Interplay between Delta Particles and Hyperons in Neutron Stars

Abstract

We analyze the effects of including ∆(1232) isobars in an equation of state (EoS) for cold, β-stable neutron star matter, employing relativistic nuclear mean field theory. The selected EoS reproduces the properties of nuclear matter and finite nuclei and, in the astrophysical context, allows for the presence of hyperons in neutron stars having masses larger than 2M . We find that the composition and structure of neutron stars is critically influenced by the addition of the ∆ isobars, which allows us to constrain their interaction with the meson fields taking into account astrophysical information. Imposing that the EoS is stable and ensures the existence of 2M neutron stars, as well as requiring agreement with data of ∆ excitation in nuclei, we find that, in the absence of other mechanisms stiffening the EoS at high densities, the interaction of the ∆ isobars with the sigma and omega meson fields must be at least 10% stronger than that of the nucleons. Moreover, the neutron star moment of inertia turns out to be sensitive to the presence of ∆ isobars, whereas the inclusion of ∆ isobars in the EoS allows for smaller stellar radii and for a lower value of the tidal deformability consistent with the analysis of the GW170817 merger event.

Neutron-star tidal deformability and equation-of-state constraints

“…7), astronomical observations can also be used to place constraints on the relevant parameter space. In general, since GW170817 provided an upper limit onΛ, any physical effect that results in a softening of the equation of state can be consistent with the data [88,[240][241][242][243][244][245][246] As such, a strong first-order phase transition might make an equation of state model compatible with the GW170817 data, even if the hadronic part on its own is not [152,[247][248][249][250]. A number of studies have constructed models that can successfully interpret the inspiral signal from GW170817 as the coalescence of any combination of hadronic and hybrid hadronic-quark neutron stars and place corresponding constraints on the relevant model parameter space [149,247,248,[251][252][253][254][255][256][257][258][259][260].…”

Light clusters in dilute heavy-baryon admixed nuclear matter

“…The formation of the heavy baryons in dense and cold nuclear matter, in particular hyperonic members of the J 1/2+ baryonic octet in combinations with the non-strange members of baryon J 3/2+ decouplet (Δ-resonances) has attracted attention in recent years [55][56][57][58][59][60][61][62][63][64]. The relativistic density functionals were successfully tuned to remove the tension between the softening of the equation of state of dense matter associated with the onset of the baryons and the astrophysical observations of the massive neutron stars with masses 2M [58][59][60].…”

Constraints on the Muon Fraction and Density Profile in Neutron Stars

“…We emphasize that this is the minimum model for studying muons in NSs. It is well known that hyperons and baryon resonances are predicted to appear above certain critical densities (see, e.g., Vidaña et al 2003;Vidaña 2016;Providência et al 2019;Ribes et al 2019). In particular, negatively charged particles, such as Σ − and ∆ − (1232) are among the first to be formed as the density increases from the crust to the core of NSs.…”