arXiv subjects

Y. H. Ahn

Publications and source records attributed to Y. H. Ahn.

At least 37 records · Page 2Linked to original sources

arXiv2013

A dynamical CP source for CKM, PMNS and Leptogenesis

We propose a simple model for the spontaneous CP violation based on $SU(2)_{L}\times U(1)_{Y}\times A_{4}\times CP\times Z_{2}$ symmetry for quarks and leptons in a seesaw framework. In our model CP is spontaneously broken at high energies, after breaking of flavor symmetry, by a complex vacuum expectation value of $A_{4}$-triplet and gauge singlet scalar field. And, certain effective dimension-5 operators are introduced in the quark Lagrangian as an equal footing, which lead the quark mixing matrix to the Cabibbo-Kobayashi-Maskawa (CKM) one in the form, while the lepton Lagrangian is renormalizable, which gives rise to a non-degenerate Dirac neutrino Yukawa matrix and an unique CP-phase, and which in turn explains the non-zero value of $θ_{13}\simeq9^{\circ}$ and two large mixing angles $θ_{12}, θ_{23}$. We show that the spontaneously generated CP phase "$ξ$" could become a natural source of leptogenesis as well as CP violations in the CKM and Pontecorvo-Maki-Nakagawa-Sakata (PMNS). Moreover, we provide a solution for the strong CP problem. Interestingly enough, we show that, for around $ξ\simeq120^{\circ}$, the quarks lead to the correct CKM CP-phase corresponding to $δ^{q}_{CP}\simeq67^{\circ}$, while the leptons with the measured value of $θ_{13}$ favor $δ_{CP}=$, $|θ_{23}-45^{\circ}|\rightarrow0$ for normal mass hierarchy and $δ_{CP}=$, $|θ_{23}-45^{\circ}|\rightarrow5^{\circ}$ for inverted one. As a numerical study in the lepton sector, we show low-energy phenomenologies and leptogenesis for the normal and inverted case, respectively, and a link between them.

hep-ph↗

arXiv2013

Spontaneous CP Violation in $A_4$ Flavor Symmetry and Leptogenesis

We propose a simple renormalizable model for the spontaneous CP violation based on $SU(2)_{L}\times U(1)_{Y}\times A_{4}$ symmetry in a radiative seesaw mechanism, which can be guaranteed by an extra $Z_{2}$ symmetry. In our model CP is spontaneously broken at high energies, after breaking of flavor symmetry, by a complex vacuum expectation value of $A_{4}$-triplet and gauge singlet scalar field. We show that the spontaneously generated CP phase could become a natural source of leptogenesis, %CP violation for neutrino oscillation and leptogenesis, respectively. Then, and also investigate CP violation at low energies in the lepton sector and show how the CP phases in PMNS could be arisen through spontaneous symmetry breaking mechanism. As a numerical study, interestingly, we show that the normal mass hierarchy favors relatively large values of $θ_{13}$, large deviations from maximality of $θ_{23}<π/4$ and Dirac-CP phase $0^{\circ}\leqδ_{CP}\leq50^{\circ}$ and $300^{\circ}\leqδ_{CP}\leq360^{\circ}$. For the inverted hierarchy case, the experimentally measured values of $θ_{13}$ favors $θ_{23}>π/4$ and discrete values of $δ_{CP}$ around $100^{\circ},135^{\circ},255^{\circ}$ and $300^{\circ}$. Finally, with a successful leptogenesis our numerical results give more predictive values on the Dirac CP phase: for the normal mass hierarchy $1^{\circ}\lesssimδ_{CP}\lesssim10^{\circ}$ and for inverted one $δ_{CP}\sim100^{\circ},135^{\circ},300^{\circ}$.

hep-ph↗

arXiv2013

Leptons and Quarks from a Discrete Flavor Symmetry

We propose a new model of leptons and quarks based on the discrete flavor symmetry $T'$, the double covering of $A_4$, in which the hierarchies of charged fermion masses and the mildness of neutrino masses are responsible for Higgs scalars. After spontaneous breaking of flavor symmetry, with the constraint of renormalizability in the Lagrangian, the leptons have $m_{e}=0$ and the quarks have the Cabibbo-Kobayashi-Maskawa (CKM) mixing angles $θ^{q}_{12}=13^{\circ}, θ^{q}_{23}=0^{\circ}$ and $θ^{q}_{13}=0^{\circ}$. Thus, certain effective dimension-5 operators are introduced, which induce $m_{e}\neq0$ and lead the quark mixing matrix to the CKM one in form. On the other hand, the neutrino Lagrangian still keeps renormalizability. For completeness, we show numerical analysis: in the lepton sector, only normal mass hierarchy is permitted within $3σ$ experimental bounds with the prediction of both large deviations from maximality in the atmospheric mixing angle $θ_{23}$ and the measured values of reactor angle. So, future precise measurements of $θ_{23}$, whether $θ_{23}\rightarrow45^{\circ}$ or $|θ_{23}-45^{\circ}|\rightarrow5^{\circ}$, will either exclude or favor our model. Together with it, our model makes predictions for the Dirac CP phase, which is almost compatible with the global analysis in $1σ$ experimental bounds. Moreover, we show the effective mass $|m_{ee}|$ measurable in neutrinoless double beta decay to be in the range $0.04\lesssim|m_{ee}|[eV]<0.11$, which can be tested in near future neutrino experiments.

