arXiv subjects

Yu Muramatsu

Publications and source records attributed to Yu Muramatsu.

15 recordsLinked to original sources

arXiv2020

SUSY threshold corrections to quark and lepton mixing inspired by $SO(10)$ GUT models

In the standard model (SM), the Cabibbo-Kobayashi-Maskawa (CKM) matrix is the only origin of flavor violations (FVs). On the other hand, in general, there are a lot of sources of the FVs in a physics beyond the SM, through the diagonalizing matrices which make Yukawa matrices diagonal. Although most of the diagonalizing matrices are unknown ones, grand unified theories (GUTs) can fix these matrices. In particular, if we consider a GUT model based on the $SO(10)$ group, these diagonalizing matrices are strongly related to each other because of the matter unification. However, this unification causes the problem on the realization of measured SM fermion masses and mixing angles. Up to now, many people showed that supersymmetric (SUSY) threshold corrections can solve this problem, especially unfavorable fermion mass relations. In this paper, we show that how these SUSY threshold corrections affect unknown diagonalizing matrices. Since these contributions are also related to the FVs induced by SUSY particles, we can estimate the maximal effect to the diagonalizing matrices. We found that the $(1, 3)$ and $(3, 1)$ elements of diagonalizing matrices for quarks can be as large as the corresponding mixing angle of the CKM matrix. Moreover, we found that the higher SUSY scale can predict the larger mixing angles, although strong cancellation between the Higgs mass parameters is needed to realize the electroweak symmetry breaking.

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arXiv2020

Proton Decay and Axion Dark Matter in SO(10) Grand Unification via Minimal Left-Right Symmetry

We study the proton lifetime in the $SO(10)$ Grand Unified Theory (GUT), which has the left-right (LR) symmetric gauge theory below the GUT scale. In particular, we focus on the minimal model without the bi-doublet Higgs field in the LR symmetric model, which predicts the LR-breaking scale at around $10^{10\text{--}12}$ GeV. The Wilson coefficients of the proton decay operators turn out to be considerably larger than those in the minimal $SU(5)$ GUT model especially when the Standard Model Yukawa interactions are generated by integrating out extra vector-like multiplets. As a result, we find that the proton lifetime can be within the reach of the Hyper-Kamiokande experiment even when the GUT gauge boson mass is in the $10^{16\text{--}17}$ GeV range. We also show that the mass of the extra vector-like multiplets can be generated by the Peccei-Quinn symmetry breaking in a consistent way with the axion dark matter scenario.

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arXiv2019

$A_4$ flavor symmetric model in SUSY SU(5) GUT

We propose a model with $A_4$ flavor symmetry for leptons and quarks in the framework of supersymmetric SU(5) grand unified theory (GUT). The running masses of quarks and charged leptons at GUT scale ($\sim 10^{16}$ GeV) are realized by the adjoint 24-dimensional Higgs multiplet and additional gauge singlet scalar fields including flavons. In this paper, we focus on a result of the quark and charged lepton masses and quark mixing since our present model is known to reproduce recent experimental results of the neutrino mass and oscillation. Those results are showed numerically.

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arXiv2019

Flavor physics in the multi-Higgs doublet models induced by the left-right symmetry

In this paper, we discuss the multi-Higgs doublet models, that could be effectively induced by the extended Standard Model (SM). In particular, we focus on the phenomenology in the supersymmetric model with left-right (LR) symmetry, where the down-type and the up-type Yukawa couplings are unified and the Yukawa coupling matrices are expected to be hermitian. In this model, several Higgs doublets are introduced to realize the realistic fermion mass matrices, and the heavy Higgs doublets have flavor changing couplings with quarks and leptons. The LR symmetry is assumed to break down at high energy to realize the Type-I seesaw mechanism. The supersymmetry breaking scale is expected to be around 100 TeV to achieve the 125 GeV Higgs. In such a setup, the flavor-dependent interaction of the Higgs fields becomes sizable, so that we especially discuss the flavor physics induced by the heavy Higgs fields in our work. Our prediction depends on the structure of neutrinos, e.g., the neutrino mass ordering. We demonstrate how the flavor structure of the SM affects the flavor violating couplings. In our analysis, we mainly focus on the four-fermi interaction induced by the scalar exchanging, and we propose a simple parameterization for the coefficients. Then, we find the correlations among the flavor observables and, for instance, see that our prediction for the $μ\to 3 e$ process could be covered by the future experiment, in one case where the neutrino mass hierarchy is normal.

