Light neutrino masses and mixing angles in SO(10) with realistic flavor structure, and the solar neutrino problem (original) (raw)

A 4 -based seesaw model for realistic neutrino masses and mixing

Physical Review D, 2016

We present an A4-based model where neutrino masses arise from a combination of seesaw mechanisms. The model is motivated by several small mixing and mass parameters indicated by the data. These are θ 13 , the solar mass splitting, and the small deviation of θ 23 from maximal mixing (= π/4). We take the above as indications that at some level the small quantities are well-approximated by zero. In particular the mixing angles, to a zero order, should be either 0 or π/4. Accordingly, in this model the Type-II seesaw dominates and generates the larger atmospheric mass splitting and sets θ 23 = π/4. The other mixing angles are vanishing as is the solar splitting. We show how the A4 assignment for the lepton doublets leads to this form. We also specify the A4 properties of the right-handed neutrinos which result in a smaller Type-I seesaw contribution that acts as a perturbation and shifts the angles θ 12 and θ 13 into the correct range and the desired value of ∆m 2 solar is produced. The A4 symmetry results in relationships between these quantities as well as with a small deviation of θ 23 from π/4. If the right-handed neutrino mass matrix, M R , is chosen real then there is no leptonic CP-violation and only Normal Ordering is admissible. If M R is complex then Inverted Ordering is also allowed with the proviso that the CP-phase, δ, is large, i.e., ∼ π/2 or −π/2. The preliminary results from NOνA favouring Normal Ordering and δ near −π/2 imply quasi-degenerate neutrino masses in this model.

The mass-hierarchy puzzle and the 17 keV neutrino in the context of a Universal Seesaw Model

Nuclear Physics B, 1992

In the light of renewed evidence for the existence of a 17 keV neutrino, we study the possible mass patterns for the charged and the neutral leptons, in the context of a generalized "seesaw"-type of model, which implements a horizontal U(l)A Peccei-Quinn symmetry. Under some general assumptions concerning the structure of the mass matrix we find that the mass hierarchy between the first two generations of charged leptons and the third one is explained in terms of the natural scales of the model. At the same time, with the additional assumption of the proportionality of Majorana-and Dirac-type couplings, the spectrum of the neutral leptons contains two very light Majorana neutrinos, such as required by the MSW interpretation of the solar neutrino deficit, and the 17 keV "Simpson" neutrino. A cosmologically consistent decay mode of this neutrino is into a~e and the axion.

07 24 3 v 2 1 A ug 2 00 0 hep-ph / 0007243 Inverted Hierarchy Models of Neutrino Masses

2000

We study models of neutrino masses which naturally give rise to an inverted mass hierarchy and bi-maximal mixing. The models are based on the seesaw mechanism with three right-handed neutrinos, which generates a single mass term of the form ν e (ν µ +ν τ) corresponding to two degenerate neutrinos ν e and ν µ +ν τ , and one massless neutrino ν µ −ν τ. Atmospheric neutrino oscillations are accounted for if the degenerate mass term is about 5 × 10 −2 eV. Solar neutrino oscillations of the Large Mixing Angle MSW type arise when small perturbations are included leading to a mass splitting between the degenerate pair of about (1.7 − 2.0) × 10 −4 eV for the successful cases. We study the conditions that such models must satisfy in the framework of a U(1) family symmetry broken by vector singlets, and catalogue the simplest examples. We then perform a renormalisation group analysis of the neutrino masses and mixing angles, assuming the supersymmetric standard model, and find modest radiativ...

Two-loop neutrino masses and the solar neutrino problem

Physical Review D, 1994

The addition of m singlet right-handed neutrinos to the Standard Model leads to radiatively generated mass corrections for the SU(2) L doublet neutrinos. For those neutrinos which are massless at the tree level after this addition, this implies a small mass generated at the two-loop level via W ± exchange. We calculate these mass corrections exactly by obtaining an analytic form for the general case of n doublets and m singlets. As a phenomenological application, we consider the m = 1 case and examine the masses and mixings of the doublet neutrinos which arise as a result of the two-loop correction in the light of experimental data from two sources which may shed light on the question of neutrino masses. These are (a) the neutrino detectors reporting a solar neutrino deficit (and its resolution via Mikheyev-Smirnov-Wolfenstein matter oscillations), and (b) the COBE satellite data on the non-zero angular variations of the cosmic microwave background temperature (and its possible implications for hot dark matter). Within the framework of the extension considered here, which leaves the gauge group structure of the Standard Model intact, we show that it is possible for neutrinos to acquire small masses naturally, with values which are compatible with current theoretical bias and experimental data.

