  We propose a nonperturbative gauge invariant regulator for d-dimensional
chiral gauge theories on the lattice. The method involves simulating domain
wall fermions in d + 1 dimensions with quantum gauge fields that reside on one
d-dimensional surface and are extended into the bulk via gradient flow. The
result is a theory of gauged fermions plus mirror fermions, where the mirror
fermions couple to the gauge fields via a form factor that becomes
exponentially soft with the separation between domain walls. The resultant
theory has a local d-dimensional interpretation only if the chiral fermion
representation is anomaly free. A physical realization of this construction
would imply the existence of mirror fermions in the standard model that are
invisible except for interactions induced by vacuum topology, and which could
gravitate differently than conventional matter.
