Induced Hyperon-Nucleon-Nucleon Interactions and the Hyperon Puzzle

TL;DR

This paper presents ab initio calculations of hypernuclei including induced hyperon-nucleon-nucleon interactions, revealing their repulsive nature and connection to the hyperon puzzle in neutron-star physics, with improved convergence and accurate excitation energies.

Contribution

First ab initio inclusion of induced YNN interactions in hypernuclear calculations using SRG, linking hyperon interactions to the hyperon puzzle.

Findings

Induced YNN interactions are strongly repulsive.

Results reproduce experimental excitation energies well.

Induced YNN interactions relate to decoupling of $ ext{Sigma}$ hyperons.

Abstract

We present the first ab initio calculations for $p$-shell hypernuclei including hyperon-nucleon-nucleon (YNN) contributions induced by a Similarity Renormalization Group transformation of the initial hyperon-nucleon interaction. The transformation including the YNN terms conserves the spectrum of the Hamiltonian while drastically improving model-space convergence of the Importance-Truncated No-Core Shell Model, allowing a precise extraction of binding and excitation energies. Results using a hyperon-nucleon interaction at leading order in chiral effective field theory for lower- to mid-$p$-shell hypernuclei show a good reproduction of experimental excitation energies while hyperon binding energies are typically overestimated. The induced YNN contributions are strongly repulsive and we show that they are related to a decoupling of the $\Sigma$ hyperons from the hypernuclear system, i.e., a suppression of the $\Lambda$-$\Sigma$ conversion terms in the Hamiltonian. This is linked to the so-called hyperon puzzle in neutron-star physics and provides a basic mechanism for the explanation of strong $\Lambda$NN three-baryon forces.