  It is argued that the cross section for production of large black holes, for
which a semiclassical description is applicable, cannot be given by the
geometric area of the black hole horizon, as claimed recently in the
literature. Rather the production cross section in a few-particle collision is
suppressed by at least a factor exp(-I_E) with I_E being the Gibbons-Hawking
(Euclidean) action for the black hole. Thus only essentially non-classical
small black holes with mass of the order of the Planck mass can possibly be
produced in few-particle collisions at trans-Planckian energies.

High Energy Physics - Phenomenology;High Energy Physics - Theory