arXiv subjects

Takeshi Araki

Publications and source records attributed to Takeshi Araki.

36 records · Page 2Linked to original sources

arXiv2011

Large θ_13 from finite quantum corrections in quasi-degenerate neutrino mass spectrum

We study finite quantum corrections for several well known neutrino mixing matrices and find that it is hard to account for the large value of θ_13 recently reported by T2K and MINOS. To nicely reproduce all experimentally favored neutrino mixing angles and masses, we propose a new neutrino mixing pattern. We also demonstrate a simple realization by slightly extending the standard model to illustrate the quantum corrections.

hep-ph↗

arXiv2011

Non-zero θ_13 in models for hierarchical neutrino mass spectrum

We introduce three right-handed Majorana neutrinos and combine the type-I seesaw and inert doublet mechanisms. The resultant (active) neutrino mass matrix is divided into rank=1 and =2 parts with different energy scales. The different energy scales are reduce to different mass scales in the hierarchical neutrino mass spectrum. We apply this scheme to both the inverted and normal hierarchy cases and find a correlation between the smallest mixing angle (θ_13) and the lightest neutrino mass.

hep-ph↗

arXiv2011

Signatures of Dark Matter in Inert Triplet Models

In this talk, we will review the signatures of dark matter in two inert triplet models. For the first model with the hypercharge Y=0, the dark matter mass around 5.5 TeV is favored by both the WMAP data and the direct detection. In contrast, for the second model of Y=2, it is excluded by the direct detection experiments although dark matter with its mass around 2.8 TeV is allowed by WMAP.

hep-ph↗

arXiv2011

Getting at large theta_13 with almost maximal theta_23 from tri-bimaximal mixing

We introduce a small correction term, δM_ν, in the neutrino sector and examine whether a large θ_13 and an almost maximal θ_23 can simultaneously be obtained starting from the tri-bimaximal neutrino mixing. It is found that one can easily gain θ_13 \simeq 10^\circ, which is favored by the recent T2K experiment, by taking account of the enhancement due to the degeneracy among three neutrino masses. We also find that (δM_ν)_22=(δM_ν)_33 is a key condition for θ_23 \simeq 45^\circ.

hep-ph↗

arXiv2011

Finite quantum corrections to the tribimaximal neutrino mixing

We calculate finite quantum corrections to the tribimaximal neutrino mixing pattern V_TB in three generic classes of neutrino mass models. We show that three flavor mixing angles can all depart from their tree-level results described by V_TB, among which θ_12 is most sensitive to such quantum effects, and the Dirac CP-violating phase can radiatively arise from two Majorana CP-violating phases. This theoretical scheme offers a new way to understand why θ_13 is naturally small and how three CP-violating phases are presumably correlated.

hep-ph↗

arXiv2011

Dark Matter in Inert Triplet Models

We study the inert triplet models, in which the standard model (SM) is extended to have a new SU(2)L triplet scalar (Y=0 or 2) with an Z2 symmetry. We show that the neutral component of the triplet can be a good dark matter candidate. In particular, for the hypercharge Y=0 triplet model, the WMAP data favors the region where the dark matter mass is around 5.5 TeV, which is also consistent with the direct detection experiments. In contrast, for the Y=2 model, although dark matter with its mass around 2.8 TeV is allowed by WMAP, it is excluded by the direct detection experiments because the spin-independent cross section is enhanced by the Z mediated tree-level scattering process.

hep-ph↗

arXiv2010

Intrinsic Deviation from the Tri-bimaximal Neutrino Mixing in a Class of A_4 Flavor Models

It is well known that the tri-bimaximal neutrino mixing pattern V_0 can be derived from a class of flavor models with the non-Abelian A_4 symmetry. We point out that small corrections to V_0, which are inherent in the A_4 models and arise from both the charged-lepton and neutrino sectors, have been omitted in the previous works. We show that such corrections may lead the 3 \times 3 neutrino mixing matrix V to a non-unitary deviation from V_0, but they cannot result in a nonzero value of θ_13 or any new CP-violating phases. Current experimental constraints on the unitarity of V allow us to constrain the model parameters to some extent.

