Complex generalized spin-c Killing spinors in low dimensions

Abstract

We classify all complex generalized spin-c Killing spinors with complex Killing function $iμ-α$ on complete Riemannian surfaces, presenting an explicit list of all possible cases. We show that, contrary to previous statements in the literature, there exist complex generalized spin-c Killing spinors on Riemannian surfaces for which $αμ\not\equiv0$. We illustrate the classification by providing several explicit local, compact, and complete examples, including a complete example for which $αμ>0$ everywhere. We then move to three dimensions, proving that a spin-c Riemannian three-manifold admits a complex generalized spin-c Killing spinor with complex Killing function $iμ-α$ if and only if it is a $μ$-exact trans-Sasakian manifold of type $(α,μ)$. In addition, we construct a geodesically incomplete Riemannian three-manifold equipped with a complex generalized spin-c Killing spinor for which neither $μ$ nor $α$ vanishes identically, and then prove that this is not possible if the characteristic vector field of the associated trans-Sasakian structure is complete. These results settle a conjecture by Große and Nakad (Results in Mathematics, 2015) stating that on two- and three-dimensional Riemannian manifolds the complex Killing function of any complex generalized spin-c Killing spinor must be either globally real or globally imaginary.