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Jisuke Kubo

Publications and source records attributed to Jisuke Kubo.

At least 55 records · Page 3Linked to original sources
arXiv2010

Triangle Relation of Dark Matter, EDM and CP Violation in B0 Mixing in a Supersymmetric Q6 Model

We consider a recently proposed supersymmetric model based on the discrete Q6 family group.Because of the family symmetry and spontaneous CP violation the electric dipole moment (EDM), the CP violation in the mixing of the neural mesons and the dark matter mass m_DM are closely related. This triangle relation is controlled by the size of the mu parameters. Loop effects can give rise to large contributions to the soft mass insertions, and we find that the model allows a large CP violation in the B0 system. Its size is comparable with the recent experimental observations at D0 and CDF, and it could be observed at LHCb in the first years. If the parameter space is constrained by the neutron EDM, and flavor changing neutral currents and CP violations in K0 as well as B0 mixing, the triangle relation yields the following bound on the dark matter candidate: 0.12 TeV < m_DM < 0.33 TeV, which is directly observable at LHC. We also compute a_sl^s - a_sl^d, which is observable at LHCb, where a_sl^s(d) is the semi-leptonic CP asymmetryfor the B_s(d) system.

hep-ph↗
arXiv2010

Large loop effects of extra SUSY Higgs doublets to CP violation in B^0 mixing

We consider more than one pair of SU(2)_L doublet Higgs supermultiplets in a generic supersymmetric extension of the standard model, and calculate their one-loop contributions to the soft mass insertions delta_{LL} etc. We find that if large supersymmetry breaking in this sector is realized, the loop effects can give rise to large contributions to the soft mass insertions, meaning that they We apply our result to a recently proposed model based on the discrete Q_6 family group, and calculate the non-diagonal matrix element M_{12} of the neutral meson systems. We focus our attention on the extra phases phi_{d,s}^Delta in B_{d,s}-mixing and flavor-specific CP-asymmetries a_{sl}^{d,s} in neutral B decays and obtain values that can be about one order of magnitude larger than the standard model predictions. Our final results are comparable with the recent experimental observations at D0 and CDF, but they are still about a factor of 5 smaller than the recently measured dimuon asymmetry from D0.

hep-ph↗
arXiv2010

Testing Flavor Symmetries by B-Factory

Predictions of the Cabibbo-Kobayashi-Maskawa (CKM) parameters are investigated in detail in recent predictive models which are based on low-energy non-abelian discrete family symmetries. Some of the models can already be excluded at the present precision of the determination of the CKM parameters, while some of them seem to survive. We find that to make the uncertainties in the predictions comparable with the assumed uncertainties of $\sim 1^{\circ}$ and $\sim 2^{\circ}$ in $ϕ_2$ and $ϕ_3$, respectively, at about 50 inverse atto barn achieved at a feature B factory, it is necessary to reduce the uncertainties in the quark masses, especially that of the strange quark mass by more than 60%.

hep-ph↗
arXiv2009

Testing the new CP phase in a Supersymmetric Model with Q6 Family Symmetry by Bs Mixing

The new contribution to the non-diagonal matrix element M_12 of the neutral B_s meson system is investigated in a supersymmetric extension of the standard model based on the discrete Q6 family symmetry. We assume that CP is explicitly, but softly broken only by the b terms in the soft supersymmetry breaking sector. We find that the new contributions to M_12 are real, and that nevertheless there exists an observable difference in the CP phase compared with the standard model. We focus our attention on the flavor-specific CP asymmetry a_fs^s, and find that a_fs^s of the model is mostly negative and its size can be one order of magnitude larger the standard model value. This prediction is consistent with the current experimental value, and can be experimentally tested in the near future.

hep-ph↗
arXiv2009

Anomaly Induced Dark Matter Decay and PAMELA/ATIC Experiments

The cosmic ray data of PAMELA/ATIC may be explained by dark matter decay with a decay rate $τ_{DM}^{-1}\sim 10^{-26}{sec}^{-1} \sim 10^{-45}{eV}$, an energy scale which could not be understood within the framework of the standard model or its simple supersymmetric extension. We propose anomaly induced dark matter decay to exponentially suppress the decay rate, and apply to a supersymmetric extension of the Ma's inert Higgs model of the radiative seesaw mechanism for neutrino masses. In this model the lightest right-handed neutrino $ψ_N$ and the lightest neutralino $χ$ can fill the observed necessary dark matter relic, and we find that $ψ_N$ can decay into $χ$ through anomaly with a right order of decay rate, emitting only leptons. All the emitted poistrons are right-handed.

hep-ph↗
arXiv2009

Radiative seesaw: Warm dark matter, collider and lepton flavour violating signals

