arXiv subjects

Koji Tsumura

Publications and source records attributed to Koji Tsumura.

At least 73 records · Page 4Linked to original sources

arXiv2011

A Higgs Quadruplet for Type III Seesaw and Implications for $μ\to eγ$ and $μ- e$ Conversion

In Type III seesaw model the heavy neutrinos are contained in leptonic triplet representations. The Yukawa couplings of the triplet fermion and the left-handed neutrinos with the doublet Higgs field produce the Dirac mass terms. Together with the Majorana masses for the leptonic triplets, the light neutrinos obtain non-zero seesaw masses. We point out that it is also possible to have a quadruplet Higgs field to produce the Dirac mass terms to facilitate the seesaw mechanism. The vacuum expectation value of the quadruplet Higgs is constrained to be small by electroweak precision data. Therefore the Yukawa couplings of a quadruplet can be much larger than those for a doublet. We also find that unlike the usual Type III seesaw model where at least two copies of leptonic triplets are needed, with both doublet and quadruplet Higgs representations, just one leptonic triplet is possible to have a phenomenologically acceptable model because light neutrino masses can receive sizable contributions at both tree and one loop levels. Large Yukawa couplings of the quadruplet can induce observable effects for lepton flavor violating processes $μ\to e γ$ and $μ- e$ conversion. Implications of the recent $μ\to eγ$ limit from MEG and also limit on $μ- e $ conversion on Au are also given. Some interesting collider signatures for the doubly charged Higgs boson in the quadruplet are discussed.

hep-ph↗

arXiv2011

$ν$-Two Higgs Doublet Model and its Collider Phenomenology

Smallness of neutrino masses can be explained by introducing a tiny vacuum expectation value of an extra-Higgs doublet which couples to right-handed neutrinos ($N_R$). This situation is naturally realized in $ν$-Two Higgs Doublet Model ($ν$THDM), where a TeV-scale seesaw mechanism can work well. We investigate observable phenomenology of $ν$THDM at LHC and ILC experiments. Charged Higgs boson ($H^\pm$) in $ν$THDM is almost originated from the extra-Higgs doublet and its coupling strength to neutrinos are not small. Then this model induces rich phenomenology at the LHC, for example, when $m_{H^\pm}^{} < M_N$, observable charged tracks can be induced from long lived charged Higgs. On the other hand, when $m_{H^\pm}^{} > M_N$, right-handed neutrinos can be long-lived, and secondary vertices may be tagged at the LHC. The $ν$THDM also predicts observable lepton number violating process at the ILC.

hep-ph↗

arXiv2011

Phenomenology in the Zee Model with the A_4 Symmetry

The Zee model generates neutrino masses at the one-loop level by adding charged SU(2)_L-singlet and extra SU(2)_L-doublet scalars to the standard model of particle physics. As the origin of the nontrivial structure of the lepton flavor mixing, we introduce the softly broken A_4 symmetry to the Zee model. This model is compatible with the tribimaximal mixing which agrees well with neutrino oscillation measurements. Then, a sum rule m_1 e^{i alpha_12} + 2 m_2 + 3 m_3 e^{i alpha_32} = 0 is obtained and it results in Delta m^2_31 < 0 and m_3 > 1.8*10^{-2}eV. The effective mass |(M_nu)_{ee}| for the neutrinoless double beta decay is predicted as | (M_ν)_{ee} | > 1.7*10^{-2}eV. The characteristic particles in this model are SU(2)_L-singlet charged Higgs bosons s^+_alpha (alpha=xi,eta,zeta) which are made from a 3-representation of A_4. Contributions of s^+_alpha to the lepton flavor violating decays of charged leptons are almost forbidden by an approximately remaining Z_3 symmetry; only BR(tau to ebar mu mu) can be sizable by the flavor changing neutral current interaction with SU(2)_L-doublet scalars. Therefore, s^+_alpha can be easily light enough to be discovered at the LHC with satisfying current constraints. The flavor structures of BR(s^-_alpha to ell nu) are also discussed.

hep-ph↗

arXiv2010

Higgs boson pair production in new physics models at hadron, lepton, and photon colliders

