UNIVERSAL SHORT-TIME BEHAVIOR IN CRITICAL-DYNAMICS NEAR SURFACES

We study the time evolution of classical spin systems with purely rela xational dynamics, quenched from T much greater than T-c to the critic al point, in the semi-infinite geometry. Shortly after the quench, as in the bulk, a nonequilibrium regime governed by universal power laws is also found near the surface. We show for ''ordinary'' and ''special '' transitions that the corresponding critical exponents differ from t heir bulk values, but can be expressed via scaling relations in terms of known bulk and surface exponents. To corroborate our scaling analys is, we present perturbative (E-expansion) and Monte Carlo results.