Search

We study the expected sensitivity to the mixing between sterile and tau neutrinos directly from the tau neutrino disappearance in the high-energy fixed target experiment. Here, the beam energy is large enough to produce tau neutrinos at the target with large luminosity. During their propagation to the detector, tau neutrinos may oscillate into sterile neutrinos. By examining the energy spectrum of the observed tau neutrino events, we can probe the mixing between sterile and tau neutrinos directly. In this paper, we consider Scattering and Neutrino Detector (SND) at SHiP experiment as a showcase, which uses 400 GeV protons from SPS at CERN, and expect to observe 7,300 tau and anti-tau neutrinos from the $2\times 10^{20}$ POT for 5 years operation. Assuming the uncertainty of 10\%, we find the sensitivity $|U_{\tau 4}|^2 \sim 0.08$\, (90\% CL) for $\Delta m_{41}^2 \sim 500\ \mathrm{eV}^2$ with 10\% background to the signal. We also consider a far SND at the end of the SHiP Hidden Sector Decay Spectrometer (HSDS), in which case the sensitivity would be enhanced to $|U_{\tau 4}|^2 \sim 0.02$. Away from this mass, the sensitivity becomes lower than $|U_{\tau 4}|^2 \sim 0.15$ for $\Delta m_{41}^2 \lesssim 100\ \mathrm{eV}^2$ or $\Delta m_{41}^2\gtrsim 10^4 \mathrm{eV}^2$., Comment: 14 pages, 8 figures

The mediator particle between the Standard Model sector and a hidden sector might have a long lifetime to show the observable displaced vertices in experiments. Considering a fermionic dark matter model in which the hidden sector is connected to the Standard Model by an additional Higgs doublet field, the mediator dark $Z$ boson may live long enough. We explore the possibility to observe the displaced vertices of the long-lived dark $Z$ boson at the CERN LHC and at the proposed SHiP experiment. We find that the ATLAS and CMS searches for the long-lived dark $Z$ boson can probe the mass range $7 < m_{Z'} < 150~{\rm MeV}$ with 150 fb$^{-1}$ integrated luminosity at the LHC run 3, and the SHiP experiment will probe $2 m_e < m_{Z'} < 15~{\rm MeV}$ range with $6 \times 10^{20}$ protons on target in total 15 years. The dark matter phenomenology is also discussed in the region where such a long-lived mediator is detectable., Comment: 11 pages, 4 figures

We investigate detection possibility of light dark photon in the forward experiments at the LHC, such as the SND@LHC and the FASER experiments. We assume that the dark photon mass is smaller than twice of the electron mass. Then the dark photon is long-lived and copiously produced through a neutral pion decay. Such dark photons would easily pass through 100 m of rock in front of the forward experiments and the detector targets, but some portion of them could be converted into an electron-positron pair inside the detector leaving an isolated electromagnetic shower as a new physics signature of the dark photon. Our estimation shows that in the range of kinetic mixing parameter $4\times10^{-5} \lesssim \epsilon \lesssim 2\times10^{-1}$, more than 10 signal events of the dark photon can be produced assuming 150 fb$^{-1}$ integrated luminosity., Comment: 8 pages, 2 figures

We study constraints on the hidden sector model mediated by an additional SU(2) Higgs doublet from the phenomenology of Higgs bosons. The hidden sector is assumed to contain a hidden U(1) gauge symmetry and the hidden U(1) gauge boson gets the mass by the electroweak symmetry breaking to be a dark Z boson. The Higgs sector of the model is similar to that of the two Higgs doublet model of type I except for the absence of the CP-odd scalar boson. Using the programs of HiggsBounds and HiggsSignals, we incorporate current experimental limits from LEP, Tevatron and LHC to examine the Higgs sector in our model and derive constraints on model parameters. We also discuss the implications of the model on the dark matter phenomenology., Comment: 18 pages, 7 figures

We study a two-component dark matter model consisting of a Dirac fermion and a complex scalar charged under new U(1) gauge group in the hidden sector. The dark fermion plays the dominant component of dark matter which explains the measured DM relic density of the Universe. It has no direct coupling to ordinary standard model particles, thus evading strong constraints from the direct DM detection experiments. The dark fermion is self-interacting through the light dark gauge boson and it would be possible to address that this model can be a resolution to the small scale structure problem of the Universe. The light dark gauge boson, which interacts with the standard model sector, is also stable and composes the subdominant DM component. We investigate the model parameter space allowed by current experimental constraints and phenomenological bounds. We also discuss the sensitivity of future experiments such as SHiP, DUNE and ILC, for the obtained allowed parameter space., Comment: 13 pages, 1 figure, journal version

