Early appearance ofΔisobars in neutron stars

Abstract

We discuss the formation of isobars in neutron star matter. We show that their threshold density strictly correlates with the density derivative of the symmetry energy of nuclear matter: the L parameter. By restricting L to the range of values indicated by recent experimental and theoretical analysis, i.e., 40 MeV L 62 MeV, we find that isobars appear at a density of the order of 2 to 3 times the nuclear matter saturation density, i.e., the same range as for the appearance of hyperons. The range of values of the couplings of the s with the mesons is restricted by the analysis of the data obtained from photoabsorption, electron and pion scattering on nuclei. If the potential of the in nuclear matter is close to the one indicated by the experimental data then the equation of state becomes soft enough that a " puzzle" exists, similar to the "hyperon puzzle" widely discussed in the literature. Possible solutions to this puzzle are also discussed.

The Hyperon Puzzle in Neutron Stars

“…Alternatively, the hyperon puzzle could be circumvented if neutron stars are hybrid or strange stars. Finally, it could be possible to have in Nature two different families of compact stars [61][62][63], hadronic stars and quark stars and as shown recently [69] the ∆ resenances could play an important role in this scenario.…”

Exotic nuclear matter

“…Charged current high energy neutrino-nucleus interactions proceed to a large part through N * excitation. Last but not least, subnuclear degrees of freedom are naturally excited in dense baryonic matter as found in neutron stars [32,33].…”

Symmetry potential of theΔ(1232)resonance and its effects on theπ−/π+ratio in heavy-ion collisions near the pion-prod

“…[44]. Indeed, there are indications from analyses of electron-nucleus, photoabsorption and pion-nucleus scattering that the ∆ isoscalar potential v ∆ is in the range of −30 MeV + v N ≤ v ∆ ≤ v N with respect to the nucleon isoscalar potential v N [45]. Since a constant potential has no dynamical effect in heavy-ion reactions and there is no information available as to how the difference in the isoscalar potentials for nucleons and ∆ resonances depend on the density and/or other properties of the medium, in this study we thus use the same isoscalar potentials for nucleons and ∆ resonances.…”