Neutrino Yukawa Matrix Research Articles

FlippedSU(5)with modularA4symmetry

We study Flipped $SU(5)\times U(1)$ Grand Unified Theories (GUTs) with $\Gamma_3\simeq A_4$ modular symmetry. We propose two models with different modular weights assignments, where the fermion mass hierarchy can arise from weighton fields. In order to relax the constraint on the Dirac neutrino Yukawa matrix we appeal to mechanisms which allow incomplete GUT representations, allowing a good fit to quark and charged lepton masses and quark mixing for a single modulus field $\tau$, with the neutrino masses and lepton mixing well determined by the type I seesaw mechanism, at the expense of some tuning. We also discuss the double seesaw possibility allowed by the extra singlets generically predicted in such string inspired theories.

Leptonic CP and flavor violations in SUSY GUT with right-handed neutrinos

We study leptonic $CP$ and flavor violations in supersymmetric grand unified theory with right-handed neutrinos, paying attention to the renormalization group effects on the slepton mass matrices due to the neutrino and grand unified theory Yukawa interactions. In particular, we study in detail the impacts of the so-called Casas-Ibarra parameters on $CP$ and flavor violating observables. The renormalization group effects induce $CP$ and flavor violating elements of the supersymmetric breaking scalar mass squared matrices, which may result in sizable leptonic $CP$ and flavor violating signals. Assuming a seesaw formula for the active neutrino masses, the renormalization group effects have been often thought to be negligible as the right-handed neutrino masses become small. With the most general form of the neutrino Yukawa matrix, i.e., taking into account the Casas-Ibarra parameters; however, this is not the case. We found that the maximal possible sizes of signals of leptonic $CP$ and flavor violating processes are found to be insensitive to the mass scale of the right-handed neutrinos and that they are as large as (or larger than) the present experimental bounds irrespective of the right-handed neutrino masses.

Diagonal reflection symmetries and universal four-zero texture * *This study is financially Supported by JSPS Grants-in-Aid for Scientific Research (JP18H01210, 20K14459) and MEXT KAKENHI (JP18H05543)

In this paper, we consider a set of new symmetries in the SM: diagonal reflection symmetries with diag . These generalized symmetries predict the Majorana phases to be or . Realization of diagonal reflection symmetries implies a broken chiral symmetry only for the first generation. The axion scale is suggested to be [GeV]. By combining the symmetries with the four-zero texture, the mass eigenvalues and mixing matrices of quarks and leptons are reproduced well. This scheme predicts the normal hierarchy, the Dirac phase and or [meV]. In this scheme, the type-I seesaw mechanism and a given neutrino Yukawa matrix completely determine the structure of the right-handed neutrino mass . A unification predicts the mass eigenvalues to be [GeV].

Assessing perturbativity and vacuum stability in high-scale leptogenesis

We consider the requirements that all coupling constants remain perturbative and the electroweak vacuum metastable up to the Planck scale in high-scale thermal leptogenesis, in the context of a type-I seesaw mechanism. We find a large region of the model parameter space that satisfies these conditions in combination with producing the baryon asymmetry of the Universe. We demonstrate these conditions require Tr[YN†YN] ≲ 0.66 on the neutrino Yukawa matrix. We also investigate this scenario in the presence of a large number NF of coloured Majorana octet fermions in order to make quantum chromodynamics asymptotically safe in the ultraviolet.

Obtaining nonvanishing 𝜃13 with constrained neutrino Yukawa matrix and implications for flavor model buildings

Assuming a diagonal Majorana neutrino mass matrix, we investigate the neutrino Yukawa textures which lead to a nonzero reactor mixing angle [Formula: see text]. The neutrino effective coupling matrix [Formula: see text] is pre-diagonalized by a constant mixing pattern [Formula: see text] with a vanishing [Formula: see text]. The resulting pre-diagonal symmetrical matrix [Formula: see text] is set to be four texture zeros with two types of off-diagonal elements nonzero, which are [Formula: see text] and [Formula: see text], respectively. With the expectation of simple textures, we thoroughly classify the linear combinations, [Formula: see text], [Formula: see text] and [Formula: see text] of Yukawa elements [Formula: see text] in the same row, according to the values, vanishing or not. Each set of the classifications can lead to a Yukawa texture which may have implications for the discrete flavor model buildings. We also present a model based on [Formula: see text] according to one set of the constraints on the three combinations with a specific choice of a coefficient in Yukawa texture.