We discuss vacuum structure and vacuum stability in classically scale-invariant renormalizable models with a scalar dark matter multiplet of global O(N) symmetry together with an electroweak singlet scalar mediator. Our conformally invariant scalar potential generates the electroweak symmetry breaking via the Coleman-Weinberg mechanism, and the new scalar singlet mediator acquires its mass through radiative corrections of the scalar dark matters as well as of the standard model particles. Taking into account the present collider bounds, we find the region of parameter space where the scalar potential is stable and all the massless couplings are perturbative up to the Planck scale. With the obtained parameter sets satisfying the vacuum stability condition, we present the allowed region of new physics parameters satisfying the recent measurement of relic abundance, and predict the elastic scattering cross section of the new scalar multiplet into target nuclei for a direct detection of the dark matter. We also discuss the collider signatures and future discovery potentials of the new scalars., Comment: 11 pages, 6 figures (partly updated), journal version. arXiv admin note: text overlap with arXiv:1904.10209

We investigate the invisible decay of positronium to probe the fermionic light dark matter mediated by the dark $Z$ boson. Too tiny is the invisible decay rate of positronium through weak interaction in the standard model to be detected in the experiment. We show that it can be enhanced to be observed in the future if the dark matter is lighter than the electron in the dark $Z$ model. We also compute the relic abundance of such light dark matter and discuss the Big Bang Nucleosynthesis constraint with an alternative thermal history scenario., Comment: 8 pages, 4 figures

We present a fermionic dark matter model mediated by the hidden gauge boson. We assume the QED-like hidden sector which consists of a Dirac fermion and U(1)$_X$ gauge symmetry, and introduce an additional scalar electroweak doublet field with the U(1)$_X$ charge as a mediator. The hidden U(1)$_X$ symmetry is spontaneously broken by the electroweak symmetry breaking and there exists a massive extra neutral gauge boson in this model which is the mediator between the hidden and visible sectors. Due to the U(1)$_X$ charge, the additional scalar doublet does not couple to the Standard Model fermions, which leads to the Higgs sector of type I two Higgs doublet model. The new gauge boson couples to the Standard Model fermions with couplings proportional to those of the ordinary $Z$ boson but very suppressed, thus we call it the dark $Z$ boson. We study the phenomenology of the dark $Z$ boson and the Higgs sector, and show the hidden fermion can be the dark matter candidate., Comment: 10 pages, 3 figures

We study a classically scale-invariant model with an electroweak singlet complex scalar mediator together with an anomaly free set of two fermionic dark matters. We introduce $U(1)_X$ gauge symmetry with a new charge $X$ in the dark sector in order to stabilize the mass of the scalar singlet with a new gauge boson. Our conformally invariant scalar potential generates the electroweak symmetry breaking via the Coleman-Weinberg mechanism, and the new scalar singlet acquires its mass through radiative corrections of the fermionic dark matters and the new gauge boson as well as of the SM particles. Taking into account the collider bounds, we present the allowed region of new physics parameters satisfying the recent measurement of relic abundance. With the obtained parameter sets, we predict the elastic scattering cross section of the new singlet fermions into target nuclei for a direct detection of the dark matter. We also discuss the collider signatures and future discovery potentials of the new scalar and gauge boson., Comment: 12 pages, 11 figures, journal version including minor corrections. arXiv admin note: text overlap with arXiv:1904.10209

We reexamine a renormalizable model of a fermionic dark matter with a gauge singlet Dirac fermion and a real singlet scalar which can ameliorate the scalar mass hierarchy problem of the Standard Model (SM). Our model setup is the minimal extension of the SM for which a realistic dark matter (DM) candidate is provided and the cancellation of one-loop quadratic divergence to the scalar masses can be achieved by the Veltman condition (VC) simultaneously. This model extension, although renormalizable, can be considered as an effective low-energy theory valid up to cut-off energies about 10 TeV. We calculate the one-loop quadratic divergence contributions of the new scalar and fermionic DM singlets, and constrain the model parameters using the VC and the perturbative unitarity conditions. Taking into account the invisible Higgs decay measurement, we show the allowed region of new physics parameters satisfying the recent measurement of relic abundance. With the obtained parameter set, we predict the elastic scattering cross section of the new singlet fermion into target nuclei for a direct detection of the dark matter. We also perform the full analysis with arbitrary set of parameters without the VC as a comparison, and discuss the implication of the constraints by the VC in detail., Comment: 11 pages, 15 figures, title changed, discussion on running couplings added, journal version

