The minimal seesaw and leptogenesis models

Abstract

Given its briefness and predictability, the minimal seesaw -a simplified version of the canonical seesaw mechanism with only two right-handed neutrino fields -has been studied in depth and from many perspectives, and now it is being pushed close to a position of directly facing experimental tests. This article is intended to provide an up-to-date review of various phenomenological aspects of the minimal seesaw and its associated leptogenesis mechanism in neutrino physics and cosmology. Our focus is on possible flavor structures of such benchmark seesaw and leptogenesis scenarios and confronting their predictions with current neutrino oscillation data and cosmological observations. In this connection particular attention will be paid to the topics of lepton number violation, lepton flavor violation, discrete flavor symmetries, CP violation and antimatter of the Universe.

Radiative decays of charged leptons as constraints of unitarity polygons for active-sterile neutrino mixing and CP violation

“…It is found that the areas of such sub-triangles can be described in terms of the Jarlskog-like invariants of CP violation J ij αβ , and their small differences may serve as a signal of slight unitarity violation of the 3 × 3 PMNS matrix U . These observations should be useful to test the unitarity of U when more accurate experimental data are available in the foreseeable future, and they can certainly be extended to those simplified seesaw cases (e.g., the minimal seesaw scenarios [49]) with fewer free parameters.…”

Double Covering of the Modular $A^{}_5$ Group and Lepton Flavor Mixing in the Minimal Seesaw Model

“…Best fit 1σ range 3σ range σ i Normal neutrino mass ordering (m 1 < m 2 < m 3 ) sin 2 [80][81][82][83][84][85][86] and assign two right-handed neutrino singlets into the two-dimensional representation of Γ 5 . Two concrete examples in the MSM have been given to explain the observed pattern of lepton flavor mixing.…”

A formula by $LDL^{T}$ decomposition for the minimal type-I seesaw mechanism and conditions of $CP$ symmetry in an arbitrary basis

“…However, such a representation obscures symmetries and relationships of the original Lagrangian. Thus, in this letter, we analyze the conditions for CP symmetry of the light neutrino mass matrix m in the minimal seesaw model [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] using a formula by LDL T decomposition [24]. As a result, basis-independent conditions are obtained for the general Lagrangian parameters.…”