Perturbed Yukawa textures in the minimal seesaw model

We revisit the minimal seesaw model, i.e., the type-I seesaw mechanism involving only two right-handed neutrinos. This model represents an important minimal benchmark scenario for future experimental updates on neutrino oscillations. It features four real parameters that cannot be fixed by the current data: two CP -violating phases, δ and σ, as well as one complex parameter, z, that is experimentally inaccessible at low energies. The parameter z controls the structure of the neutrino Yukawa matrix at high energies, which is why it may be regarded as a label or index for all UV completions of the minimal seesaw model. The fact that z encompasses only two real degrees of freedom allows us to systematically scan the minimal seesaw model over all of its possible UV completions. In doing so, we address the following question: suppose δ and σ should be measured at particular values in the future — to what extent is one then still able to realize approximate textures in the neutrino Yukawa matrix? Our analysis, thus, generalizes previous studies of the minimal seesaw model based on the assumption of exact texture zeros. In particular, our study allows us to assess the theoretical uncertainty inherent to the common texture ansatz. One of our main results is that a normal light-neutrino mass hierarchy is, in fact, still consistent with a two-zero Yukawa texture, provided that the two texture zeros receive corrections at the level of mathcal{O} (10%). While our numerical results pertain to the minimal seesaw model only, our general procedure appears to be applicable to other neutrino mass models as well.

Radiative corrections to light neutrino masses in low scale type I seesaw scenarios and neutrinoless double beta decay

We perform a detailed analysis of the one-loop corrections to the light neutrino mass matrix within low scale type I seesaw extensions of the Standard Model and their implications in experimental searches for neutrinoless double beta decay. We show that a sizable contribution to the effective Majorana neutrino mass from the exchange of heavy Majorana neutrinos is always possible, provided one requires a fine-tuned cancellation between the tree-level and one-loop contribution to the light neutrino masses. We quantify the level of fine-tuning as a function of the seesaw parameters and introduce a generalisation of the Casas-Ibarra parametrization of the neutrino Yukawa matrix, which easily allows to include the one-loop corrections to the light neutrino masses.

Leptogenesis in minimal predictive seesaw models

We estimate the Baryon Asymmetry of the Universe (BAU) arising from leptogenesis within a class of minimal predictive seesaw models involving two right-handed neutrinos and simple Yukawa structures with one texture zero. The two right-handed neutrinos are dominantly responsible for the “atmospheric” and “solar” neutrino masses with Yukawa couplings to (ν e , ν μ , ν τ ) proportional to (0, 1, 1) and (1, n, n − 2), respectively, where n is a positive integer. The neutrino Yukawa matrix is therefore characterised by two proportionality constants with their relative phase providing a leptogenesis-PMNS link, enabling the lightest right-handed neutrino mass to be determined from neutrino data and the observed BAU. We discuss an SU(5) SUSY GUT example, where A 4 vacuum alignment provides the required Yukawa structures with n = 3, while a $$ {\mathrm{\mathbb{Z}}}_9 $$ symmetry fixes the relatives phase to be a ninth root of unity.

Confronting four zero neutrino Yukawa textures with N2 -dominated leptogenesis

We consider a restricted Type-I seesaw scenario with four texture zeros in the neutrino Yukawa matrix, in the weak basis where both the charged-lepton Yukawa matrix and the Majorana mass matrix for right-handed neutrinos are diagonal and real. Inspired by grand unified theories, we further require the neutrino Yukawa matrix to exhibit a similar hierarchical pattern to that in the up-type quark Yukawa matrix. With such a hierarchy requirement, we find that leptogenesis, which would operate in a $N_2^{}$-dominated scenario with the asymmetry generated by the next-to-lightest right-handed neutrino $N_2^{}$, can greatly reduce the number of allowed textures, and disfavors the scenario that three light neutrinos are quasi-degenerate. Such a quasi-degenerate scenario of light neutrinos may soon be tested in upcoming neutrino experiments.

Lepton flavor violation in the supersymmetric seesaw model after the LHC 8 TeV run

We study the lepton flavor violation in the supersymmetric seesaw model, taking into account recent experimental improvements, especially for the Higgs boson mass measurement, direct searches of superpartners, and the rare decay of ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ at the LHC; the neutrino mixing angle of ${\ensuremath{\theta}}_{13}$ in the neutrino experiments; and the search of $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$ in the MEG experiment. We obtain the latest constraints on the parameters in the supersymmetry-breaking terms and study the effect on the lepton-flavor-violating decays of $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$ and $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$. In particular, we consider two kinds of assumption on the structures in the Majorana mass matrix and the neutrino Yukawa matrix. In the case of the Majorana mass matrix proportional to the unit matrix, allowing nonvanishing $CP$-violating parameters in the neutrino Yukawa matrix, we find that the branching ratio of $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$ can be larger than ${10}^{\ensuremath{-}9}$ within the improved experimental limit of $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$. We also consider the neutrino Yukawa matrix that includes the mixing only in the second and third generations, and we find that a larger branching ratio of $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$ than ${10}^{\ensuremath{-}9}$ is possible while satisfying the recent constraints.

