Electronic Journal of Qualitative Theory of Differential Equations (Jan 2024)
Weighted Lorentz estimates for subquadratic quasilinear elliptic equations with measure data
Abstract
In this work we mainly prove the following interior gradient estimates in weighted Lorentz spaces $$ g^{-1} \left[\mathcal M_1(\mu) \right] \in L^{q, r}_{w, loc} (\Omega) \Longrightarrow |Du| \in L^{q, r}_{w, loc} (\Omega), $$ where $g(t)= t a(t)$ for $t\geq 0$ and $\mathcal{M}_1(\mu)(x)$ is the first-order fractional maximal function $$ \mathcal{M}_1(\mu)(x):=\sup_{r>0}\frac{r|\mu|(B_r(x))}{|B_r(x)|}, $$ for a class of non-homogeneous divergence quasilinear elliptic equations with measure data in the subquadratic case \begin{equation*} -\operatorname{div}\left[a \left( \left( A D u \cdot D u\right)^{\frac{1}{2}} \right)A D u \right] =\mu \quad \mbox{in}~ \Omega, \end{equation*} whose model cases are the classical elliptic $p$-Laplacian equation with measure data \begin{align*} -\operatorname{div} \left( \left| D u \right|^{p-2} D u \right)=\mu \quad \mbox{for } 1<p<2 \end{align*} and the elliptic $p$-Laplacian equation with the logarithmic term and measure data \begin{equation*} -\operatorname{div} \left( \left| D u \right|^{p-2}\log \left(1+ \left| D u \right|\right) D u \right)=\mu \quad \mbox{for } 1<p<2. \end{equation*} It deserves to be specially noted that the subquadratic case is a little different from the superquadratic case since as an example, the modulus of ellipticity in the above-mentioned special cases tends to infinity when $|Du| \rightarrow 0$ for $1<p<2$.