Gradient estimates for some $f$-heat equations driven by Lichnerowicz's equation on complete smooth metric measure spaces

Given a complete, smooth metric measure space $(M,g,e^{-f}dv)$ with the Bakry-\'Emery Ricci curvature bounded from below, various gradient estimates for solutions of the following general $f$-heat equations $$u_t=\Delta_f u+au\log u+bu +Au^p+Bu^{-q}$$ and $$u_t=\Delta_f u+Ae^{pu}+Be^{-pu}+D$$ are studied. As by-product, we obtain some Liouville-type theorems and Harnack-type inequalities for positive solutions of several nonlinear equations including the Schr\"{o}dinger equation, the Yamabe equation, and Lichnerowicz-type equations as special cases.