We study Higgs boson pair production processes at future hadron and lepton colliders including the photon collision option in several new physics models; i.e., the two-Higgs-doublet model, the scalar leptoquark model, the sequential fourth generation fermion model and the vector-like quark model. Cross sections for these processes can deviate significantly from the standard model predictions due to the one-loop correction to the triple Higgs boson coupling constant. For the one-loop induced processes such as $gg \to hh$ and $γγ\to hh$, where $h$ is the (lightest) Higgs boson and $g$ and $γ$ respectively represent a gluon and a photon, the cross sections can also be affected by new physics particles via additional one-loop diagrams. In the two-Higgs-doublet model and scalar leptoquark models, cross sections of $e^+e^-\to hhZ$ and $γγ\to hh$ can be enhanced due to the non-decoupling effect in the one-loop corrections to the triple Higgs boson coupling constant. In the sequential fourth generation fermion model, the cross section for $gg\to hh$ becomes very large because of the loop effect of the fermions. In the vector-like quark model, effects are small because the theory has decoupling property. Measurements of the Higgs boson pair production processes can be useful to explore new physics through the determination of the Higgs potential.

hep-ph↗

arXiv2010

Measuring Higgs boson associated Lepton Flavour Violation in electron-photon collisions at the ILC

We study the LFV Higgs production processes $e^-γ\to\ell^-ϕ\;(\ell=μ,τ; ϕ=H, A)$ as a probe of Higgs mediated LFV couplings at an electron-photon collider, where $H$ and $A$ are extra CP even and odd Higgs bosons, respectively, in the two Higgs doublet model. Under the constraints from the current data of muon and tau rare decay, the cross section can be significantly large. It would improve the experimental upper bounds on the effective LFV coupling constants. In addition, the chirality nature of the LFV Higgs coupling constants can be measured by selecting electron beam polarizations.

hep-ph↗

arXiv2010

Phenomenology in the Higgs Triplet Model with the A_4 Symmetry

We discuss the phenomenology of doubly and singly charged Higgs bosons (of SU(2)_L-triplet fields) in the simplest A_4-symmetric version of the Higgs Triplet Model. Mass eigenstates of these Higgs bosons are obtained explicitly from the Higgs potential. It is shown that their decays into a pair of leptons have unique flavor structures which can be tested at the LHC if some of their masses are below the TeV scale. Sizable decay rates for tau to bar(mu) e e and tau to bar(e) mu mu can be obtained naturally while other tau to l l' l'', mu to bar(e) e e, and l to l' gamma are almost forbidden in this model. Contributions of these Higgs bosons to the non-standard interactions of neutrinos are also considered.

hep-ph↗

arXiv2010

Higgs boson pair production at the Photon Linear Collider in the two Higgs doublet model

We calculate the cross section of the lightest Higgs boson pair production at the Photon Linear Collider in the two Higgs doublet model. We focus on the scenario in which the lightest Higgs boson has the standard model like couplings to gauge bosons. We take into account the one-loop correction to the $hhh$ coupling as well as additional one-loop diagrams due to charged bosons to the $γγ\to hh$ helicity amplitudes. We discuss the impact of these corrections on the $hhh$ coupling measurement at the Photon Linear Collider.

hep-ph↗

arXiv2010

Phenomenology of flavon fields at the LHC

We study low energy constraints from flavour violating processes, production and decay at the LHC of a scalar field varphi (flavon) associated to the breaking of a non-supersymmetric Abelian family symmetry at the TeV scale. This symmetry is constrained to reproduce fermion masses and mixing, up to O(1) coefficients. The non-supersymmetric gauged U(1) models considered are severely restricted by cancellation of anomalies and LEP bounds on contact interactions, consequently its phenomenology is out of the LHC reach. We therefore introduce an effective U(1) which is not gauged and it is broken explicitly by a CP odd term at the TeV scale. This helps us to explore flavour violating processes, production and decay at the LHC for these kind of light scalars. In this context we first study the constraints on the flavon mass and its vacuum expectation value from low energy flavour changing processes such as μ-> eγ. We find that a flavon of about m_ϕ<~ 150 GeV could be experimentally allowed. These kind of flavons could be significantly generated at the LHC via the gluon fusion mechanism and the single top production channel g u -> t ϕ. The produced flavons can have characteristic decay modes such as t \bar{c} for m_ϕ>~ m_t, and τ\barμ for m_ϕ<~ m_t, which could be effectively useful to detect flavons.

