Regularity of a Solution to the Multidimensional Free Boundary Problem for the Porous Medium Equation

The regularity properties of solutions to the initial boundary value problem with free boundary for the nonlinear degenerate equation $u_t=\Delta(u^m)$, $m>1$, are studied in the multi-dimensional case. The condition $u=0$ holds on the free boundary whose velocity obeys the Darcy law. The differential properties of the free boundary are established in dependence on the smoothness of the initial data.