Black Hole Non-Formation in the Matrix Model

TL;DR

The paper demonstrates that in the full string theory, collapsing shells in two-dimensional models do not form black holes but instead backscatter, with no leading-order particle production, challenging traditional effective field theory expectations.

Contribution

It shows that typical collapsing shells do not form black holes in the full string theory, using the matrix model to reveal backscattering and absence of particle production.

Findings

Collapsing shells backscatter before horizon formation.

String loop corrections are small, but α' corrections are significant.

No leading-order particle production occurs during collapse.

Abstract

The leading classical low-energy effective actions for two-dimensional string theories have solutions describing the gravitational collapse of shells of matter into a black hole. It is shown that string loop corrections can be made arbitrarily small up to the horizon, but $\alpha'$ corrections cannot. The matrix model is used to show that typical collapsing shells do not form black holes in the full string theory. Rather, they backscatter out to infinity just before the horizon forms. The matrix model is also used to show that the naively expected particle production induced by the collapsing shell vanishes to leading order. This agrees with the string theory computation. From the point of view of the effective low energy field theory this result is surprising and involves a delicate cancellation between various terms.