Extending the standard model with three right-handed neutrinos ($N_k$) and a second Higgs doublet ($η$), odd under the discrete parity symmetry $Z_2$, Majorana neutrino masses can be generated at 1-loop order. In the resulting model, the lightest stable particle, either a boson or a fermion, might be a dark matter candidate. Here we assume a specific mass spectrum ($M_1\ll M_2 < M_3 < m_η$) and derive its consequences for dark matter and collider phenomenology. We show that (i) the lightest right-handed neutrino is a warm dark matter particle that can give a $\sim$10% contribution to the dark matter density; (ii) several decay branching ratios of the charged scalar can be predicted from measured neutrino data. Especially interesting is that large lepton flavour violating rates in muon and tau final states are expected. Finally, we derive upper bounds on the right-handed neutrino Yukawa couplings from the current experimental limit on $Br(μ\to eγ)$.

hep-ph↗
arXiv2008

(Non-)Abelian discrete anomalies

We derive anomaly constraints for Abelian and non-Abelian discrete symmetries using the path integral approach. We survey anomalies of discrete symmetries in heterotic orbifolds and find a new relation between such anomalies and the so-called `anomalous' U(1).

hep-th↗
arXiv2008

D6 Family Symmetry and Cold Dark Matter at LHC

We consider a non-supersymmetric extension of the standard model with a family symmetry based on D6 Z2 Z2, where one of Z2's is exactly conserved. This Z2 forbids the tree-level neutrino masses and simultaneously ensures the stability of cold dark matter candidates. From the assumption that cold dark matter is fermionic we can single out the D6 singlet right-handed neutrino as the best cold dark mater candidate. We find that an inert charged Higgs with a mass between 300 and 750 GeV decays mostly into an electron (or a positron) with a large missing energy, where the missing energy is carried away by the cold dark matter candidate. This will be a clean signal at LHC.

hep-ph↗
arXiv2007

Flavor Changing Neutral Higgs Bosons in a Supersymmetric Extension based on a $Q_6$ Family Symmetry

A supersymmetric extension of the standard model based on the discrete $Q_6$ family symmetry is considered, and we investigate flavor-changing neutral current (FCNC) processes, especially those mediated by heavy flavor-changing neutral Higgs bosons. Because of the family symmetry the number of the independent Yukawa couplings is smaller than that of the observed quantities such as the Cabibbo-Kobayashi-Maskawa matrix and the quark masses, so that the FCNCs can be parametrized only by the mixing angles and masses of the Higgs fields. We focus our attention on the mass differences of the neutral $K, D$ and $B$ mesons. All the constraints including that from the ratio $ΔM_{B_s}/ΔM_{B_d}$ can be satisfied, if the heavy Higgs bosons are heavier than $\sim 1.5$ TeV. If the constraint from $ΔM_K$ is slightly relaxed, the heavy Higgs bosons can be as light as $\sim 0.4$ TeV, which is within the accessible range of LHC.

hep-ph↗
arXiv2007

Discrete R-symmetry anomalies in heterotic orbifold models

Anomalies of discrete R-symmetries appearing in heterotic orbifold models are studied. We find that the mixed anomalies for different gauge groups satisfy the universal Green-Schwarz (GS) condition, indicating that these anomalies are canceled by the GS mechanism. An exact relation between the anomaly coefficients of the discrete R-symmetries and one-loop beta-function coefficients is obtained. We also find that the discrete R-symmetries have a good chance to be unbroken down to the supersymmetry breaking scale. Even below this scale a $Z_2$ subgroup is unbroken, which may be an origin of the R-parity of the minimal supersymmetric standard model. Relations between the R-symmetry anomalies and T-duality anomalies are also investigated.

hep-ph↗
arXiv2006

Neutrino masses and CDM in a non-supersymmetric model

We propose a model for neutrino mass generation based on both the tree-level seesaw mechanism with a single right-handed neutrino and one-loop radiative effects in a non-supersymmetric framework. The generated mass matrix is composed of two parts which have the same texture and produce neutrino mass eigenvalues and mixing suitable for the explanation of neutrino oscillations. The model has a good CDM candidate which contributes to the radiative neutrino mass generation. The stability of the CDM candidate is ensured by $Z_2$ which is the residual symmetry of a spontaneously broken U(1)$^\prime$. We discuss the values of $U_{e3}$ and also estimate the masses of the relevant fields to realize an appropriate abundance of the CDM.

hep-ph↗
arXiv2006

Cold Dark Matter, Radiative Neutrino Mass, mu to e gamma, and Neutrinoless Double Beta Decay

