Whittaker modules for the twisted affine Nappi-Witten Lie algebra (H)over-cap4 [τ]

The Whittaker module M-psi and its quotient Whittaker module L-psi,L-xi for the twisted affine Nappi-Witten Lie algebra (H) over cap (4) [tau] are studied. For nonsingular type, it is proved that if xi not equal 0, then L-psi,L-xi is irreducible and any irreducible Whittaker (H) over cap (4)[tau]-module of type psi with k acting as a non-zero scalar xi is isomorphic to L-psi,L-xi. Furthermore, for xi = 0, all Whittaker vectors of L-psi,L-0 are completely determined. For singular type, the Whittaker vectors of L-psi,L-xi with xi not equal 0 are fully characterized. (C) 2019 Elsevier Inc. All rights reserved.