arXiv subjects

J. T. Penedo

Publications and source records attributed to J. T. Penedo.

26 records · Page 2Linked to original sources

arXiv2019

Modular $S_4$ Models of Lepton Masses and Mixing

We investigate models of charged lepton and neutrino masses and lepton mixing based on broken modular symmetry. The matter fields in these models are assumed to transform in irreducible representations of the finite modular group $Γ_4 \simeq S_4$. We analyse the minimal scenario in which the only source of symmetry breaking is the vacuum expectation value of the modulus field. In this scenario there is no need to introduce flavon fields. Using the basis for the lowest weight modular forms found earlier, we build minimal phenomenologically viable models in which the neutrino masses are generated via the type I seesaw mechanism. While successfully accommodating charged lepton masses, neutrino mixing angles and mass-squared differences, these models predict the values of the lightest neutrino mass (i.e., the absolute neutrino mass scale), of the Dirac and Majorana CP violation (CPV) phases, as well as specific correlations between the values of the atmospheric neutrino mixing parameter $\sin^2θ_{23}$ and i) the Dirac CPV phase $δ$, ii) the sum of the neutrino masses, and iii) the effective Majorana mass in neutrinoless double beta decay. We consider also the case of residual symmetries $\mathbb{Z}^{ST}_3$ and $\mathbb{Z}^S_2$ respectively in the charged lepton and neutrino sectors, corresponding to specific vacuum expectation values of the modulus.

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arXiv2018

Lepton Masses and Mixing from Modular $S_4$ Symmetry

We study models of lepton masses and mixing based on broken modular invariance. We consider invariance under the finite modular group $Γ_4 \simeq S_4$ and focus on the minimal scenario where the expectation value of the modulus is the only source of symmetry breaking, such that no flavons need to be introduced. After constructing a basis for the lowest weight modular forms, we build two minimal models, one of which successfully accommodates charged lepton masses and neutrino oscillation data, while predicting the values of the Dirac and Majorana CPV phases.

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arXiv2018

The $10^{-3}$ eV Frontier in Neutrinoless Double Beta Decay

The observation of neutrinoless double beta decay would allow to establish lepton number violation and the Majorana nature of neutrinos. The rate of this process in the case of 3-neutrino mixing is controlled by the neutrinoless double beta decay effective Majorana mass $|\langle m \rangle|$. For a neutrino mass spectrum with normal ordering, which is favoured over the spectrum with inverted ordering by recent global fits, $|\langle m \rangle|$ can be significantly suppressed. Taking into account updated data on the neutrino oscillation parameters, we investigate the conditions under which $|\langle m \rangle|$ in the case of spectrum with normal ordering exceeds $10^{-3}~(5\times 10^{-3})$ eV: $|\langle m \rangle|_\text{NO} > 10^{-3}~(5\times 10^{-3})$ eV. We analyse first the generic case with unconstrained leptonic CP violation Majorana phases. We show, in particular, that if the sum of neutrino masses is found to satisfy $Σ> 0.10$ eV, then $|\langle m \rangle|_\text{NO} > 5\times 10^{-3}$ eV for any values of the Majorana phases. We consider also cases where the values for these phases are either CP conserving or are in line with predictive schemes combining flavour and generalised CP symmetries.

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arXiv2018

Low-Scale Seesaw and the CP Violation in Neutrino Oscillations

We consider a version of the low-scale type I seesaw mechanism for generating small neutrino masses, as an alternative to the standard seesaw scenario. It involves two right-handed (RH) neutrinos $ν_{1R}$ and $ν_{2R}$ having a Majorana mass term with mass $M$, which conserves the lepton charge $L$. The RH neutrino $ν_{2R}$ has lepton-charge conserving Yukawa couplings $g_{\ell 2}$ to the lepton and Higgs doublet fields, while small lepton-charge breaking effects are assumed to induce tiny lepton-charge violating Yukawa couplings $g_{\ell 1}$ for $ν_{1R}$, $l=e,μ,τ$. In this approach the smallness of neutrino masses is related to the smallness of the Yukawa coupling of $ν_{1R}$ and not to the large value of $M$: the RH neutrinos can have masses in the few GeV to a few TeV range. The Yukawa couplings $|g_{\ell 2}|$ can be much larger than $|g_{\ell 1}|$, of the order $|g_{\ell 2}| \sim 10^{-4} - 10^{-2}$, leading to interesting low-energy phenomenology. We consider a specific realisation of this scenario within the Froggatt-Nielsen approach to fermion masses. In this model the Dirac CP violation phase $δ$ is predicted to have approximately one of the values $δ\simeq π/4,\, 3π/4$, or $5π/4,\, 7π/4$, or to lie in a narrow interval around one of these values. The low-energy phenomenology of the considered low-scale seesaw scenario of neutrino mass generation is also briefly discussed.

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arXiv2018

Neutrino Mixing and Leptonic CP Violation from $S_4$ and Generalised CP Symmetries

We consider a class of models of neutrino mixing with $S_4$ flavour symmetry and generalised CP symmetry, broken to $Z_2$ and $Z_2 \times {\rm CP}$ residual symmetries in the charged lepton and neutrino sectors, respectively. In this scheme, and up to discrete ambiguities, the neutrino mixing matrix is determined by two angles and one phase. We classify the phenomenologically viable mixing patterns, deriving predictions for the Dirac and Majorana CPV phases and for the effective Majorana mass in neutrinoless double beta decay.

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arXiv2017

Neutrino Mixing and Leptonic CP Violation from $S_4$ Flavour and Generalised CP Symmetries

We consider a class of models of neutrino mixing with $S_4$ lepton flavour symmetry combined with a generalised CP symmetry, which are broken to residual $Z_2$ and $Z_2 \times H^ν_{\rm CP}$ symmetries in the charged lepton and neutrino sectors, respectively, $H^ν_{\rm CP}$ being a remnant CP symmetry of the neutrino Majorana mass term. In this set-up the neutrino mixing angles and CP violation (CPV) phases of the neutrino mixing matrix depend on three real parameters - two angles and a phase. We classify all phenomenologically viable mixing patterns and derive predictions for the Dirac and Majorana CPV phases. Further, we use the results obtained on the neutrino mixing angles and leptonic CPV phases to derive predictions for the effective Majorana mass in neutrinoless double beta decay.

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arXiv2015

Radiative charged-lepton masses with more than one Higgs doublet

We discuss how charged-lepton masses can be induced in multi-Higgs doublet models (NHDMs) through renormalization group running of Yukawa couplings. Examples of electron and muon mass generation are presented within scenarios with two- and three-Higgs-doublet models. We also show that quantum corrections to the Yukawa couplings can be naturally of the same order as the tree-level values. The impact of such corrections in NHDMs with right-handed neutrinos is briefly commented.

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arXiv2014

Radiative charged-lepton mass generation in multi-Higgs doublet models

We show that charged-lepton masses can be radiatively induced in multi-Higgs doublet models (NHDMs) through the renormalization group running of Yukawa couplings from high to low energies. Some extreme examples of electron and muon mass generation are discussed in the context of two and three Higgs doublet models. It is also shown that quantum corrections to the Yukawa couplings can be naturally of the same order as the tree-level values. We also comment on the implications of considering extensions of NHDMs in which right-handed neutrinos are added.

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