Delta-shocks as limits of vanishing viscosity for multidimensional zero-pressure gas dynamics

In this paper we study zero-pressure gas dynamics, which is a nonstrict hyperbolic system of nonlinear conservation laws with delta-shock waves in solutions. By using the generalized Rankine-Hugoniot relations to solve the Riemann problem with two pieces of constant initial data, multidimensional planar delta-shock waves dependent upon a family of one parameter are obtained. Furthermore! we choose a unique entropy solution through the process of a viscosity vanishing, and obtain a stability for delta shocks in multidimensions.