hep-ph↗

arXiv2009

Constraints from muon g-2 and LFV processes in the Higgs Triplet Model

Constraints from the muon anomalous magnetic dipole moment and lepton flavor violating processes are translated into lower bounds on v_Delta*m_H++ in the Higgs Triplet Model by considering correlations through the neutrino mass matrix. The discrepancy of the sign of the contribution to the muon anomalous magnetic dipole moment between the measurement and the prediction in the model is clarified. It is shown that mu to e gamma, tau decays (especially, tau to mu e e), and the muonium conversion can give a more stringent bound on v_Delta*m_H++ than the bound from mu to eee which is expected naively to give the most stringent one.

hep-ph↗

arXiv2009

Models of Yukawa interaction in the two Higgs doublet model, and their collider phenomenology

Possible models of Yukawa interaction are discussed in the two Higgs doublet model (THDM) under the discrete symmetry imposed to avoid the flavor changing neutral current at the leading order. It is known that there are four types of such models corresponding to the possible different assignment of charges for the discrete symmetry on quarks and leptons. We first examine decay properties of Higgs bosons in each type of the models, and summarize constraints on the models from current experimental data. We then shed light on the differences among these models in collider phenomenology. In particular, we mainly discuss so-called the Type-II THDM and the Type-X THDM. The Type-II THDM corresponds to the model with the same Yukawa interaction as the minimal supersymmetric standard model (MSSM). On the other hand, in the Type-X THDM, additional Higgs bosons can predominantly decay into leptons. This scenario may be interesting because of the motivation for a light charged Higgs boson scenario such as in the TeV scale model of neutrino, dark matter and baryogenesis. We study how we can distinguish the Type-X THDM from the MSSM at the Large Hadron Collider and the International Linear Collider.

hep-ph↗

arXiv2009

Effects of the anomalous Higgs couplings on the Higgs boson production at the Large Hadron Collider

We study the impact of dimension-six operators on single- and double-Higgs production rates via gluon fusion at the Large Hadron Collider (LHC). If the top-Yukawa coupling is modified by some new physics whose scale is of the TeV scale, its effect changes the cross sections of single-Higgs production $gg\to H$ and double-Higgs production $gg\to HH$ through the top-loop diagram. In particular, double-Higgs production can receive significant enhancement from the effective top-Yukawa coupling and the new dimension-five coupling $t{\bar t}HH$ which are induced by the dimension-six operator. Comparing these results to the forthcoming data at the LHC, one can extract information of the dimension-six operators relevant to the top quark and the Higgs boson.

hep-ph↗

arXiv2009

Optimal Quantization of Signals for System Identification

In this paper, we examine the optimal quantization of signals for system identification. We deal with memoryless quantization for the output signals and derive the optimal quantization schemes. The objective functions are the errors of least squares parameter estimation subject to a constraint on the number of subsections of the quantized signals or the expectation of the optimal code length for either high or low resolution. In the high-resolution case, the optimal quantizer is found by solving Euler-Lagrange's equations and the solutions are simple functions of the probability densities of the regressor vector. In order to clarify the minute structure of the quantization, the optimal quantizer in the low resolution case is found by solving recursively a minimization of a one-dimensional rational function. The solution has the property that it is coarse near the origin of its input and becomes dense away from the origin in the usual situation. Finally the required quantity of data to decrease the total parameter estimation error, caused by quantization and noise, is discussed.

math.OC↗

arXiv2009

A powerful tool for measuring Higgs boson associated Lepton Flavour Violation

In models with extended Higgs sectors, Higgs-boson-mediated Lepton Flavour Violation (LFV) can naturally appear. We study the physics potential of an electron-photon collider %as an option of the International Linear Collider on searching LFV processes $e^-γ\to\ell^-φ(\ell=μ,τ; φ=H, A)$ where $H$ and $A$ are extra CP even and odd Higgs bosons, respectively, in the minimal supersymmetric standard model and the effective two Higgs doublet model. The production cross section can be significantly large for the maximal allowed values of the LFV coupling constants under the current experimental data. Present experimental upper bounds on the effective LFV coupling constants would be considerably improved by searching these processes, which would be better than MEG and COMET experiments and also those at LHCb and SuperKEKB. Moreover, one can separately measure chirality of effective LFV coupling constants via these processes by selecting electron polarizations.

