String black holes as particle accelerators to arbitrarily high energy

Abstract

We show that an extremal Gibbons-Maeda-Garfinkle-Horowitz-Strominger black hole may act as a particle accelerator with arbitrarily high energy when two uncharged particles falling freely from rest to infinity on the near horizon. We show that the center of mass energy of collision is independent of the extreme fine tuning of the angular momentum of the colliding particles. We further show that the center of mass energy of collisions of particles at the ISCO (r _ISCO ) or at the photon orbit (r _ph ) or at the marginally bound circular orbit (r _mb ) i.e. at r≡r _ISCO =r _ph =r _mb =2M could be arbitrarily large for the aforementioned space-time, which is quite different from the Schwarzschild and the Reissner-Nordstrøm space-time. For non-extremal GMGHS space-time the CM energy is finite and depends upon the asymptotic value of the dilation field (ϕ ₀).