We consider an existing framework of models where the neutrino Dirac and Majorana mass terms are related, and clarify how the mass structures interact through the type I seesaw mechanism, producing exact tri-bi-maximal mixing for the effective neutrinos in the limit of strong Majorana mass hierarchy (sequential dominance). In order to better illustrate this, we draw the seesaw diagrams expanded to show the relevant details, discuss an underlying symmetry that must be preserved by the neutrino mass terms, and diagonalise the effective neutrino mass matrix corresponding to the sequential dominance limit.
We review the mechanism of sequential right-handed neutrino dominance proposed in the framework of the type I see-saw mechanism to account for bi-large neutrino mixing and a neutrino mass hierarchy in a natural way. We discuss how sequential dominance may also be applied to the right-handed charged leptons, which alternatively allows bi-large lepton mixing from the charged lepton sector. We review how such sequential dominance models may be upgraded to include type II see-saw contributions, resulting in a partially degenerate neutrino mass spectrum with bi-large lepton mixing arising from sequ…
Neutrinos with hierarchical masses and two large mixing angles may naturally originate from sequential dominance (SD). Within this framework we present analytic expressions for the neutrino mixing angles including the next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) corrections arising from the second lightest and lightest neutrino masses. The analytic results for neutrino mixing angles in SD presented here, including the NLO and NNLO corrections, are applicable to a wide class of models and may provide useful insights when confronting the models with data from high precisi…
We systematically analyze the possibility that bi-large lepton mixing originates from the charged lepton sector in models with sequential dominance for the right-handed charged leptons. We derive analytical expressions for the mixing angles and CP phases of the MNS matrix for the case of zero mixing from the neutrino sector, which is arranged for with the help of sequential dominance for the right-handed neutrinos. For small $θ_{13}$, the two large mixing angles $θ_{12}$ and $θ_{23}$ are determined by the Yukawa couplings to the dominant right-handed tau. The mixing angle $θ_{13}$ is then gove…
We consider charged Lepton Flavour Violation (LFV) in the Constrained Minimal Supersymmetric Standard Model, extended to include the see-saw mechanism with Constrained Sequential Dominance (CSD), where CSD provides a natural see-saw explanation of tri-bimaximal neutrino mixing. When charged lepton corrections to tri-bimaximal neutrino mixing are included, we discover characteristic correlations among the LFV branching ratios, depending on the mass ordering of the right-handed neutrinos, with a pronounced dependence on the leptonic mixing angle $θ_{13}$ (and in some cases also on the Dirac CP p…
Leptogenesis via Resonant Sequential Dominance and TBC3 Mixing in a Type-I Seesaw Model
Graduate School of Science and Technology, Tokai University（东海大学理学院）；Micro/Nano Technology Center, Tokai University（东海大学微纳技术中心）；Department of Physics, School of Science, Tokai University（东海大学理学院物理系）
Following the recent T2K indication of a sizeable reactor angle, we present a class of models which fix θ_{13} while preserving trimaximal solar mixing. The models are based on a new type of constrained sequential dominance involving new vacuum alignments, along the (1,2,0)^T or (1,0,2)^T directions in flavour space. We show that such alignments are easily achieved using orthogonality, and may replace the role of the subdominant flavon alignment (1,1,1)^T in constrained sequential dominance. In such models, with a normal hierarchical spectrum, the reactor angle is related to a ratio of neutrin…
In the constrained sequential dominance (CSD), tri-bimaximal mixing (TBM) pattern in the neutrino sector has been explained, by proposing a certain Yukawa coupling structure for the right-handed neutrinos of the model. However, from the current experimental data it is known that the values of neutrino mixing angles are deviated from the TBM values. In order to explain this neutrino mixing, we first propose a phenomenological model where we consider Yukawa couplings which are modified from that of CSD. Essentially, we add small complex parameters to the Yukawa couplings of CSD. Using these modi…
We study thermal leptogenesis in classes of neutrino mass models based on the seesaw mechanism with three right-handed neutrinos and sequential right-handed neutrino dominance. The flavour-dependent Boltzmann equations are solved appropriate to both the Standard Model and the Minimal Supersymmetric Standard Model. Within these classes of models we investigate constraints and expectations on the individual decay asymmetries and washout parameters from the present data on neutrino masses and mixings. In many cases of physical interest flavour effects are shown to have important consequences for …