Inspired by the recent measurement of the $h \to \mu \tau$ decays by the CMS collaboration at the LHC, we study the lepton flavour-violating (LFV) $B_s \to \mu \tau$ decays in the general two Higgs doublet model. Those LFV interactions could accommodate the present deviation of the muon anomalous magnetic moment and also predict the LFV $\tau$ decay processes such as $\tau \to \mu \mu \mu$ and $\tau \to \mu \gamma$. We find that the $B_s \to \mu \tau$ decay rates should be sizable with above experimental conditions in the framework of our model. These processes are expected to be observed at the colliders such as LHCb and Belle-II in the future., Comment: 9 pages, 4 figures

We examine the possibility that the dark matter (DM) interpretation of the GeV scale Fermi gamma-ray excess at the Galactic Center can be realized in a specific framework - secluded singlet fermionic dark matter model with small mixing between the dark and Standard Model sector. Within this framework it is shown that the DM annihilation into bottom-quark pair, Higgs pair, and new scalar pair can give good fits to the Fermi gamma-ray data. Moreover unavoidable constraints from the antiproton ratio by the PAMELA and AMS-02, the gamma-ray emission from the dwarf spheroidal galaxies by the Fermi-LAT, and the Higgs measurements by the LHC are also considered. Then we found our best-fit parameters for the Fermi gamma-ray excess without conflicting other experimental and cosmological constraints if uncertainties on the DM density profile of the Milky Way Galaxy are taken into account. Successfully surviving parameters are benchmark points for future study on the collider signals., Comment: 20 pages, 8 figures, 1 table

We examine direct limits on masses of the extra neutral gauge bosons in the SU(4)_L \times U(1)_X model with a little Higgs mechanism confronted with the LHC data, especially by embedding anomaly-free set of fermions. There exist two extra neutral gauge bosons, calling Z' and Z", in this model. The lower exclusion limit of the mass of the lighter extra neutral gauge boson is about 3 TeV while that of the heavier one 5 TeV. For comparison, we examine the mass limit of Z'_3 boson in the SU(3)_L \times U(1)_X model as well, and discuss the implication of our result in the SU(4)_L \times U(1)_X model with a standard Higgs mechanism. We also discuss the discovery potential of Z' and Z" at the future LHC with the center-of-momentum energy of 14 TeV. Our results can be applicable to the models with regular Higgs mechanism if the same type of fermion family is assigned., Comment: 9 pages, 11 figures, references added, typos corrected

We study the phenomenology of heavy gauge bosons at the LHC in a nonuniversal gauge interaction model with the separate electroweak SU(2) gauge group for the third generation. Considered are the Drell-Yan processes into the final states of dilepton, dijet, $\tau^- \tau^+$, and $t \bar{t}$ for $Z'$ boson and those of lepton-neutrino for $W'$ boson. We find that the present LHC data provides lower bounds on the masses of the heavy gauge bosons, $m_{Z'},~m_{W'} > 2$ TeV, more stringent than indirect bounds, when $\sin^2 \phi > 0.15$ for the mixing angle of two SU(2) gauge groups.We also note that the study of heavy resonances into the third generation fermions may provide some valuable information in the future., Comment: 7 pages, 4 figures

A new iteration method is proposed for analyzing both the multiplicities and the transverse momentum spectra measured only within a small rapidity interval and with low momentum limit without any inconsistency or ad hoc assumptions and applied to the hadron data by the ALICE collaboration in Pb+Pb collisions at 2.76 TeV/A. In order to correctly consider the resonance contribution only to the small rapidity interval, ratios involving only those hadrons whose transverse momentum spectrum is available are considered. In spite of the small number of ratios considered, the fittings of both the ratios the transverse momentum spectra are excellent. Also the calculated ratios involving strange baryons with parameters obtained agree with data surprisingly well., Comment: 5 pages, 2 figures

