arXiv subjects
Publications and source records attributed to Ken-ichi Hikasa.
We set up a general framework to describe $ππ$ scattering below 1 GeV based on chiral low-energy expansion with possible spin-0 and 1 resonances. Partial wave amplitudes are obtained with the $N/D$ method, which satisfy unitarity, analyticity and approximate crossing symmetry. Comparison with the phase shift data in the J=0 channel favors a scalar resonance near the $ρ$ mass.
Some mechanisms of supersymmetry breaking result in splitting of the third generation sfermions from the other sfermions. We show that the three-body decay branching ratio of the lighter chargino gives a sensitive probe of the sfermion mass spectrum if the chargino has a large gaugino component.
We study QCD correction to the pair production of colored scalar particles in electron-positron annihilation with an emphasis on gluon emission in the final state. We discuss the usefulness of working in a ``quasi-two-body'' frame and present the helicity amplitudes for the process. We compare the final state configuration with fermion pair production and find that the three-jet fraction for the scalars shows quantitative difference from that for fermions.
We discuss the sensitivity of the $e^+ e^- \rightarrow W^+ W^-$ cross section at a future $e^+ e^-$ collider with $\sqrt{s}=500$GeV to the non-decoupling effects of a techni-$ρ$ like vector resonance. The non-decoupling effects are parametrized by the chiral coefficients of the electroweak chiral perturbation theory. We define renormalization scale independent chiral coefficients by subtracting the Standard Model loop contributions. We also estimate the size of the decoupling effects of the techni-$ρ$ resonance by using a phenomenological Lagrangian including the vector resonance.
Supersymmetric relations between dimensionless couplings receive finite correction at one-loop when supersymmetry is broken softly. We calculate the $O(α_s)$ correction to the squark decay width to a quark and an electroweak gaugino, which is found to be nonvanishing. Logarithmic correction appears when the gluino is heavy.
We calculate four-fermion decays of a Higgs boson via $WW$ and/or $ZZ$ intermediate states for Higgs masses below $m_W$. We examine models with a doubly-charged Higgs boson $H^{++}$ and show that the four-fermion decay is the dominant mode for a wide range of parameter space. Existing searches for $H^{++}$ in $Z$ decays have not looked for this mode. We also derive four-fermion decay rate for a neutral Higgs boson.