Upper Limit on the Central Density of Dark Matter in the Eddington-inspired Born–Infeld (eibi) Gravity

We investigate the stability of circular material orbits in the analytic galactic metric recently derived by Harko \textit{et al.} (2014). It turnsout that stability depends more strongly on the dark matter central density $%\rho_{0}$ than on other parameters of the solution. This property then yields an upper limit on $\rho _{0}$ for each individual galaxy, which we call here $\rho _{0}^{\text{upper}}$, such that stable circular orbits are possible \textit{only} when the constraint $\rho _{0}\leq \rho _{0}^{\text{upper}}$ is satisfied. This is our new result. To approximately quantify the upper limit, we consider as a familiar example our Milky Way galaxy that has a projected dark matter radius $R_{\text{DM}}\sim 180$ kpc and find that $\rho _{0}^{\text{upper}}\sim 2.37\times 10^{11}$ $M_{\odot }$kpc$^{-3}$. This limit turns out to be about four orders of magnitude larger than the latest data on central density $\rho _{0}$ arising from the fit to the Navarro-Frenk-White (NFW) and Burkert density profiles. Such consistency indicates that the EiBI solution could qualify as yet another viable alternative model for dark matter.