Interpolation for analytic families of multilinear operators on metric measure spaces

Abstract

Let (Xj , dj , μj), j = 0, 1, . . . ,m be metric measure spaces. Given 0 < pκ ≤ ∞ for κ = 1, . . . ,m and an analytic family of multilinear operators Tz : L 1(X1)× · · ·L m (Xm)→ Lloc(X0), for z in the complex unit strip, we prove a theorem in the spirit of Stein’s complex interpolation for analytic families. Analyticity and our admissibility condition are defined in the weak (integral) sense and relax the pointwise definitions given in [9]. Continuous functions with compact support are natural dense subspaces of Lebesgue spaces over metric measure spaces and we assume the operators Tz are initially defined on them. Our main lemma concerns the approximation of continuous functions with compact support by similar functions that depend analytically in an auxiliary parameter z. An application of the main theorem concerning bilinear estimates for Schrödinger operators on Lp is included.