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K. Matsuda

Publications and source records attributed to K. Matsuda.

At least 37 records · Page 2Linked to original sources
arXiv2006

New Magnetic State in Incommensurate Magnetic Phase of Heavy-Fermion Superconductor CeRh0.6Co0.4In5

We performed elastic neutron scattering experiments on solid solution CeRh1-xCoxIn5 with x=0.4 to clarify the nature of the antiferromagnetic (AF) phase in the vicinity of the quantum critical point. We observed the incommensurate AF order below T_Nh=3.5 K. The structure of the incommensurate AF order is basically unchanged from that for pure CeRhIn5. We further found the evolution of a new commensurate AF order with the modulation of q_c=(1/2,1/2,1/2) below T_Nc=2.9 K. The volume-averaged moments for the incommensurate and commensurate AF phases are 0.38 mu_B/Ce and 0.21 mu_B/Ce, respectively, which are reduced from the incommensurate AF moment (0.75 mu_B/Ce) for pure CeRhIn5. We suggest from these results that the commensurate magnetic correlation may be tightly coupled with the superconductivity observed below T_c=1.4 K.

cond-mat.str-el↗
arXiv2004

Yukawa Matrix for the Neutrino and Lepton Flavour Violation

We estimate the magnitude of Lepton Flavour Violation (LFV) from the phase of the neutrino Yukawa matrix. In the minimal supersymmetric standard model with right-handed neutrinos, the LFV processes l_i \to l_j γcan appear through the slepton mixing, which comes from the renormalization group effect on the right-handed neutrino Yukawa interaction between the Grand Unified Theory scale and the heavy right-handed neutrino mass scale. Two types of phases exist in the neutrino Yukawa matrix. One is the Majorana phase, which can change the magnitude of the LFV branching ratios by a few factor. The other phases relate for the size of the Yukawa hierarchy and its phase effect can change the LFV branching ratios by several orders of magnitude.

hep-ph↗
arXiv2004

Phase contribution to LFV

We analyze the phase effect of the neutrino Yukawa matrix in the context of the Minimal Supersymmetric Standard Model with right-handed neutrinos. Its effect can change the Lepton Flavor Violation branching ratios by a few order of magnitude.

hep-ph↗
arXiv2004

Phenomenological analysis of lepton and quark Yukawa couplings in SO(10) two Higgs model

We investigate a model that the Yukawa coupling form is constructed by two kinds of matrix (M_0 and M_1). For example, in the SO(10) GUT model, M_0 and M_1 are Yukawa couplings generated by the 10 and 126 Higgs scalars. We study how this model can give the observed mass and mixings of quarks and leptons. Parameter fitting is fully scanned by assuming all the input data to be normally distributed around the center value.

hep-ph↗
arXiv2003

Can The Majorana neutrino CP-violating phases be restricted ?

We reanalyze the constraints in neutrino masses and MNS lepton mixing parameters using the new data from the terrestrial (KamLAND) and astrophysical (WMAP) observations together with the HEIDELBERG-MOSCOW double beta decay experiment. It leads us to the almost degenerate or inverse hierarchy neutrino mass scenario. We discuss the possibility of getting the bound for the Majorana CP violating phase.

hep-ph↗
arXiv2002

Constraints from Neutrinoless Double Beta Decay

We examine the constraints from the recent HEIDELBERG-MOSCOW double beta decay experiment. It leads us to the almost degenerate or inverse hierarchy neutrino mass scenario. In this scenario, we obtain possible upper bounds for the Majorana CP violating phase in the lepton sector by incorporating the data from the neutrino oscillation, the single beta decay experiments, and from the astrophysical observation. We also predict the neutrino mass that may be measurable in the future beta decay experiments.

hep-ph↗
arXiv2002

How Far Can the SO(10) Two Higgs Model Describe the Observed Neutrino Masses and Mixings ?

