Muneyuki Ishida

Analysis of a Kπ-Scattering Phase Shift and Evidence for the κ(900) Meson

Recently we have shown an evidence for existence of \sigma-particle in the previous works; where the \pi\pi S-wave phase shift is reanalyzed, by introducing a repulsive background suggested by the chiral symmetry, and by applying a new method of Interfering Breit-Wigner Amplitudes. In this work we also show, reanalyzing the K\pi S-wave phase shift from a similar standpoint, an evidence for existence of \kappa(900), possibly to be a member of \sigma-nonet.

Total width of 125 GeV Higgs boson.

By using the LHC and Tevatron measurements of the cross sections to various decay channels relative to the standard model Higgs boson, the total width of the putative 125 GeV Higgs boson is determined as 6.1(-2.9)(+7.7) MeV. We describe a way to estimate the branching fraction for the Higgs-boson decay to dark matter. We also discuss a no-go theorem for the γγ signal of the Higgs boson at the LHC.

Differentiating the Higgs boson from the dilaton and radion at Hadron colliders.

A number of candidate theories beyond the standard model (SM) predict new scalar bosons below the TeV region. Among these, the radion, which is predicted in the Randall-Sundrum model, and the dilaton, which is predicted by the walking technicolor theory, have very similar couplings to those of the SM Higgs boson, and it is very difficult to differentiate these three spin-0 particles in the expected signals of the Higgs boson at the LHC and Tevatron. We demonstrate that the observation of the ratio σ(γγ)/σ(WW) gives a simple and decisive way to differentiate these, independent of the values of model parameters, the vacuum expectation values of the radion, and dilaton fields.

Predictions of pp,p¯p total cross section and ρ ratio at LHC and cosmic-ray energies

Abstract We propose to use rich informations on the p p , p ¯ p total cross sections σ tot below N ( ∼ 10 GeV ) in order to predict the total cross section and ρ ratio at very high energies. Using the FESR as a constraint for high energy parameters, we search for the simultaneous best fit to the data points of σ tot and ρ ratio up to some energy (e.g., ISR, Tevatron) to determine the high-energy parameters. We then predict σ tot and ρ in the LHC and high-energy cosmic-ray regions. Using the data up to s = 1.8 TeV (Tevatron), we predict σ tot p p and ρ p p at the LHC energy ( s = 14 TeV ) as 106.3 ± 5.1 syst ± 2.4 stat mb and 0.126 ± 0.007 syst ± 0.004 stat , respectively. The predicted values of σ tot in terms of the same parameters are in good agreement with the cosmic-ray experimental data sample up to P lab ∼ 10 8 – 9 GeV by Block, Halzen, and Stanov.

Scalar-top masses from SUSY loops with 125 GeV mh and precise MW,mt

Abstract We constrain the masses of scalar-tops (stop) by analyzing the new precision Tevatron measurement of the W -boson mass and the LHC/Tevatron indications of a Higgs boson of mass 125.5 ± 1 GeV . Our study adopts Natural SUSY with low fine-tuning, which has multi-TeV first- and second-generation squarks and a light Higgsino mixing parameter μ = 150 GeV . An effective Lagrangian calculation is made of m h to 3 loops using the H3m program with weak scale SUSY parameters obtained from RGE evolution from the GUT scale in the Natural SUSY scenario. The SUSY radiative corrections to the Higgs mass imply maximal off-diagonal elements of the stop mass matrix and a mass splitting of the two stops larger than 400 GeV.

Randall–Sundrum reality at the LHC

Abstract The radion is expected to be the first signal of the Randall–Sundrum (RS) model. We explore the possibility of finding it in the ongoing Higgs searches at the LHC. The little RS model (LRS), which has a fundamental scale at ∼ 10 3 TeV, is excluded over wide ranges of the radion mass from the latest WW and γγ data by ATLAS and CMS.

Dilaton at the LHC

The dilaton, a pseudo-Nambu-Goldstone boson appearing in spontaneous scale symmetry breaking at a TeV scale f, may be found in Higgs boson searches. The dilaton couples to standard model fermions and weak bosons with the same structure as the Higgs boson except for the overall strength. Additionally, the dilaton couples to a Higgs boson pair. The couplings of the dilaton to a gluon pair and a photon pair, appearing at loop level, are largely enhanced compared to the corresponding Higgs couplings. We present regions of the mass and VEV of the dilaton allowed by WW, ZZ, and gammagamma limits from the LHC at 7 TeV with 1.0-2.3 fb-1 integrated luminosity. A scale of f less than 1 TeV is nearly excluded. We discuss how the dilaton chi can be distinguished from the Higgs boson h by observation of the decays chi -> gammagamma and chi -> hh -> (WW)(WW).

The Present Status on σ and κ Meson Properties

The recent experimental data of both ππ/Kπ scattering anti production processes, suggesting the existence of scalar a and κ mesons, are reviewed. In many ππ/Kπ production processes the direct effects of their productions are observed, while they are, because of chiral symmetry, hidden in scattering processes. and now σ(500∼600) and κ(800∼900) are considered to be confirmed experimentally. The recent criticism on our method of analyses, which is based on the long believed prejudice of universal ππ/Kπ phase through scattering and production amplitudes. is explained not to be valid.

The σ-meson production in excited ϒ decay processes: constraint from chiral symmetry

Abstract In the recent letter [T. Komada, M. Ishida, S. Ishida, Phys. Lett. B 508 (2001) 31], hereafter referred to as I, we have shown that the ππ mass spectra in various excited ϒ decay processes are phenomenologically well reproduced by a coherent sum of σ Breit–Wigner amplitude and of the direct 2 π -production amplitude. On the other hand, the ππ -production amplitude was widely believed to be suppressed generally near the threshold, because of the derivative coupling property of Nambu–Goldstone π meson. In this Letter we show that the “threshold-suppression” does not hold in the process with large energy release, in conformity with the steep increase from the ππ threshold observed in the transition ϒ (3 S →1 S ), and that the method of I is consistent with chiral symmetry. Furthermore, applying an effective amplitude explicitly consistent with chiral symmetry, we reanalyze the typical ππ -spectra.

Hadronic Weak Decays of Λb Baryon in the Covariant Oscillator Quark Model

Cabibbo allowed two-body hadronic weak decays of Λb baryons are analyzed in the factorization approximation. We use the covariant oscillator quark model to evaluate the heavy → heavy and heavy → light form factors. When applied in the heavy quark limit, our form factors satisfy all the constraints imposed by heavy quark symmetry. The decay rates and up-down asymmetries for Λb baryon decaying into Λc + P (V ) are calculated. It is found that the up-down asymmetry is negative in all these decay modes. Furthermore, the prediction Br(Λb → Λ + J/ψ )=2 .49 × 10 −4 is consistent with the recent experimental data. Finally it is pointed out that the CKM-Wolfenstein parameter ρ 2 + η 2 , where η is the CP phase, can be determined from the ratio of the widths Λb → Λ ¯ D 0 and Λb → ΛJ/ψ, independent of the QCD parameter. The value of (ρ 2 + η 2 ) 1/2 calculated in our model agrees very well with the value recently predicted by Rosner.