Seesaw neutrino mass ratios with radiative corrections

1993

Unlike neutrino masses, the ratios of neutrino masses can be predicted by up-quark seesaw models using the known quark masses and including radiative corrections, with some restrictive assumptions. The uncertainties in these ratios can be reduced to three: the type of seesaw (quadratic, linear, etc.), the top quark mass, and the Landau-triviality value of the top quark mass. * Work supported by the U.S. Department of Energy under contract no. DOE-AC02-76-CHO-3000. The inconclusive but suggestive results of recent solar and atmospheric neutrino and beta decay experiments [1] lead to the possibility of neutrino masses, which additionally may have important application to cosmology, astrophysics and laboratory searches for neutrino oscillations. The most economical model of light neutrinos is the so-called "seesaw" of the grand-unified type, which requires a superheavy right-handed neutrino for each ordinary neutrino and arises naturally in partially or completely unified theories with leftright symmetry, such as SO(10) [2,3,4]. These grand unified seesaw models predict small but non-zero Majorana masses for the ordinary neutrinos in terms of the Dirac masses of the up-type quarks (u, c, t) and the superheavy right-handed Majorana masses. These predictions are made uncertain, however, by the unknown right-handed masses and by radiative corrections. But the ratios of neutrino masses are more definite in seesaw models, under some neccesary and minimal assumptions (printed below in italics) about the physics underlying the seesaw [5]. The uncertainties in the mass ratios can then be narrowed to a

Neutrino masses: evidences and implications

Journal of Physics: Conference Series, 2014

I give an overview of the evidences for neutrino masses and mixing, the associated neutrino mass generation schemes, as well as the resulting implications in particle physics experiments and cosmology.

The Origin of Neutrino Masses and Physics Beyond the SM

2010

We discuss the simplest models for the generation of neutrinos masses at tree level and one-loop level. The realization of the different seesaw mechanisms in the context of renormalizable SU(5) and SO(10) theories is reviewed. A new mechanism for the generation of neutrino masses at one-loop level is presented. We discuss the first realization of the Type III seesaw mechanism in the context of a renormalizable SU(5) theory, called "Adjoint SU(5)".

Neutrino masses and leptogenesis in type I and type II seesaw models

Physical Review D, 2014

The baryon to photon ratio in the present Universe is very accurately measured to be (6.065 ± 0.090) × 10 −10 . We study the possible origin of this baryon asymmetry in the neutrino sector through the generic mechanism of baryogenesis through leptogenesis. We consider both type I and type II seesaw origin of neutrino masses within the framework of left right symmetric models (LRSM). Using the latest best fit global neutrino oscillation data of mass squared differences, mixing angles and Dirac CP phase, we compute the predictions for baryon to photon ratio keeping the Majorana CP phases as free parameters for two different choices of lightest neutrino mass eigenvalue for both normal and inverted hierarchical patterns of neutrino masses. We do our calculation with and without lepton flavor effects being taken into account. We choose different diagonal Dirac neutrino mass matrix for different flavor effects in such a way that the lightest right handed neutrino mass is in the appropriate range. We also study the predictions for baryon asymmetry when the neutrino masses arise from a combination of both type I and type II seesaw (with dominating type I term) and discriminate between several combinations of Dirac and Majorana CP phases by demanding successful predictions for baryon asymmetry.

A model of radiative neutrino masses. Mixing and a possible fourth generation

Physics Letters B, 1989

We consider the phenomenological consequences of a recently proposed model with four lepton generations such that the three known neutrinos have radiatively induced Majorana masses. Mixing among generations in the presence of a heavy fourth neutrino necessitates a reevaluation of the usual experimental tests of the standard model. One interesting possibility is to have a "~ lifetime longer than predicted by the standard three-generation model. Another is to have neutrino masses and mixing angles in the range needed for a natural explanation of the solar-neutrino puzzle in terms of the Mikbeyev-Smirnov-Wolfenstein effect.