On the Harnack inequality for degenerate and singular elliptic equations   with unbounded lower order terms via sliding paraboloids
  We use the method of sliding paraboloids to establish a Harnack inequality for linear, degenerate and singular elliptic equation with unbounded lower order terms. The equations we consider include uniformly elliptic equations and linearized Monge-Amp\`ere equations. Our argument allows us to prove the doubling estimate for functions which, at points of large gradient, are solutions of (degenerate and singular) elliptic equations with unbounded drift. 
Nam Q. Le
math.AP