Let G be a connected
semisimple Lie group of real rank one. We denote by 𝒰(g)K the algebra of left
invariant differential operators on G right invariant by K, and let 𝒵(𝒰(g)K) be its
center.
In this paper we give a sufficient condition for a differential operator
P ∈𝒵(𝒰(g)K) to have a fundamental solution on G. We verify that this
condition implies P C∞(G) = C∞(G). If G has a compact Cartan subgroup, we
also give a sufficient condition for a differential operator P ∈𝒵(𝒰(g)K) to
have a parametrix on G. Finally we prove a necessary condition for the
existence of parametrix of P ∈𝒵(𝒰(g)K) for a connected semisimple Lie
group.