Dirac-Harmonic Maps
  We introduce a functional that couples the nonlinear sigma model with a spinor field:   $L=\int_M[|d\phi|^2+(\psi,\D\psi)]$. In two dimensions, it is conformally invariant. The critical points of this functional are called Dirac-harmonic maps. We study some geometric and analytic aspects of such maps, in particular a removable singularity theorem. 
Qun Chen, Juergen Jost, Jiayu Li, Guofang Wang