$Δ$-admixed neutron stars: spinodal instabilities and dUrca processes

Abstract

Within the covariant density functional theory of nuclear matter we build equations of state of ∆-admixed compact stars. Uncertainties in the interaction of ∆(1232) resonance states with nuclear matter, due to lack of experimental data, are accounted for by varying the coupling constants to scalar and vector mesonic fields. We find that, over a wide range of the parameter space allowed by nuclear physics experiments and astrophysical observations, cold catalyzed star matter exhibits a first order phase transition which persists also at finite temperature and out of β-equilibrium in the neutrino-transparent matter. Compact stars featuring such a phase transition in the outer core have small radii and, implicitly, tidal deformabilities. The parameter space is identified where simultaneously ∆-admixed compact stars obey the astrophysical constraint on maximum mass and allow for dUrca processes, which is otherwise forbidden.

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

“…Note that within a certain range of the parameters the Δadmixed matter undergoes spinodal instability [56]; for fixed R ρΔ = R σ Δ = 1 this occurs for R ωΔ ≤ 0.8, therefore the choice (38) avoids such instabilities.…”

“…As well-known (see, e.g., Refs. [32,56]), the onset of Δ − shifts the balance between the chemical potentials of particles participating in the Urca reactions n → p + e + ν and e + p → n + ν. The proton fraction becomes large enough (compared to the npeμ-matter) so that the first Urca process can take place in the matter.…”

Exotic Baryons in Hot Neutron Stars

“…The expressions for P d and ε d are similar to (18) and (19) with the replacement of b with d. The pressure further receives a correction from the rearrangement term to guarantee thermodynamic consistency and energymomentum conservation [34,35]…”

“…We consider different values of S/n B for different Y L,e in accordance with the various stages of PNS evolution [36,37]: for the newly born neutron star (at t = 0 s) we consider S/n B = 1 and Y L,e = 0.4, but a few seconds (∼ 0.5 − 1.0 s) after the star is born it starts heating, so the entropy increases (1 < S/n B < 3) and the lepton number concentration decreases, thus we consider S/n B = 2 and Y L,e = 0.2 at this stage. Further discussions on fixed entropy calculations can be found, for example, in [18]. The star gets maximally heated and becomes neutrino-free (Y νe = 0) with S/n B = 2, and finally it shrinks to a catalysed neutron star with S/n B = 0, Y νe = 0 [23,38,39].…”

“…We investigate the behavior of the EoS and the particle abundances in the evolution of a newly born PNS until it catalyzes. Several studies of cold neutron stars have been carried out within the framework of relativistic models within a mean-field approximation taking into account all of the spin-1/2 octet and/or ∆-resonances using various mesonbaryon coupling formalism at zero temperature [14][15][16][17][18][19][20][21].…”