Systematic classification of two-loop realizations of the Weinberg operator

We systematically analyze the d = 5 Weinberg operator at 2-loop order. Using a diagrammatic approach, we identify two different interesting categories of neutrino mass models: (i) Genuine 2-loop models for which both, tree-level and 1-loop contributions, are guaranteed to be absent. And (ii) finite 2-loop diagrams, which correspond to the 1-loop generation of some particular vertex appearing in a given 1-loop neutrino mass model, thus being effectively 2-loop. From the large list of all possible 2-loop diagrams, the vast majority are infinite corrections to lower order neutrino mass models and only a moderately small number of diagrams fall into these two interesting classes. Moreover, all diagrams in class (i) are just variations of three basic diagrams, with examples discussed in the literature before. Similarly, we also show that class (ii) diagrams consists of only variations of these three plus two more basic diagrams. Finally, we show how our results can be consistently and readily used in order to construct two-loop neutrino mass models

Linear Collider Test of a Neutrinoless Double Beta Decay Mechanism in left-right Symmetric Theories

There are various diagrams leading to neutrinoless double beta decay in left-right symmetric theories based on the gauge group SU(2)_L x SU(2)_R. All can in principle be tested at a linear collider running in electron-electron mode. We argue that the so-called lambda-diagram is the most promising one. Taking the current limit on this diagram from double beta decay experiments, we evaluate the relevant cross section e e to W_L W_R, where W_L is the Standard Model W-boson and W_R the one from SU(2)_R. It is observable if the life-time of double beta decay and the mass of the W_R are close to current limits. Beam polarization effects and the high-energy behaviour of the cross section are also analyzed.Comment: 17 pages, 6 figures. v2: minor changes, references added, to be published in EPJ

Invisible decays of ultra-high energy neutrinos

Gamma-ray bursts (GRBs) are expected to provide a source of ultra high energy cosmic rays, accompanied with potentially detectable neutrinos at neutrino telescopes. Recently, IceCube has set an upper bound on this neutrino flux well below theoretical expectation. We investigate whether this mismatch between expectation and observation can be due to neutrino decay. We demonstrate the phenomenological consistency and theoretical plausibility of the neutrino decay hypothesis. A potential implication is the observability of majoron-emitting neutrinoless double beta decay.Work supported by MINECO grants FPA2011-22975 and MULTIDARK Consolider CSD2009-00064, by Prometeo/2009/091 (Gen. Valenciana), and by EPLANET. L. D. is supported by JAE Predoctoral fellowship. O. G. M. was supported by CONACyT grant 132197.Peer reviewedPeer Reviewe