[en] Neutron-induced charged-particle reactions are ubiquitous in nature and their understanding is needed for a variety of applications, ranging from fundamental Nuclear Physics to energy production and medical applications. Motivated by recent measurements at CERN n-TOF facility, we have performed calculations of the charge-exchange 12C(n,p)12B reaction within the ab initio no-core-shell model with continuum (NCSMC). The NCSMC method [1,2] can describe both bound and unbound states in light nuclei in a unified way. With chiral two- and three-nucleon interactions as the only input, we can predict structure and dynamics of light nuclei and, by comparing to available experimental data, test the quality of chiral nuclear forces.

[en] We derive expressions for cluster overlap integrals or channel cluster form factors for ab initio no-core shell model (NCSM) wave functions. These are used to obtain the spectroscopic factors and can serve as a starting point for the description of low-energy nuclear reactions. We consider the composite system and the target nucleus to be described in the Slater determinant (SD) harmonic oscillator (HO) basis while the projectile eigenstate to be expanded in the Jacobi coordinate HO basis. This is the most practical case. The spurious center of mass components present in the SD bases are removed exactly. The calculated cluster overlap integrals are translationally invariant. As an illustration, we present results of cluster form factor calculations for <⁵He vertical bar⁴He+n>, <⁵He vertical bar³H+d>, <⁶Li vertical bar⁴He+d>, <⁶Be vertical bar³He+³He>, <⁷Li vertical bar⁴He+³H>, <⁷Li vertical bar⁶Li+n>, <⁸Be vertical bar⁶Li+d>, <⁸Be vertical bar⁷Li+p>, <⁹Li vertical bar⁸Li+n>, and <¹³C vertical bar¹²C+n>, with all the nuclei described by multi-(ℎ/2π)Ω NCSM wave functions

[en] Based on an effective nucleon-nucleon interaction, a microscopic cluster model of the nucleus-nucleus bremsstrahlung, including implicitly a part of the effects of meson-exchange currents via an extension of the Siegert theorem is applied to the α + p and α + n systems. The contributions of the E1 and E2 transitions to the bremsstrahlung cross sections are evaluated and their relative importance for the mirror systems α + p and α + n is compared. Another approach based on realistic two- and three-nucleon interactions and the No-Core Shell Model/Resonating-Group Method is also investigated. Some preliminary results for the α + p bremsstrahlung are displayed. (author)

[en] Translationally invariant nuclear density is derived from the shell model one-body densities by removing their spurious 0(ℎ/2π)Ω center-of-mass (c.m.) motion component. This paves the way to utilizing the ab initio no-core shell-model (NCSM) nuclear structure in folding approaches to optical potentials. As an illustration, the ⁶He diagonal and transitional densities are calculated from the NCSM wave functions obtained using the CD-Bonn nucleon-nucleon potential in the 10(ℎ/2π)Ω basis space. A particularly significant impact of the exact removal of the spurious c.m. motion is found for the spin-orbit part of the optical potential proportional to the derivative of the nuclear density

[en] One major ambition of ab initio nuclear theory is the description of nuclear-structure and reaction observables on equal footing. This is accomplished by combining the no-core shell model (NCSM) with the resonating-group method (RGM) to a unified ab initio approach to bound and continuum states, which is developed further to the no-core shell model with continuum (NCSMC). We present the formal developments to include three-nucleon interactions in both the NCSM/RGM and NCSMC formalism. This provides the possibility to assess the predictive power of chiral two- and three-nucleon forces in the variety of scattering observables. We study three-nucleon force effects on phase-shifts, cross sections and analyzing powers in first ab-initio studies of nucleon-⁴He scattering with chiral two- and three-nucleon forces. Finally, we focus on heavier target nuclei using the NCSMC, e.g., in neutron-⁸Be scattering and study the impact of the continuum on the spectrum of ⁹Be.

[en] We develop a new ab initio many-body approach capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group method with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters. This approach preserves translational symmetry and Pauli principle. We present phase shifts for neutron scattering on ³H, ⁴He, and ¹⁰Be and proton scattering on ^3,4He, using realistic nucleon-nucleon potentials. Our A=4 scattering results are compared to earlier ab initio calculations. We demonstrate that a proper treatment of the coupling to the n-¹⁰Be continuum is successful in explaining the parity-inverted ground state in ¹¹Be

[en] We develop a new ab initio many-body approach capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group method with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters. This approach preserves translational symmetry and the Pauli principle. We outline technical details and present phase-shift results for neutron scattering on ³H, ⁴He, and ¹⁰Be and proton scattering on ^3,4He, using realistic nucleon-nucleon (NN) potentials. Our A=4 scattering results are compared to earlier ab initio calculations. We find that the CD-Bonn NN potential in particular provides an excellent description of nucleon-⁴HeS-wave phase shifts. In contrast, the experimental nucleon-⁴HeP-wave phase shifts are not well reproduced by any NN potential we use. We demonstrate that a proper treatment of the coupling to the n-¹⁰Be continuum is successful in explaining the parity-inverted ground state in ¹¹Be.

[en] We report on an ab initio calculation of the ⁴He total photo-absorption cross section using two- and three-nucleon interactions based upon chiral effective field theory. The microscopic treatment of the continuum problem is achieved using the Lorentz integral transform method, applied within the no-core shell model approach

[en] The ab initio no-core shell model (NCSM) is extended to include a realistic three-body interaction in calculations for p-shell nuclei. The NCSM formalism is reviewed and new features needed in calculations with three-body forces are discussed in detail. We present results of first applications to ^6,7Li, ⁶He, ^7,8,10Be, ^10,11,12B, ¹²N, and ^10,11,12,13C using the Argonne V8^' nucleon-nucleon (NN) potential and the Tucson-Melbourne TM^'(99) three-nucleon interaction (TNI). In addition to increasing the total binding energy, we observe a substantial sensitivity in the low-lying spectra to the presence of the realistic three-body force and an overall improvement in level ordering and level spacing in comparison to experiment. The greatest sensitivity occurs for states where the spin-orbit interaction strength is known to play a role. In particular, with the TNI we obtain the correct ground-state spin for ^10,11,12B and ¹²N, contrary to calculations with NN potentials only

[en] Shell-model calculations have been limited by the size of the model space and by the need for an effective interaction within the model space. To simplify the interaction, we propose working in a large model space, in which all A nucleons of a given nucleus are active for a complete N(ℎ/2π)Ω basis space and a large value for N. We call this procedure the large-basis, no-core shell model. We briefly describe this approach and discuss some of our results for A(less-or-similar sign)12