Searching for non-minimally coupled scalar hairs

In this work we study the asymptotically flat, static, and spherically symmetric black-hole solutions of the theory described by the action $$S = \int d^nx\sqrt{-g} \left\{\left(1-\xi\phi^2 \right)R - g^{\mu\nu}\partial_\mu\phi\partial_\nu\phi\right\},$$ with $n>3$ and arbitrary $\xi$. We demonstrate the absence of scalar hairs for $\xi\xi_c=\frac{n-2}{4(n-1)}$, we show that there is no scalar hair obeying $|\phi(r)| < 1/\sqrt{\xi}$ or $|\phi(r)| > 1/\sqrt{\xi}$. For $0<\xi<\xi_c$, we prove the absence of scalar hairs such that $|\phi(r)| < 1/\sqrt{\xi}$ or $\frac{1}{\xi} < \phi^2(r) < \frac{\xi_c}{\xi(\xi_c-\xi)}$.