Polarization of the Massless Fermionic Vacuum in the Background of a   Singular Magnetic Vortex in 2+1-Dimensional Space-Time
  Effects of the configuration of an external static magnetic field in the form of a singular vortex on the vacuum of a quantized massless spinor field are determined. The most general boundary conditions at the punctured singular point which make the twodimensional Dirac Hamiltonian to be self-adjoint are employed. 
Yu. A. Sitenko (Bogolyubov Inst. Theor. Phys., Kiev)