Ab Initio Complex Scaling and Similarity Renormalization Group for Continuum Properties of Nuclei

TL;DR

This paper presents a new ab initio method combining complex scaling and similarity renormalization group techniques with the No-Core Shell Model to accurately compute continuum properties of nuclei, demonstrated on helium-4 and tetraneutron systems.

Contribution

The paper introduces a novel combined approach that overcomes previous numerical limitations in continuum nuclear calculations, enabling applications to larger nuclei.

Findings

Method accurately reproduces known results for helium-4.

Different NN parametrizations do not reproduce resonance properties.

The approach is extendable to nuclei with mass number greater than 4.

Abstract

We introduce a novel \abinitio many-body method designed to compute the properties of nuclei in the continuum. This approach combines well-established techniques, namely the Complex Scaling (CS) and Similarity Renormalization Group (SRG) methods while employing the translationally invariant No-Core Shell Model (NCSM) as a few-body solver. We demonstrate that this combination effectively overcomes numerical limitations previously encountered in exploring continuum properties of light nuclei with standard many-body techniques, and at the same time makes less imperative the need for a continuous set of basis states for the continuum. To benchmark the method for applications in the many-body sector, we apply it to the \textsuperscript{4}He system, where semi-exact calculations within a finite basis are feasible. Our extrapolated results agree with exact calculations already published in the literature. We argue that different NN parametrizations of chiral EFT Hamiltonians will not permit to reproduce evaluated resonance properties of \textsuperscript{4}He. As an application, we showcase the case of the tetraneutron. This work enables the application of the method to $A>4$-mass systems, providing a reliable representation of the initial Hamiltonian and its continuum properties.