DynamicalCPsource for Cabibbo-Kobayashi-Maskawa and Pontecorvo-Maki-Nakagawa-Sakata matrices and leptogenesis

We propose a model for the spontaneous $CP$ violation based on $SU(2{)}_{L}\ifmmode\times\else\texttimes\fi{}U(1{)}_{Y}\ifmmode\times\else\texttimes\fi{}{A}_{4}\ifmmode\times\else\texttimes\fi{}CP\ifmmode\times\else\texttimes\fi{}{Z}_{2}$ symmetry for quarks and leptons in a seesaw framework. We investigate a link between the $CP$ phase in the Cabibbo-Kobayashi-Maskawa (CKM) matrix and $CP$ phase in the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix by using the present data of quark sector. 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 considered in the Lagrangian as an equal footing, in which the quarks lead to the CKM matrix of the quark mixing. However, the lepton Lagrangian still keep renormalizability, which gives rise to a nondegenerate Dirac neutrino Yukawa matrix, a unique $CP$-phase, and the nonzero value of ${\ensuremath{\theta}}_{13}\ensuremath{\simeq}9\ifmmode^\circ\else\textdegree\fi{}$ as well as two large mixing angles ${\ensuremath{\theta}}_{12}$, ${\ensuremath{\theta}}_{23}$. We show that the generated $CP$ phase ``$\ensuremath{\xi}$'' from the spontaneous $CP$ violation could become a natural source of leptogenesis as well as $CP$ violations in the CKM and PMNS. Interestingly enough, we show that, for around $\ensuremath{\xi}\ensuremath{\simeq}110\ifmmode^\circ\else\textdegree\fi{}(140\ifmmode^\circ\else\textdegree\fi{})$, we obtain the measured CKM $CP$ phase ${\ensuremath{\delta}}_{CP}^{q}\ensuremath{\simeq}70\ifmmode^\circ\else\textdegree\fi{}$ for normal (inverted) hierarchy. For the measured value of ${\ensuremath{\theta}}_{13}$ we favor the PMNS $CP$ phase around 30\ifmmode^\circ\else\textdegree\fi{}, 200\ifmmode^\circ\else\textdegree\fi{}, and $|{\ensuremath{\theta}}_{23}\ensuremath{-}45\ifmmode^\circ\else\textdegree\fi{}|\ensuremath{\rightarrow}0$ for normal mass hierarchy and around 60\ifmmode^\circ\else\textdegree\fi{}, 110\ifmmode^\circ\else\textdegree\fi{}, 230\ifmmode^\circ\else\textdegree\fi{}, $|{\ensuremath{\theta}}_{23}\ensuremath{-}45\ifmmode^\circ\else\textdegree\fi{}|\ensuremath{\rightarrow}5\ifmmode^\circ\else\textdegree\fi{}$ 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 interplay between them.

Seesaw mechanism with four texture zeros in the neutrino Yukawa matrix

With the recent observation of nonzero \theta_{13}, five neutrino oscillation parameters are now known. By imposing four zeros in the Yukawa coupling matrix of the type I seesaw model, the number of parameters in the neutrino mass matrix is reduced to seven, and we are able to make predictions for the lightest neutrino mass, Dirac CP phase, and neutrinoless double beta decay. Four texture zeros in the Yukawa coupling matrix is equivalent to either a single texture zero or a single cofactor zero for an off-diagonal element of the light neutrino mass matrix. We find strong similarities between single texture zero models with one mass ordering and single cofactor zero models with the opposite mass ordering. In the context of a specific class of single-flavor leptogenesis models, we find additional constraints on the parameter space.

Nonzeroθ13andCPviolation in a model withA4flavor symmetry

Motivated by recent observations of non-zero $\theta_{13}$ 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.

Anarchy and leptogenesis

We study if leptogenesis works successfully together with the neutrino mass anarchy hypothesis. We find that the predicted neutrino mass spectrum is sensitive to the reheating temperature or the inflaton mass, while the distributions of the neutrino mixing angles and CP violation phases remain intact as determined by the invariant Haar measure of U(3). In the case of thermal leptogenesis, the light neutrino mass distribution agrees well with the observations if the reheating temperature is O(10^{9-11}) GeV. The mass spectrum of the right-handed neutrinos and the neutrino Yukawa matrix exhibit a certain pattern, as a result of the competition between random matrices with elements of order unity and the wash-out effect. Non-thermal leptogenesis is consistent with observation only if the inflaton mass is larger than or comparable to the typical right-handed neutrino mass scale. Cosmological implications are discussed in connection with the 125GeV Higgs boson mass.