hep-ph↗

arXiv2012

Non-zero $θ_{13}$ and CP violation in a model with $A_4$ flavor symmetry

Motivated by recent observations of non-zero $θ_{13}$ from the Daya Bay and RENO experiments, we propose a renormalizable neutrino model with $A_4$ discrete symmetry accounting for deviations from the tri-bimaximal mixing pattern of neutrino mixing matrix indicated by neutrino oscillation data. In the model, the light neutrino masses can be generated by radiative corrections, and we show how the light neutrino mass matrix can be diagonalized by the Pontecorvo-Maki-Nakagawa-Sakata mixing matrix whose entries are determined by the current neutrino data including the Daya Bay result. We show that the origin of the deviations from the TBM mixing is non-degeneracy of the neutrino Yukawa coupling constants, and unremovable CP phases in the neutrino Yukawa matrix give rise to both low energy CP violation measurable from neutrino oscillation and high energy CP violation.

hep-ph↗

arXiv2012

Simple renormalizable flavor symmetry for neutrino oscillations

The recent measurement of a non-zero neutrino mixing angle $θ_{13}$ requires a modification of the tri-bimaximal mixing pattern that predicts a zero value for it. We propose a new neutrino mixing pattern based on a spontaneously-broken $A_{4}$ flavor symmetry and a type-I seesaw mechanism. Our model allows for approximate tri-bimaximal mixing and non-zero $θ_{13}$, and contains a natural way to implement low and high energy CP violation in neutrino oscillations, and leptogenesis with a renormalizable Lagrangian. Both normal and inverted mass hierarchies are permitted within $3σ$ experimental bounds, with the prediction of small (large) deviations from maximality in the atmospheric mixing angle for the normal (inverted) case. Interestingly, we show that the inverted case is excluded by the global analysis in $1σ$ experimental bounds, while the most recent MINOS data seem to favor the inverted case. Our model make predictions for the Dirac CP phase in the normal and inverted hierarchies, which can be tested in near-future neutrino oscillation experiments. Our model also predicts the effective mass $|m_{ee}|$ measurable in neutrinoless double beta decay to be in the range $0.04\lesssim |m_{ee}| \lesssim 0.15$ eV for the normal hierarchy and $0.06\lesssim |m_{ee}| \lesssim 0.11$ eV for the inverted hierarchy, both of which are within the sensitivity of the next generation experiments.

hep-ph↗

arXiv2012

Recent Neutrino Data and a Realistic Tribimaximal-like Neutrino Mixing Matrix

In light of the recent neutrino experimental results from Daya Bay and RENO Collaborations, we construct a realistic tribimaximal-like Pontecorvo-Maki-Nakagawa-Sakata (PMNS) leptonic mixing matrix. Motivated by the Qin-Ma (QM) parametrization for the quark mixing matrix in which the CP-odd phase is approximately maximal, we propose a simple ansatz for the charged lepton mixing matrix, namely, it has the QM-like parametrization, and assume the tribimaximal mixing (TBM) pattern for the neutrino mixing matrix. The deviation of the leptonic mixing matrix from the TBM one is then systematically studied. While the deviation of the solar and atmospheric neutrino mixing angles from the corresponding TBM values, i.e. $\sin^2θ_{12}=1/3$ and $\sin^2θ_{23}=1/2$, is fairly small, we find a nonvanishing reactor mixing angle given by $\sinθ_{13}\approx λ/\sqrt{2}$ ($λ\approx 0.22$ being the Cabibbo angle). Specifically, we obtain $θ_{13}\simeq 9.2^{\circ}$ and $δ_{CP} \simeq δ_{\rm QM} \simeq {\cal O}(90^{\circ})$. Furthermore, we show that the leptonic \CP violation characterized by the Jarlskog invariant is $|J^{\ell}_{CP}|\simeq λ/6$, which could be tested in the future experiments such as the upcoming long baseline neutrino oscillation ones.

