Neutron star masses in $R^{2}$-gravity

Understand

We address the issue of the existence of inequivalent definitions of gravitational mass in $R^{2}$-gravity.

• We present several definitions of gravitational mass, and discuss the formal relations between them.
• We then consider the concrete case of a static and spherically symmetric neutron star, and solve numerically the equations of motion for several values of the free parameter of the model.
• We compare the features of the mass-radius relations obtained for each definition of gravitational mass, and we comment on their dependence on the free parameter.