Natural neutrino masses and mixings from warped geometry

We demonstrate that flavor symmetries in warped geometry can provide a natural explanation for large mixing angles and economically explain the distinction between the quark and lepton flavor sectors. We show how to naturally generate Majorana neutrino masses assuming a gauged a U(1)B−L symmetry broken in the UV that generates see-saw masses of the right size. This model requires lepton minimal flavor violation (LMFV) in which only Yukawa matrices (present on the IR brane) break the flavor symmetries. The symmetry-breaking is transmitted to charged lepton bulk mass parameters as well to generate the hierarchy of charged lepton masses. With LMFV, a GIM-like mechanism prevents dangerous flavor-changing processes for charged leptons and permits flavor-changing processes only in the presence of the neutrino Yukawa interaction and are therefore suppressed when the overall scale for the neutrino Yukawa matrix is slightly smaller than one in units of the curvature. In this case the theory can be consistent with a cutoff of 10 TeV and 3 TeV Kaluza-Klein masses.

Leptogenesis in a seesaw model with Fritzsch-type lepton mass matrices

We investigate how the baryon asymmetry of our Universe via leptogenesis can be achieved within the framework of the seesaw model with Fritzsch-type lepton mass matrices proposed by Fukugita et al. We study the cases with $CP$-violating phases in charged-lepton Yukawa matrix, however, with and without Dirac neutrino Yukawa phases. We consider both flavor-independent and flavor-dependent leptogenesis, and demonstrate how they lead to different amounts of lepton asymmetries in detail. In particular, it is shown that flavor-dependent leptogenesis in this model can be achieved only for very tiny or zero values of $CP$ phases in Dirac neutrino Yukawa matrix at the grand unified theory scale. In addition to the $CP$ phases, for successful leptogenesis in the model it is required that the degeneracy of the heavy Majorana neutrino mass spectrum should be broken and we also show that the breakdown of the degeneracy can be radiatively induced.

SO(10) unified models and soft leptogenesis

Motivated by the fact that, in some realistic models combining SO(10) GUTs and flavour symmetries, it is not possible to achieve the required baryon asymmetry through the CP asymmetry generated in the decay of right-handed neutrinos, we take a fresh look on how deep this connection is in SO(10). The common characteristics of these models are that they use the see-saw with right-handed neutrinos, predict a normal hierarchy of masses for the neutrinos observed in oscillating experiments and in the basis where the right-handed Majorana mass is diagonal, the charged lepton mixings are tiny. In addition these models link the up-quark Yukawa matrix to the neutrino Yukawa matrix Y^\nu with the special feature of Y^\nu_{11}-> 0 Using this condition, we find that the required baryon asymmetry of the Universe can be explained by the soft leptogenesis using the soft B parameter of the second lightest right-handed neutrino whose mass turns out to be around 10^8 GeV. It is pointed out that a natural way to do so is to use no-scale supergravity where the value of B ~1 GeV is set through gauge-loop corrections.

Can measurements of electric dipole moments determine the seesaw parameters?

In the context of the supersymmetrized seesaw mechanism embedded in the Minimal Supersymmetric Standard Model (MSSM), complex neutrino Yukawa couplings can induce Electric Dipole Moments (EDMs) for the charged leptons, providing an additional route to seesaw parameters. However, the complex neutrino Yukawa matrix is not the only possible source of CP violation. Even in the framework of Constrained MSSM (CMSSM), there are additional sources, usually attributed to the phases of the trilinear soft supersymmetry breaking couplings and the mu-term, which contribute not only to the electron EDM but also to the EDMs of neutron and heavy nuclei. In this work, by combining bounds on various EDMs, we analyze how the sources of CP violation can be discriminated by the present and planned EDM experiments.

Publisher’s Note: Phase effects from the general neutrino Yukawa matrix on lepton flavor violation [Phys. Rev. DPRVDAQ0556-282172, 055012 (2005)

We examine contributions from Majorana phases to lepton flavor violating processes in the framework of the minimal supersymmetric standard model with heavy right-handed neutrinos. All phases in the complex neutrino Yukawa matrix are taken into account in our study. We find that in the scenario with universal soft-breaking terms sizable phase effects can appear on the lepton flavor violating processes such as $\mu \to e \gamma$, $\tau \to e \gamma$, and $\tau \to \mu \gamma$. In particular, the branching ratio of $\mu \to e \gamma$ can be considerably enhanced due to the Majorana phases, so that it can be much greater than that of $\tau \to \mu \gamma$.

Phase effects from the general neutrino Yukawa matrix on lepton flavor violation

We examine contributions from Majorana phases to lepton flavor violating processes in the framework of the minimal supersymmetric standard model with heavy right-handed neutrinos. All phases in the complex neutrino Yukawa matrix are taken into account in our study. We find that in the scenario with universal soft-breaking terms sizable phase effects can appear on the lepton flavor violating processes such as $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$, $\ensuremath{\tau}\ensuremath{\rightarrow}e\ensuremath{\gamma}$, and $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$. In particular, the branching ratio of $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$ can be considerably enhanced due to the Majorana phases, so that it can be much greater than that of $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$.