arXiv subjects

Yusuke Shimizu

Publications and source records attributed to Yusuke Shimizu.

At least 55 records · Page 3Linked to original sources

arXiv2016

Mass Limit for Light Flavon with Residual $Z_3$ Symmetry

We present a modified Altarelli and Feruglio $A_4$ model where an additional $A_4$ singlet-prime flavon is introduced. In this model, non-zero $θ_{13}$ is given by this additional $A_4$ singlet-prime flavon which breaks tri-bimaximal mixing. In the framework of the supersymmetry with $U(1)_R$ symmetry, we obtain vacuum expectation values (VEVs) and VEV alignments of flavons through driving fields. It is considered that flavon induces distinctive flavor violating process if flavon mass is light. Assuming mass of SUSY particles are sufficiently heavy so that the SUSY contributions can be negligible, we discuss the flavor violating Yukawa interaction through flavon exchange in the charged lepton sector. According to the potential analysis, the VEV of flavon breaks $A_4$ down to $Z_3$ in the charged lepton sector and relation among flavon masses is determined. Thanks for the residual $Z_3$ symmetry, many lepton flavor violating decay modes are forbidden except for $τ\rightarrow μμ\bar{e}$ and $τ\rightarrow e e \barμ$. A mass limit of the flavon from these three-body decay modes is $60$~GeV taking into account the current experimental lower bounds at the Belle experiment. In our model, we predict a ratio of the branching ratios $τ\rightarrow μμ\bar{e}$ and $τ\rightarrow e e \barμ$ by using known charged lepton masses. We also find that the production cross section for the flavon can be $\mathcal{O}(1)$ fb. Thus the flavon would be found at the LHC run 2 by searching for 4-tau lepton signal.

hep-ph↗

arXiv2016

Occam's Razor in Lepton Mass Matrices - The Sign of Universe's Baryon Asymmetry -

We discuss the neutrino mass matrix based on the Occam's Razor approach in the framework of the seesaw mechanism. We impose four zeros in the Dirac neutrino mass matrix, which give the minimum number of parameters needed for the observed neutrino masses and lepton mixing angles, while the charged lepton mass matrix and the right-handed Majorana neutrino mass matrix are taken to be real diagonal ones. The low-energy neutrino mass matrix has only seven physical parameters. We show successful predictions for the mixing angle $θ_{13}$ and the CP violating phase $δ_{CP}$ with the normal mass hierarchy of neutrinos by using the experimental data on the neutrino mass squared differences, the mixing angles $θ_{12}$ and $θ_{23}$. The most favored region of $\sinθ_{13}$ is around $0.13\sim 0.15$, which is completely consistent with the observed value. The CP violating phase $δ_{CP}$ is favored to be close to $\pm π/2$. We also discuss the Majorana phases as well as the effective neutrino mass for the neutrinoless double-beta decay $m_{ee}$, which is around $7\sim 8$ meV. It is extremely remarkable that we can perform a "complete experiment" to determine the low-energy neutrino mass matrix, since we have only seven physical parameters in the neutrino mass matrix. In particular, two CP violating phases in the neutrino mass matrix are directly given by two CP violating phases at high energy. Thus, assuming the leptogenesis we can determine the sign of the cosmic baryon in the universe from the low-energy experiments for the neutrino mass matrix.

hep-ph↗

arXiv2015

AIC for Non-concave Penalized Likelihood Method

Non-concave penalized maximum likelihood methods, such as the Bridge, the SCAD, and the MCP, are widely used because they not only do parameter estimation and variable selection simultaneously but also have a high efficiency as compared to the Lasso. They include a tuning parameter which controls a penalty level, and several information criteria have been developed for selecting it. While these criteria assure the model selection consistency and so have a high value, it is a severe problem that there are no appropriate rules to choose the one from a class of information criteria satisfying such a preferred asymptotic property. In this paper, we derive an information criterion based on the original definition of the AIC by considering the minimization of the prediction error rather than the model selection consistency. Concretely speaking, we derive a function of the score statistic which is asymptotically equivalent to the non-concave penalized maximum likelihood estimator, and then we provide an asymptotically unbiased estimator of the Kullback-Leibler divergence between the true distribution and the estimated distribution based on the function. Furthermore, through simulation studies, we check that the performance of the proposed information criterion gives almost the same as or better than that of the cross-validation.

