Inelastic Neutrino-Nucleus Interactions within the Spectral Function Formalism.

We report the results of a study of neutrino-carbon interactions at beam energies ranging between a few hundred MeV's and a few tens of GeVs carried out within the framework of the impulse approximation using a realistic spectral function. The contributions of quasielastic scattering, resonance production, and deep inelastic scattering-consistently obtained, for the first time, from a model based on a realistic description of the nuclear ground state-are compared and analyzed.

Unified Description of Electron-Nucleus Scattering within the Spectral Function Formalism.

The formalism based on factorization and nuclear spectral functions has been generalized to treat transition matrix elements involving two-nucleon currents, whose contribution to the nuclear electromagnetic response in the transverse channel is known to be significant. We report the results of calculations of the inclusive electron-carbon cross section, showing that the inclusion of processes involving two-nucleon currents appreciably improves the agreement between theory and data in the dip region, between the quasielastic and Δ-production peaks. The relation to approaches based on the independent particle of the nucleus and the implications for the analysis of flux-integrated neutrino-nucleus cross sections are discussed.

Analysis of γ-ray production in neutral-current neutrino-oxygen interactions at energies above 200 MeV.

It has long been recognized that the observation of γ rays originating from nuclear deexcitation can be exploited to identify neutral-current neutrino-nucleus interactions in water-Cherenkov detectors. We report the results of a calculation of the neutrino- and antineutrino-induced γ-ray production cross section for the oxygen target. Our analysis is focused on the kinematical region of neutrino energy larger than ∼200 MeV, in which a single-nucleon knockout is known to be the dominant reaction mechanism. The numerical results have been obtained using for the first time a realistic model of the target spectral function, extensively tested against electron-nucleus scattering data. We find that at a neutrino energy of 600 MeV the fraction of neutral-current interactions leading to emission of γ rays of energy larger than 6 MeV is ∼41%, and that the contribution of the p_{3/2} state is overwhelming.

Electroweak nuclear response in the quasielastic regime.

The availability of the double-differential charged-current neutrino cross section, measured by the MiniBooNE Collaboration by using a carbon target, allows for a systematic comparison of nuclear effects in quasielastic electron and neutrino scattering. The results of our study, based on the impulse approximation scheme and a state-of-the-art model of the nuclear spectral functions, suggest that the electron cross section and the flux averaged neutrino cross sections, corresponding to the same target and comparable kinematical conditions, cannot be described within the same theoretical approach using the value of the nucleon axial mass obtained from deuterium measurements. We analyze the assumptions underlying the treatment of electron-scattering data and argue that the description of neutrino data will require a new paradigm, suitable for application to processes in which the lepton kinematics is not fully determined.

Shear viscosity of neutron matter from realistic nucleon-nucleon interactions.

The calculation of transport properties of Fermi liquids, based on the formalism developed by Abrikosov and Khalatnikov, requires the knowledge of the probability of collisions between quasiparticles in the vicinity of the Fermi surface. We have carried out a study of the shear viscosity of pure neutron matter, whose value plays a pivotal role in determining the stability of rotating neutron stars, in which these processes are described using a state-of-the-art nucleon-nucleon potential. Medium modifications of the scattering cross section have been consistently taken into account through an effective interaction obtained from the matrix elements of the bare interaction between correlated states. Medium effects produce a large increase of the viscosity at densities rho > or approximately0.1 fm;{-3}.

Estimates of the uncertainties associated with models of the nucleon structure functions in the Delta production region.

Theoretical studies of the inclusive electron-nucleus cross section at beam energies up to a few GeV show that, while the region of the quasielastic peak is understood at the quantitative level, the data in the Delta production region are sizably underestimated. We analyze the uncertainty associated with the description of the nucleon structure functions W1 and W2 and its impact on the nuclear cross section. The results of our study suggest that the failure to reproduce the data is to be mostly ascribed to the poor knowledge of the neutron structure functions at low Q2.