Can the SO(10) model with one {\bf 10} and one {\bf 126} Higgs scalars give the observed masses and mixings of quarks and leptons without any other additional Higgs scalars? Recently, at least, for quarks and charged leptons, it has been demonstrated that it is possible. However, for the neutrinos, it is usually said that parameters which are determined from the quark and charged lepton masses cannot give the observed large neutrino mixings. This problem is systematically investigated, and it is concluded that the present data cannot exclude SO(10) model with two Higgs scalars although it cannot give the best fit values of the data.

hep-ph↗
arXiv2002

Phenomenological Analysis of Lepton and Quark Mass Matrices

We propose a model that all quark and lepton mass matrices originally have the same zero texture. Namely their (1,1), (1,3) and (3,1) components are zeros. For the neutrino mass matrix, we further impose the symmetry between the second and the third generations. Then the neutrino mass matrix has a maximal (ν_μ) - (ν_τ) mixing. Our model is consistent with all the neutrino oscillation experiments and the experimental data in the quark sector too. The neutrino mass matrix can also be well incorporated with the seesaw mechanism.

hep-ph↗
arXiv2001

Can the SO(10) Model with Two Higgs Doublets Reproduce the Observed Fermion Masses?

It is usually considered that the SO(10) model with one 10 and one 126 Higgs scalars cannot reproduce the observed quark and charged lepton masses. Against this conventional conjecture, we find solutions of the parameters which can give the observed fermion mass spectra. The SO(10) model with one 10 and one 120 Higgs scalars is also discussed.

hep-ph↗
arXiv2001

MNS Parameters from Neutrino Oscillations, Single Beta Decay and Double Beta Decay

We examine the constraints on the MNS lepton mixing matrix =66rom the present and future experimental data of the neutrino oscillation, tritium beta decay, and neutrinoless double beta decay for Majorana neutrinos. We show that the small mixing angle solutions for solar neutrino problem are disfavored for small averaged mass ($ $) of neutrinoless double beta decay ($\leq 0.01$ eV) in the inverse neutrino mass hierarchy scenario. This is the case even in the normal mass hierarchy scenario except for very restrictive value of the averaged neutrino mass ($\bar{m_ν}$) of single beta decay. The lower mass bound for $\bar{m_ν}$ is given from the present neutrino oscillation data. We obtain some relations between $ $ and $\bar{m_ν}$. The constraints on the Majorana CP violating phases are also given.

hep-ph↗
arXiv2000

Graphical Representation of CP Violation Effects in Neutrinoless Double Beta Decay

We illustrate the graphical method that gives the constraints on the parameters appearing in the neutrino oscillation experiments and the neutrinoless double beta decay. This method is applicable in three and four generations. Though this method is valid for more general case, we examine explicitly the cases in which the CP violating factors take $\pm 1$ or $\pm i$ in the neutrinoless double beta decay for illustrative clearance. We also discuss some mass matrix models which lead to the above CP violating factors.

hep-ph↗
arXiv2000

CP Violations in Lepton Number Violation Processes and Neutrino Oscillations

We examine the constraints on the MNS lepton mixing matrix from the present and future experimental data of the neutrino oscillation and lepton number violation processes. We introduce a graphical representation of the CP violation phases which appear in the lepton number violation processes such as neutrinoless double beta decay, the $μ^--e^+$ conversion, and the K decay, $K^-\toπ^+μ^-μ^-.$ Using this graphical representation, we derive the constraints on the CP violation phases in the lepton sector.

hep-ph↗
arXiv1999

SO(10) GUT and Quark-Lepton Mass Matrices

The phenomenological model that all quark and lepton mass matrices have the same zero texture, namely their (1,1), (1,3) and (3,1) components are zeros, is discussed in the context of SO(10) Grand Unified Theories (GUTs). The mass matrices of type I for quarks are consistent with the experimental data in the quark sector. For the lepton sector, consistent fitting to the data of neutrino oscillation experiments force us to use the mass matrix for the charged leptons which is slightly deviated from type I. Given quark masses and charged lepton masses, the model includes 19 free parameters, whereas the SO(10) GUTs gives 16 constrained equations. Changing the remaining three parameters freely, we can fit all the entries of the CKM quark mixing matrix and the MNS lepton mixing matrix, and three neutrino masses consistently with the present experimental data.

