Abstract
We show that the four high-energy Littlest Seesaw parameters in the flavour basis, namely two real Yukawa couplings plus the two right-handed neutrino masses, can be determined by an excellent fit to the seven currently constrained observables of low-energy neutrino data and leptogenesis. Taking into account renormalisation group corrections, we estimate χ2 ≃ 1.5-2.6 for the three d.o.f., depending on the high-energy scale and the type of non-supersymmetric Littlest Seesaw model. We extract allowed ranges of neutrino parameters from our fit data, including the approximate mu-tau symmetric predictions θ23 = 45° ± 1° and δ = −90° ± 5°, which, together with a normal mass ordering with m1 = 0, will enable Littlest Seesaw models to be tested in future neutrino experiments.
Highlights
We show that the four high-energy Littlest Seesaw parameters in the flavour basis, namely two real Yukawa couplings plus the two right-handed neutrino masses, can be determined by an excellent fit to the seven currently constrained observables of low-energy neutrino data and leptogenesis
We extract allowed ranges of neutrino parameters from our fit data, including the approximate mu-tau symmetric predictions θ23 = 45◦ ± 1◦ and δ = −90◦ ± 5◦, which, together with a normal mass ordering with m1 = 0, will enable Littlest Seesaw (LS) models to be tested in future neutrino experiments
From these benchmark points we can conclude that both cases of the LS give excellent fits to the experimental data, and that the χ2/d.o.f. for each benchmark point are too close to degeneracy to say that any one is preferred over the others, only that they all give a good fit to data
Summary
If the right-handed neutrino masses are above the TeV scale, as generally expected by leptogenesis, it is difficult to test directly This motivates the study of minimal seesaw models involving fewer input parameters. In this paper we show that the four high-energy LS parameters in the flavour basis — two real Yukawa couplings a, b plus the two right-handed neutrino masses — can be determined by an excellent fit to the seven currently constrained observables of lowenergy neutrino data and leptogenesis. We extract allowed ranges of neutrino parameters from our fit data, including the approximate mu-tau symmetric predictions θ23 = 45◦ ± 1◦ and δ = −90◦ ± 5◦, which, together with a normal mass ordering with m1 = 0, will enable LS models to be tested in future neutrino experiments. Initial results from NOνA excluded maximal atmospheric mixing and were in tension with the model, and future updates from this experiment may provide an early test of the LS
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