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Elucidating the appropriate microscopic degrees of freedom within neutron stars remains an open question which impacts nuclear physics, particle physics and astrophysics. The recent discovery of the first non-trivial dibaryon, the d ⁎ ( 2380 ) , provides a new candidate for an exotic degree of freedom in the nuclear equation of state at high matter densities. In this paper a first calculation of the role of the d ⁎ ( 2380 ) in neutron stars is performed based on a relativistic mean field description of the nucleonic degrees of freedom supplemented by a free boson gas of d ⁎ ( 2380 ) . The calculations indicate that the d ⁎ ( 2380 ) would appear at densities around three times normal nuclear matter saturation density and comprise around 20% of the matter in the centre of heavy stars with higher fractions possible in the higher densities of merger processes. The d ⁎ ( 2380 ) would also reduce the maximum star mass by around 15% and have significant influence on the fractional proton/neutron composition. New possibilities for neutron star cooling mechanisms arising from the d ⁎ ( 2380 ) are also predicted. [ABSTRACT FROM AUTHOR]

The properties of the D and D charmed mesons in normal nuclear matter density are studied within a coupled channel approach using a t-channel vector-meson exchange mechanism as driving force. The in-medium scattering amplitudes are obtained by solving the Lippmann-Schwinger equation including Pauli blocking effects and medium self-energies in a self-consistent way. [ABSTRACT FROM AUTHOR]

Only one-third of the nucleons in 208Pb occupy the saturation density area. Consequently, nuclear observables related to the average properties of nuclei, such as masses or radii, constrain the equation of state not at the saturation density but rather around the so-called crossing density, localized close to the mean value of the density of nuclei: p ≈ 0.11 fm-3. This provides an explanation for the empirical fact that several equation of state quantities calculated with various functionals cross at a density significantly lower than the saturation one. The third derivative M of the energy per unit of volume at the crossing density is constrained by the giant monopole resonance measurements in an isotopic chain rather than the incompressibility at saturation density. The giant monopole resonance measurements provide M = 1100 ± 70 MeV (6% uncertainty), whose extrapolation gives K∞ = 230 ± 40 MeV (17% uncertainty). [ABSTRACT FROM AUTHOR]

We investigate the possibility that the low mass companion of the black hole in the source of GW190814 was a strange quark star. This possibility is viable within the so-called two-families scenario in which neutron stars and strange quark stars coexist. Strange quark stars can reach the mass range indicated by GW190814, M∼(2.5-2.67)  M⊙ due to a large value of the adiabatic index, without the need for a velocity of sound close to the causal limit. Neutron stars (actually hyperonic stars in the two-families scenario) can instead fulfill the presently available astrophysical and nuclear physics constraints which require a softer equation of state. In this scheme it is possible to satisfy both the request of very large stellar masses and of small radii while using totally realistic and physically motivated equations of state. Moreover it is possible to get a radius for a 1.4  M⊙ star of the order or less than 11 km, which is impossible if only one family of compact stars exists. [ABSTRACT FROM AUTHOR]