An Exactly Solvable Interacting Edge Theory for a Weak 2D Topological Superconductor.

We study interacting edge states of a 2D weak topological superconductor protected by time-reversal symmetry. Such a system can be viewed as a stack of Marjorana/Kitaev chains (class BDI), possessing translation symmetry in the transverse direction. Interestingly, in this model, time-reversal symmetry forbids terms quadratic in fermionic degrees of freedom on the edge, so any edge dynamics must be inherently interacting. We proposed an exactly solvable model for the edge and worked out its phase diagram. It is shown that the edge is either symmetry breaking or gapless as expected from the bulk-boundary correspondence of a topological phase. We then construct a low energy field theory for the model in the gapless phase. We propose that the same field theory describes the edge of an intrinsically interacting fermionic symmetry-protected phase with Z_4 x Z_2^T symmetry.