Phenomenology of Axionic Static Neutron Stars with Masses in the Mass-Gap Region

Understand

In this work we consider an axionic scalar-tensor theory of gravity and its effects on static neutron stars.

• The axionic theory is considered in the regime in which the axion oscillates around its potential minimum, which cosmologically occurs post-inflationary, when the Hubble rate is of the same order as the axion mass.
• We construct the TOV equations for this axionic theory and for a spherically symmetric static spacetime and we solve these numerically using a quite robust double shooting LSODA based python integration method.
• Regarding the equations of state, we used nine mainstream and quite popular ones, namely, the WFF1, the SLy, the APR, the MS1, the AP3, the AP4, the ENG, the MPA1 and the MS1b, using the piecewise polytropic description for each.