Neutron star matter equation of state including $d^{\ast }$-hexaquark degrees of freedom

Abstract

We present an extension of a previous work where, assuming a simple free bosonic gas supplemented with a relativistic meand field model to describe the pure nucleonic part of the EoS, we studied the consequences that the first non-trivial hexaquark $d^{\ast }$(2380) could have on the properties of neutron stars. Compared to that exploratory work we employ a standard non-linear Walecka model including additional terms that describe the interaction of the $d^{\ast }(2380)$ di-baryon with the other particles of the system through the exchange of $\sigma$- and $\omega$-meson fields. Our results have show that the presence of the $d^{\ast }(2380)$ leads to maximum masses compatible with the recent observations of $\sim 2$M${}_{\odot }$ millisecond pulsars if the interaction of the $d^{\ast }(2380)$ is slightly repulsive or the $d^{\ast }(2380)$ does not interacts at all. An attractive interaction makes the equation of state too soft to be able to support a $2$M${}_{\odot }$ neutron star whereas an extremely repulsive one induces the collapse of the neutron star into a black hole as soon as the $d^{\ast }(2380)$ appears.