Updated LHC data on the new 126 GeV boson during the 7 and 8 TeV runnings strengthen the standard model Higgs boson interpretation further. Through the global $\chi^2$ analysis, we investigate whether the new particle could be one of the scalar particles in two Higgs doublet models. Four types (Type I, II, X and Y) are comprehensively studied. Taking the recent analysis on the spin-parity of the new boson, we consider two scenarios: the new boson is either the light CP-even one ($h^0$) or the heavy CP-even one ($H^0$). It is found that both scenarios are consistent with the new data, not only in the parameter regions near the decoupling limit but also in other regions far from the decoupling limit. In addition, the current data are compatible with the possibility that the light Higgs boson $h^0$ is hidden in the mass window of 90-100 GeV. The diphoton or $\tau\tau$ channel can provide a probe of this possibility by the enhanced signal rates., Comment: To appear in JHEP

In the littlest Higgs model with T-parity, the production cross section of the T-odd heavy gauge boson pair $Z_H W_H$ is quite sizable at the LHC. In addition, both the $W_H$ and $Z_H$ bosons have almost exclusively one decay channel into $W A_H$ and $H A_H$ respectively, where the dark matter candidate $A_H$ yields a large missing energy signal. Upon the discovery of the Higgs boson at 125 GeV, we study the discovery sensitivity of the final state $ pp \to b\bar{b} l+\rlap{\,/}{E}_T$ to probe the model at the LHC. We find that the standard model backgrounds are manageable by applying suitable kinematic cuts. The LHC running at $\sqrt{s}=14$ TeV with a 100/fb total luminosity is sensitive to the model if the symmetry breaking scale $f$ is below about 850 GeV., Comment: references added: 12 pages, 2 figures, 1 table

In the two body hadronic tau decays, such as tau->to K pi (eta)nu, vector mesons play important role. Belle and Babar measured hadronic invariant mass spectrum of tau -> K pi nu decay. To compare the spectrum with theoretical prediction, we develop the chiral Lagrangian with vector mesons in Kimura:2012nx. We compute the form factors of the hadronic tau decay taking account of the quantum corrections of Nambu Goldstone bosons. We also show how to renormalizethe divergence of the Feynman diagrams with arbitrary number of loops and determine the counterterms within one loop using background field method.In this report, we discuss the renormalization of Kimura:2012nx by considering the one loop Feynman diagrams., Comment: 5 pages 3 figures, poster talk presented at The 12th International Workshop on Tau lepton Physics (tau 2012, Nagoya, Japan)

The recent discovery of a new boson of mass roughly 125 GeV has been reported by the ATLAS and CMS collaborations. Although its signals in various decay modes resemble those of the standard model (SM) Higgs boson, observed are the combinations of entangled information about the production, decay rates and total decay width of the new boson. In addition, some decay channels show non-negligible deviation from the SM expectation, such as the $2\sigma$ excess in the diphoton channel. In the four types (I, II, X and Y) of two Higgs doublet models, we perform the global $\chi^2$ fit in three scenarios: (i) the new boson is the light CP-even Higgs boson $h^0$; (ii) it is the heavy CP-even Higgs boson $H^0$; (iii) the signals are from degenerate $h^0$ and the pseudoscalar $A^0$. Considering other phenomenological constraints such as flavor physics, electroweak precision data, and the LEP search for the Higgs boson, we find that the the first scenarios in Type II and Type Y models actually provide better or similarly good fit to the data than the SM. All the other models are excluded at 95% C.L.., Comment: References are added with 18 pages, 2 figures, 4 tables

In the minimal Universal Extra Dimension (mUED) model, the second Kaluza-Klein (KK) gluon $g^{(2)}$ has loop-induced vertices with the standard model quarks, mediated by the first KK modes of the quark and the gluon/Higgs boson. With a top quark pair, this vertex is enhanced by the cooperation of the strong coupling of a gluon and the large Yukawa coupling of a top quark, leading to substantial branching ratio of $Br(g^{(2)} \to t \bar{t}) \approx 7%-8%$. As the $g^{(2)}$ coupling with two gluons appears via dimension-6 operator, $q\bar{q}\to g^{(2)}\to t\bar{t}$ is the golden mode for the mUED model. Hence the best channel is the $t\bar{t}$ resonance search in $p\bar{p}$ collisions. The recent Tevatron data at $\sqrt{s}=1.96$ TeV with an integrated luminosity of 8.7 fb$^{-1}$ are shown to give the first direct bound on the $g^{(2)}$ mass above 800 GeV. The implication and future prospect at the LHC are discussed also., Comment: referenced minor corrections added; 13 pages with 4 figures

