[en] We employ the density matrix renormalization group (DMRG) and the wave function factorization method for the numerical solution of large scale nuclear structure problems. The DMRG exhibits an improved convergence for problems with realistic interactions due to the implementation of the finite algorithm. The wave function factorization of fpg-shell nuclei yields rapidly converging approximations that are at the present frontier for large-scale shell model calculations

[en] Simulations - utilizing computers to solve complicated science and engineering problems - are a key ingredient of modern science. The U.S. Department of Energy (DOE) is a world leader in the development of high-performance computing (HPC), the development of applied math and algorithms that utilize the full potential of HPC platforms, and the application of computing to science and engineering problems. An interesting general question is whether the DOE can strategically utilize its capability in simulations to advance innovation more broadly. In this article, I will argue that this is certainly possible.

[en] Nuclear theory today aims for a comprehensive theoretical framework that can describe all nuclei. I discuss recent progress in this pursuit and the associated challenges as we move forward, paying particular attention to progress in the application of coupled-cluster theory to the challenges.

[en] Nuclear theory today aims for a comprehensive theoretical framework that can describe all nuclei. I discuss recent progress in this pursuit and the associated challenges as we move forward.

[en] This Resource Letter provides a guide to the literature on the spherical shell model as applied to nuclei. The nuclear shell model describes the structure of nuclei starting with a nuclear core developed by the classical neutron and proton magic numbers N,Z=2,8,20,28,50,82, 126, where gaps occur in the single-particle energies as a shell is filled, and the interactions of valence nucleons that reside beyond that core. Various modern extensions of this model for spherical nuclei are likewise described. Significant extensions of the nuclear shell model include new magic numbers for spherical nuclei and now for deformed nuclei as well. When both protons and neutrons have shell gaps at the same spherical or deformed shapes, they can reinforce each other to give added stability to that shape and lead to new magic numbers. The vanishings of the classical spherical shell model energy gaps and magic numbers in new neutron-rich nuclei are described. Spherical and deformed shell gaps are seen to be critical for the existence of elements with Z > 100.

[en] Kawai, Kerman and McVoy (KKM) derived an optical background-plus-fluctuations representation of T-matrix, T = T^opt + T^fluct, so that an energy average of T^fluct over a single-particle resonance width is expected to be negligibly small (Ann. of Phys. 75, 156 (1973)). We investigate this property numerically in a simple model with 1,600 compound nuclear levels and 40 channels, coupled via a random interaction. We find that the energy average of the fluctuating term is much smaller than the optical background, T^opt, in support of the KKM result. A self-contained derivation of KKM T-matrix is presented.

[en] This article presents several challenges to nuclear many-body theory and our understanding of the stability of nuclear matter. In order to achieve this, we present five different cases, starting with an idealized toy model. These cases expose problems that need to be understood in order to match recent advances in nuclear theory with current experimental programs in low-energy nuclear physics. In particular, we focus on our current understanding, or lack thereof, of many-body forces, and how they evolve as functions of the number of particles. We provide examples of discrepancies between theory and experiment and outline some selected perspectives for future research directions.

[en] We discuss peculiarities of open-quantum systems, as compared to closed-quantum systems. We emphasize the importance of taking continuum degrees of freedom into account when dealing with systems with a tendency to decay through emission of fragments. In this context, we introduce the coupled-cluster theory and argue that this method allows for an accurate description of such systems starting from nucleon-nucleon degrees of freedom. We present ab-initio coupled-cluster calculations with singles and doubles excitations (CCSD) for the ground states of the helium isotopes ^3-10He. The correlated many-body wave function is built from a single-particle basis which treats bound-, resonant-, and non-resonant continuum states on equal footing, which is a Berggren basis. In order to keep the basis size manageable, we use a renormalized interaction of the low-momentum type derived from the N³LO nucleon-nucleon interaction. The calculated masses and decay widths are in semi-quantitative agreement with experiment. The discrepancy with experiment is suspected to be attributed to the three-nucleon force (3NF) which is not included at this point

[en] Coupled-cluster theory represents an important theoretical tool that we use to solve the quantum many-body problem. Coupled-cluster theory also lends itself to computation in a parallel computing environment. In this article, we present selected results from ab initio studies of stable and weakly bound nuclei utilizing computational techniques that we employ to solve coupled-cluster theory. We also outline several perspectives for future research directions in this area.

[en] We present ab-initio calculations for ³H, ⁴He, ¹⁶O, and ⁴⁰Ca based on two-nucleon low-momentum interactions V_lowk within coupled-cluster theory. For ³H and ⁴He, our results are within 70 keV and 10 keV of the corresponding Faddeev and Faddeev-Yakubovsky energies. We study in detail the convergence with respect to the size of the model space and the single-particle basis. For the heavier nuclei, we report practically converged binding energies and compare with other approaches