LAUNCHING OF NONDISPERSIVE SUB-LUMINAL AND SUPERLUMINAL BEAMS

In this paper we analyze the physical meaning of sub-and superluminal soliton-like solutions (as the X-waves) of the relativistic wave equat ions and of some non-trivial solutions of the free Schrodinger equatio ns for which the concepts of phase and group velocities have a differe nt meaning than in the case of plane-wave solutions. If we accept the strict validity of the principle of relativity, such solutions describ e objects of two essentially different nature: carrying energy wave pa ckets and inertia-free proper phase vibrations. The speeds of the firs t-type objects can exceed the plane-wave velocity c only inside media and are always less than the vacuum light speed c. Particularly, very fast sound pulses with speeds c, < v < c have already been launched. The second-type objects are incapable of carrying energy and informati on but have superluminal speed. If we admit the possibility of a break down of Lorentz invariance, pulses described, for example, by superlum inal solutions of the Maxwell equations can be generated. Only experim ent will give the final answer.