NuLattice: Ab initio computations of atomic nuclei on lattices

This talk introduces NuLattice, a Python software package for ab initio computations of atomic nuclei on lattices. The computational tools consist of Hartree Fock, the coupled-cluster method, the in-medium similarity renormalization group, and full configuration interaction. At present, the employed interactions are from pion-less effective field theory at leading order and consist of two-body and three-body contacts. We present results for light nuclei 2H, 3,4He, 8Be, 12C, and 16O. NuLattice algorithms exploit the sparsity and locality of lattice interactions, and as a result computations can be run on laptops. This approach yielded analytical insights about the exactness of the normal-ordered two-body approximation, where contributions of three-nucleon forces are truncated at the two-body rank after normal ordering with respect to a product state. On the lattice, the normal-ordered two-body truncation is exact for zero-range three-body forces when nuclei are computed using the coupled cluster with singles and doubles method. As the nuclear three-nucleon force is short ranged and a three-body contact is a leading term in effective field theories of quantum chromodynamics, this result provides an analytical basis for the popular normal-ordered two-body approximation.