arXiv subjects

Ricardo Cepedello

Publications and source records attributed to Ricardo Cepedello.

21 records · Page 2Linked to original sources

arXiv2019

Systematic classification of three-loop realizations of the Weinberg operator

We study systematically the decomposition of the Weinberg operator at three-loop order. There are more than four thousand connected topologies. However, the vast majority of these are infinite corrections to lower order neutrino mass diagrams and only a very small percentage yields models for which the three-loop diagrams are the leading order contribution to the neutrino mass matrix. We identify 73 topologies that can lead to genuine three-loop models with fermions and scalars, i.e. models for which lower order diagrams are automatically absent without the need to invoke additional symmetries. The 73 genuine topologies can be divided into two sub-classes: Normal genuine ones (44 cases) and special genuine topologies (29 cases). The latter are a special class of topologies, which can lead to genuine diagrams only for very specific choices of fields. The genuine topologies generate 374 diagrams in the weak basis, which can be reduced to only 30 distinct diagrams in the mass eigenstate basis. We also discuss how all the mass eigenstate diagrams can be described in terms of only five master integrals. We present some concrete models and for two of them we give numerical estimates for the typical size of neutrino masses they generate. Our results can be readily applied to construct other $d=5$ neutrino mass models with three loops.

hep-ph↗

arXiv2019

Neutrinoless Double-$β$ Decay with Nonstandard Majoron Emission

We present a novel mode of neutrinoless double beta decay with emission of a light Majoron-like scalar particle phi. We assume it couples via an effective seven-dimensional operator with a (V+A) lepton current and (V+-A) quark currents leading to a long-range contribution that is unsuppressed by the light neutrino mass. We calculate the total double beta decay rate and determine the fully differential shape for this mode. We find that future double beta decay searches are sensitive to scales of the order Lambda_NP ~ 1 TeV for the effective operator and a light scalar m_phi < 0.2 MeV, based on ordinary double beta decay Majoron searches. The angular and energy distributions can deviate considerably from that of two-neutrino double beta decay, which is the main background. We point out possible ultraviolet completions where such an effective operator can emerge.

hep-ph↗

arXiv2019

Scotogenic Dark Symmetry as a residual subgroup of Standard Model Symmetries

We show that the scotogenic dark symmetry can be obtained as a residual subgroup of the global $U(1)_{B-L}$ symmetry already present in Standard Model. We propose a general framework where the $U(1)_{B-L}$ symmetry is spontaneously broken to an even $\mathcal{Z}_{2n}$ subgroup, setting the general conditions for neutrinos to be Majorana and the dark matter stability in terms of the residual $\mathcal{Z}_{2n}$. Under this general framework, as examples, we build a class of simple models where, in the scotogenic spirit, the dark matter candidate is the lightest particle running inside the neutrino mass loop. The global $U(1)_{B-L}$ symmetry in our framework being anomaly free can also be gauged in a straightforward manner leading to a richer phenomenology.

hep-ph↗