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Hiroaki Sugiyama

Publications and source records attributed to Hiroaki Sugiyama.

50 records · Page 3Linked to original sources
arXiv2008

Neutralino Dark Matter in Light Higgs Boson Scenario

Phenomenology of neutralino dark matter in the minimal supersymmetric model is discussed for a scenario where the lightest Higgs boson mass is lighter than 114.4 GeV. We show that the scenario is consistent not only with many collider experiments but also with the observed relic abundance of dark matter. The allowed region may be probed by experiments of Bs to mu^+ mu^- in near future. The scenario predicts a large scattering cross section between the dark matter and ordinary matter and thus it may be tested in present direct detection experiments of dark matter.

hep-ph↗
arXiv2008

Probing Majorana Phases and Neutrino Mass Spectrum in the Higgs Triplet Model at the LHC

Doubly charged Higgs bosons (H^++) are a distinctive signature of the Higgs Triplet Model of neutrino mass generation. If H^++ is relatively light (m_{H^++} < 400GeV) it will be produced copiously at the LHC, which could enable precise measurements of the branching ratios of the decay channels H^++ to l_i l_j. Such branching ratios are determined solely by the neutrino mass matrix which allows the model to be tested at the LHC. We quantify the dependence of the leptonic branching ratios on the absolute neutrino mass and Majorana phases, and present the permitted values for the channels ee, emu and mumu. It is shown that precise measurements of these three branching ratios are sufficient to extract information on the neutrino mass spectrum and probe the presence of CP violation from Majorana phases.

hep-ph↗
arXiv2007

More on Non-standard Interaction at MINOS

We discuss about effects of the non-standard interaction of neutrinos with matter on the nu_e appearance search in the MINOS experiment. We consider the effects of the complex phase of the interaction and of the uncertainty on theta_23 also. We show that the oscillation probability can be so large that can not be explained by the ordinary oscillation. We show also how much constraints on the non-standard effects can be improved if the experiment does not observe nu_e appearance signal.

hep-ph↗
arXiv2006

Will MINOS see new physics?

The effect of non-standard neutrino interactions with matter at long baseline neutrino experiments is examined in a model independent way, taking into account the constraints from all the experiments. It is found that such a non-standard interaction can enhance the flavor transition probability so significantly that the ongoing experiment MINOS may see the signal of $ν_μ\toν_e$ which is much more than the prediction by the standard scenario. It is also found that the silver channel $ν_e\toν_τ$ at a neutrino factory could have a huge enhancement.

hep-ph↗
arXiv2006

Resolving theta_{23} Degeneracy by Accelerator and Reactor Neutrino Oscillation Experiments

If the lepton mixing angle theta_{23} is not maximal, there arises a problem of ambiguity in determining theta_{23} due to the existence of two degenerate solutions, one in the first and the other in the second octant. We discuss an experimental strategy for resolving the theta_{23} octant degeneracy by combining reactor measurement of theta_{13} with accelerator nu_{mu} disappearance and nu_{e} appearance experiments. The robustness of the theta_{23} degeneracy and the difficulty in lifting it only by accelerator experiments with conventional nu_{mu} (and nu_{mu}-bar) beam are demonstrated by analytical and numerical treatments. Our method offers a way to overcome the difficulty and can resolve the degeneracy between solutions sin^2 theta_{23} = 0.4 and sin^2 theta_{23} = 0.6 if sin^2 (2 theta_{13}) \gsim 0.05 at 95% CL by assuming the T2K phase II experiment and a reactor measurement with an exposure of 10 GW.kt.yr. The dependence of the resolving power of the octant degeneracy on the systematic errors of reactor experiments is also examined.

hep-ph↗
arXiv2004

Determination of theta_{23} in Long-Baseline Neutrino Oscillation Experiments with Three-Flavor Mixing Effects

We examine accuracy of theta_{23} determination in future long-baseline (LBL) nu_{mu} disappearance experiments in the three-flavor mixing scheme of neutrinos. Despite that the error of sin^2{2theta_{23}} is indeed a few % level at around the maximal mixing, we show that the error of physics variable s^2_{23} is large, delta(s^2_{23})/s^2_{23} \simeq 10-20%, depending upon regions of theta_{23}. The errors are severely affected by the octant degeneracy of theta_{23}, and delta(s^2_{23}) is largely amplified by the Jacobian factor relating these two variables in a region near to the maximal mixing. The errors are also affected by the uncertainty due to unknown value of theta_{13}; delta(s^2_{23}) is doubled at off maximal in the second octant of theta_{23} where the effect is largest. To overcome this problem, we discuss combined analysis with nu_e appearance measurement in LBL experiments, or with reactor measurement of theta_{13}. For possible relevance of sub-leading effects even in the next-generation LBL experiments, we give a self-contained derivation of the survival probability to the next to leading order in s^2_{13} and Delta m^2_{21} / Delta m^2_{31}.