stat.ME↗

arXiv2015

Testing the minimal $S_4$ model of neutrinos with the Dirac and Majorana phases

We propose two new simple lepton flavor models in the framework of the $S_4$ flavor symmetry. The neutrino mass matrices, which are given by two complex parameters, lead to the inverted mass hierarchy. The charged lepton mass matrix has the 1-2 lepton flavor mixing, which gives the non-vanishing reactor angle $θ_{13}$. These models predict the Dirac phase and the Majorana phases, which are testable in the future experiments. The predicted magnitudes of the effective neutrino mass for the neutrino-less double beta decay are in the regions as $32~\text{meV}\lesssim |m_{ee}|\lesssim 49~\text{meV}$ and $34~\text{meV}\lesssim |m_{ee}|\lesssim 59~\text{meV}$, respectively. These values are close to the expected reaches of the coming experiments. The total sum of the neutrino masses are predicted in both models as $0.0952~\text{eV}\lesssim \sum m_i\lesssim 0.101~\text{eV}$ and $0.150~\text{eV}\lesssim \sum m_i\lesssim 0.160~\text{eV}$, respectively.

hep-ph↗

arXiv2015

Update estimation of diffusion parameter observed at high frequency

We propose an update estimation method for a diffusion parameter from high-frequency dependent data under a nuisance drift element. We ensure the asymptotic equivalence of the estimator to the corresponding quasi-MLE, which has the asymptotic normality and the asymptotic efficiency. We give a simulation example to illustrate the theory.

math.ST↗

arXiv2015

Higgs $\to μτ$ in Abelian and Non-Abelian Flavor Symmetry Models

We study lepton flavor violating Higgs decays in two models, with the recently found hint for Higgs $\to μτ$ at CMS as a benchmark value for the branching ratio. The first model uses the discrete flavor symmetry group $A_4$, broken at the electroweak scale, while the second is renormalizable and based on the Abelian gauge group $L_μ- L_τ$. Within the models we find characteristic predictions for other non-standard Higgs decay modes, charged lepton flavor violating decays and correlations of the branching ratios with neutrino oscillation parameters.

hep-ph↗

arXiv2014

Predicting CP violation in Deviation from Tri-bimaximal mixing of Neutrinos

We study the CP violation in the deviation from the tri-bimaximal mixing (TBM) of neutrinos. We examine non-trivial relations among the mixing angles and the CP violating Dirac phase in the typical four cases of the deviation from the TBM. The first two cases are derived by the additional rotation of the 2-3 or 1-3 generations of neutrinos in the TBM basis. The other two cases are given by the additional rotation of the 1-3 or 1-2 generations of charged leptons with the TBM neutrinos. These four cases predict different relations among three mixing angles and the CP violating Dirac phase. The rotation of the 2-3 generations of neutrinos in the TBM basis predicts $\sin ^2θ_{12}<1/3$, and the CP violating Dirac phase to be $\pm (0.09π\sim 0.76π)$ for NH ($\pm (0.15π\sim 0.73π) \ \text{for IH}$) depending on $\sin ^2θ_{23}$. The rotation of the 1-3 generations of neutrinos in the TBM basis gives $\sin ^2θ_{12}>1/3$. The CP violating Dirac phase is not constrained by the input of the present experimental data. For the case of the 1-3 and 1-2 rotations of charged leptons in the TBM basis, the CP violating Dirac phase is predicted in $\pm(0.35π\sim 0.60π)$ depending on $\sin ^2θ_{12}$ for both NH and IH cases. We also discuss the specific case that $θ_{13}$ is related with the Cabibbo angle $λ$ such as $\sinθ_{13}=λ/\sqrt{2}$, in which the maximal CP violation is preferred. The CP violating Dirac phase can distinguish the lepton flavor mixing patterns at T2K and NO$ν$A experiments in the future.

hep-ph↗

arXiv2014

Neutrino Mass and Mixing: from Theory to Experiment

The origin of fermion mass hierarchies and mixings is one of the unresolved and most difficult problem in high-energy physics. One possibility to address the flavour problem is by extending the Standard Model to include a family symmetry. In the recent years it has become very popular to use non-Abelian discrete flavour symmetries because of their power in the prediction of the large leptonic mixing angles relevant for neutrino oscillation experiments. Here we give an introduction to the flavour problem and to discrete groups which have been used to attempt a solution for it. We review the current status of models in the light of the recent measurement of the reactor angle and we consider different model building directions taken. The use of the flavons or multi Higgs scalars in model building is discussed as well as the direct vs. indirect approaches. We also focus on the possibility to distinguish experimentally flavour symmetry models by means of mixing sum rules and mass sum rules. In fact, we illustrate in this review the complete path from mathematics, via model building, to experiments, so that any reader interested to start working in the field could use this text as a starting point in order to get a broad overview of the different subject areas.

hep-ph↗

arXiv2014

Searching for the squark flavor mixing in CP violations of Bs -> K+ K- and K0bar K0 decays

