Setting realistic constraints on X17 boson from compact objects

Abstract

We examine the hypothetical X17 boson on neutron stars and quark stars using various hadronic equations of state with phenomenological or microscopic origin. Our aim is to set realistic constraints on its coupling constant and the mass scaling. Everything done with respect to causality and various possible upper mass limits and the dimensionless tidal deformability Λ1.4. We focused on two main phenomenological parameters, the coupling constant g that X17 it has with hadrons or quarks and the in-medium effects through regulator C. We came to the general conclusion that the effect of the X17 both on neutron stars and quark stars is constrained mainly by the causality limit, which is a specific property of each equation of state, and it depends on the interplay between g and C.