hep-ph↗

arXiv2012

Recent Neutrino Data and Type III Seesaw with Discrete Symmetry

In light of the recent neutrino experiment results from Daya Bay and RENO Collaborations, we study phenomenology of neutrino mixing angles in the Type III seesaw model with an discrete $A_4 \times Z_2$ symmetry, whose spontaneously breaking scale is much higher than the electroweak scale. At tree level, the tri-bimaximal (TBM) form of the lepton mixing matrix can be obtained from leptonic Yukawa interactions in a natural way. We introduce all possible effective dimension-5 operators, invariant under the Standard Model gauge group and $A_4 \times Z_2$, and explicitly show that they induce a deviation of the lepton mixing from the TBM mixing matrix, which can explain a large mixing angle $θ_{13}$ together with small deviations of the solar and atmospheric mixing angles from the TBM. Two possible scenarios are investigated, by taking into account either negligible or sizable contributions from the light charged lepton sector to the lepton mixing matrix. Especially it is found in the latter scenario that all the neutrino experimental data, including the recent best-fit value of $θ_{13} = 8.68^{\circ}$, can be accommodated. The leptonic CP violation characterized by the Jarlskog invariant $J_{CP}$ has a non-vanishing value, indicating a signal of maximal CP violation.

hep-ph↗

arXiv2012

Non-zero θ_{13} linking to Dark Matter from Non-Abelian Discrete Flavor Model in Radiative Seesaw

We propose a new scenario in a radiative seesaw model based on A_4 flavor symmetry. In this model, we explore a possibility of linking non-zero θ_{13} to dark matter. And we analyze the lepton sector to predict the observed neutrinos and mixings, especially obtaining a lower bound of θ_{13}~3.5 [Deg.]. We show that the non-zero θ_{13} is correlated with our heavy Majorana type of dark matter. Also we predict that the mass be O(1-10) TeV, as a result of analyzing the Wilkinson-Microwave-Anisotropy-Probe and lepton flavor violation.

hep-ph↗

arXiv2011

An extension of tribimaximal lepton mixing

Harrison, Perkins and Scott have proposed simple charged lepton and neutrino mass matrices that lead to the tribimaximal mixing $U_{\rm TBM}$. We consider in this work an extension of the mass matrices so that the leptonic mixing matrix becomes $U_{\rm PMNS}=V_L^{\ell\dagger}U_{\rm TBM}W$, where $V_L^\ell$ is a unitary matrix needed to diagonalize the charged lepton mass matrix and $W$ measures the deviation of the neutrino mixing matrix from the bimaximal form. Hence, corrections to $U_{\rm TBM}$ arise from both charged lepton and neutrino sectors. Following our previous work to assume a Qin-Ma-like parametrization $V_{\rm QM}$ for the charged lepton mixing matrix $V_L^\ell$ in which the {\it CP}-odd phase is approximately maximal, we study the phenomenological implications in two different scenarios: $V_L^\ell=V_{\rm QM}^\dagger$ and $V_L^\ell=V_{\rm QM}$. We find that the latter is more preferable, though both scenarios are consistent with the data within $3σ$ ranges. The predicted reactor neutrino mixing angle $θ_{13}$ in both scenarios is consistent with the recent T2K and MINOS data. The leptonic {\it CP} violation characterized by the Jarlskog invariant $J_{\rm CP}$ is generally of order $10^{-2}$.

hep-ph↗

arXiv2011

Wolfenstein Parametrization at Higher Order: Seeming Discrepancies and Their Resolution

In different Wolfenstein parametrizations derived from different exact parametrizations of the Cabibbo-Kobayashi-Maskawa matrix, we explicitly study seeming discrepancies between the matrix elements at the higher order of the expansion parameter $λ$. A systematic way of resolving the seeming discrepancies is proposed. We find that most of the discrepancies can be naturally resolved by a proper redefinition of the numerically small (of order $λ$) parameters. Our approach is further applied to the cases for the Wolfenstein-{\it like} parametrizations, such as the Qin-Ma parametrization.

