Sofia Quaglioni

Recent developments in no-core shell-model calculations

We present an overview of recent results and developments of the no-core shell model (NCSM), an ab initio approach to the nuclear many-body problem for light nuclei. In this approach, we start from realistic two-nucleon or two- plus three-nucleon interactions. Many-body calculations are performed using a finite harmonic-oscillator (HO) basis. To facilitate convergence for realistic inter-nucleon interactions that generate strong short-range correlations, we derive effective interactions by unitary transformations that are tailored to the HO basis truncation. For soft realistic interactions, this might not be necessary. If this is the case, the NCSM calculations are variational. In either case, the ab initio NCSM preserves translational invariance of the nuclear many-body problem. In this review, we, in particular, highlight results obtained with the chiral two- plus three-nucleon interactions. We discuss efforts to extend the applicability of the NCSM to heavier nuclei and larger model spaces using importance-truncation schemes and/or use of effective interactions with a core. We outline an extension of the ab initio NCSM to the description of nuclear reactions by the resonating group method technique. A future direction of the approach, the ab initio NCSM with continuum, which will provide a complete description of nuclei as open systems with coupling of bound and continuum states, is given in the concluding part of the review.

Ab initio many-body calculations of n-3H, n-4He, p-3,4He, and n-10Be scattering.

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.

Three-Nucleon Low-Energy Constants from the Consistency of Interactions and Currents in Chiral Effective Field Theory

The chiral low-energy constants c(D) and c(E) are constrained by means of accurate ab initio calculations of the A = 3 binding energies and, for the first time, of the triton beta decay. We demonstrate that these low-energy observables allow a robust determination of the two undetermined constants, a result of the surprising fact that the determination of c(D) depends weakly on the short-range correlations in the wave functions. These two- plus three-nucleon interactions, originating in chiral effective field theory and constrained by properties of the A = 2 system and the present determination of c(D) and c(E), are successful in predicting properties of the A = 3 and 4 systems.

Ab InitioMany-Body Calculations ofn−H3,n−He4,p−He3,4, andn−Be10Scattering

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.

Ab initio many-body calculations of nucleon-nucleus scattering

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 {sup 3}H, {sup 4}He, and {sup 10}Be and proton scattering on {sup 3,4}He, 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-{sup 4}HeS-wave phase shifts. In contrast, the experimental nucleon-{sup 4}HeP-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-{sup 10}Be continuum is successful in explaining the parity-inverted ground state in {sup 11}Be.

Ab initio many-body calculations of the (3)H(d,n)(4)He and (3)He(d,p)(4)He fusion reactions.

We apply the ab initio no-core shell model combined with the resonating-group method approach to calculate the cross sections of the (3)H(d,n)(4)He and (3)He(d,p)(4)He fusion reactions. These are important reactions for the big bang nucleosynthesis and the future of energy generation on Earth. Starting from a selected similarity-transformed chiral nucleon-nucleon interaction that accurately describes two-nucleon data, we performed many-body calculations that predict the S factor of both reactions. Virtual three-body breakup effects are obtained by including excited pseudostates of the deuteron in the calculation. Our results are in satisfactory agreement with experimental data and pave the way for microscopic investigations of polarization and electron-screening effects, of the (3)H(d,γn)(4)He bremsstrahlung and other reactions relevant to fusion research.

Ab initio many-body calculation of the Be7(p,γ)B8 radiative capture

Abstract We apply the ab initio no-core shell model/resonating group method (NCSM/RGM) approach to calculate the cross section of the Be 7 ( p , γ ) B 8 radiative capture. This reaction is important for understanding the solar neutrino flux. Starting from a selected similarity-transformed chiral nucleon–nucleon interaction that accurately describes two-nucleon data, we performed many-body calculations that simultaneously predict both the normalization and the shape of the S-factor. We study the dependence on the number of 7Be eigenstates included in the coupled-channel equations and on the size of the harmonic oscillator basis used for the expansion of the eigenstates and of the localized parts of the integration kernels. Our S-factor result at zero energy is on the lower side of, but consistent with, the latest evaluation.

Ab Initio Many-Body Calculations of Nucleon Scattering on 4He, 7Li, 7Be, 12C and 16O

We combine a recently developed ab initio many-body approach capable of describing simultaneously both bound and scattering states, the ab initio no-core shell model/resonating-group method (NCSM/RGM), with an importance-truncation scheme for the cluster eigenstate basis and demonstrate its applicability to nuclei with mass numbers as high as 17. By using soft similarity renormalization-group-evolved chiral nucleon-nucleon interactions, we first calculate nucleon-{sup 4}He phase shifts, cross sections, and analyzing powers. Next, we investigate nucleon scattering on {sup 7}Li, {sup 7}Be, {sup 12}C, and {sup 16}O in coupled-channel NCSM/RGM calculations that include low-lying excited states of these nuclei. We check the convergence of phase shifts with the basis size and study A=8,13, and 17 bound and unbound states. Our calculations predict low-lying resonances in {sup 8}Li and {sup 8}B that have not been experimentally clearly identified yet. We are able to reproduce reasonably well the structure of the A=13 low-lying states. However, we find that A=17 states cannot be described without an improved treatment of {sup 16}O one-particle-one-hole excitations and {alpha} clustering.

Unified ab initio approaches to nuclear structure and reactions

The description of nuclei starting from the constituent nucleons and the realistic interactions among them has been a long-standing goal in nuclear physics. In addition to the complex nature of the nuclear forces, with two-, three- and possibly higher many-nucleon components, one faces the quantum-mechanical many-nucleon problem governed by an interplay between bound and continuum states. In recent years, significant progress has been made in ab initio nuclear structure and reaction calculations based on input from QCD-employing Hamiltonians constructed within chiral effective field theory. After a brief overview of the field, we focus on ab initio many-body approaches - built upon the No-Core Shell Model - that are capable of simultaneously describing both bound and scattering nuclear states, and present results for resonances in light nuclei, reactions important for astrophysics and fusion research. In particular, we review recent calculations of resonances in the

Ab initio description of the exotic unbound 7He nucleus

^6