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arXiv2019

R-parity violating solutions to the $R_{D^{(\ast)}}$ anomaly and their GUT-scale unifications

Recently, several $B$-physics experiments report interesting anomalies in the semi-leptonic decays of $B$-mesons, such as the excess in the $R_{D^{(\ast)}}$ measurements. These anomalies seem to suggest intriguing hints of lepton flavor non-universality, and the R-parity violating (RPV) interactions are candidates for explaining this non-universality. In this paper, we discuss the RPV interactions for resolving the $R_{D^{(\ast)}}$ anomaly with the Grand Unified Theory (GUT) assumption. To solve the $R_{D^{(\ast)}}$ anomaly, it is known that large RPV couplings and around $1~{\rm TeV}$ sfermion masses are required. At the same time, large RPV couplings are conducive to realize the bottom-tau Yukawa unification which appears in the GUT models. On the other hand, there are problems for realizing favorable sfermion masses in the constrained minimal supersymetric standard model. To resolve these problems, we show that two non-universalities, the non-universal sfermion masses and the non-universal gaugino masses, are favorable.

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arXiv2017

Light flavon signals at electron - photon colliders

Flavor symmetries are useful to realize fermion flavor structures in the standard model. In particular, discrete $A_4$ symmetry is used to realize lepton flavor structures, and some scalars which are called flavon are introduced to break this symmetry. In many models, flavons are assumed to be much heavier than the electroweak scale. However, our previous work showed that flavon mass around 100 GeV is allowed by experimental constraints in the $A_4$ symmetric model with residual $Z_3$ symmetry. In this paper, we discuss collider search of such a light flavon $φ_T$. We find that an electron - photon collision, as a considerable option at the international linear collider, has advantages to search for the signals. At the electron - photon collider flavons are produced as $e^-γ\to l^- φ_T$ and decay into two charged leptons. Then we analyze signals of flavor-conserving final-state $τ^+ τ^- e^-$, and flavor-violating final-states $τ^+ μ^- μ^-$ and $μ^+ τ^- τ^-$ by carrying out numerical simulation. For the former final-state, SM background can be strongly suppressed by imposing cuts on the invariant masses of final-state leptons. For the later final-states, SM background is extremely small, because in the SM there are no such flavor-violating final-states. We then find that sufficient discovery significance can be obtained, even if flavons are heavier than the lower limits from flavor physics.

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arXiv2017

Constraints of chromoelectric dipole moments to natural SUSY type sfermion spectrum

We investigate the lower bounds of sfermion masses from the constraints of chromoelectric dipole moments (CEDMs) in the natural SUSY-type sfermion mass spectrum, in which stop mass $m_{\tilde t}$ is much smaller than the other sfermion masses $m_0$. The natural SUSY-type sfermion mass spectrum has been studied since the supersymmetric (SUSY) flavor-changing neutral currents (FCNC) are suppressed because of large sfermion masses of the first two generations, and the weak scale is stabilized because of the light stop. However, this type of sfermion mass spectrum is severely constrained by CEDM, because the light stop contributions to the up quark CEDM are not decoupled in the limit $m_0\rightarrow\infty$, while the down quark CEDM is decoupled in the limit. It is important that the constraints are severe even if SUSY-breaking parameters (and Higgsino mass) are taken to be real because complex diagonalizing matrices of Yukawa matrices, which are from complex Yukawa couplings, generate nonvanishing CP phases in off-diagonal elements of sfermion mass matrices. We calculate the CEDM of up and down quarks numerically in the minimal SUSY standard model, and give the lower bounds for stop mass and the other sfermion masses. We show that the lower bound of stop mass becomes 7 TeV to satisfy the CEDM constraints from Hg EDM. The result is not acceptable if the weak scale stability is considered seriously. We show that if the up-type Yukawa couplings are taken to be real at the grand unification scale, the CEDM constraints are satisfied even if $m_{\tilde t}\sim 1$ TeV.

