The $N to Delta$ weak vertex provides an important contribution to the one pion production in neutrino-nucleon and neutrino-nucleus scattering for $pi N$ invariant masses below 1.4 GeV. Beyond its interest as a tool in neutrino detection and their ba
ckground analyses, one pion production in neutrino-nucleon scattering is useful to test predictions based on the quark model and other internal symmetries of strong interactions. Here we try to establish a connection between two commonly used parametrizations of the weak $N to Delta$ vertex and form factors (FF) and we study their effects on the determination of the axial coupling $C_5^A(0)$, the common normalization of the axial FF, which is predicted to hold 1.2 by using the PCAC hypothesis. Predictions for the $ u_{mu} p to mu^- ppi^+$ total cross sections within the two approaches, which include the resonant $Delta^{++}$ and other background contributions in a coherent way, are compared to experimental data.
The neutrino-nucleon --> lepton pion QE reaction on the A-target is used as a signal event or/and to reconstruct the neutrino energy, using two-body kinematics. Competition of another processes could lead to misidentification of the arriving neutrino
s, being important the fake events coming from the CC1-pion background. A precise knowledge of cross sections is a prerequisite in order to make simulations in event generators to substract the fake ones from the QE countings, and in this contribution we analyze the different nuclear effects on the CC1-pion channel. Our calculations also can be extended for the NC case.
The study of neutrinoless double beta decays of nuclei and hyperons require the calculation of hadronic matrix elements of local four-quark operators that change the total charge by two units Delta Q=2 . Using a low energy effective Lagrangian that i
nduces these transitions, we compute these hadronic matrix elements in the framework of the MIT bag model. As an illustrative example we evaluate the amplitude and transition rate of Sigma- -> p e- e-, a decay process that violates lepton number by two units (Delta L=2). The relevant matrix element is evaluated without assuming the usual factorization approximation of the four-quark operators and the results obtained in both approaches are compared.
The quasielastic charged current (CCQE) $ u_e n rightarrow e^- p$ scattering is the dominant mechanism to detect appearance of a $ u_e$ in an almost $ u_mu$ flux at the 1 GeV scale. Actual experiments show a precision below 1% and between less known
background contributions, but necessary to constraint the event excess, we have the radiative corrections. A consistent model recently developed for the simultaneous description of elastic and radiative $pi N$ scattering, pion-photoproduction and single pion production processes, both for charged and neutral current neutrino-nucleon scattering, is extended for the evaluation of the radiative $ u_l Nrightarrow u_l N gamma$ cross section. Our results are similar to a previous (but inconsistent) theoretical evaluation in the low energy region, and show an increment in the upper region where the $Delta$ resonance becomes relevant.
We compute the rates of semileptonic B_A to B_Bl^-l^- (l=e or mu) hyperon transitions in a model where intermediate states involve loops of baryons and a Majorana neutrino. These rates turn out to be well below present experimental bounds and other t
heoretical estimates. From the experimental upper limit on the Xi^- to pmu^-mu^- decay, we derive the bound <m_{mu mu}> < 22 TeV for the effective Majorana mass of the muon neutrino. Also, an estimate of background contributions for these decays due to the allowed B_A to B_Bl^-l^-bar{ u}bar{ u} decays are provided.
