H\"older gradient estimates for a class of singular or degenerate parabolic equations

We prove interior H\"older estimate for the spatial gradients of the viscosity solutions to the singular or degenerate parabolic equation $$u_t=|\nabla u|^{\kappa}\mbox{div} (|\nabla u|^{p-2}\nabla u),$$ where $p\in (1,\infty)$ and $\kappa\in (1-p,\infty).$ This includes the from $L^\infty$ to $C^{1,\alpha}$ regularity for parabolic $p$-Laplacian equations in both divergence form with $\kappa=0$, and non-divergence form with $\kappa=2-p$. This work is a continuation of a paper by the last two authors \cite{JS}.