Center of mass energy of two charged particles around a magnetic Kerr black hole

It is known that the center of mass energy (CME) of two neutral colliding particles, a charged and a neutral particle and two charged particles, is arbitrarily high at the outer horizon of the Kerr black hole (BH). However, in the literature, a term is missed in the formula used to obtain results when collision of two charged particles and of a charged and a neutral particle occur. Considering the motion of the particles falling toward the BH in the equatorial plane, i.e. theta=pi 2, we study the CME in the vicinity of a magnetic Kerr BH. It is commonly believed that only extremal BHs can accelerate particle energies to arbitrarily high levels. However, we emphasize that such extreme conditions are not necessary. We find, under some restrictions, that the CME is arbitrarily high when particles are closer to the horizon(s) in both extremal and nonextremal cases.