We study CP violations in the B_s-> K+K- and Bs->K0K0 decays in order to find the contribution of the supersymmetry, which comes from the gluino-squark mediated flavor changing current. We obtain the allowed region of the squark flavor mixing parameters by putting the experimental data, the mass difference Delta M_Bs, the CP violating phase phi_s in Bs to J/psi phi decay and the b to s gamma branching ratio. In addition to these data, we take into account the constraint from the asymmetry of B0->K+pi because the Bs->K+K- decay is related with the B0->K+pi- decay by replacing the spectator s with d. Under these constraints, we predict the magnitudes of the CP violation in the Bs->K+K- and Bs->K0K0 decays. The predicted region of the CP violation C_{K+K-} is strongly cut from the direct CP violation of barB0 to K-pi+, therefore, the deviation from the SM prediction of C_{K+K-} is not found. On the other hand, the CP violation S_{K+K-} is possibly deviated from the SM prediction considerably, in the region of 0.1- 0.5. Since the standard model predictions of C_{K0bar K0} and S_{K0bar K0} are very small, the squark contribution can be detectable in C_{K0bar K0} and S_{K0bar K0}. These magnitudes are expected in the region C_{K0bar K0}=-0.06-0.06 and S_{K0bar K0}=-0.5-0.3. More precise data of these CP violations provide us a crucial test for the gluino-squark mediated flavor changing current.

hep-ph↗

arXiv2013

Sensitivity of the squark flavor mixing to the CP violation of K, B0 and Bs mesons

We study the sensitivity of the squark flavor mixing to the CP violating phenomena of $K$, $B^0$ and $B_s$ mesons in the framework of the split-family scenario, where the first and second family squarks are very heavy, ${\cal O}(10)$TeV, on the other hand, the third family squark masses are at ${\cal O}(1)$TeV. In order to constrain the gluino-sbottom-quark mixing parameters, we input the experimental data of the CP violations of $K$, $B^0$, and $B_s$ mesons, that is $ε_K$, $ϕ_d$, and $ϕ_s$. The experimental upper bound of the chromo-EDM of the strange quark is also input. In addition, we take account of the observed values $ΔM_{B^0}$, $ΔM_{B_s}$, the CKM mixing $|V_{ub}|$, and the branching ratio of $b\to sγ$. The allowed region of the mixing parameters are obtained as $|δ_{13}^{dL(dR)}|=0\sim 0.01$ and $|δ_{23}^{dL(dR)}|=0\sim 0.04$. By using these values, the deviations from the SM are estimated in the CP violations of the $B^0$ and $B_s$ decays. The deviation from the SM one is tiny in the CP asymmetries of $B^0\to ϕK_S$ and $B^0\to η'K^0$ due to the chromo-EDM of the strange quark. On the other hand, the CP asymmetries $B_s \to ϕϕ$ and $B_s \to ϕη'$ could be largely deviated from the SM predictions. We also predict the time dependent CP asymmetry of $B^0\to K^0\bar K^0$ and the semi-leptonic CP asymmetries of $B^0 \to μ^-X$ and $B_s \to μ^-X$. We expect those precise measurements at Belle II, which will provide us interesting tests for the squark flavor mixing.

hep-ph↗

arXiv2013

SUSY contributions to CP violations in $b\to s$ and $b\to d$ transitions facing on new data

We study the contribution of the gluino-squark mediated flavor changing process for the CP violation in $b\to s$ and $b\to d$ transitions facing on recent experimental data. The mass insertion parameters of squarks are constrained by the branching ratios of $b\to sγ$ and $b\to dγ$ decays. In addition, the time dependent CP asymmetries of $B^0\to ϕK_S$ and $B^0\to η' K^0$ decays severely restrict the allowed region of the mass insertion parameter for the $b\to s$ transition. By using these constraints with squark and gluino masses of 1.5 TeV, we predict the CP asymmetries of $B_s\to ϕϕ$, $B_s\to η'ϕ$, and $B^0\to K^0\bar K^0$ decays, as well as the CP asymmetries in $b\to sγ$ and $b\to dγ$ decays. The CP violation in the $B_s\to ϕϕ$ decay is expected to be large owing to the squark flavor mixing, which will be tested at LHCb soon.

