Naked singularity and black hole formation in self-similar Einstein-scalar fields with exponential potentials

Abstract

Motivated by cosmic censorship in general relativity and string theory, we extend Christodoulou's celebrated examples of naked singularity formation in the Einstein-massless scalar field system to include a positive or negative scalar potential of exponential forms, i.e., $V(\phi)=\pm\exp(2\phi/\kappa)$ with a parameter $\kappa$. Under spherical symmetry and a self-similar ansatz depending on $\kappa$, we derive a 3-dimensional autonomous system of first-order ordinary differential equations, which incorporates the equations for massless scalar fields as a special case. Local behavior of the phase space is studied analytically with global solutions constructed numerically. Within the 3-dimensional solution manifold, we observe, for the negative potentials, naked singularity formation from nonsingular initial data for $\kappa^2<1$. Meanwhile, transitions between solutions containing naked singularities and black holes are also identified. However, when the potential is taken positive, numerical evolutions result in formation of black holes, but not naked singularities.