We revisit a two right-handed neutrino model with two texture zeros, namely an indirect model based on A4 with the recently proposed new type of constrained sequential dominance (CSD2), involving vacuum alignments along the (0,1,-1)^T and (1,0,2)^T directions in flavour space, which are proportional to the neutrino Dirac mass matrix columns. In this paper we construct a renormalizable and unified indirect A4xSU(5) model along these lines and show that, with spontaneous CP violation and a suitable vacuum alignment of the phases, the charged lepton corrections lead to a reactor angle in good agr…
In this talk I discuss the connection between neutrino mass, flavour and CP violation. I focus on three neutrino patterns of neutrino masses and mixing angles, and the corresponding Majorana mass matrices. I discuss the see-saw mechanism, and show how it may be applied in a very natural way to give a neutrino mass hierarchy with large atmospheric and solar angles by assuming sequential right-handed neutrino dominance. I then distinguish between heavy sequential dominance and light sequential dominance, and show how lepton flavour violation in the CMSSM provides a way to discriminate between th…
We propose an invariant see-saw (ISS) approach to model building, based on the observation that see-saw models of neutrino mass and mixing fall into basis invariant classes labelled by the Casas-Ibarra $R$-matrix, which we prove to be invariant not only under basis transformations but also non-unitary right-handed neutrino transformations $S$. According to the ISS approach, given any see-saw model in some particular basis one may determine the invariant $R$ matrix and hence the invariant class to which that model belongs. The formulation of see-saw models in terms of invariant classes puts the…
Constrained sequential dominance (CSD) is a natural framework for implementing the see-saw mechanism of neutrino masses which allows the mixing angles and phases to be accurately predicted in terms of relatively few input parameters. We analyze a class of CSD($n$) models where, in the flavour basis, 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. These coupling patterns may arise in indirect family symmetry …
Tri-bimaximal neutrino mixing may arise from see-saw models based on family symmetry which is spontaneously broken by flavons with particular vacuum alignments. However recent analyses hint that tri-bimaximal mixing may be insensitive to the precise form of vacuum alignment. In this paper we derive approximate analytic results which express the deviations from tri-bimaximal neutrino mixing due to vacuum misalignment. We also relate vacuum misalignment to departures from form dominance, corresponding to deviations from the real orthogonal $R$ matrix, where such corrections are necessary to allo…
We introduce the idea of Form Dominance in the (type I) see-saw mechanism, according to which a particular right-handed neutrino mass eigenstate is associated with a particular physical neutrino mass eigenstate, leading to a form diagonalizable effective neutrino mass matrix. Form Dominance, which allows an arbitrary neutrino mass spectrum, may be regarded as a generalization of Constrained Sequential Dominance which only allows strongly hierarchical neutrino masses. We consider alternative implementations of the see-saw mechanism in minimal A4 see-saw models and show that such models satisfy …
We emphasize that the vanishing of the CP asymmetry in leptogenesis, previously observed for models with tri-bimaximal mixing and family symmetry, may be traced to a property of the type I see-saw mechanism satisfied by such models known as Form Dominance, corresponding to the case of a diagonal Casas-Ibarra R-matrix. Form Dominance leads to vanishing flavour-dependent CP asymmetries irrespective of whether one has tri-bimaximal mixing or a family symmetry. Successful leptogenesis requires violation of Form Dominance, but not necessarily violation of tri bimaximal mixing. This may be achieved …
We discuss the relation between leptogenesis and the MNS phases in the class of see-saw models called light sequential dominance in which the right-handed neutrinos dominate sequentially, with the dominant right-handed neutrino being the lightest one. The heaviest right-handed neutrino then decouples, leaving effectively two right-handed neutrinos. Light sequential dominance is motivated by SO(10) models which predict three right-handed neutrinos. With an approximate Yukawa texture zero in the 11 position there are only two see-saw phases which are simply related to the MNS phase measurable at…
We propose an extension of tri-bimaximal mixing to include a non-zero reactor angle $θ_{13}$ while maintaining the tri-bimaximal predictions for the atmospheric angle $θ_{23}=45^o$ and solar angle $θ_{12}=35^o$. We show how such tri-bimaximal-reactor mixing can arise at leading order from the(type I) see-saw mechanism with partially constrained sequential dominance. Partially constrained sequential dominance can be realized in GUT models with a non-Abelian discrete family symmetry, such as $A_4$, spontaneously broken by flavons with a particular vacuum alignment.
