Precision neutrino experiments vs the Littlest Seesaw

Abstract

Abstract:We study to what extent upcoming precision neutrino oscillation experiments will be able to exclude one of the most predictive models of neutrino mass and mixing: the Littlest Seesaw. We show that this model provides a good fit to current data, predicting eight observables from two input parameters, and provide new assessments of its predictions and their correlations. We then assess the ability to exclude this model using simulations of upcoming neutrino oscillation experiments including the medium-distance reactor experiments JUNO and RENO-50 and the long-baseline accelerator experiments DUNE and T2HK. We find that an accurate determination of the currently least well measured parameters, namely the atmospheric and solar angles and the CP phase δ, provide crucial independent tests of the model. For θ 13 and the two mass-squared differences, however, the model's exclusion requires a combination of measurements coming from a varied experimental programme. Our results show that the synergy and complementarity of future experiments will play a vital role in efficiently discriminating between predictive models of neutrino flavour, and hence, towards advancing our understanding of neutrino oscillations in the context of the flavour puzzle of the Standard Model.

Comprehensive renormalization group analysis of the littlest seesaw model

“…For example, the littlest seesaw (LS) model consists of two righthanded (RH) neutrino singlets N atm R and N sol R together with a tightly constrained Dirac neutrino Yukawa coupling matrix, leading to a highly predictive scheme [22][23][24][25][26][27]. Since the mass ordering of the RH neutrinos as well as the particular choice of the Dirac neutrino Yukawa coupling matrix can vary, it turns out that there are four distinct LS cases, namely cases A-D, as defined later.…”

An S4 × SU(5) SUSY GUT of flavour in 6d

“…We generate the S 4 symmetry from the orbifold, by a generalisation of the mechanism previously used to obtain A 4 . The motivation for considering the group S 4 is that it is better suited to yielding the so called "CSD3" vacuum alignments [35,36] that we desire, leading to the highly predictive Littlest Seesaw structure [37,38], with 3 input parameters predicting 9 observables in the neutrino sector, which agrees perfectly with current neutrino oscillation measurements [39][40][41]. With the help of the orbifold conditions, we shall show that obtaining this alignment can be much simpler than just using a 4d superpotential.…”

“…In the CSD3 alignment, a good fit for all the neutrino data requires this phase to be very close to η ≈ 2π/3, so here we assume this value [39][40][41].…”

A natural S 4 × SO(10) model of flavour

“…In the limit µ 3 = m 1 = 0, this effectively reduces to a two RH neutrino model, with only two real parameters µ 1 and µ 2 . The resulting model is known as Littlest Seesaw (LS) [29][30][31]. 1 It is remarkable that, with µ 1,2 fitted to the neutrino masses, the entire PMNS matrix is then uniquely determined with no free parameters, giving predictions for mixing angles and the CP phase in agreement with current data.…”

“…A particularly successful scheme is known as CSD3 [24,[28][29][30][31] where the neutrino Yukawa matrix is controlled by particular vacuum expectation values (VEVs) of three triplet flavon fields, φ i , as discussed later. The flavon vacuum alignments are fixed by a superpotential which we do not specify here, but may be enforced by an S 4 symmetry, as discussed in [30].…”