. There could be interesting signatures of new fermions and new gauge bosons at the LHC.

hep-ph↗

arXiv2011

Light dark matter in leptophobic Z' models

Recent experimental results in direct dark matter detection may be interpreted in terms of a dark matter particle of mass around 10 GeV/c^2. We show that the required scenario can be realized with a new dark matter particle charged under an extra abelian gauge boson Z' that couples to quarks but not leptons. This is possible provided the Z' gauge boson is very light, around 10-20 GeV/c^2 in mass, and the gauge coupling constant is small, alpha' ~ 10^(-5). Such scenarios are not constrained by accelerator data.

hep-ph↗

arXiv2009

Supersymmetry breaking, R-symmetry, and conformal dynamics

We study N=1 global and local supersymmetric theories with a continuous global U(1)_R symmetry. We discuss conditions for supersymmetry (SUSY) breaking and vacuum structures of R-symmetric SUSY models. Especially we find the conditions for R-symmetry breaking and runway vacua in global supersymmetric theories. We introduce explicit R-symmetry breaking terms into such models in global and local supersymmetric theories. We classify explicit R-symmetry breaking terms by the structure of newly appeared SUSY stationary points as a consequence of the R-breaking effect. Based on the generic argument, we propose the scenario that conformal dynamics causes approximate R-symmetry and metastable SUSY breaking vacua at a low energy scale. Furthermore, we find that conformal dynamics also leads approximate R-symmetry in softly SUSY breaking theories, even in more complicated models such as the duality cascade. We investigate the RG flow of SUSY breaking terms as well as supersymmetric couplings in the duality cascade of softly broken supersymmetric theories. We also show the possibility that cascading would be terminated by the gauge symmetry breaking, which is induced by the so-called B-term. Finally, we find some models to arrive at standard-model-like models and to cause gauge symmetry breaking corresponding to electro-weak symmetry breaking.

hep-ph↗

arXiv2008

Duality cascade of softly broken supersymmetric theories

We study the duality cascade of softly broken supersymmetric theories. We investigate the renormalization group (RG) flow of SUSY breaking terms as well as supersymmetric couplings. It is found that the magnitudes of SUSY breaking terms are suppressed in most regimes of the RG flow through the duality cascade. At one stage of cascading, the gaugino mass of the strongly coupled sector and scalar masses converge to certain values, which are determined by the gauge coupling and the gaugino mass of the weakly coupled sector. At the next stage, the strongly and weakly coupled sectors are interchanged with each other. We also show the possibility that cascading would be terminated by the gauge symmetry breaking, which is induced by the so-called B-term.

hep-th↗

arXiv2008

Soft supersymmetry breaking terms from A4 lepton flavor symmetry

We study the supersymmetric model with the A4 lepton flavor symmetry, in particular soft supersymmetry breaking terms, which are predicted from the A4 lepton flavor symmetry. We evaluate soft slepton masses and A-terms within the framework of supergravity theory. Constraints due to experiments of flavor changing neutral current processes are examined.

hep-ph↗