Two of the most important and pressing questions in cosmology and particle physics are: (1) What is the nature of cold dark matter? and (2) Will near-future experiments on neutrinoless double beta decay be able to ascertain that the neutrino is a Majorana particle, i.e. its own antiparticle? We show that these two seemingly unrelated issues are intimately connected if neutrinos acquire mass only because of their interactions with dark matter.

hep-ph↗
arXiv2005

Nonabelian Discrete Family Symmetry to Soften the SUSY Flavor Problem and to Suppress Proton Decay

Family symmetry could explain large mixing of the atmospheric neutrinos. The same symmetry could explain why the flavor changing current processes in supersymmetric standard models can be so suppressed. It also may be able to explain why the proton is so stable. We investigate these questions in a supersymmetric, renormalizable extension of the standard model, which possess a family symmetry based on a binary dihedral group Q_6. We find that the amplitude for μ\to e+γenjoys a suppression factor proportional to |(V_{MNS})_{e3}| ~ m_e/(\sqrt{2}m_μ) ~ 3.4\times 10^{-3}, and that B(p \to K^0 μ^+)/B(p \to K^0 e^+) ~ |(V_{MNS})_{e3}|^2 ~ 10^{-5}, where V_{MNS} is the neutrino mixing matrix.

hep-ph↗
arXiv2005

Majorana Phase in Minimal S_3 Invariant Extension of the Standard Model

The leptonic sector in a recently proposed minimal extension of the standard model, in which the permutation symmetry S_3 is assumed to be an exact flavor symmetry at the weak scale, is revisited. We find that S_3 with an additional Z_{N} symmetry allows CP violating phases in the neutrino mixing. The leptonic sector contains six real parameters with two independent phases to describe charged lepton and neutrino masses and the neutrino mixing. The model predicts: an inverted spectrum of neutrino mass, tan theta_{23}=1+O(m_e^2/m_mu^2) and sin theta_{13}=m_e/sqrt{2}m_mu+O(m_em_mu/m_{tau}^2) simeq 0.0034. Neutrino mass as well as the effective Majorana mass in the neutrinoless double-beta decay can be expressed in a closed form as a function of phi_nu, Delta m^2_{21},Delta m^2_{23} and tantheta_{12}, where phi_nu is one of the independent phases. The model also predicts geq (0.036 - 0.066) eV.

hep-ph↗
arXiv2005

Dihedral Flavor Symmetry from Dimensional Deconstruction

Extra dimension deconstructed on a closed chain has naturally the symmetry of a regular polygon, the dihedral symmetry D_N. We assume that the fields are irreducible representations of the binary dihedral group Q_2N, which is the covering group of D_N. It is found that although the orbifold boundary conditions break the dihedral invariance explicitly, the Q_2N symmetry appears as an intact internal, global flavor symmetry at low energies. A concrete predictive model based on Q_6N$ with an odd N is given.

hep-ph↗
arXiv2005

Dihedral Families of Quarks, Leptons and Higgs Bosons

We consider finite groups of small order for family symmetry. It is found that the binary dihedral group Q_6, along with the assumption that the Higgs sector is of type II, predicts mass matrix of a nearest neighbor interaction type for quarks and leptons. We present a supersymmetric model based on Q_6 with spontaneously induced CP phases. The quark sector contains 8 real parameters with one independent phase to describe the quark masses and their mixing. Predictions in the |V_{ub}|-bar{eta}, |V_{ub}|-sin 2 beta(phi_1) and |V_{ub}|-|V_{td}/V_{ts}| planes are given. The lepton sector contains also 9 parameters. A normal as well as an inverted spectrum of neutrino masses is possible, and we compute V_{e3}. We find that |V_{e3}|^2 > 10^{-4} in the case of a normal spectrum, and |V_{e3}|^2 >8 10^{-4} in the case of an inverted spectrum. It is also found that Q_6 symmetry forbids all Baryon number violating terms of d=4, and the contributions to EDMs from the A terms vanish in this model.

hep-ph↗
arXiv2005

S_3 Flavor Symmetry and Leptogenesis

We consider leptogenesis in a minimal S_3 extension of the standard model with an additional Z_2 symmetry in the leptonic sector. It is found that the CP phase appearing in the neutrino mixing is the same as that for the CP asymmetries responsible for leptogenesis. Because of the discrete S_3 x Z_2 flavor symmetries, the CP asymmetries are strongly suppressed. We therefore assume that the resonant enhancement of the CP asymmetries takes place to obtain a realistic size of baryon number asymmetry in theuniverse. Three degenerate right-handed neutrino masses of O(10) TeV are theoretically expected in this model.

hep-ph↗