hep-ph↗

arXiv2010

mu-tau symmetry in Zee-Babu model

We study the Zee-Babu two-loop neutrino mass generation model and look for a possible flavor symmetry behind the tri-bimaximal neutrino mixing. We find that there probably exists the mu-tau symmetry in the case of the normal neutrino mass hierarchy, whereas there may not be in the inverted hierarchy case. We also propose a specific model based on a Froggatt-Nielsen-like $Z_5$ symmetry to naturally accomplish the mu-tau symmetry on the neutrino mass matrix for the normal hierarchy case.

hep-ph↗

arXiv2010

Leptogenesis with Friedberg-Lee Symmetry

We consider the $μ-τ$ symmetric Friedberg-Lee (FL) symmetry for the neutrino sector and show that a specific FL translation leads to the tribimaximal mixing pattern of the Maki-Nakagawa-Sakata (MNS) matrix. We also apply the symmetry to the type-I seesaw framework and address the baryon asymmetry of the universe through the leptogenesis mechanism. We try to establish a relation between the net baryon asymmetry and CP phases included in the MNS matrix.

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

Leptogenesis in a model with Friedberg-Lee symmetry

We study the matter-antimatter asymmetry through the leptogenesis mechanism in a specific model with the Friedberg-Lee (FL) symmetry.We relate the leptogenesis with the CP violating Dirac and Majorana phases in the Maki-Nakagawa-Sakata leptonic mixing matrix and illustrate the net baryon asymmetry of the universe in terms of these phases.

hep-ph↗

arXiv2009

Constraints on the Timeon Model

The timeon model recently proposed by Friedberg and Lee has a potential problem of flavor changing neutral currents (FCNCs) if the mass of the timeon is small. In order to avoid, we introduce a small dimensionless parameter to suppress FCNCs. Even in this case, we find that the timeon mass must be larger than 151 GeV to satisfy all the constraints from processes involving FCNCs in the quark sectors. We also extend the timeon model to the lepton sector and examine the leptonic processes.

hep-ph↗

arXiv2009

Tri-Bimaximal Mixing from Twisted Friedberg-Lee Symmetry

We investigate the Friedberg-Lee (FL) symmetry and its promotion to include the $μ- τ$ symmetry, and call that the twisted FL symmetry.Based on the twisted FL symmetry, two possible schemes are presented toward the realistic neutrino mass spectrum and the tri-bimaximal mixing.In the first scheme, we suggest the semi-uniform translation of the FL symmetry.The second one is based on the $S_3$ permutation family symmetry.The breaking terms, which are twisted FL symmetric, are introduced.Some viable models in each scheme are also presented.

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↗

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↗

arXiv2007

Anomalies of Discrete Symmetries and Gauge Coupling Unification

The anomaly of a discrete symmetry is defined as the Jacobian of the path-integral measure. Assuming that the anomaly at low energies is cancelled by the Green-Schwarz (GS) mechanism at a fundamental scale, we investigate possible Kac-Moody levels for anomalous discrete family symmetries. As the first example, we consider discrete abelian baryon number and lepton number symmetries in the minimal supersymmetric standard model with the see-saw mechanism, and we find that the ordinary unification of gauge couplings is inconsistent with the GS conditions, indicating the possible existence of further Higgs doublets. We consider various recently proposed supersymmetric models with a non-abelian discrete family symmetry. In a supersymmetric example with $Q_{6}$ family symmetry, the GS conditions are such that the gauge coupling unification appears close to the Planck scale.

hep-ph↗

arXiv2006

Anomaly of discrete family symmetries and gauge coupling unification

Anomaly of discrete symmetries can be defined as the Jacobian of the path-integral measure. We assume that an anomalous discrete symmetry at low energy is remnant of an anomaly free discrete symmetry, and that its anomaly is cancelled by the Green-Schwarz(GS) mechanism at a more fundamental scale. If the Kac-Moody levels k_i assume non-trivial values, the GS cancellation conditions of anomaly modify the ordinary unification of gauge couplings. This is most welcome, because for a renormalizable model to be realistic any non-abelian family symmetry, which should not be hardly broken low-energy, requires multi SU(2)_L doublet Higgs fields. As an example we consider a recently proposed supersymmetric model with Q_6 family symmetry. In this example, k_2=1, k_3=3 satisfies the GS conditions and the gauge coupling unification appears close to the Planck scale.

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↗