Search for lepton flavor violation via the intense high-energy muon beam

A deep inerastic scattering process \mutau is discussed to study lepton flavor violation between muons and tau leptons. In supersymmetric models, the Higgs boson mediated diagrams could be important for this reaction. We find that at a muon energy ($E_{\mu}$) higher than 50 GeV, the predicted cross section significantly increases due to the contribution from sea $b$-quarks. The number of produced tau leptons can be $\mathcal{O}(10^4)$ at $E_{\mu}$= 300 GeV from $10^{20}$ muons, whereas $\mathcal{O}(10^2)$ events are given at $E_{\mu}= 50$ GeV.Comment: Contribution to the 6th International Workshop on Neutrino Factories & Superbeams(NuFact04), Jul. 26-Aug. 1, 2004, Osaka Univerisity, Osaka, Japan, talk given by S.K., to appear in the Proceedings, 3 pages, 4 figure

Possible non-decoupling effects of heavy Higgs bosons in e+ e- -> W+ W- within THDM

We discuss the origin of the nondecoupling effects of the heavy Higgs bosons within the two Higgs doublet extension (THDM) of the Standard Model (SM) and illustrate it by means of the one-loop calculation of the differential cross-sections of the process e+ e- -> W+ W- in both the decoupling and the non-decoupling regimes. We argue that there are many regions in the THDM parametric space in which the THDM and SM predictions differ by several percents and such effects could, at least in principle, be testable at the future experimental facilities.Comment: 8 pages, 2 figures; to appear soon in EPJC. v2 - several minor corrections (typos), references adde

Triple gauge vertices at one-loop level in THDM

Renormalized triple gauge vertices (TGV) are examined within the two-Higgs-doublet model of electroweak interactions. Deviations of the TGV from their standard-model values are calculated at the one-loop level, in the on-shell renormalization scheme. As a consistency check, UV divergence cancellations anticipated on symmetry grounds are verified explicitly. Dependence of the TGV finite parts on the masses of possible heavy Higgs scalars is discussed briefly.Comment: 10pages, 13figure

Magnetic Instability in a Parity Invariant 2D Fermion System

We consider the parity invariant (2+1)-dimensional QED where the matter is represented as a mixture of fermions with opposite spins. It is argued that the perturbative ground state of the system is unstable with respect to the formation of magnetized ground state. Carrying out the finite temperature analysis we show that the magnetic instability disappears in the high temperature regime.Comment: 7 pages, RevTe

Some aspects of radiative corrections and non-decoupling effects of heavy Higgs bosons in two Higgs Doublet Model

The possibility of having relatively large non-decoupling effects of the heavy Higgs particles within the two-Higgs doublet extension of the electroweak standard model is briefly discussed and demonstrated on an example of the one-loop amplitude of the process e^+e^- -> W^+W^-Comment: 6 pages, 3 figures; to appear in the proceedings of the AM2003 conferenc

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 $e^-e^+ \to W^-W^+ \nu \bar \nu \to t \bar t \nu \bar \nu$ 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.Comment: 22 pages, RevTex4, 20 eps figure

A light Higgs scenario based on the TeV-scale supersymmetric strong dynamics

We consider a model based on the supersymmetric QCD theory with N_c=2 and N_f=3. The theory is strongly coupled at the infrared scale \Lambda_H. Its low energy effective theory below \Lambda_H is described by the supersymmetric standard model with the Higgs sector that contains four iso-spin doublets, two neutral iso-spin singlets and two charged iso-spin singlets. If \Lambda_H is at the multi-TeV to 10 TeV, coupling constants for the F-terms of these composite fields are relatively large at the electroweak scale. Nevertheless, the SM-like Higgs boson is predicted to be as light as 125 GeV because these F-terms contribute to the mass of the SM-like Higgs boson not at the tree level but at the one-loop level. A large non-decoupling effect due to these F-terms appears in the one-loop correction to the triple Higgs boson coupling, which amounts to a few tens percent. Such a non-decoupling property in the Higgs potential realizes the strong first order phase transition, which is required for a successful scenario of electroweak baryogenesis

Triviality and vacuum stability bounds in the three-loop neutrino mass model

We study theoretical constraints on the parameter space under the conditions from vacuum stability and triviality in the three-loop radiative seesaw model with TeV-scale right-handed neutrinos which are odd under the $Z_2$ parity. In this model, some of the neutrino Yukawa coupling constants can be of the order of one. Requirement of strongly first order phase transition for successful electroweak baryogenes is also prefers order-one coupling constants in the scalar sector. Hence, it is important to clarify whether this model satisfies those theoretical conditions up to a given cutoff scale. It is found that the model can be consistent up to the scale above 10 TeV in the parameter region where the neutrino data, the lepton flavor violation data, the thermal relic abundance of dark matter as well as the requirement from the strongly first order phase transition are satisfied.Comment: 22 pages, 14 figure

Enhancement of W+/- H-/+ Production at Hadron Colliders in the Two Higgs Doublet Model

We discuss the associated W+/- H-/+ production at the CERN Large Hadron Collider. The dependence of the hadronic cross section on the Higgs sector parameters is investigated in detail in the framework of the general Two Higgs Doublet Model (THDM). We study the possible enhancement of the THDM prediction for the cross section compared to the prediction of the Minimal Supersymmetric Standard Model (MSSM). We find regions in the THDM parameter space where the THDM prediction can exceed the one of the MSSM by two orders of magnitude. These regions of large cross section are in agreement with theoretical bounds on the model, derived from the requirement of vacuum stability and perturbative unitarity, and are not excluded by experimental constraints.Comment: 19 pages, 5 figure

Tree-unitarity bounds for THDM Higgs masses revisited

We have reconsidered theoretical upper bounds on the scalar boson masses within the two-Higgs-doublet model (THDM), employing the well-known technical condition of tree-level unitarity. Our treatment provides a modest extension and generalization of some previous results of other authors. We present a rather detailed discussion of the solution of the relevant inequalities and offer some new analytic formulae as well as numerical values for the Higgs mass bounds in question. A comparison is made with the earlier results on the subject that can be found in the literature.Comment: 20 pages, 6 figures; correction to typos; will appear in Eur. Phys. J.