We implement type-II seesaw dominance for neutrino mass and baryogenesis through heavy scalar triplet leptogenesis in a class of minimal non-supersymmetric SO(10) models where matter parity as stabilising discrete symmetry as well as WIMP dark matter (DM) candidates are intrinsic predictions of the GUT symmetry. We also find modifications of relevant CP-asymmetry formulas in such minimal models. Baryon asymmetry of the universe as solutions of Boltzmann equations is further shown to be realized for both normal and inverted mass orderings in concordance with cosmological bound and best fit valu…
Allowed region for the (second) lightest mass $M_{1,2}$ of right-handed neutrino $ν_{R 1,2}$ with $SO (10)$-inspired relations and sequential dominance
本文在 I 型跷跷板与 SO(10) 启发关系下，利用手征微扰和序列优势推导右手中微子最轻及次轻质量的允许区间，并给出 NH/IH 下的具体质量界。
Grand unified theories where the neutrino mass is given by Type II seesaw have the potential to provide interesting connections between the neutrino and charged fermion sectors. We explore the possibility of having a dominant Type II seesaw contribution in supersymmetric SO(10). We show that this can be achieved in the model where symmetry breaking is triggered by 54 and 45-dimensional representations, without the need for additional fields other than those already required to have a realistic charged fermion mass spectrum. Physical consequences, such as the implementation of the BSV mechanism…
In this letter we present a simple scenario where the mass scales associated to atmospheric and solar neutrino oscillations are obtained through the dynamical generation of neutrino masses. The main idea is that the two different scales are the result of two independent mechanisms, namely a type-I seesaw generating the atmospheric scale and a radiative 1-loop process providing the solar one. A relation of the two scales, reminiscent of the so-called sequential dominance, is thus obtained.
Recently SO(10) models with type-II see-saw dominance have been proposed as a promising framework for obtaining Grand Unification theories with approximate Tri-bimaximal (TB) mixing in the neutrino sector. We make a general study of SO(10) models with type-II see-saw dominance and show that an excellent fit can be obtained for fermion masses and mixings, also including the neutrino sector. To make this statement more significant we compare the performance of type-II see-saw dominance models in fitting the fermion masses and mixings with more conventional models which have no built-in TB mixing…
In this paper we address the question: ``do the limits on technirho production at the Tevatron mean what we think they do ?'' These limits are based on calculations that rely on Vector Meson Dominance (VMD). VMD was invented in order to describe the interaction of electrons with hadrons (the rho meson and pions). The method has been used also as a tool in the study of Technicolor phenomenology. Nevertheless there are evidences in the sense that, even in its original, context VMD is not completely realized. In this work we investigate the consequences of a deviation from complete VMD for the ph…
We study renormalisation group (RG) corrections relevant for leptogenesis in the case of family symmetry models such as the Altarelli-Feruglio A4 model of tri-bimaximal lepton mixing or its extension to tri-maximal mixing. Such corrections are particularly relevant since in large classes of family symmetry models, to leading order, the CP violating parameters of leptogenesis would be identically zero at the family symmetry breaking scale, due to the form dominance property. We find that RG corrections violate form dominance and enable such models to yield viable leptogenesis at the scale of ri…
We derive the lower bound on the absolute scale of lightest neutrino mass for normal hierarchy and inverted hierarchy pattern of light neutrinos by studying the new physics contributions to charged lepton flavour violations in the framework of a TeV scale left-right symmetric model. In the model, the fermion sector comprises the usual quarks and leptons plus a fermion singlet per generation and the scalar sector consists of isospin doublets, triplets and a bidoublet. The framework allows large light-heavy neutrino mixing where the light neutrino mass formula is governed by a natural type-II se…
We perform an exhaustive analysis of all possible breaking patterns arising from $S_4\rtimes H_{CP}$ in a new {\it tri-direct CP approach} to the minimal seesaw model with two right-handed neutrinos, and construct a realistic flavour model along these lines. According to this approach, separate residual flavour and CP symmetries persist in the charged lepton, `atmospheric' and `solar' right-handed neutrino sectors, i.e. we have {\it three} symmetry sectors rather than the usual two of the {\it semi-direct CP approach} (charged leptons and neutrinos). Following the {\it tri-direct CP approach},…
We discuss a class of left-right symmetric theories with a universal seesaw mechanism for fermion masses and mixing and the implications for neutrinoless double beta ($0νββ$) decay where neutrino masses are governed by natural type-II seesaw dominance. The scalar sector consists of left- and right-handed Higgs doublets and triplets, while the conventional Higgs bidoublet is absent in this scenario. We use the Higgs doublets to implement the left-right and the electroweak symmetry breaking. On the other hand, the Higgs triplets with induced vacuum expectation values can give Majorana masses to …
We present a detailed discussion on neutrinoless double beta decay within a class of left-right symmetric models where neutrino mass originates by natural type-II seesaw dominance. The spontaneous symmetry breaking is implemented with doublets, triplets and bidoublet scalars. The fermion sector is extended with an extra sterile neutrino per generation that helps in implementing the seesaw mechanism. The presence of extra particles in the model exactly cancels type-I seesaw and allows large value for Dirac neutrino mass matrix $M_D$. The key feature of this work is that all the physical masses …
