Full Classification of Static Spherical Vacuum Solutions to Bumblebee Gravity with General VEVs

Abstract

The static spherical vacuum solution in a bumblebee gravity model where the bumblebee field $B_\mu$ has a two-component space-like, light-like, and time-like vacuum expectation value $b_\mu$ is studied. Based on the results, we present a comprehensive classification of the static spherical vacuum solutions in bumblebee gravity with general vacuum expectation values. We find that the model becomes degenerate for a specific set of parameter combinations, where the solution can be characterized by an arbitrary function, which indicates that the non-minimally coupled massless vector tensor theory is ill-defined when $\xi=\kappa/2$. We also find that contrary to the situation in general relativity, the bumblebee gravity admits the exact Schwarzschild solution with non-zero matter distributions of certain forms. The implications of this result are discussed, suggesting that the experimental constraints within the solar system would be invalid.