Analytical validation of a continuum model for the evolution of a crystal surface in multiple space dimensions

In this paper we are concerned with the existence of a weak solution to the initial boundary value problem for the equation $\frac{\partial u}{\partial t} = \Delta\left(\Delta u\right)^{-3}$. This problem arises in the mathematical modeling of the evolution of a crystal surface. Existence of a weak solution $u$ with $\mathrm{\Delta }u\ge 0$ is obtained via a suitable substitution. Our investigations reveal the close connection between this problem and the equation ${\mathrm{\partial }}_t\rho +{\rho }^2{\mathrm{\Delta }}^2{\rho }^3=0$, another crystal surface model first proposed by H. Al Hajj Shehadeh, R. V. Kohn and J. Weare in Physica D: Nonlinear Phenomena, bf 240 (2011), no. 21, 1771-1784.