We study the impact of the CP violation of the extra Higgs sector on $D^0$ decay. The CP even and CP odd neutral Higgs mixing of the two Higgs doublet model is studied and we show how the CP violating effect of the mixing may lead to the longitudinal muon polarization asymmetry of $D^0 \to \mu^+ \mu^-$. The asymmetry of the short-distance contribution is sensitive to the CP violating phase of the extended Higgs sector., Comment: 7 pages, 2 figures, presented as a poster in GUT2012 (YITP,Kyoto,15-17 March2012)

The presence of the light CP-odd scalar boson predicted in the next-to-minimal supersymmetric model (NMSSM) and the simplest little Higgs model (SLHM) dramatically changes the phenomenology of the Higgs sector. We suggest a practical strategy to discriminate the underlying model of the CP-odd scalar boson produced in the decay of the standard model-like Higgs boson. We define the decay rate of "the non $b$-tagged jet pair" with which we compute the ratio of decay rates into lepton and jets. They show much different behaviors between the NMSSM and the SLHM., Comment: 5 pages, 2 figures (5 figure files)

In a supersymmetry model with an axino as the lightest supersymmetric particle (LSP) and a Bino as the next LSP (NLSP), supersymmetry particles produced in pair at a high energy collider end up with including two Binos, followed by each Bino's decay into a photon and an axino. Final states are diphoton with large missing energy. We have comprehensively studied the implication of $\gamma\gamma+$MET data from the ALEPH, CDF II, and recent ATLAS and CMS experiments. No excess over the standard model backgrounds can be explained in this model if the NLSP Bino decays outside the detector, which happens when the axino decay constant $f_a$ is large enough. The ALEPH and CDF II data put a very strong bound on $f_a$ for light Bino case with $m_{\tilde{B}} < 150$ GeV: the narrow hadronic axion window around $f_a \sim 10^6$ GeV is completely closed. In the case where the gluino mass is smaller than about 776 GeV, the recent ATLAS data limit $f_a > 10^5$ GeV for the Bino mass below 700 GeV. This is already stronger than the previous laboratory bounds., Comment: to be appeared in Phys. Lett. B. 10 pages with 2 figure

Recently the ATLAS and CMS collaborations reported their search for a new heavy gauge boson $W'$ with one lepton plus missing transverse momentum. We find that $W^{(2)}$, the second Kaluza-Kelin (KK) state of the $W$ boson in the minimal Universal Extra Dimension (mUED) model, can be a good candidate for this signal, as its branching ratio into $\ell\nu$ is sizable. Moreover, nearly degenerate KK mass spectra in the mUED model yield generically very soft SM particle accompanying $W^{(2)}$ from the subsequent decays of the second KK quarks and gluons. In a hadron collider, this indirect $W^{(2)}$ production is difficult to distinguish from the $W^{(2)}$ single production. The involved strong interactions make it more important than the single production. The early LHC data on $\ell+\met$ signal for 1.1 fb$^{-1}$ integrated luminosity is shown insufficient to limit our model even with significant indirect production of $W^{(2)}$. However, the results show that the present LHC 5.6 fb$^{-1}$ data can cover most of the reasonable parameter space of the mUED model., Comment: 11 pages, 5 figures

The recently measured charge asymmetry of like-sign dimuon events by the D0 collaboration at Tevatron shows the 3.9 \sigma\ deviation from the standard model prediction. In order to solve this mismatch, we investigate the right-handed current contributions to $B_s-\bar{B}_s$ and $B_d-\bar{B}_d$ mixings which are the major source of the like-sign dimuon events in $b \bar{b}$ production in general left-right models without imposing manifest or pseudo-manifest left-right symmetry. We find the allowed region of new physics parameters satisfying the current experimental data., Comment: 9 pages, 4 figures

We study the phenomenology of the heavy charged gauge boson and obtain the lower bounds on its mass with the early LHC data at 7 TeV center-of-mass energy in the nonuniversal gauge interaction model, in which the electroweak SU(2) gauge group depends upon the fermion family. We found that the direct bound on the mass of the $W'$ boson is compatible to the indirect bound with only the early data of the LHC., Comment: 6 pages, 3 figures

