Heuristic approach to the strong-coupling regime of the Kardar-Parisi-Zhang equation

We propose a heuristic approach of treating the strong-coupling regime of the Kardar-Parisi-Zhang (KPZ) equation. The method, which suggests that d(uc) = 4 is the upper critical dimension of the KPZ equation, enables one to use the epsilon expansion below d = 4 substrate dimensions to compute the critical exponents in the strong-coupling regime. We compute the dynamic exponent z and the roughness exponent chi to the first order in epsilon = 4 - d as z = 2 - (4 - d)/5 and chi = (4 - d)/5.