Surface waves in a plasma flow

Dispersion characteristics of surface waves in a semibounded plasma flow wi th relativistic velocity u(0) parallel to the plasma-vacuum interface are p resented. The plasma is considered to be cold and collisionless, which allo ws us to take into account only the electron motion. It is shown that - in contrast to the bulk waves, which are invariant with respect to Lorentz tra nsformations and whose spectrum is independent of the flow velocity - the s urface waves are not invariant, which leads to a dependence of their spectr um on the flow velocity and, correspondingly, to non-reciprocity. The latte r peculiarity is due to the fact that the boundary conditions are not invar iant.