Recently the CDF collaboration has reported the excess in the dijet invariant-mass distribution of the Wjj events, corresponding to a significance of 3.2 standard deviations. Considering the lack of similar excesses in the $\gamma jj$ and $Z jj$ events yet, we propose a new Z' model: Z' couples only to the second generation quarks. Single production of $\zsc$ as well as associated production with $W,\gamma, Z$ are mainly from the sea quarks. Only $W Z'$ production has additional contribution from one valence quark and one sea quark, which is allowed by CKM mixing. We found that if the new gauge coupling is large enough, marginally permitted by perturbativity, this new model can explain the observed CDF $Wjj$ anomaly as well as the lack of $\gm jj$ and $Z jj$ anomalies. Vanishing coupling of Z'-b-b protects this model from the constraint of p pbar ->WH -> l\nu b \bar{b}., Comment: references added

Loop-induced decay of a neutral Higgs boson into a pair of gluons or photons has great implications for the Higgs discovery at the LHC. If the Higgs boson is heavy with mass above $\sim 500\gev$, however, these radiative branching ratios are very suppressed in the standard model (SM), as the new decay channels are kinematically open. We note that these radiative decays can be sizable for the heavy CP-odd second Kaluza-Klein (KK) mode of the Higgs boson, $\chi^\tw$, in the minimal universal extra dimension model: highly degenerate mass spectrum of the theory prohibits kinematically the dominant KK-number-conserving decays into the first KK modes of the $W$, $Z$ and top quark. We find that the CP-even decay of $h^{(2)} \to g g$ is absent at one-loop level since $h^{(2)}$ couples with different mass eigenstates of $t_{1,2}^\on$ while a gluon does with the same mass eigenstates. The $h^\tw$ production at the LHC is very suppressed. On the contrary, the process $ gg \to \chi^\tw \to \gamma\gamma$ in an optimal scenario can be observed with manageable SM backgrounds at the LHC., Comment: 22 pages, 7 figures

We show that the recently measured 3.2 $\sigma$ deviations of the charge asymmetry of like-sign dimuon events from the standard model prediction by the D0 collaboration at Tevatron can be explained by introducing the anomalous right-handed top quark couplings. Combined analysis with the $\bs$ and $\bd$ mixings and $B \to X_s \gamma$ decays has been performed. We discuss how to discriminate the effects on the dimuon charge asymmetry of the anomalous $\tsW$ and $\tbW$ couplings., Comment: 9 pages, 5 figures

The flavour-changing neutral currents (FCNC) are derived at tree level if the electroweak gauge group depends on the fermion family, which are absent in the standard model. We study the lepton flavour violation (LFV) through the FCNC interactions in a nonuniversal gauge interaction model where the third generation fermions are subjected to the separate SU(2)$_L$ gauge group., Comment: 5 pages, 2 figures

We discuss the aspects of the fermions and gauge bosons in $SU(4)_L \times U(1)_X$ models with little Higgs. We introduce a set of fermions which ensures the cancellation of gauge anomaly, and explicitly show the cancellation of one-loop quadratic divergence to the Higgs mass from all fermion multiplets and all gauge bosons. We present the interactions of the standard model fermions with the physical gauge bosons. We also discuss some phenomenological implications of the model based on recent experimental results., Comment: Revtex, 13 pages, 2 figures

CP violation of the charged lepton sector has not been found yet. Tau is a unique charged lepton which can decay into hadrons. In this talk, we argue what kind of new physics can be studied with CP violation of tau lepton decays. We also disucuss how to handle hadronic final state interactions for a prediction of the direct CP violation., Comment: 6 pages, 10 figures. The work was presented at "Heavy Quarks and Leptons, Melbourne, 2008"

We propose a renormalizable model of a fermionic dark matter by introducing a gauge singlet Dirac fermion and a real singlet scalar. The bridges between the singlet sector and the standard model sector are only the singlet scalar interaction terms with the standard model Higgs field. The singlet fermion couples to the standard model particles through the mixing between the standard model Higgs and singlet scalar and is naturally a weakly interacting massive particle (WIMP). The measured relic abundance can be explained by the singlet fermionic dark matter as the WIMP within this model. Collider implication of the singlet fermionic dark matter is also discussed. Predicted is the elastic scattering cross section of the singlet fermion into target nuclei for a direct detection of the dark matter. Search of the direct detection of the dark matter provides severe constraints on the parameters of our model., Comment: 3 pages, 2 figures, Proceeding of the talk given in SUSY08, Seoul, Korea, 16-17 June 2008 and the poster session in Summer Institute 2008, Chi-tou, Taiwan, 10-17 August 2008

