Gradient estimates for nonlinear elliptic equations involving the Witten Laplacian on smooth metric measure spaces and implications

This article presents new local and global gradient estimates of Li-Yau type for positive solutions to a class of nonlinear elliptic equations on smooth metric measure spaces involving the Witten Laplacian. The estimates are derived under natural lower bounds on the associated Bakry-Émery Ricci curvature tensor and find utility in proving general Harnack inequalities and Liouville-type theorems to mention a few. The results here unify, extend and improve various existing results in the literature for special nonlinearities already of huge interest and applications. Some important consequences are presented and discussed.