hep-ph↗

arXiv2011

Remarks on the Qin-Ma Parametrization of Quark Mixing Matrix

Recently, Qin and Ma (QM) have advocated a new Wolfenstein-like parametrization of the quark mixing matrix based on the triminimal expansion of the Cabibbo-Kobayashi-Maskawa (CKM) parametrization. The CP-odd phase in the QM parametrization is around $90^\circ$ just as that in the CKM parametrization. We point out that the QM parametrization can be readily obtained from the Wolfenstein parametrization after appropriate phase redefinition for quark fields and that the phase $δ$ in both QM and CKM parametrizations is related to the unitarity angles $α$, $β$ and $γ$, namely, $δ= β+γ$ or $π-α$. We show that both QM and Wolfenstein parametrizations can be deduced from the CKM and Chau-Keung-Maiani ones. By deriving the QM parametrization from the Fritzsch-Xing (FX) parametrization of the quark mixing matrix, we find that the phase of the FX form is in the vicinity of $-270^\circ$ and hence $\sinδ\approx 1$. We discuss the seeming discrepancy between the Wolfenstein and QM parametrizations at the high order of $λ\approx |V_{us}|$.

hep-ph↗

arXiv2011

Quark-lepton complementarity and tribimaximal neutrino mixing from discrete symmetry

The quark-lepton complementarity (QLC) relations indicate a deep structure that interrelates quarks and leptons. We propose new scenarios, in a seesaw framework with discrete $A_4$ flavor symmetry, which can accommodate the QLC relations and the nonzero neutrino mixing angle $θ_{13}$ together with all the available neutrino experimental data, in a consistent way to generate the Cabibbo-Kobayashi-Maskawa (CKM) matrix for the quark mixing. Certain effective dimension-5 operators are introduced, which induce a deviation of the lepton mixing matrix from the tribimaximal mixing (TBM) pattern and lead the quark mixing matrix to the CKM one in form. We explicitly demonstrate three different possibilities of constructing the charged lepton mixing matrix and point out that the {\it phases} of whose elements play a crucial role to satisfy the QLC relations. We find that for the reactor mixing angle $θ_{13}$ its possible values can vary around the center value $\sin θ_{13} \simeq λ/\sqrt{2}$ ($λ\simeq 0.22$ being the Cabbibo angle) and have the lower bound $θ_{13} \gtrsim 3.5^{\circ}$. We also show that sizable leptonic CP violation characterized by the Jarlskog invariant $|J_{\rm CP}|\sim{\cal O}(10^{-2})$ is allowed, which is expected to be tested in the future experiments such as the upcoming long baseline neutrino oscillation ones.

hep-ph↗

arXiv2010

A direct link between neutrinoless double beta decay and leptogenesis in a seesaw model with $S_4$ symmetry

We study how leptogenesis can be implemented in a seesaw model with $S_4$ flavor symmetry, which leads to the neutrino tri-bimaximal mixing matrix and degenerate right-handed (RH) neutrino spectrum. Introducing a tiny soft $S_4$ symmetry breaking term in the RH neutrino mass matrix, we show that the flavored resonant leptogenesis can be successfully realized, which can lower the seesaw scale much so as to make it possible to probe in colliders. Even though such a tiny soft breaking term is essential for leptogenesis, it does not significantly affect the low energy observables. We also investigate how the effective light neutrino mass $| |$ associated with neutrinoless double beta decay can be predicted along with the neutrino mass hierarchies by imposing experimental data of low-energy observables. We find a direct link between leptogenesis and neutrinoless double beta decay characterized by $| |$ through a high energy CP phase $ϕ$, which is correlated with low energy Majorana CP phases. It is shown that our predictions of $| |$ for some fixed parameters of high energy physics can be constrained by the current observation of baryon asymmetry.

hep-ph↗

arXiv2010

Probing lepton flavor violation with nonzero $U_{e3}$ and leptogenesis through $A_4$ symmetry breaking

We study how lepton flavor violation (LFV) is related to the reactor angle $θ_{13}$, LHC/dark matter (DM) signal with a successful leptogenesis in a radiative seesaw model through $A_4$ flavor symmetry breaking, in the light of the deviation of tri-bimaximal mixing (TBM) angles and the recent precision oscillation data. To do this, we consider the normal mass spectrum of light neutrino giving a successful leptogenesis at electroweak (EW) scale or more with a relatively large $\sinθ_{13}\simeq{\cal O}(0.1)$, where a successful leptogenesis requires LHC/DM signal $m_{-}\lesssim$ a few keV in our scenario, and we show that the measurement of $τ\rightarrowμγ$ is strongly dependent on $m_{-}$ and the leptogenesis scale. Especially, we show that $μ\rightarrow eγ$ and $μ-e$ conversion are proportional to the value of $θ_{13}$, and the measurements of both $μ\rightarrow eγ$ (and/or $μ-e$ conversion) and $θ_{13}$ can give a prediction of $τ\rightarrowμγ$ with a successful leptogenesis.

hep-ph↗

arXiv2010

New charged Higgs effects on $Γ_{K_{e2}}/Γ_{K_{μ2}}$, $f_{D_s}$ and ${\cal B}(B^+\to τ^+ ν)$ in the Two-Higgs-Doublet model

