Perturbation of elliptic operators in 1-sided NTA domains satisfying the capacity density condition

Let ω ⊂ Rn+1, n ≥ 2, be a 1-sided non-tangentially accessible domain (aka uniform domain), that is, ω satisfies the interior Corkscrew and Harnack chain conditions, which are respectively scale-invariant/quantitative versions of openness and path-connectedness. Let us assume also that ω satisfies the so-called capacity density condition, a quantitative version of the fact that all boundary points are Wiener regular. Consider L0 u = - div (A0 ∇ u), Lu = - div (A ∇ u), two real (non-necessarily symmetric) uniformly elliptic operators in ω, and write ω L0, ωL for the respective associated elliptic measures. The goal of this program is to find sufficient conditions guaranteeing that ωL satisfies an A ∞-condition or a RHq-condition with respect to ω L0. In this paper we establish that if the discrepancy of the two matrices satisfies a natural Carleson measure condition with respect to ω L 0, then ω L A ∞ (ω L 0). Additionally, we can prove that ωL RH q (ω L0) for some specific q (1, ∞), by assuming that such Carleson condition holds with a sufficiently small constant. This "small constant"case extends previous work of Fefferman-Kenig-Pipher and Milakis-Pipher together with the last author of the present paper who considered symmetric operators in Lipschitz and bounded chord-arc domains, respectively. Here we go beyond those settings, our domains satisfy a capacity density condition which is much weaker than the existence of exterior Corkscrew balls. Moreover, their boundaries need not be Ahlfors regular and the restriction of the n-dimensional Hausdorff measure to the boundary could be even locally infinite. The "large constant"case, that is, the one on which we just assume that the discrepancy of the two matrices satisfies a Carleson measure condition, is new even in the case of nice domains (such as the unit ball, the upper-half space, or non-tangentially accessible domains) and in the case of symmetric operators. We emphasize that our results hold in the absence of a nice surface measure: all the analysis is done with the underlying measure ω L0, which behaves well in the scenarios we are considering. When particularized to the setting of Lipschitz, chord-arc, or 1-sided chord-arc domains, our methods allow us to immediately recover a number of existing perturbation results as well as extend some of them.