arXiv subjects

Daisuke Nomura

Publications and source records attributed to Daisuke Nomura.

30 records · Page 2Linked to original sources

arXiv2007

Improved predictions for g-2 of the muon and α_{\rm QED}(M_Z^2)

We update the Standard Model predictions of the anomalous magnetic moment of the muon, a_μ= (g-2)/2, and the value of the QED coupling at the Z-boson mass, incorporating the new e^+e^- \to ππdata obtained by CMD-2 and KLOE, as well as the corrected SND data, and other improvements. The prediction for a_μ=11659180.4 (5.1) \times 10^{-10} is about 3 \times 10^{-10} lower than before, and has a smaller uncertainty, which corresponds to a 3.4σdeviation from the measured value. The prediction for the QED coupling is α(M_Z^2)^{-1}= 128.937 \pm 0.030.

hep-ph↗

arXiv2006

Hunting for the Top Partner in the Littlest Higgs Model with T-parity at the LHC

We study the Littlest Higgs model with T-parity at the LHC through pair productions of the T-odd top quark partner (T_-) which decays into the top quark and the lightest T-odd particle. We identify the region of parameters favored by the electroweak and cosmological considerations. The signal and background events are simulated with fast detector simulation to study the discovery potential at the LHC. We find that the hemisphere analysis recently proposed by the CMS collaboration is very useful to separate the signal from the t\bar{t} background. We discuss the observability of the top tagged signal in the effective mass (M_{eff}) versus the transverse missing energy (E_{Tmiss}) plane. We show that, for all our sample parameter sets with M_{T_-} \leq 900 GeV, the excess of the signal over the background can be visible as a bump structure in the E_{Tmiss} distribution for 50 fb^{-1} at relatively high M_{eff} intervals.

hep-ph↗

arXiv2006

Light MSSM Higgs boson scenario and its test at hadron colliders

We show that in the Minimal Supersymmetric Standard Model, the possibility for the lightest CP-even Higgs boson to be lighter than $Z$ boson (as low as about 60 GeV) is, contrary to the usual belief, not yet excluded by LEP2 data or any other existing experimental data. The characteristic of the light Higgs boson scenario (LHS) is that the $ZZh$ coupling and the decay branching ratio ${\rm Br}(h/A\to b\bar{b})$ are simultaneously suppressed as a result of generic supersymmetric loop corrections. Consequently, the $W^\pm H^\mp h$ coupling has to be large due to the sum rule of Higgs couplings to weak gauge bosons. In addition to discussing the potential of the Tevatron and $B$-factories to test the LHS, we show that the associate neutral and charged Higgs boson production process, $pp\to H^\pm h (A)$, can completely probe LHS at the CERN Large Hadron Collider.

hep-ph↗

arXiv2006

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 $e^-e^+ \to W^-W^+ ν\bar ν\to t \bar t ν\bar ν$ 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.

hep-ph↗

arXiv2005

Enhancement of "CP-odd" Higgs Boson Production in the Minimal Supersymmetric Standard Model with Explicit CP Violation

We calculate the production cross section of the ``CP-odd'' Higgs boson via gluon fusion in the minimal supersymmetric standard model with explicit CP violation in the stop sector. We show that there is a parameter region in which the cross section is enhanced by a factor of about 1000, as compared to the case without CP violation in the stop sector. In the parameter region where the ``CP-odd'' Higgs boson can decay into a stop pair, the stop pair events will be the important signature of the enhanced ``CP-odd'' Higgs boson. In the case where the ``CP-odd'' Higgs boson cannot decay into any superparticles, the gamma gamma and tau tau decay channels could become important for discovering the ``CP-odd'' Higgs boson. We also discuss the constraints from electric dipole moments of electron, neutron and mercury on the viable parameter space mentioned above.

hep-ph↗

arXiv2004

Predictions for g-2 of the muon and alpha_QED(M_Z^2)

We calculate (g-2) of the muon and the QED coupling alpha(M_Z^2), by improving the determination of the hadronic vacuum polarization contributions and their uncertainties. We include the recently re-analysed CMD-2 data on e^+e^- -> pi^+ pi^-. We carefully combine a wide variety of data for the e^+e^- production of hadrons, and obtain the optimum form of R(s) = sigma_had^0(s)/sigma_pt(s), together with its uncertainty. Our results for the hadronic contributions to g-2 of the muon are a_mu^(had, LO) = (692.4 +- 5.9_exp +- 2.4_rad) * 10^(-10) and a_mu^(had, NLO) = (-9.8 +- 0.1_exp +- 0.0_rad) * 10^(-10), and for the QED coupling Delta alpha^(5)_had (M_Z^2)= (275.5 +- 1.9_exp +- 1.3_rad) * 10^(-4). These yield (g-2)/2 = 0.00116591763(74), which is about 2.4 sigma below the present world average measurement, and alpha(M_Z^2)^(-1) = 128.954 +- 0.031. We compare our (g-2) value with other predictions and, in particular, make a detailed comparison with the latest determination of (g-2) by Davier et al.

hep-ph↗

arXiv2002

The SM prediction of g-2 of the muon

We calculate (g-2)/2 of the muon, by improving the determination of the hadronic vacuum polarisation contribution, a_mu^{had,LO}, and its uncertainties. The different e+e- data sets for each exclusive (and the inclusive) channel are combined in order to obtain the optimum estimate of the cross sections and their uncertainties. QCD sum rules are evaluated in order to resolve an apparent discrepancy between the inclusive data and the sum of the exclusive channels. We conclude a_mu^{had,LO}=(683.1 +- 5.9_{exp} +- 2.0_{rad}) 10^{-10} which, when combined with the other contributions to (g-2)/2, is about 3 sigma below the present world average measurement.

