\textit{Ab initio} Gamow density matrix renormalization group for broad nuclear many-body resonances

TL;DR

This paper extends the ab initio Gamow DMRG method to accurately describe broad nuclear resonances, enabling systematic tests of nuclear forces in exotic light nuclei with improved stability and convergence.

Contribution

It introduces new truncation and orbital ordering schemes to stabilize and accelerate ab initio G-DMRG calculations for broad nuclear resonances, including the first direct ab initio calculation of 5H ground state.

Findings

Controlled entanglement due to continuum couplings in extreme conditions.

Achieved convergence in low-lying states of 5He, 6He, and 4H.

First ab initio calculation of 5H ground state.

Abstract

\textbf{Background} The reach of \textit{ab initio} theory has greatly increased in recent decades. However, predicting the location of the drip lines remains challenging due to uncertainties in nuclear forces and difficulties in describing nuclei that behave as open quantum systems. \textbf{Purpose} In this work, we extend the \textit{ab initio} Gamow Density Matrix Renormalization Group (G-DMRG) approach to the regime of broad many-body resonances to pave the way for systematic tests of nuclear forces in light exotic nuclei. \textbf{Methods} To stabilize calculations, we introduce a new truncation scheme in the reference space, and propose an orbital ordering based on entanglement considerations. We then show how continuum couplings increase entanglement in the many-body problem, and propose a new truncation scheme to stabilize the renormalization and accelerate calculations in extreme conditions. Finally, we demonstrate that natural orbitals can be used to efficiently describe broad resonances by introducing a new ordering scheme and by redefining the reference space based on occupations. \textbf{Results} Leveraging our findings, we propose a recipe to converge \textit{ab initio} G-DMRG calculations and apply it in low-lying states of \isotope[5,6]{He} and \isotope[4]{H}, demonstrating control of the renormalization and the emergence of convergence patterns. We also obtain the first direct \textit{ab initio} calculation of the $J^\pi = {1/2}^+$ ground state of \isotope[5]{H}. \textbf{Conclusions} We demonstrate that entanglement due to continuum couplings can be controlled in extreme conditions and successfully extend the G-DMRG approach in the regime of broad many-body resonances.