arXiv subjects

Tadashi Kon

Publications and source records attributed to Tadashi Kon.

At least 19 recordsLinked to original sources

arXiv2021

Higgs triplet extension of GRACE

Much theoretical effort and automatization are required to confront new physics models with experimental data for many types of particle reactions at future colliders. In this context, we extend GRACE, an automatic calculation system for invariant amplitudes, to incorporate particles and interactions in the Georgi-Machacek model. With the extended GRACE system, we study fermiophobic Higgs boson production processes at $e^+ e^-$ and $e^- e^-$ colliders in the model. The results show some advantages of $e^- e^-$ colliders over $e^+ e^-$ colliders for new physics search and thus its complementary role.

hep-ph↗

arXiv2019

Double Higgs boson production at $e^+e^-$ colliders in the two-Higgs-doublet model

We study the double Higgs boson production processes $e^+e^- \to hh f\bar{f}$ ($f\neq t$) with $h$ being the 125 GeV Higgs boson in the two-Higgs-doublet model with a softly-broken $Z_2$ symmetry. The cross section can be significantly enhanced, typically a few hundreds percent, as compared to the standard model prediction due to resonant effects of heavy neutral Higgs bosons, which becomes important in the case without the alignment limit. We find a strong correlation between the enhancement factor of the cross section and the scaling factor of the $hf\bar{f}$ couplings under constraints from perturbative unitarity, vacuum stability and current experimental data at the LHC as well as the electroweak precision data.

hep-ph↗

arXiv2018

One-loop effects of MSSM particles in e^-e^+ \to Zh and e^-e^+ \to ν\barνh at the ILC

The 1-loop effects of the MSSM at the ILC are investigated through numerical analysis. We studied the higgs production processes $e^-e^+\rightarrow Zh$ and $e^-e^+\rightarrow ν\barνh$ at the ILC. It is found that the magnitude of the MSSM contribution through the 1-loop effects is sizable enough to be detected. In the study, three sets of the MSSM parameters are proposed, which are consistent with the observed higgs mass, the muon $g$-$2$, the dark matter abundance and the decay branching ratios of $B$ mesons. In the $e^-e^+\rightarrow Zh$ process, the 1-loop effects of the MSSM are visible and the distinction of the parameter sets is partially possible. For the study of $e^-e^+\rightarrow ν\barνh$, we used the equivalent $\it W$-boson approximation in the evaluation of the 1-loop cross section. While the 1-loop effect of the MSSM is visible, the distinction of the parameter sets might not be possible in this process under the value of realistic luminosity at the ILC.

hep-ph↗

arXiv2017

One loop effects of natural SUSY in third generation fermion production at the ILC

Within the framework of the Minimal Supersymmetric Standard Model, we investigate the 1-loop effects of supersymmetric particles on the third-generation fermion-pair production at the ILC. Three sets of the SUSY parameters are proposed which are consistent with the observed Higgs mass, the muon g-2, the Dark Matter abundance and the decay branching ratio of B meson. We discuss on the possibility of discovering the signals consistent with SUSY as well as of experimentally distinguishing the proposed sets of SUSY parameters.

hep-ph↗

arXiv2013

Measurement of a Phase of a Radio Wave Reflected from Rock Salt and Ice Irradiated by an Electron Beam for Detection of Ultra-High-Energy Neutrinos

We have found a radio-wave-reflection effect in rock salt for the detection of ultra-high energy neutrinos which are expected to be generated in Greisen, Zatsepin, and Kuzmin (GZK) processes in the universe. When an UHE neutrino interacts with rock salt or ice as a detection medium, a shower is generated. That shower is formed by hadronic and electromagnetic avalanche processes. The energy of the UHE neutrino shower converts to thermal energy through ionization processes. Consequently, the temperature rises along the shower produced by the UHE neutrino. The refractive index of the medium rises with temperature. The irregularity of the refractive index in the medium leads to a reflection of radio waves. This reflection effect combined with the long attenuation length of radio waves in rock salt and ice would yield a new method to detect UHE neutrinos. We measured the phase of the reflected radio wave under irradiation with an electron beam on ice and rock salt powder. The measured phase showed excellent consistence with the power reflection fraction which was measured directly. A model taking into account the temperature change explained the phase and the amplitude of the reflected wave. Therefore the reflection mechanism was confirmed. The power reflection fraction was compared with that calculated with the Fresnel equations, the ratio between the measured result and that obtained with the Fresnel equations in ice was larger than that of rock salt.