hep-ph↗

arXiv2013

Minimal Neutrino Texture with Neutrino Mass Ratio and Cabibbo Angle

We present neutrino mass matrix textures in a minimal framework of the type-I seesaw mechanism where two right-handed Majorana neutrinos are introduced in order to reproduce experimental results of neutrino oscillations. The textures can lead to experimentally favored leptonic mixing angles described by the tri-bimaximal mixing with one additional rotation. We present minimal and next to minimal textures for the normal mass hierarchy case in a context of the texture zero. A minimal texture in the inverted hierarchy case is also constructed, which does not have any vanishing entries in a Dirac neutrino mass matrix. We also discuss some cases that model parameters in the textures are supposed to be a neutrino mass ratio and/or the Cabibbo angle. Predicted regions of mixing angles, a leptonic CP-violation parameter, and an effective mass for the neutrino-less double beta decay are presented in all textures.

hep-ph↗

arXiv2012

$θ_{13}$ in Neutrino Mass Matrix with the Minimal Texture

We show that the neutrino mass matrix with the minimal texture leads to the neutrino mass and mixing that are empirically determined, including $θ_{13}$ that is measured recently at a high precision. This mass matrix, where the Majorana nature of the neutrino is essential, only allows the normal hierarchy of the neutrino mass, excluding either inverse mass hierarchy or degenerate mass neutrinos, and hence predicts the effective mass of double beta decay to lie within the range $m_{ee}=3.7-5.6$ eV.

hep-ph↗

arXiv2012

Realisability of SUSY discrete flavour symmetry in our universe

We study the realisation of supersymmetric discrete flavour symmetry models to the thermal history of our universe. We focus on the evolution of the pseudo moduli field among the flavons by taking into account finite temperature corrections. We show that the pseudo moduli flavon dominates the energy density of our universe and this domination makes crucially difficult to realise the flavour symmetry models in our universe. We also discuss possible extensions of the supersymmetric discrete flavour symmetry models which can ensure the consistency of the models with the thermal history of our universe. Finally, we show an extension to realise the thermal inflation by the flavon domination.

hep-ph↗

arXiv2012

Direct CP violation of $b \rightarrow sγ$ and CP asymmetries of non-leptonic B decays in squark flavor mixing

We study the contribution of the squark flavor mixing from the $LR(RL)$ component of the squark mass matrices to the direct CP violation of the $b\to sγ$ decay and the CP-violating asymmetry in the non-leptonic decays of $B$ mesons. The magnitude of the $LR(RL)$ component is constrained by the branching ratio and the direct CP violation of $b\to sγ$. We predict the correlation of the CP asymmetries among $A_{\text{CP}}^{b \to s γ}$, $\mathcal{S}_{ϕK_S}$ and $\mathcal{S}_{η'K^0}$ of the B decays. The precise data of these CP violations will give us the crucial test for our framework of the squark flavor mixing.

hep-ph↗

arXiv2012

Squark flavor mixing and CP asymmetry of neutral $B$ mesons at LHCb

The CP violation of the neutral $B$ meson is the important phenomenon to search for the new physics. The like-sign dimuon charge asymmetry observed by the D$Ø$ Collaboration indicates the CP-violating new physics in the $B_s-\bar B_s$ mixing. On the other hand, LHCb observed the CP-violating asymmetry in $B_s^0\to J/ψϕ$ and $B_s^0\to J/ψf_0(980)$, which is consistent with the SM prediction. However, there is still room for new physics of the CP violation. The CKMfitter has presented the allowed region of the new physics parameters taking account of the LHCb data. Based on these results, we discuss the effect of the squark flavor mixing on the CP violation in the $B_d$ and $B_s$ mesons. We predict asymmetries in the non-leptonic decays $B_d^0\to ϕK_S$, $B_d^0\to η'K^0$, $B_s^0\to ϕϕ$ and $B_s^0\to ϕη'$.

hep-ph↗

arXiv2012

Proceedings of the first workshop on Flavor Symmetries and consequences in Accelerators and Cosmology (FLASY2011)

The main goals of the first "Workshop on FLAvor SYmmetries and consequences in accelerators and cosmology" (FLASY) was to summarize the theoretical status of flavor symmetries, bringing together young researchers in the field to stimulate discussions and new collaborations, with the aim of investigating possible new physics scenarios to be tested at the LHC, as well as in future neutrino, cosmology experiments and dark matter searches.

hep-ph↗

arXiv2011

Relating quarks and leptons without grand-unification

In combination with supersymmetry, flavor symmetry may relate quarks with leptons, even in the absence of a grand-unification group. We propose an SU(3)xSU(2)xU(1) model where both supersymmetry and the assumed A4 flavor symmetries are softly broken, reproducing well the observed fermion mass hierarchies and predicting: (i) a relation between down-type quarks and charged lepton masses, and (ii) a correlation between the Cabibbo angle in the quark sector, and the reactor angle characterizing CP violation in neutrino oscillations.

hep-ph↗