EXACT GRAVITATIONAL SHOCK-WAVE SOLUTION OF HIGHER-ORDER THEORIES

We fmd an enact pp-gravitational wave solution of the fourth-order gra vity field equations. Outside the (delta-like) source this is not a va cuum solution of general relativity. It represents the contribution of the massive, m=(-beta)(-1/2), spin-two field associated while the Ric ci-squared term in the gravitational Lagrangian. The fourth-order term s tend to make the singularity of the curvature milder at the point wh ere the particle is located. We generalize this analysis to D dimensio ns, extended sources, and higher than fourth-order theories. We also b riefly discuss the scattering of fields by these kinds of plane gravit ational waves.