arXiv subjects

Y. Okada

Publications and source records attributed to Y. Okada.

82 records · Page 5Linked to original sources

arXiv2003

Mid- to Far-Infrared spectroscopy of Sharpless 171

We have collected one-dimensional raster-scan observations of the active star-forming region Sharpless 171 (S171), a typical HII region-molecular cloud complex, with the three spectrometers (LWS, SWS, and PHT-S) on board ISO. We have detected 8 far-infrared fine-structure lines, [OIII] 52um, [NIII] 57um, [OI] 63um, [OIII] 88um, [NII] 122um, [OI] 146um, [CII] 158um, and [SiII] 35um together with the far-infrared continuum and the H2 pure rotation transition (J=5-3) line at 9.66um. The physical properties of each of the three phases detected, highly-ionized, lowly-ionized and neutral, are investigated through the far-infrared line and continuum emission. Toward the molecular region, strong [OI] 146um emission was observed and the [OI] 63um to 146um line ratio was found to be too small (about 5) compared to the values predicted by current photodissociation region (PDR) models. We examine possible mechanisms to account for the small line ratio and conclude that the absorption of the [OI] 63um and the [CII] 158um emission by overlapping PDRs along the line of sight can account for the observations and that the [OI] 146um emission is the best diagnostic line for PDRs. We propose a method to estimate the effect of overlapping clouds using the far-infrared continuum intensity and derive the physical properties of the PDR. The [SiII] 35um emission is quite strong at almost all the observed positions. The correlation with [NII] 122um suggests that the [SiII] emission originates mostly from the ionized gas. The [SiII] 35um to [NII] 122um ratio indicates that silicon of 30% of the solar abundance must be in the diffuse ionized gas, suggesting that efficient dust destruction is undergoing in the ionized region.

astro-ph↗

arXiv2002

Measurement of the Higgs self-coupling at JLC

We examine the double Higgs production process at JLC. We focus our attention on the measurement of the Higgs self-coupling. The sensitivity of the triple Higgs coupling measurement is discussed in the Higgs mass range 100-200 GeV and the center of mass energy to be 500 GeV-1.5 TeV.

hep-ph↗

arXiv2002

The Snowmass Points and Slopes: Benchmarks for SUSY Searches

The ``Snowmass Points and Slopes'' (SPS) are a set of benchmark points and parameter lines in the MSSM parameter space corresponding to different scenarios in the search for Supersymmetry at present and future experiments. This set of benchmarks was agreed upon at the 2001 ``Snowmass Workshop on the Future of Particle Physics'' as a consensus based on different existing proposals.

hep-ph↗

arXiv2002

Report of Snowmass 2001 Working Group E2 : Electron-positron Colliders from the $ϕ$ to the Z

We report on the status and plans of experiments now running or proposed for electron-positron colliders at energies between the $ϕ$ and the Z. The $e^{+}e^{-}$ B and charm factories we considered were PEP-II/BABAR, KEKB/Belle, superKEK, SuperBABAR, and CESR-c/CLEO-c. We reviewed the programs at the $ϕ$ factory at Frascati and the proposed PEP-N facility at Stanford Linear Accelerator Center. We studied the prospects for B physics with a dedicated linear collider Z factory, associated with the TESLA high energy linear collider. In all cases, we compared the physics reach of these facilities with that of alternative experiments at hadron colliders or fixed target facilities.

hep-ex↗

arXiv1999

Upper and lower bounds of the lightest CP-even Higgs boson in the two-Higgs-doublet model

By imposing validity of the perturbation and stability of vacuum up to an energy scale $Λ$ ($\leq 10^{19}$ GeV), we evaluate mass bounds of the lightest CP-even Higgs-boson mass ($m_h$) in the two-Higgs-doublet model (2HDM) with a softly-broken discrete symmetry. The most general bounds are obtained as a function of $Λ$ vering all the free parameters under the experimental constraint from the $rho$ parameter and the b \to s γ$ results. We find that, while the upper bound is almost the same as in the SM, the lower bound is significantly reduced. In the decoupling regime where the model behaves like the SM at low energy, the lower bound is given, for example, by about 100 GeV for $Λ= 10^{19}$ GeV and $m_t = 175$ GeV, which is smaller by about 40 GeV than the corresponding lower bound in the SM. In general case, the $m_h$ is no longer bounded from below by these conditions. If we consider the experimental $b \to s γ$ constraint, small $m_h$ are excluded in Model II of the 2HDM.

