In this paper we establish gradient estimates for positive solutions to the equation
on any smooth metric measure space whose
m -Bakry–Émery curvature is bounded from below by
−(m−1)K with
K≥0. These estimates imply Liouville theorems for
(0.1). When
p→1, our main theorem reduces to the gradient estimate of Wang (2010)
[9]. As applications, several Harnack inequalities are obtained.