The Spin$^c$ Dirac Operator on Hypersurfaces and Applications
  We extend to the eigenvalues of the hypersurface Spin$^c$ Dirac operator well known lower and upper bounds. Examples of limiting cases are then given. Futhermore, we prove a correspondence between the existence of a Spin$^c$ Killing spinor on homogeneous 3-dimensional manifolds $\mathbb E^*(\kappa, \tau)$ with 4-dimensional isometry group and isometric immersions of $\mathbb E^*(\kappa, \tau)$ into the complex space form $\mathbb M^4(c)$ of constant holomorphic sectional curvature $4c$, for some $c\in \mathbb R^*$. As applications, we show the non-existence of totally umbilic surfaces in $\mathbb E^*(\kappa, \tau)$ and we give necessary and sufficient geometric conditions to immerse a 3-dimensional Sasaki manifold into $\mathbb M^4(c)$. 
Roger Nakad and Julien Roth
math.DG