hep-ph↗

arXiv2009

Higgs boson pair production at a photon-photon collision in the two Higgs doublet model

We calculate the cross section of Higgs boson pair production at a photon collider in the two Higgs doublet model. We focus on the scenario in which the lightest CP even Higgs boson ($h$) has the standard model like couplings to the gauge bosons. We take into account the one-loop correction to the $hhh$ coupling as well as additional one-loop diagrams due to charged Higgs bosons to the $γγ\to hh$ helicity amplitudes. It is found that the full cross section can be enhanced by both these effects to a considerable level. We discuss the impact of these corrections on the $hhh$ coupling measurement at the photon collider.

hep-ph↗

arXiv2008

Detecting Majorana nature of neutrinos in muon and tau decay

The Majorana nature of neutrinos can be detected by the precise measurement of muon decay. This possibility comes from the presence of charged Higgs boson interaction for Majorana neutrinos. We study the effects of the neutrino Yukawa interaction via charged Higgs bosons in muon decay processes such as $μ\to eν\barν$ and $μ\to eγ$. The Higgs triplet model with small vacuum expectation value is of special importance whose neutrino Yukawa coupling can affect significantly muon decays. External neutrino lines in the Feynman diagrams of $μ\to eν\barν$ can be crossed because of its Majorana nature. This fact provides the interference contribution between the W boson exchange diagram and that of charged Higgs boson, which may be detectable in near future experiments.

hep-ph↗

arXiv2007

New physics effect on the top-Yukawa coupling at ILC

Measurement of the top-Yukawa coupling is important to understand the fermion mass generation mechanism and dynamics of electroweak symmetry breaking. We discuss the top quark anomalous couplings which can be described by higher dimensional operators. We investigate the process $e^-e^+ \to W^-W^+ν\barν\to t \bar t ν\barν$ to study the contribution of the anomalous top-Higgs coupling to the cross section. The effect of the dimension-six top-Higgs interaction on the cross section can be a few hundred percent greater than the SM prediction. Such a large effect can be measured at the International Linear Collider.

hep-ph↗

arXiv2007

CP violation due to multi Froggatt-Nielsen fields

We study how to incorporate CP violation in the Froggatt--Nielsen (FN) mechanism. To this end, we introduce non-renormalizable interactions with a flavor democratic structure to the fermion mass generation sector. It is found that at least two iso-singlet scalar fields with imposed a discrete symmetry are necessary to generate CP violation due to the appearance of the relative phase between their vacuum expectation values. In the simplest model, ratios of quark masses and the Cabibbo-Kobayashi-Maskawa (CKM) matrix including the CP violating phase are determined by the CKM element |V_{us}| and the ratio of two vacuum expectation values R=|R|e^{i*alpha} (a magnitude and a phase). It is demonstrated how the angles phi_i (i=1--3) of the unitarity triangle and the CKM off-diagonal elements |V_{ub}| and |V_{cb}| are predicted as a function of |V_{us}|, |R| and α. Although the predicted value of the CP violating phase does not agree with the experimental data within the simplest model, the basic idea of our scenario would be promising to construct a more realistic model of flavor and CP violation.

hep-ph↗

arXiv2006

Dimension-six top-Higgs interaction and its effect in collider phenomenology

Measurement of the Yukawa interaction between the top quark and the Higgs boson should be useful to clarify the mechanism of fermion mass generation. We discuss the impact of non-standard interactions characterized by dimension-six operators on the effective top Yukawa coupling. The cross section of the process $e^-e^+ \to W^-W^+ ν\bar ν\to t \bar t ν\bar ν$ is calculated including these operators, and possible deviation from the standard model prediction is evaluated under the constraint from perturbative unitarity and current experimental data. We find that if the new physics scale is in a TeV region, the cross section can be significantly enhanced due to the non-standard interactions. Such a large effect should be detectable at the International Linear Collider.

hep-ph↗