hep-ph↗

arXiv2002

B^0_{d,s} - \bar{B}^0_{d,s} mass-differences from QCD spectral sum rules

We present the first QCD spectral sum rules analysis of the SU(3) breaking parameter ξand an improved estimate of the renormalization group invariant (RGI) bag constant \hat{B}_{B_q} both entering into the B^0_{d,s} - \bar{B}^0_{d,s} mass-differences. The averages of the results from the Laplace and moment sum rules to order α_s are f_B\sqrt{\hat B_B} \simeq (247 \pm 59) MeV and ξ\equiv f_{B_s} \sqrt{\hat B_{B_s}} / f_{B} \sqrt{\hat B_{B}} \simeq (1.18\pm 0.03), in units where f_π=130.7 MeV. Combined with the experimental data on the mass-differences ΔM_{d,s}, one obtains the constraint on the CKM weak mixing angle |V_{ts}/V_{td}|^2 > 20.0 (1.1). Alternatively, using the weak mixing angle from the analysis of the unitarity triangle and the data on ΔM_d, one predicts ΔM_s=18.6 (2.2) ps^{-1} in agreement with the present experimental lower bound and within the reach of Tevatron 2.

hep-ph↗

arXiv2001

Probing Left-handed Slepton Flavor Mixing at Future Lepton Colliders

It has been argued in the literature that the search for the slepton oscillation phenomenon can be a powerful probe of intergenerational mixing between sleptons, once sleptons are found at future colliders. In this article we estimate possible reach of future lepton colliders in probing left-handed slepton flavor mixing, especially mixing between the first and third generations, on which constraints imposed by other processes like $τ\to e γ$ are very weak. $e^+e^-$ collider is suitable for this purpose, since it can produce, if kinematically allowed, sleptons of the first generation via t-channel, in addition to s-channel. Utilizing $e^+e^- \to τe + 4jets + \E$ signal at $e^+e^-$ linear collider with integrated luminosity L=50 fb^{-1}(500 fb^{-1}) it may be possible to reach mixing angle $\sin 2θ_{\tildeν} \gtrsim 0.06 (0.04)$ and mass difference $Δm_{\tildeν} \gtrsim 0.07 (0.04)$ GeV for sneutrinos in the first and third generations at the statistical significance of 5 σ.

hep-ph↗

arXiv1999

Solar and Atmospheric Neutrino Oscillations and Lepton Flavor Violation in Supersymmetric Models with Right-handed Neutrinos

Taking the solar and the atmospheric neutrino experiments into account we discuss the lepton flavor violating processes, such as $τ\toμγ$ or $μ\to eγ$, in the minimal supersymmetric standard model with right-handed neutrinos (MSSMRN) and the supersymmetric SU(5) GUT with right-handed neutrinos (SU(5)RN). The predicted branching ratio of $μ\to eγ$ in the MSSMRN with the MSW large angle solution is so large that it goes beyond the current experimental bound if the second-generation right-handed Majorana mass $M_{ν_2}$ is greater than $\sim 10^{13}(\sim 10^{14})$GeV for $\tanβ=30(3)$. When we take the MSW small angle solution, the $μ\to eγ$ rate is at most about 1/100 of that of the MSW large angle solution. The 'just so' solution implies $10^{-5}$ of that of the MSW large angle solution. Also, in the SU(5)RN the large $μ\to eγ$ rate naturally follows from the MSW large angle solution, and the predicted rate is beyond the current experimental bound if the typical right-handed Majorana mass $M_N$ is larger than $\sim 10^{13}(\sim 10^{14})$GeV for $\tanβ=30(3)$, similarly to the MSSMRN. We show the multimass insertion formulas and their applications to $τ\toμγ$ and $μ\to eγ$.

hep-ph↗

arXiv1998

Enhancement of μ\to e γin the supersymmetric SU(5) GUT at large \tanβ

Branching ratio of $μ\to \e γ$ is evaluated in the supersymmetric SU(5) grand unified theory taking account of higher dimensional operators, which reproduce the realistic quark and lepton masses and the mixing parameters. It is shown by numerical calculation that at large $\tanβ$ the branching ratio is enhanced by a few orders of magnitude since the flavor mixings for both the left- and the right-handed sleptons are induced by the effect of the higher dimensional operators.

hep-ph↗

arXiv1997

Atmospheric Neutrino Oscillation and Large Lepton-Flavour Violation in the SUSY SU(5) GUT

The atmospheric neutrino anomaly reported by the super-Kamiokande collaboration suggests existence of a large flavour violating Yukawa coupling in the lepton sector. We discuss lepton-flavour violation at low energies in the framework of the supersymmetric SU(5)_{GUT} model with right-handed neutrinos. We find that for a wide range of parameter space suggested from the atmospheric neutrino anomaly, if the tau-neutrino Yukawa coupling is as large as that of top quark, lower bounds of the branching ratios of mu -> e gamma, tau -> mu gamma, and the mu-e conversion rate on $^{48}_{22}Ti$ become around 10^{-14}, 10^{-9}, and 10^{-16}, respectively. These reaction rates may be in the region accessible by near future experiments.

hep-ph↗