A no-go theorem for polytropic spheres in Palatini f(R) gravity

Non-vacuum static spherically symmetric solutions in Palatini f(R) gravity are examined. It is shown that for generic choices of f(R), there are commonly used equations of state for which no satisfactory physical solution of the field equations can be found within this framework, apart from in the special case of general relativity, casting doubt on whether Palatini f(R) gravity can be considered as giving viable alternatives to general relativity. (fast track communication)