On the decoupling of mirror fermions
  We study an approach to chiral gauge theories on the lattice that involves decoupling "mirror" fermions from a vector-like theory. We have computed the polarization tensor in the "3-4-5" theory and find a directional discontinuity that appears to be nonzero in the continuum limit. This strongly suggests that the mirror fermions do not decouple. 
Joel Giedt, Chen Chen, Erich Poppitz
hep-lat