We explore the effects of the anomalous $tbW$ couplings on the $\bd$ mixing and recently measured $\bs$ mixing. The combined analysis of mixings via box diagrams with penguin decays provides strong constraints on the anomalous top quark couplings. We find the bound from the $\bd$ mixing data is stronger than that from the $\bs$ mixing., Comment: 6 pages, 2 figures

We study direct CP violation of tau -> K pi(eta,eta')nu decays. By studying the forward and backward asymmetry, the interference of L=0 and L=1 amplitudes of the hadronic system can be extracted. By including the scalar and vector mesons into the chiral Lagrangian, we compute the form factors which correspond to L=0 and L=1 angular momentum state of the hadronic system. We include real and imaginary parts of the one loop corrections to the self-energies of the scalar and vector mesons. The direct CP violation of the forward and backward asymmetry is computed using a two Higgs doublet model in which a new CP violating phase is introduced. We show how the CP violation of the forward and the backward asymmetry may depend on the new CP violating phase and the strong phase of the form factors., Comment: 28pages, 9 figures V2: Typos in Eq.(48)-(49) were corrected. (A->AR,B->BR,C->CR,D->DR)

Combined analysis of recent measured $\bs$ mixing and $B \to X_s \gamma$ decays provides constraints on the anomalous $\bar{t}sW$ couplings. We discuss the perspectives to examine the anomalous $\bar{t}sW$ couplings through CKM-suppressed $ t \to s W$ decays at the LHC., Comment: 7 pages, 4 eps figures

We propose a renormalizable model of a fermionic dark matter by introducing a gauge singlet Dirac fermion and a real singlet scalar. The bridges between the singlet sector and the standard model sector are only the singlet scalar interaction terms with the standard model Higgs field. The singlet fermion couples to the standard model particles through the mixing between the standard model Higgs and singlet scalar and is naturally a weakly interacting massive particle (WIMP). The measured relic abundance can be explained by the singlet fermionic dark matter as the WIMP within this model. Collider implication of the singlet fermionic dark matter is also discussed. Predicted is the elastic scattering cross section of the singlet fermion into target nuclei for a direct detection of the dark matter. Search of the direct detection of the dark matter provides severe constraints on the parameters of our model., Comment: 12 pages, 7 figures

We study the production of the charged Higgs boson at the LHC in the left-right symmetric model. It is shown that there exists a lower bound of the cross section. We investigate that predicted cross sections of this model are generally larger than those of the two Higgs doublet model or the minimal supersymmetric model., Comment: The version which will appear in PRD. References are added

We explore constraints on the charged Higgs sector in the left-right (LR) model from the present experimental data. Due to the different Yukawa structure, the allowed parameter space of the charged Higgs boson in the LR model is different from that in the two Higgs doublet model. We find that the constraint from $t \to b H^\pm$ decay at Tevatron is most significant, while $B \to \tau \nu$ decay could provide no constraint on the LR model. Bounds from $e^- e^+ \to H^- H^+$ process at LEP are similar to that in the two Higgs doublet model.

We explore the minimal extension of the Standard Model with fermionic cold dark matter. The interactions between the dark matter and the Standard Model matters are described by the non-renormalizable dimension-5 term. We show that the measured relic abundance of the cold dark matter can be explained in our model and predict the direct detection cross section. The direct search of the dark matter provides severe constraints on the mass and coupling of the minimal fermionic dark matter with respect to the Higgs boson mass., Comment: 6 pages, 2 figures

The colored SU(2)-singlet heavy T-quark is one of the most crucial ingredients in little Higgs models, which is introduced to cancel the largest contribution of the SM top quark to the Higgs boson mass at one-loop level. In two representative little Higgs models, the littlest Higgs model and the SU(3) simplest Higgs model, we comprehensively study the single heavy T-quark production at Large Hadron Collider (LHC). After presenting the possibility of relatively light (~500 GeV) T-quark in the simplest little Higgs model, we consider all the relevant processes, the 2->2 process of qb->q'T, the 2->3 process of qg->q'Tb, the s-channel process of q bar(q)'->T bar{b}, and the gluon fusion process of gg->T bar{t}. We found that the 2->3 process can be quite important, as its cross section is about 30% of the 2->2 one and it is dominant in high p_T distributions. The s-channel and the gluon fusion processes also show distinctive features in spite of their suppressed cross sections. In the gluon fusion process of the simplest little Higgs model, for example, the pseudo-scalar contribution is rather dominant over the Higgs contribution for relatively light M_T., Comment: 27 pages, using RevTeX; references added

