Pseudoscalar Transition Form Factors from Rational Approximants

The $\pi^0$, $\eta$, and $\eta^\prime$ transition form factors in the space-like region are analyzed at low and intermediate energies in a model-independent way through the use of rational approximants. Slope and curvature parameters as well as their values at infinity are extracted from experimental data. These results are suited for constraining hadronic models such as the ones used for the hadronic light-by-light scattering piece of the anomalous magnetic moment of the muon, and for the mixing parameters of the $\eta - \eta^\prime$ system.Comment: Contribution to the 13th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2013), Rome, Italy, 30 September - October 4, 2013. 4 pages, 3 figures. v2: Reference adde

η\eta and η′\eta' transition form factors from Pad\'e approximants

We employ a systematic and model-independent method to extract, from space- and time-like data, the $\eta$ and $\eta'$ transition form factors (TFFs) obtaining the most precise determination for their low-energy parameters and discuss the $\Gamma_{\eta\rightarrow\gamma\gamma}$ impact on them. Using TFF data alone, we also extract the $\eta-\eta'$ mixing parameters, which are compatible to those obtained from more sophisticated and input-demanding procedures.Comment: 4 pages, 2 figures, presented at the 13th International Workshop on Meson Production, Properties and Interaction (MESON 2014); added reference

Heavy neutrino decays at MiniBooNE

It has been proposed that a sterile neutrino \nu_h with m_h \approx 50 MeV and a dominant decay mode (\nu_h -> \nu\gamma) may be the origin of the experimental anomaly observed at LSND. We define a particular model that could also explain the MiniBooNE excess consistently with the data at other neutrino experiments (radiative muon capture at TRIUMF, T2K, or single photon at NOMAD). The key ingredients are (i) its long lifetime (\tau_h\approx 3-7x10^{-9} s), which introduces a 1/E dependence with the event energy, and (ii) its Dirac nature, which implies a photon preferably emitted opposite to the beam direction and further reduces the event energy at MiniBooNE. We show that these neutrinos are mostly produced through electromagnetic interactions with nuclei, and that T2K observations force BR(\nu_h -> \nu_\tau\gamma) \le 0.01 \approx BR(\nu_h -> \nu_\mu\gamma). The scenario implies then the presence of a second sterile neutrino \nu_{h'} which is lighter, longer lived and less mixed with the standard flavors than \nu_h. Since such particle would be copiously produced in air showers through (\nu_h -> \nu_{h'}\gamma) decays, we comment on the possible contamination that its photon-mediated elastic interactions with matter could introduce in dark matter experiments.Comment: 18 pages, typo in Eq.(6) correcte