Some New Velocity Averaging Results

Let (R, μ) be a nonatomic finite measure space and E = Lr(R, μ) a Lebesgue space over R. Then we consider tempered distributions f and g (depending on x ∈ Rn and v ∈ R), for which divx(af) = g in S′(Rn, E). Here a : R −→ Rn is a bounded function of v (a velocity field) satisfying a nondegeneracy condition. We study the regularity of the average f̄ = R R f(·, v)ψ(v) dμ(v) ∈ S′(Rn) (with ψ ∈ Lr (R, μ) a suitable weight function) when f and g are bounded in Banach space valued Besov spaces. We also present some compactness results for sequences of averages.