astro-ph.IM↗

arXiv2011

Discrimination of SUSY breaking models using single-photon processes at future e+e- linear colliders

We examine the single-photon processes in the frame work of supersymmetric models at future e+e- linear colliders. According to the recent experimental achievement, the optimistic polarization degrees for both electron and positron beams are taken into account to enhance the signal-to-noise ratio revealing the observable difference between supersymmetry breaking models. The minimal supergravity model and the minimal SU(5) grand unified model in gaugino mediation have been examined as examples. We see that after several years of accummulating data, the difference of the number of single-photon events between the two models received from the collider would be in excess of three times the statistical error, providing us the possibility to probe which model would be realized in nature. The result is well suitable for the future running of the International Linear Collider.

hep-ph↗

arXiv2007

Reflection of microwave from energy deposit by X-ray irradiation in rock salt: Implication of an ultra high energy salt neutrino detector to act like a radio bubble chamber

Existence of GZK neutrinos (ultra high energy neutrinos) have been justified although the flux is very low. A new method is desired to use a huge mass of a detector medium to detect them. A fundamental study of radar method was carried out to measure microwave reflection from electromagnetic energy deposit by X-ray irradiation in a small rock salt sample. The reflection rate of 1x10^-6 was found at the energy deposit of 1x10^19 eV which was proportional to square of the X-ray intensity suggesting the effect to be coherent scattering. The decay time of the reflection was several seconds. This effect implies a large scale natural rock salt formation could be utilized like a bubble chamber irradiated by radio wave instead of visible light to detect GZK neutrinos.

astro-ph↗

arXiv2002

Scalar neutrino production in R-parity violating supersymmetric model at HERA

We investigate a single scalar neutrino production at the upgraded HERA with high luminosity in the framework of an R-parityviolating supersymmetric model. We find that the scalar neutrino with mass around 100GeV could be observed through investigating the multilepton production process e- p -> mu- sneutrino(tau) X -> mu- (e- mu+) X. The signal would be characterized by mu+ and e- with high transverse momentum as well as a sharp peak in the invariant mass M(e-,mu+) distribution.

hep-ph↗

arXiv2000

Single scalar top production with polarized beams in ep collisions at HERA

From the point of view of the R-parity breaking supersymmetric model, we propose a scalar top (stop) search with longitudinally polarized electron (e-) and positron(e+) beams which will soon be available at the upgraded HERA. Fully polarized e- or e+ beams could produce the stop two times as much as unpolarized beams, while they increase background events due to the process of the standard model by about 30% in comparison with unpolarized ones. We show that right-handed e+ beams at HERA is efficient to produce the stop in the model. With 1 fb**(-1) of integrated luminosity we estimate reach in the coupling constant lambda'(131) for masses of the stop in the range 160-400 GeV. We can set a 95% confidence-level exclusion limit for lambda'(131) > 0.01-0.05 in the stop mass range of 240-280 GeV if no singal of the stop is observed. We also point out that y(=Q**2/sx) distributions of e+ coming from the stop shows the different behavior from those of the standard model.

hep-ph↗

arXiv2000

Single Sbottom/Scharm Production at HERA in an R-Parity Breaking Supersymmetric Model

We investigate the production process of the single scalar bottom quark (sbottom) and scalar charm quark (scharm) at HERA. The sbottom and scharm could be produced via an R-parity breaking interactions $λ'_{123} \neq 0$ in the Minimal Supersymmetric Standard Model (MSSM). These processes give a slight excess in the invariant mass $M_{eq}$ distribution of the high $Q^2$ deep inelastic scattering for sufficiently heavy gauginos and the scalar top (stop). For the light gauginos and stop, it is shown that the tagging of $b/c$-quarks and charged leptons with high transverse energies will be indispensable to search for the processes.

hep-ph↗

arXiv1996

Impact of squark pair decay modes on search for supersymmetric neutral Higgs bosons

We present a detailed study of the decays of the neutral Higgs bosons $H^0$ and $A^0$ within the Minimal Supersymmetric Standard Model. We find that the supersymmetric modes ${\tilde{t}}\bar{\tilde{t}}$ and ${\tilde{b}}\bar{\tilde{b}}$ can dominate the $H^0$ and $A^0$ decays in a wide range of the model parameters due to large Yukawa couplings and mixings of ${\tilde{t}}$ and ${\tilde{b}}$. Compared to the conventional modes $t\bar{t}$ and $b\bar{b}$, these modes have very distinctive signatures. This could have a decisive impact on the neutral Higgs boson searches at future colliders.

