In this review paper (http://arxiv.org/pdf/1202.1293.pdf), the author shows that threading a $\pi$ flux through a 2D $p_x+ip_y$ superconductor will trap a Majorana zero mode at the flux center. The deduction involves solving differential equations, and is hard to generalize to arbitrary dimensions or arbitrary gauge defects. Since Majorana zero mode is topologically robust, I would expect a simpler and less detail-dependent way to show that there is indeed a Majorana zero mode in the $\pi$ flux of a $p_x+ip_y$ superconductor. Does anyone know such a simpler approach?
PS: The answer I expect should be general enough that can be applied to $\pi$-flux tubes in 3D topological insulator or topological superconductors as well.