Abstract On a compact connected group G, consider the infinitesimal generator -L - L of a central symmetric Gaussian convolution semigroup (ₜ) ₓ>₀ (μ t) t > 0. We establish several regularity results of the solution to the Poisson equation LU=F L U = F, both in strong and weak senses. To this end, we introduce two classes of Lipschitz spaces for 1 p 1 ≤ p ≤ ∞: ᵖ Λ θ p, defined via the associated Markov semigroup, and L ᵖ L θ p, defined via the intrinsic distance. In the strong sense, we prove a priori Sobolev regularity and Lipschitz regularity in the class of ᵖ Λ θ p space. In the distributional sense, we further show local regularity in the class of L ^ L θ ∞ space. These results require some strong assumptions on -L - L. Our main techniques build on the differentiability of the associated semigroup, explicit dimension-free Lᵖ L p (1 1 p ∞) boundedness of first and second order Riesz transforms, and a comparison between the two Lipschitz norms.
Bendikov et al. (Fri,) studied this question.