hep-ph↗

arXiv1996

Automatic Calculation of SUSY-particle Production

We introduce a new method to treat Majorana fermions and interactions with fermion-number violation on the GRACE system which has been developed for the automatic computation of the matrix elements for the processes of the standard model. Thus we have constructed a system for the automatic computation of cross-sections for the processes of the minimal SUSY standard model (MSSM).

hep-ph↗

arXiv1995

Quantum Mechanics Violating Effects to Masses of Nambu-Goldstone Bosons: A Lesson for Majoron

We study gravitational quantum mechanics violating (QMV) effects to masses of Nambu-Goldstone bosons, taking majoron as an example. We show a supersymmetric majoron has either mass of O(keV) for the dimension five potential or smaller mass for effective potentials with higher dimensions. We extend the Dashen's formula for pseudo Nambu-Goldstone bosons to include possible effects of QMV.

hep-th↗

arXiv1995

Polarization Effects in Chargino Production at High Energy $γγ$ Colliders

We investigate the chargino production process $γγ\rightarrow\tilde{W}^{+}\tilde{W}^{-}$ at high energy $γγ$ colliders in the framework of the minimal supersymmetric standard model (MSSM). Here the high energy $γ$ beams are obtained by the backward Compton scattering of the laser flush by the electron in the basic linear TeV $ee$ colliders. We consider the polarization of the laser photons as well as the electron beams. Appropriate beam polarization could be effective to enhance the cross section and for us to extract the signal from the dominant background $γγ\rightarrow{W}^{+}{W}^{-}$.

hep-ph↗

arXiv1995

The automatic computation for SUSY processes

We have constructed a system for the automatic computation of cross-sections for the processes of the SUSY QED by the extension of the GRACE system including a Majorana fermion. The system has also been applied to another model including Majorana fermions, MSSM, by the definition of the model file.

hep-ph↗

arXiv1994

Light Scalar Top and Heavy Top Signature at CDF

We propose a mechanism which could explain a slight excess of top signal rate recently reported by CDF in the framework of the supersymmetric standard model. If the scalar partner of the top (stop) is sufficiently light, the gluino with an appropriate mass could decay into the stop plus the top with almost 100\% branching ratio and experimental signatures of the gluino pair production could be indistinguishable from those of the top production in the present integrated luminosity Tevatron running. In this case the standard top signal, $W$ $+$ multi-jets events, would be effectively enhanced by the additional gluino contribution. It is shown, moreover, that such a mechanism can actually work in the radiative SU(2)$\times$U(1) breaking model without the GUT relations between the gaugino mass parameters.

hep-ph↗

arXiv1994

A Light Scalar Top Quark in MSGUT

We reexamine a possibility for the existence of a light supersymmetric partner of the top quark (stop) with mass 15$\sim$16GeV in the framework of the minimal supergravity GUT model (MSGUT). Such a stop could explain the slight excess of the high $p_{T}$ cross section of the $D^{*\pm}$-meson production in the two-photon process at TRISTAN. We find two types of solution for the RGEs in the MSGUT allowing the existence of the light stop. The type I [type II] solution is characterized by the heavy [light] top quark, $m_t\simeq$ 150GeV [100GeV], and the light [heavy] squarks . It is found that the type II solution is more favorable because these parameter sets seem to satisfy all constraints settled by the recent collider experiments as well as by the cosmological considerations. The existence of such a stop could change the dominant decay mode of sparticles, the top quark and the Higgs bosons. Consequently,the present experimental bounds on the supersymmetric parameters as well as on masses of the top and the Higgs could be weakened substantially. However, the allowed parameter region is rather restricted and in turn masses and mixing parameters of the other SUSY partners as well as masses of the Higgs and the top are severely constrained.

hep-ph↗

arXiv1994

Signatures of Scalar Top with R-parity Breaking Coupling at HERA

In the framework of the minimal supersymmetric standard model with an R-parity breaking coupling of the scalar top quark (stop) we investigate production processes and decay properties of the stop at HERA energies. The model is characterized by a light stop possibly lighter than the other squarks. We show that the stop could be singly produced not only in the neutral current processes but also in associated processes whose final states contain some heavy flavor quarks, bottom and top quarks. These signatures would be useful to discriminate the stop from leptoquarks.

hep-ph↗