Density of the domain of doubly nonlinear operators in $L^1$

The aim of this paper is to provide sufficient conditions implying that the effective domain $D(A\phi)$ of an $m$-accretive operator $A\phi$ in $L^1$ is dense in $L^1$. Here, $A\phi$ refers to the composition $A\circ \phi$ in $L^1$ of the part $A=(\partial\mathcal{E})_{\vert L^{1\cap \infty}}$ in $L^{1\cap\infty}\times L^{1\cap\infty}$ of the subgradient $\partial\mathcal{E}$ in $L^2$ of a convex, proper, lower semicontinuous functional $\mathcal{E}$ on $L^2$ and a continuous, strictly increasing function $\phi$ on the real line $\mathbb{R}$. To illustrate the role of the sufficient conditions, we apply our main result to the class of doubly nonlinear operators $A\phi$, where $A$ is a classical Leray-Lions operator.