7 research outputs found
Low-Scale Leptogenesis with Low-Energy Dirac CP-Violation
We study the freeze-in scenario of leptogenesis via oscillations within the
type-I seesaw model with two quasi-degenerate heavy Majorana neutrinos
having masses ,
, focusing on the role of the CP-violation provided by the
Dirac phase of the Pontecorvo-Maki-Nakagawa-Sakata lepton mixing
matrix. We find that viable leptogenesis can be due solely to CP-violating
values of and that the total mixing squared
needed is within the reach of future
experiments, parameterising the coupling to the charged lepton
. Furthermore, the required parameter space differs from
that associated with additional Casas-Ibarra sources of CP-violation. Future
determination of , and/or the ratios
would provide a critical test of the
considered scenario.Comment: 7 pages, 2 figure
Generalised Geometrical CP Violation in a T\u27 Lepton Flavour Model
We analyse the interplay of generalised CP transformations and the non-Abelian discrete group T ′ and use the semi-direct product G f = T ′ ⋊ H CP , as family symmetry acting in the lepton sector. The family symmetry is shown to be spontaneously broken in a geometrical manner. In the resulting flavour model, naturally small Majorana neutrino masses for the light active neutrinos are obtained through the type I see-saw mechanism. The known masses of the charged leptons, lepton mixing angles and the two neutrino mass squared differences are reproduced by the model with a good accuracy. The model allows for two neutrino mass spectra with normal ordering (NO) and one with inverted ordering (IO). For each of the three spectra the absolute scale of neutrino masses is predicted with relatively small uncertainty. The value of the Dirac CP violation (CPV) phase δ in the lepton mixing matrix is predicted to be δ = π/ 2 or 3 π/ 2. Thus, the CP violating effects in neutrino oscillations are predicted to be maximal (given the values of the neutrino mixing angles) and experimentally observable. We present also predictions for the sum of the neutrino masses, for the Majorana CPV phases and for the effective Majorana mass in neutrinoless double beta decay. The predictions of the model can be tested in a variety of ongoing and future planned neutrino experiments
Large U_{e3} and Tri-bimaximal Mixing
We investigate in a model-independent way to what extent one can perturb
tri-bimaximal mixing in order to generate a sizable value of |U_{e3}|, while at
the same time keeping solar neutrino mixing near its measured value, which is
close to sin^2 theta_{12} = 1/3. Three straightforward breaking mechanisms to
generate |U_{e3}| of about 0.1 are considered. For charged lepton corrections,
the suppression of a sizable contribution to sin^2 theta_{12} can be achieved
if CP violation in neutrino oscillations is almost maximal. Generation of the
indicated value of |U_{e3}| of about 0.1 through renormalization group
corrections requires the neutrinos to be quasi-degenerate in mass. The
consistency with the allowed range of sin^2 theta_{12} together with large
running of |U_{e3}| forces one of the Majorana phases to be close to pi. This
implies large cancellations in the effective Majorana mass governing
neutrino-less double beta, constraining it to lie near its minimum allowed
value of m_0 cos 2 theta_{12}, where m_0 is greater than about 0.1 eV. Finally,
explicit breaking of the neutrino mass matrix in the inverted hierarchical and
quasi-degenerate neutrino mass spectrum cases is similarly correlated with the
effective Majorana mass, although to a lesser extent. The implied values for
the atmospheric neutrino mixing angle theta_{23} are given in all cases.Comment: 20 pages, 9 figure
Leptogenesis in an SU(5) x A5 golden ratio flavour model
In this paper we discuss a minor modification of a previous SU(5) x A5 flavour model which exhibits at leading order golden ratio mixing and sum rules for the heavy and the light neutrino masses. Although this model could predict all mixing angles well it fails in generating a sufficient large baryon asymmetry via the leptogenesis mechanism. We repair this deficit here, discuss model building aspects and give analytical estimates for the generated baryon asymmetry before we perform a numerical parameter scan. Our setup has only a few parameters in the lepton sector. This leads to specific constraints and correlations between the neutrino observables. For instance, we find that in the model considered only the neutrino mass spectrum with normal mass ordering and values of the lightest neutrino mass in the interval 10-18 meV are compatible with the current data on the neutrino oscillation parameters. With the introduction of only one NLO operator, the model can accommodate successfully simultaneously even at 1\u3c3 level the current data on neutrino masses, on neutrino mixing and the observed value of the baryon asymmetry
Sizeable \theta_13 from the Charged Lepton Sector in SU(5), (Tri-)Bimaximal Neutrino Mixing and Dirac CP Violation
The recent results from T2K and MINOS experiments point towards a relatively
large value of the reactor angle \theta_13 in the lepton sector. In this paper
we show how a large \theta_13 can arise from the charged lepton sector alone in
the context of an SU(5) GUT. In such a scenario (tri-)bimaximal mixing in the
neutrino sector is still a viable possibility. We also analyse the general
implications of the considered scenario for the searches of CP violation in
neutrino oscillations.Comment: 19 pages, 3 figures; version to be published in JHE