Mass-gap for black hole formation in higher derivative and ghost free gravity

TL;DR

This paper investigates gravitational collapse in higher derivative and ghost free gravity theories, revealing a mass gap for black hole formation and conditions for finite curvature during collapse.

Contribution

It demonstrates the existence of a mass gap for mini black hole production in these theories and analyzes conditions for finite curvature invariants during collapse.

Findings

Existence of a mass gap for black hole formation in higher derivative and ghost free gravity.

Conditions identified for finite curvature invariants at the collapse center.

Constructed solutions for null shell collapse in linearized higher derivative gravity.

Abstract

We study a spherical gravitational collapse of a small mass in higher derivative and ghost free theories of gravity. By boosting a solution of linearized equations for a static point mass in such theories we obtain in the Penrose limit the gravitational field of an ultra-relativistic particle. Taking a superposition of such solutions we construct a metric of a collapsing null shell in the linearized higher derivative and ghost free gravity. The latter allows one to find the gravitational field of a thick null shell. By analysing these solutions we demonstrate that in a wide class of the higher dimensional theories of gravity as well as for the ghost free gravity there exists a mass gap for the mini black hole production. We also found conditions when the curvature invariants remain finite at $r=0$ for the collapse of the thick null shell.