We study the neutral Higgs boson production at the CERN Large Hadron Collider (LHC) and the future $e^- e^+$ linear collider (ILC) in the two Higgs doublet model with CP violation. The CP-even and CP-odd scalars are mixed in this model, which affects the production processes of neutral Higgs boson. We examine the correlation of the Higgs production at LHC and ILC and provide a strategy to distinguish the model from the CP conserving model and to determine the parameters of the Higgs sector., Comment: 10 pages, 3 figures

In the extra dimensional scenarios with gauge fields in the bulk, the Kaluza-Klein (KK) gauge bosons can induce Nambu-Jona-Lasinio (NJL) type attractive four-fermion interactions, which can break electroweak symmetry dynamically with accompanying composite Higgs fields. We consider a possibility that electroweak symmetry breaking (EWSB) is triggered by both a fundamental Higgs and a composite Higgs arising in a dynamical symmetry breaking mechanism induced by a new strong dynamics. The resulting Higgs sector is a partially composite two-Higgs doublet model with specific boundary conditions on the coupling and mass parameters originating at a compositeness scale $\Lambda$. The phenomenology of this model is discussed including the collider phenomenology at LHC and ILC., Comment: 20 pages, 7 figures

We explore the unitarity violation of the CKM matrix in the model in which the third generation fermions are subjected to the separate SU(2)$_L$ gauge interaction. With the recent LEP and SLC data at $Z$-pole and low-energy neutral current interaction data, the analysis on the parameter space of the model is updated, and the unitary violation is predicted under the constraint., Comment: 12 pages, 3 figures

Since the CP violation in the $B$ system has been investigated up to now only through processes related to the $B$--$\bar{B}$ mixing, urgently required is new way of study for the CP violation and establishing its origin in the $B$ system independent of the mixing process. In this work, we explore the exclusive $ B^0 \to \rho^0 \gamma$ decay to obtain the time-dependent CP asymmetry in $b \to d$ decay process in the standard model and the supersymmetric model. We find that the complex RL and RR mass insertion to the squark sector in the MSSM can lead to a large CP asymmetry in $b \to d \gamma$ decay through the gluino-squark diagrams, which is not predicted in the Standard Model induced by the $B$--$\bar{B}$ mixing., Comment: 10 pages, 4 eps figures

We explore the exclusive $ B^0 \to \rho^0 \gamma$ decay to obtain the time-dependent CP asymmetry in $b \to d \gamma$ decay process. We find that the complex RL and RR mass insertion to the squark sector in the MSSM can lead to a large deviation of CP asymmetry from that predicted in the Standard Model., Comment: 4 pages, talk given at the 32nd International Conference on High Energy Physics (ICHEP'04), Beijing, China, 16-22 Aug. 2004

We study the neutral Higgs boson production at the $e^- e^+$ linear collider in the two Higgs doublet model with the CP violation. The CP-even and CP-odd scalars are mixed in this model, which affects the production process of neutral Higgs boson., Comment: 5 pages, 2 eps figures, to appear in the Proceedings for the Linear Collider Workshop (LCWS 2004), April 19-23, 2004, Paris, France

This paper has been withdrawn by the authors., Comment: This paper withdrawn

We explore the CP violation in the charged Higgs production associated with a top quark at the LHC in the MSSM. The supersymmetric phases of gaugino masses and trilinear $A$ terms lead to a CP violating asymmetry of the cross section in the $ p p \to g b \to t H^\pm$ process through loop corrections to the $tbH^\pm$ vertex. We find that a CP violation more than 10 % is possible if the charged Higgs boson is heavy enough., Comment: 8 pages including 5 eps figures, JHEP, corrections made

The observed neutrino oscillation data might be explained by new physics at a TeV scale, which is testable in the future experiments. Among various possibilities, the low-energy Higgs triplet model is a prime candidate of such new physics since it predicts clean signatures of lepton flavor violating processes directly related to the neutrino masses and mixing. It is discussed how various neutrino mass patterns can be discriminated by examining the lepton flavor violating decays of charged leptons as well as the collider signatures of a doubly charged Higgs boson in the model., Comment: 13 pages, revtex