General stationary charged black holes as charged particle accelerators

TL;DR

This paper investigates conditions under which charged particles colliding near stationary charged black holes can achieve infinite or ultra-high center-of-mass energy, revealing new mechanisms and restrictions related to black hole horizon degeneracy.

Contribution

It provides a general analysis of particle collisions near various types of charged black holes, including degenerate and non-degenerate horizons, and introduces conditions for ultra-high energy collisions without fine-tuning.

Findings

Infinite energy possible near degenerate horizons with critical parameters.

Multiple scattering enables ultra-high energy in non-degenerate black holes.

Conditions for stable orbits with critical parameters are established.

Abstract

We study the possibility of getting infinite energy in the center of mass frame of colliding charged particles in a general stationary charged black hole. For black holes with two-fold degenerate horizon, it is found that arbitrary high center-of-mass energy can be attained, provided that one of the particle has critical angular momentum or critical charge, and the remained parameters of particles and black holes satisfy certain restriction. For black holes with multiple-fold degenerate event horizons, the restriction is released. For non-degenerate black holes, the ultra-high center-of-mass is possible to be reached by invoking the multiple scattering mechanism. We obtain a condition for the existence of innermost stable circular orbit with critical angular momentum or charge on any-fold degenerate horizons, which is essential to get ultra-high center-of-mass energy without fine-tuning problem. We also discuss the proper time spending by the particle to reach the horizon and the duality between frame dragging effect and electromagnetic interaction. Some of these general results are applied to braneworld small black holes.