Green's function Monte Carlo calculations of the electromagnetic and neutral-weak response functions in the quasi-elastic sector

A quantitative understanding of neutrino-nucleus interactions is demanded to achieve precise measurement of neutrino oscillations, and hence the determination of their masses. In addition, next generation detectors will be able to detect supernovae neutrinos, which are likely to shed some light on the open questions on the dynamics of core collapse. In this context, it is crucial to account for two-body meson-exchange currents along within realistic models of nuclear dynamics. We summarize our progresses towards the construction of a consistent framework, based on the Green's function Monte Carlo method, that can be exploited to accurately describe neutrino interactions with atomic nuclei in the quasi-elastic sector.Comment: 8 pages, 3 figures. arXiv admin note: substantial text overlap with arXiv:1509.0045

Contribution of two particle-two hole final states to the nuclear response

The excitation of two particle-two hole final states in neutrino-nucleus scattering has been advocated by many authors as the source of the excess cross section observed by the MiniBooNE Collaboration in the quasi elastic sector. We analyse the mechanisms leading to the appearance of these final states, and illustrate their significance through the results of accurate calculations of the nuclear electromagnetic response in the transverse channel. A novel approach, allowing for a consistent treatment of the amplitudes involving one- and two-nucleon currents in the kinematical region in which the non relativistic approximation breaks down, is outlined.Comment: Physical Review C, in press. arXiv admin note: text overlap with arXiv:1312.121

Muon capture in nuclei: an ab initio approach based on quantum Monte Carlo methods

An ab initio quantum Monte Carlo method is introduced for calculating total rates of muon weak capture in light nuclei with mass number $A \leq 12$. As a first application of the method, we perform a calculation of the rate in $^4$He in a dynamical framework based on realistic two- and three-nucleon interactions and realistic nuclear charge-changing weak currents. The currents include one- and two-body terms induced by $\pi$- and $\rho$-meson exchange, and $N$-to-$\Delta$ excitation, and are constrained to reproduce the empirical value of the Gamow-Teller matrix element in tritium. We investigate the sensitivity of theoretical predictions to current parametrizations of the nucleon axial and induced pseudoscalar form factors as well as to two-body contributions in the weak currents. The large uncertainties in the measured values obtained from bubble-chamber experiments (carried out over 50 years ago) prevent us from drawing any definite conclusions.Comment: 6 pages, 1 figur

The Asypow S(plus) Library for Asymptotic Power Calculations

The asypow library consists of routines written in the S language that calculate power and related quantities utilizing asymptotic methods. A paper describing these methods with examples is in preparation [1]. Two methods are available. The likelihood ratio method (LR) is described in [2]. Another general method appears recently in [3]; and we designate it the SMO method after the initials of the authors.