Infinitely degenerate exact Ricci-flat solutions in f(R) gravity

Understand

We obtain an infinite number of exact static, Ricci-flat spherically symmetric vacuum solutions for a class of f(R) theories of gravity.

• We analytically derive two exact vacuum black-hole solutions for the same class of f(R) theories.
• The two black-hole solutions have the event-horizon at the same point; however, their asymptotic features are different.
• Our results suggest that no-hair theorem may not hold for generic modified gravity theories.