We investigate spontaneous scalarization of static and spherically symmetric black hole (BH) solutions in scalar-tensor theories with higher-derivative interactions. Spontaneous scalarization of BHs is a phenomenon that the scalar field spontaneously obtains a nontrivial profile and nonzero scalar charge in the vicinity of the event horizon via nonminimal couplings,and a scalarized BH solution differs from a Schwarzschild BH.
First, we consider spontaneous scalarization of BHs in the presence of the coupling to the Gauss-Bonnet (GB) term. For the simplest quadratic coupling to the GB term, it was known that scalarized BH solutions are unstable against radial perturbations. We verify that the existence of the higher order power of the scalar field in the GB coupling function can realize scalarized BHs which are stable against the radial perturbation.
Second, we investigate the possibility of spontaneous scalarization of static and spherically symmetric BHs in a generic class of the Horndeski theory. In the theory in which spontaneous scalarization takes place, the Schwarzschild solution with a trivial profile of the scalar field exhibits a tachyonic instability in the vicinity of the event horizon. We clarify the conditions on the individual galileon coupling functions for the existence of the vanishing scalar field solution on top of the Schwarzschild spacetime, and for nonzero but finite imprints into radial perturbations about the constant scalar solution. We then consider models with minimal power that satisfies the above conditions, which includes the Einstein-scalar-GB theory as the special case.
2019 June 26, 14:30
Faculdade de Ciências da Universidade de Lisboa (C8.2.02)
Campo Grande, 1749-016 Lisboa