---
author:
- Dominik Gerstung
- Norbert Kaiser
- Wolfram Weise
title: 'Hyperon-nucleon three-body forces and strangeness in neutron stars'
---

Introduction {#sec:intro}
============

The existence of heavy neutron stars with masses around 2$M_\odot$ [@Demorest2010; @Antoniadis2013; @Fonseca2016; @Cromartie2019] sets strong constraints on the equation of state (EoS) of dense baryonic matter. This EoS must be sufficiently stiff, i.e. the pressure $P(\cal{E})$ at energy densities $\cal{E}\sim$ 1 GeV/fm$^3$ must be large enough to support such massive compact objects against gravitational collapse. The detection of gravitational wave signals from two merging neutron stars [@Abbott2017] adds further important information on the EoS, by providing limits for the tidal deformability and for neutron star radii [@Most2018; @De2018].

The composition and properties of strongly interacting matter at high baryon densities is a topic of continuing interest. Various options are under discussion. A time-honored description of matter in the core of neutron stars uses hadronic degrees of freedom (baryons and mesons) with strong many-body correlations [@APR1998]. A modern version that arrives at a similar EoS, consistent with observations, is based on a chiral nucleon-meson field theory combined with functional renormalization group methods [@DW2015; @DW2017]. In this latter approach neutron star matter can be represented as a 