Weyl groups, the Dirac inequality, and isolated unitary unramified representations

Abstract I present several applications of the Dirac inequality to the determination of isolated unitary representations and associated “spectral gaps” in the case of unramified principal series. The method works particularly well in order to attach irreducible unitary representations to the large nilpotent orbits (e.g., regular, subregular) in the Langlands dual complex Lie algebra. The results could be viewed as a p -adic analogue of Salamanca-Riba’s classification of irreducible unitary ( g , K ) -modules with strongly regular infinitesimal character.