## Very weak solutions of higher-order degenerate parabolic systems.(English)Zbl 1178.35215

The author study the parabolic $$p$$-Laplacian system of order $$2m$$, $$m \in \mathbb N$$, in its weak formulation
$\int_{\Omega_T}u\cdot\varphi - \langle |D^mu|^{p-2}D^mu,D^m\varphi\rangle \,dz = 0,\quad \forall\varphi \in C_0^{\infty}(\Omega_T;\mathbb R^N).$
The so-called very weak solution of the associated parabolic system is defined as a function
$u \in L^{p-\beta}(-T,0;W^{m,p-\beta}(\Omega;\mathbb R^N))\cap L^2(\Omega_T;\mathbb R^N)$
satisfying the above-mentioned integral identity. The main result of the paper is to ensure the existence of an exponent $$\beta > 0$$ depending only on the data such that any very weak solution $$u$$ is a weak solution i.e. $$D^m u \in L^{p-\beta} \Rightarrow D^mu \in L^{p+\beta}$$.

### MSC:

 35K65 Degenerate parabolic equations 46E35 Sobolev spaces and other spaces of “smooth” functions, embedding theorems, trace theorems 35K59 Quasilinear parabolic equations 35D30 Weak solutions to PDEs 35B65 Smoothness and regularity of solutions to PDEs 35K41 Higher-order parabolic systems