hep-ph↗

arXiv1998

Non-Fermi liquid behavior of SrRuO_3 -- evidence from infrared conductivity

The reflectivity of the itinerant ferromagnet SrRuO_3 has been measured between 50 and 25,000 cm-1 at temperatures ranging from 40 to 300 K, and used to obtain conductivity, scattering rate, and effective mass as a function of frequency and temperature. We find that at low temperatures the conductivity falls unusually slowly as a function of frequency (proportional to ω^{-1/2}), and at high temperatures it even appears to increase as a function of frequency in the far-infrared limit. The data suggest that the charge dynamics of SrRuO_3 are substantially different from those of Fermi-liquid metals.

cond-mat.str-el↗

arXiv1996

Studying the Higgs Potential via $e^+e^- \to Zhh$

The physics prospect at future linear $e^+e^-$ colliders for the study of the Higgs triple self-coupling via the process of $e^+e^-$ $\rightarrow Zhh$ is investigated. The measurement of this cross section leads us to the first non-trivial information on the Higgs potential. We found that the Standard Model and the model without the Higgs self-coupling can be distinguished at the level of one standard deviation for a rather light Higgs mass with 100 fb$^{-1}$ integrated luminosity. In the MSSM, the cross section is enhanced if the production of at least one of heavy Higgs bosons ($H$ or $A$) and its subsequent decay ($H \rightarrow hh$, $A \rightarrow Zh$) are kinematically allowed. When such processes are not allowed, the cross section in the region of small $m_A$ is significantly suppressed relative to the SM cross section.

hep-ph↗

arXiv1995

Probing the heavy Higgs mass by the measurement of the Higgs decay branching ratios in the minimal supersymmetric standard model

We examine whether the parameters in the Higgs sector of the minimal supersymmetric standard model can be determined by detailed study of production cross section and decay branching ratios of the Higgs particle. Assuming that the lightest CP-even Higgs boson ($h$) is observed at a future $e^+ e^-$ linear collider with $\sqrt{s}=300\sim500$GeV, we show that the value of CP-odd scalar mass is determined from the ratio of the two branching ratios, $Br(h\to b\bar{b})$ and $Br(h\to c\bar{c})+Br(h\to gg)$, almost independently of the stop mass scale.

hep-ph↗

arXiv1995

Time reversal violation in $K^+ \to μ^+ νγ$ decay and three Higgs model

Transverse muon polarization in the $K^+ \rightarrow μ^+ νγ$ decay is calculated in the model with scalar and pseudo scalar four-Fermi interactions. Combined with a similar calculation in the $K^+ \rightarrow μ^+ νπ^0$ decay, a possible constraint on parameters in the three-Higgs model is obtained assuming sensitivity of the up-coming KEK experiment. It is pointed out that the predictions for the two polarizations are strongly correlated in the three Higgs model.

hep-ph↗

arXiv1995

Model-independent analysis of $\bbox{B}$-$\bbox{\bar B}$ mixing and $\bbox{CP}$ violation in $\bbox{B}$ decays

We present a framework to analyze effects of new physics beyond the standard model on $B$-$\bar B$ mixing and $CP$ violation in $B$ decays in a model-independent manner. Assuming that tree level decay amplitudes are dominated by the standard model ones, new physics contribution to the $B$-$\bar B$ mixing can be extracted from several measurements at $B$ factories. Using this framework, we show the present constraint on new physics contribution to the $B$-$\bar B$ mixing, and illustrate constraints expected to be given by future experiments at $B$ factories. We also point out a possibility that $CP$ asymmetries in $B\rightarrowψK_S$, $B\rightarrowππ$, and $B\rightarrow DK$ modes look consistent with the standard model, even if a large new physics contribution is present in the $B$-$\bar B$ mixing.

hep-ph↗