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arXiv2017

Flavor physics induced by light $Z'$ from SO(10) GUT

In this paper, we investigate predictions of the SO(10) Grand Unified Theory (GUT), where an extra U(1)$^\prime$ gauge symmetry remains up to the supersymmetry (SUSY) breaking scale. The minimal setup of SO(10) GUT unifies quarks and leptons into a ${\bf 16}$-representational field in each generations. The setup, however, suffers from the realization of the realistic Yukawa couplings at the electroweak scale. In order to solve this problem, we introduce ${\bf 10}$-representational matter fields, and then the two kinds of matter fields mix with each other at the SUSY breaking scale, where the extra U(1)$^\prime$ gauge symmetry breaks down radiatively. One crucial prediction is that the Standard Model quarks and leptons are given by the linear combinations of the fields with two different U(1)$^\prime$ charges. The mixing also depends on the flavor. Consequently, the U(1)$^\prime$ interaction becomes flavor violating, and the flavor physics is the smoking-gun signal of our GUT model. The flavor violating $Z'$ couplings are related to the fermion masses and the CKM matrix, so that we can derive some explicit predictions in flavor physics. We especially discuss $K$-$\overline{K}$ mixing, $B_{(s)}$-$\overline{B_{(s)}}$ mixing, and the (semi)leptonic decays of $K$ and $B$ in our model. We also study the flavor violating $μ$ and $τ$ decays and discuss the correlations among the physical observables in this SO(10) GUT framework.

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arXiv2017

Flavor changing nucleon decay

Recent discovery of neutrino large mixings implies the large mixings in the diagonalizing matrices of $\bf\bar 5$ fields in $SU(5)$ grand unified theory (GUT), while the diagonalizing matrices of $\bf 10$ fields of $SU(5)$ are expected to have small mixings like Cabibbo-Kobayashi-Maskawa matrix. We calculate the predictions of flavor changing nucleon decays (FCND) in $SU(5)$, $SO(10)$, and $E_6$ GUT models which have the above features for mixings. We found that FCND can be the main decay mode especially for GUT with higher rank unification group. Recent report for $P\rightarrow π^0μ^+$ process implies $E_6$ or $SO(10)$ GUT if the signal is from the nucleon decay.

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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.

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arXiv2015

Flavor violating $Z'$ from $SO(10)$ SUSY GUT in High-Scale SUSY

We propose an $SO(10)$ supersymmetric grand unified theory (SUSY GUT), where the $SO(10)$ gauge symmetry breaks down to $SU(3)_c \times SU(2)_L \times U(1)_Y\times U(1)_{X}$ at the GUT scale and $U(1)_X$ is radiatively broken at the SUSY-braking scale. In order to achieve the observed Higgs mass around $126$ GeV and also to satisfy constraints on flavor- and/or CP-violating processes, we assume that the SUSY-breaking scale is $O(100)$ TeV, so that the $U(1)_X$ breaking scale is also $O(100)$ TeV. One big issue in the SO(10) GUTs is how to realize realistic Yukawa couplings. In our model, not only ${\bf 16}$-dimensional but also ${\bf 10}$-dimensional matter fields are introduced to predict the observed fermion masses and mixings. The Standard-Model quarks and leptons are linear combinations of the ${\bf 16}$- and ${\bf 10}$-dimensional fields so that the $U(1)_{X}$ gauge interaction may be flavor-violating. We investigate the current constraints on the flavor-violating $Z'$ interaction from the flavor physics and discuss prospects for future experiments.

