Kerr-Sen black hole as accelerator for spinning particles

It has been proved that arbitrarily high-energy collision between two particles can occur near the horizon of an extremal Kerr black hole as long as the energy E and angular momentum L of one particle satisfies a critical relation, which is called the Banados, Silk, and West mechanism. Previous researchers mainly concentrated on the geodesic motion of particles. In this paper, we will take the spinning particle that will not move along a timelike geodesic into our consideration; hence, another parameter s describing the particle's spin angular momentum was introduced. By employing the Mathisson-Papapetrou-Dixon equation describing the movement of the spinning particle, we will explore whether a Kerr-Sen black hole that is slightly different from the Ken' black hole can be used to accelerate a spinning particle to an arbitrarily high energy. We found that when one of the two colliding particles satisfies a critical relation between the energy E and the total angular momentum J, or has a critical spinning angular momentum s(c), a divergence of the center-of-mass energy E-cm will be obtained.