hep-ph↗
arXiv2003

Exploring Leptonic CP Violation by Reactor and Neutrino Superbeam Experiments

We point out the possibility that reactor measurement of theta_{13}, when combined with high-statistics nu_e appearance accelerator experiments, can detect leptonic CP violation. Our proposal is based on a careful statistical analysis under reasonable assumptions on systematic errors, assuming 2 years running of the neutrino mode J-PARC -> Hyper-Kamiokande experiment and a few years running of a reactor experiment with 100 ton detectors at the Kashiwazaki-Kariwa nuclear power plant. We show that the method can be arranged to be insensitive to the intrinsic parameter degeneracy but is affected by the one due to unknown sign of Delta m^2_{31}.

hep-ph↗
arXiv2003

Neutrinoless Double Beta Decay Constraints

A brief overview is given of theoretical analyses with neutrinoless double beta decay experiments. Theoretical bounds on the ``observable'', _betabeta, are presented. By using experimental bounds on _betabeta, allowed regions are obtained on the m_l-cos{2theta_12} plane, where m_l stands for the lightest neutrino mass. It is shown that Majorana neutrinos can be excluded by combining possible results of future neutrinoless double beta decay and {}^3H beta decay experiments. A possibility to constrain one of two Majorana phases is discussed also.

hep-ph↗
arXiv2003

Double Beta Decay Constraints on Neutrino Masses and Mixing; Reanalysis with KamLAND Data

In the light of KamLAND data just released, we reanalyze and update the constraints on neutrino masses and mixing parameters, the most general ones that can be derived in three-flavor mixing scheme of neutrinos with use of the bounds imposed by neutrinoless double beta decay search and reactor experiments. We point out that with KamLAND data and assuming Majorana neutrinos one can derive, for the first time, an upper bound on neutrino contribution to the cosmological Ωparameter, Ω_ν \leq 0.070 h^{-2}, by using the current upper bound on mass parameters obtained by Heidelberg-Moscow group, < m >_{ββ} < 0.35 eV (90 % CL). If the bound is tighten to < m >_{ββ} < 0.1 eV by future experiments, it would lead to a far severer bound Ω_ν \lsim 0.01 h^{-2}.

hep-ph↗
arXiv2002

Constraints on Neutrino Parameters by Neutrinoless Double Beta Decay Experiments

Allowed regions on the m_l - cos{2θ_{12}} plane are extracted from results of neutrinoless double beta decay experiments. It is shown that 0.05 eV (0 eV) < m_l < 1.85 eV is obtained for the normal (inverted) hierarchy by using the LMA best fit parameters and the 0νββresult announced late last year, which is 0.05 eV < _ββ< 0.84 eV with +/- 50% uncertainty of the nuclear matrix elements.

hep-ph↗
arXiv2002

Constraints on Neutrino Mixing Parameters By Observation of Neutrinoless Double Beta Decay

Assuming positive observation of neutrinoless double bata decay together with the CHOOZ reactor bound, we derive constraints imposed on neutrino mixing parameters, the solar mixing angle θ_{12} and the observable mass parameter < m >_β in single beta decay experiments. We show that 0.05 eV < < m >_β < 2 eV at the best fit parameters of the LMA MSW solar neutrino solution by requiring the range of the parameter < m >_{ββ} deduced from recently announced double beta decay events at 95 % CL with +/- 50 % uncertainty of nuclear matrix elements.

hep-ph↗
arXiv2001

Lower Bound on |U_{e3}|^2 from Single and Double Beta Decay Experiments

We point out under the assumption of Majorana neutrinos that a lower bound on the MNS matrix element |U_{e3}|^2 can be derived by using constraint imposed by neutrinoless double beta decay experiments and by positive detection of neutrino mass by single beta decay experiments. We show that the lower bound exists in a narrow region of the ratio of the observables in these two experiments, _{ββ}/ _β. It means that once the neutrino mass is detected in the bound-sensitive region one must soon observe signal in neutrinoless double beta decay experiments.

hep-ph↗