Entropy, area, and the choice of regulator during gravitational collapse

Abstract: We present a real time formalism to numerically describe the gravitational collapse of a scalar quantum field in the spherically symmetric case. We employ a Pauli-Villars regulator that is specifically designed to cancel the ultraviolet divergences in the energy-momentum tensor identified by covariant point splitting, including the logarithmic ones. Using this regulator, we find that the leading term of the entanglement entropy, which is proportional to the surface area, vanishes for a spherical region of flat spacetime. First numerical results for the dynamical case indicate that for a collapsing shell of a massless scalar field, the area normalized entropy is concentrated on the shell and has an approximately constant maximum value during time evolution. This maximum value appears to be finite in the continuum limit and only mildly dependent on the regulator mass.