hep-ph↗
arXiv1999

Lepton and Quark Mass Matrices

We propose a model that all quark and lepton mass matrices have the same zero texture. Namely their (1,1), (1,3) and (3,1) components are zeros. The mass matrices are classified into two types I and II. Type I is consistent with the experimental data in quark sector. For lepton sector, if seesaw mechanism is not used, Type II allows a large $ν_μ- ν_τ$ mixing angle. However, severe compatibility with all neutrino oscillation experiments forces us to use the seesaw mechanism. If we adopt the seesaw mechanism, it turns out that Type I instead of II can be consistent with experimental data in the lepton sector too.

hep-ph↗
arXiv1998

Constraints of Mixing Angles from Lepton Number Violating Processes

We discuss the constraints of lepton mixing angles from lepton number violating processes such as neutrinoless double beta decay, (μ^-)-(e^+) conversion and K decay, $K^- \to π^+μ^-μ^-$ which are allowed only if neutrinos are Majorana particles. The rates of these processes are proportional to the averaged neutrino mass defined by $ _{a b}\equiv |\sum_{j=1}^{3}U_{a j} U_{b j}m_j|$ in the absence of right-handed weak coupling. Here $a, b (j)$ are flavour(mass) eigen states and $U_{a j}$ is the left-handed lepton mixing matrix. We obtain the consistency conditions which are satisfied irrelevant to the concrete values of CP violation phases (three phases in Majorana neutrinos). These conditions constrain the lepton mixing angles, neutrino masses $m_i$ and (< m_ν >_{a b}). By using these constraints we obtain the limits on the averaged neutrino masses for (μ^-)-(e^+) conversion and K decay, $K^- \to π^+μ^-μ^-$.

hep-ph↗
arXiv1998

Constraints of mixing angles from neutrino oscillation experiments and neutrinoless double beta decay

From the analyses of the recent data of neutrino oscillation experiments (especially the CHOOZ and the Super KAMIOKANDE experiments), we discuss how these data affect the neutrinoless double beta decay ($(ββ)_{0ν}$) rate and vice versa assuming that neutrinos are Majorana particles. For the case that $m_1 \sim m_2 \ll m_3$ ($m_i$ are neutrino masses), we obtain, from the data of the CHOOZ and Super KAMIOKANDE, $0.28 \le \sin^2θ_{23} \le 0.76$ and $\sin^2θ_{13} \le 0.05$. Combining the latter constraint with the analysis of the "averaged" neutrino mass (< m_ν>) appeared in $(ββ)_{0ν}$, we find that (\frac{< m_ν>-m_2}{m_3-m_2}<\sin^2 θ_{13} \le 0.05), which leads to the constraint on (< m_ν>) as (< m_ν> \le 0.05 m_3+(1-0.05)m_2). For the case that $m_1 \ll m_2 \sim m_3$, we find that the data of neutrino oscillation experiments and$(ββ)_{0ν}$ imply the constraints of mixing angles.

hep-ph↗
arXiv1998

CP Violation in Neutrinoless Double Beta Decay and Neutrino Oscillation

Taking account of possible CP violation, we discuss about the constraints on the lepton mixing angles from the neutrinoless double beta decay and from the neutrino oscillation for the three flavour Majorana neutrinos. From the CHORUS oscillation experiment, combined with the data of neutrinoless double beta decay, we show that the large angle solution of (θ_{23}) is improbable if the neutrino mass (m_3) of the third generation is a candidate of hot dark matters.

hep-ph↗