SHOCK-WAVE MIXING IN EINSTEIN AND DILATON GRAVITY

We consider possible mixing of electromagnetic and gravitational shock waves, in the Planckian energy scattering of point particles in Minko wski space. By boosting a Reissner-Nordstrom black hole solution to th e velocity of light, it is shown that no mixing of shock waves takes p lace for arbitrary finite charge carried by the black hole. However, a similar boosting procedure for a charged black hole solution in dilat on gravity yields some mixing: the wave function of even a neutral tes t particle, acquires a small additional phase factor depending on the dilatonic black hole charge. Possible implications for poles in the am plitudes for the dilaton gravity case are discussed.