Equation of state and composition of proto-neutron stars and merger remnants with hyperons

Abstract

Finite-temperature equation of state (EoS) and composition of dense nuclear and hypernuclear matter under conditions characteristic for neutron star binary merger remnants and supernovas are discussed. We consider both the neutrino free-streaming and the trapped regimes which are separated by a temperature of a few MeV. The formalism is based on covariant density functional (CDF) theory for the full baryon octet with density-dependent couplings, suitably adjusted in the hypernuclear sector. The softening of the EoS with the introduction of the hyperons is quantified under various conditions of lepton fractions and temperatures. We find that Λ, Ξ − , and Ξ 0 hyperons appear in the given order with the sharp density increase at zero temperature at the threshold being replaced by an extended increment over a wide density range at high temperatures. The Λ hyperon survives in the deep subnuclear regime. The triplet of Σs is suppressed in cold hypernuclear matter up to around seven times the nuclear saturation density, but appears in significant fractions at higher temperatures T ≥ 20 MeV in both supernova and merger remnant matter. We point out that there exists a special isospin degeneracy point where the baryon abundances within each of the three isospin-multiplets are equal to each other as a result of (approximate) isospin symmetry. At that point the charge chemical potential of the system vanishes. We find that under the merger remnant conditions the fractions of electron and µ-on neutrinos are close and are about 1%, whereas in the supernova case, we find only a significant fraction (∼10%) of electron neutrinos, given that in this case, the µ-on lepton number is zero.

Delta-resonances and hyperons in proto-neutron stars and merger remnants

“…[30] with the extensions in the hypernuclear sector described previously in Ref. [29]. The zero-temperature counterpart of this CDF and its astrophysical consequences were already discussed extensively by Li et al [31][32][33].…”

“…As pointed out in the previous work [29], where resonances were neglected, there is a special isospin degeneracy (ID) point where the fractions within each isospin multiplet coincide. We find that in the Δ-resonance admixed matter this feature is maintained and extended to the Δ ± Δ ++ , and Δ 0 resonances.…”

“…In this work, we report an extension of our previous study of hot hypernuclear matter [29] which builds upon the work of Ref. [30] to include non-strange J P = 3 2 + members of the baryons decuplet -the Δ-resonances.…”

“…Our numerical implementation is based on the code of Ref. [30] supplemented with hidden strangeness σ * and φ mesons which account for the interactions amongst hyperons [29]. In the hypernuclear sector, we will adopt the parameter set already discussed in Refs.…”