A new scheme for Yukawa matrices is proposed for free of flavor changing neutral currents (FCNCs) at tree level in general two-Higgs-doublet model (THDM) without imposing symmetry. We find that the new type couplings of charged Higgs to fermions not only depend on the flavors, but also can be ascribed by new CP violating phases. Unlike conventional THDM, the resulted new charged Higgs effects could have the specialties: (a) the influence on $Γ(K^\pm_{e 2})/Γ(K^\pm_{μ2})$ cannot be eliminated, (b) the decay constant of $D_s$ could be enhanced, and (c) enhancement of branching ratio for $B^+\to τ^+ ν$ could be achieved.

hep-ph↗

arXiv2010

Non-zero U_{e3} and TeV-Leptogenesis through A_4 symmetry breaking

We consider an effective theory with an $SU(2)\times U(1)\times A_{4}\times Z_{2}\times Z_{4}$ symmetry and investigate the possibility of a linking TeV-leptogenesis with a reactor angle $|U_{e3}|$ through spontaneous $A_{4}$ symmetry breaking which is at a scale higher than electroweak scale under the framework of radiative seesaw. It has been shown that tri-bimaximal(TBM) can be obtained by forging vacuum expectation value (VEV) alignment of the $A_{4}$. Especially, one $A_{4}$ triplet scalar field with cut-off scale $Λ$ is added in neutrino Yukawa sector, which is responsible for the deviation of the exact TBM, to explain leptogenesis as well as a non-zero $|U_{e3}|$. Above the scale of $Λ$ the leptonic Yukawa sectors will lead to the exact TBM. We analyze possible spectrums of light neutrinos and their flavor mixing angles corresponding to heavy Majorana neutrino mass ordering, and show that non-resonance leptogenesis at TeV-scale constrained by low energy data is achievable, both analytically as well as numerically. We show that only normal hierarchical spectrum of light neutrino would be strongly favored by the current Wilkinson Microwave Anisotropy Probe (WMAP) data, and also show that a relatively large $|U_{e3}|$ corresponds to the value of baryon asymmetry $6.2\times10^{-10}$.

hep-ph↗

arXiv2008

Bridges of Low Energy observables with Leptogenesis in mu-tau Reflection Symmetry

We consider an exact mu-tau reflection symmetry in neutrino sectorrealized at the GUT scale in the context of the seesaw model with and without supersymmetry. Assuming the two lighter heavy Majorana neutrinos are degenerate at the GUT scale, it is shown that the renormalization group (RG) evolution from the GUT scale to the seesaw scale gives rise to breaking of the mu-tau symmetry and a tiny splitting between two degenerate heavy Majorana neutrino masses as well as small variations of the CP phases in Y_nu, which are essential to achieve a successful leptogenesis. Such small RG effects lead to tiny deviations of theta_{23} from the maximal value and the CP phase delta_{CP} from pi/2 imposed at the GUT scale due to mu-tau reflection symmetry. In our scenario, the required amount of the baryon asymmetry eta_B can be generated via so-called resonant e-leptogenesis, in which the wash-out factor concerned with electron flavor plays a crucial role in reproducing a successful leptogenesis. We show that CP violation responsible for the generation of baryon asymmetry of our universe can be directly linked with CP violation measurable through neutrino oscillation as well as neutrino mixing angles theta_{12} and theta_{13}. We expect that, in addition to the reactor and long baseline neutrino experiments, the measurements for the supersymmetric parameter tan{beta} at future collider experiments would serve as an indirect test of our scenario of baryogenesis based on the mu-tau reflection symmetry.

hep-ph↗

arXiv2008

$μ-τ$ Reflection Symmetry in in Lepton Mixing and Radiatively Generated Leptogenesis

We study a $μ- τ$ reflection symmetry in neutrino sector realized at the GUT scale in the context of the seesaw model. In our scenario, the exact $μ- τ$ reflection symmetry realized in the basis where the charged lepton and heavy Majorana mass matrices are diagonal, leads to vanishing lepton asymmetries. We find that, in the minimal supersymmetry extension of the seesaw model with appropriate values of $\tanβ$, the renormalization group (RG) evolution from the GUT scale to seesaw scale can induce a successful leptogenesis. It is shown that the right amount of the baryon asymmetries $η_B$ can be achieved via so-called resonant leptogenesis, which can be realized at rather low seesaw scale in our scenario, so that the well-known gravitino problem is safely avoided. In this work, we consider both flavor dependent and flavor independent leptogenesis, and demonstrate how they lead to different amounts of baryon asymmetries in detail.

hep-ph↗