Particle acceleration in Kerr-(anti-)de Sitter black hole backgrounds

Banados, Silk and West (BSW) proved that Kerr black holes could act as particle accelerators with arbitrarily high center-of-mass energy, if two conditions are satisfied: (1) these black holes are extremal; (2) one of the colliding particles has critical angular momentum. In this paper, we extend the research to the cases of Kerr-(anti-)de Sitter black holes and find that the cosmological constant has an important effect on the result. In order for the case of Kerr-anti-de Sitter black holes (with negative cosmological constant) to get arbitrary high center-of-mass energy, we need an additional condition besides the above two for Kerr ones. While, for the case of general Kerr-de Sitter black holes (with positive cosmological constant), the collision of two particles can take place on the outer horizon of the black holes and the center-of-mass energy of collision can blow up arbitrarily if the above second condition is satisfied. Hence, non-extremal Kerr-de Sitter black holes could also act as particle accelerators with arbitrarily high center-of-mass energy.