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arXiv2014

Nucleon decay via dimension 6 operators in anomalous U(1)_A SUSY GUT

Nucleon lifetimes for various decay modes via dimension 6 operators are calculated in the anomalous $U(1)_A$ GUT scenario, in which the unification scale $Λ_u$ becomes smaller than the usual supersymmetric (SUSY) unification scale $Λ_G=2\times 10^{16}$ GeV in general. Since the predicted lifetime $τ(p\rightarrow π^0+e^c)$ becomes around the experimental lower bound though it is strongly dependent on the explicit models, the discovery of the nucleon decay in near future can be expected. We explain why the two ratios $R_1\equiv\frac{Γ_{n \rightarrow π^0 + ν^c}}{Γ_{p \rightarrow π^0 + e^c}}$ and $R_2\equiv\frac{Γ_{p \rightarrow K^0 + μ^c}}{Γ_{p \rightarrow π^0 + e^c}}$ are important in identifying grand unification group and we show that three anomalous $U(1)_A$ SUSY GUT models with $SU(5)$, $SO(10)$ and $E_6$ grand unification group can be identified by measuring the two ratios. If $R_1$ is larger than $0.4$, the grand unification group is not $SU(5)$, and moreover if $R_2$ is larger than $0.3$, the grand unification group is implied to be $E_6$.

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arXiv2014

Sizable D-term contribution as a signature of $E_6 \times SU(2)_F \times U(1)_A$ SUSY GUT model

We show that the sizable $D$-term contributions to sfermion mass spectrum can be signatures of certain GUT, $E_6\times SU(2)_F\times U(1)_A$ GUT. Note that these $D$-term contributions deviate the degenerate sfermion masses among different generations in this model. This is different from the previous works which have argued the $D$-term contributions, which deviate masses only between sfermions with different quantum charges, as a signature of GUT with larger rank unification group. Such $D$-terms are strongly constrained by the FCNC processes if the SUSY breaking scale is the weak scale. However, in $E_6\times SU(2)_F\times U(1)_A$, natural SUSY type sfermion mass spectrum is obtained, and if the masses of ${\bf 10}_3$ sfermions are larger than $O(1{\rm TeV})$ to realize 126 GeV Higgs and the other sfermion masses are $O(10{\rm TeV})$, then sizable $D$-term contribution is allowed. If the deviations by these $D$-terms can be observed in future experiments like 100 TeV proton collider or muon collider, we may confirm the $E_6\times SU(2)_F\times U(1)_A$ GUT.

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arXiv2014

Nucleon decay via dimension-6 operators in $E_6 \times SU(2)_F \times U(1)_A$ SUSY GUT model

In the previous paper, we have shown that $R_1\equiv\frac{Γ_{n \rightarrow π^0 + ν^c}}{Γ_{p \rightarrow π^0 + e^c}}$ and $R_2\equiv\frac{Γ_{p \rightarrow K^0 + μ^c}}{Γ_{p \rightarrow π^0 + e^c}}$ can identify the grand unification group $SU(5)$, $SO(10)$, or $E_6$ in typical anomalous $U(1)_A$ supersymmetric (SUSY) grand unified theory (GUT) in which nucleon decay via dimension-6 operators becomes dominant. When $R_1 > 0.4$ the grand unification group is not $SU(5)$, while when $R_1 > 1$ the grand unification group is $E_6$. Moreover, when $R_2 > 0.3$, $E_6$ is implied. Main ambiguities come from the diagonalizing matrices for quark and lepton mass matrices in this calculation once we fix the vacuum expectation values of GUT Higgs bosons. In this paper, we calculate $R_1$ and $R_2$ in $E_6\times SU(2)_F$ SUSY GUT with anomalous $U(1)_A$ gauge symmetry, in which realistic quark and lepton masses and mixings can be obtained though the flavor symmetry $SU(2)_F$ constrains Yukawa couplings at the GUT scale. The ambiguities of Yukawa couplings are expected to be reduced. We show that the predicted region for $R_1$ and $R_2$ is more restricted than in the $E_6$ model without $SU(2)_F$ as expected. Moreover, we re-examine the previous claim for the identification of grand unification group with $100$ times more model points ($10^6$ model points), including $E_6 \times SU(2)_F$ model.

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arXiv2013

Two-loop Renormalization Factors of Dimension-six Proton Decay Operators in the Supersymmetric Standard Models

The renormalization factors of the dimension-six effective operators for proton decay are evaluated at two-loop level in the supersymmetric grand unified theories. For this purpose, we use the previous results in which the quantum corrections to the effective Kahler potential are evaluated at two-loop level. Numerical values for the factors are presented in the case of the minimal supersymmetric SU(5) grand unified model. We also derive a simple formula for the one-loop renormalization factors for any higher-dimensional operators in the Kahler potential, assuming that they are induced by the gauge interactions.

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