Let $X_t$ be reflected Brownian motion (RBM) in a cone with radially homogeneous reflection, killed upon reaching the vertex of the cone. We determine the adjoint process and use it to find the Martin boundary of the killed RBM together with all the corresponding positive harmonic functions. Then we can identify and prove uniqueness (up to positive scalar multiples) of the invariant measure for killed RBM and RBM without killing. Along the way, we prove the strong Feller property of the resolvent of RBM (no killing).
"The Adjoint Process of Killed Reflected Brownian Motion in a Cone and Applications." Ann. Probab. 27 (4) 1679 - 1737, October 1999. https://doi.org/10.1214/aop/1022874812