Implications of finite one-loop corrections for seesaw neutrino masses

In the standard seesaw model, finite corrections to the neutrino mass matrix arise from one-loop self-energy diagrams mediated by a heavy neutrino. We discuss the impact that these corrections may have on the different low-energy neutrino observables paying special attention to their dependence with the seesaw model parameters. It is shown that sizable deviations from the tri-bimaximal mixing pattern can be obtained when these corrections are taken into account.Comment: 4 pages, 3 figures. Prepared for the proceedings of the 12th International Conference on Topics in Astroparticle and Underground Physics (TAUP 2011), Munich, Germany, 5-9 September 201

The Matrix Product Approach to Quantum Spin Ladders

We present a manifestly rotational invariant formulation of the matrix product method valid for spin chains and ladders. We apply it to 2 legged spin ladders with spins 1/2, 1 and 3/2 and different magnetic structures labelled by the exchange coupling constants, which can be ferromagnetic or antiferromagnetic along the legs and the rungs of the ladder We compute ground state energy densities, correlation lengths and string order parameters. We present numerical evidence of the duality properties of the 3 different non ferromagnetic spin 1/2 ladders. We show that the long range topological order characteristic of isolated spin 1 chains is broken by the interchain coupling. The string order correlation function decays exponentially with a finite correlation length that we compute. A physical picture of the spin 1 ladder is given in terms of a collection of resonating spin 1 chains. Finally for ladders with spin equal or greater than 3/2 we define a class of AKLT states whose matrix product coefficients are given by 9-j symbols.Comment: REVTEX file, 16 pages, 12 figures, 6 Table

Experimental tests for the Babu-Zee two-loop model of Majorana neutrino masses

The smallness of the observed neutrino masses might have a radiative origin. Here we revisit a specific two-loop model of neutrino mass, independently proposed by Babu and Zee. We point out that current constraints from neutrino data can be used to derive strict lower limits on the branching ratio of flavour changing charged lepton decays, such as $\mu \to e \gamma$. Non-observation of Br($\mu \to e \gamma$) at the level of $10^{-13}$ would rule out singly charged scalar masses smaller than 590 GeV (5.04 TeV) in case of normal (inverse) neutrino mass hierarchy. Conversely, decay branching ratios of the non-standard scalars of the model can be fixed by the measured neutrino angles (and mass scale). Thus, if the scalars of the model are light enough to be produced at the LHC or ILC, measuring their decay properties would serve as a direct test of the model as the origin of neutrino masses.Comment: 14 pages, 16 figure