  We argue that the nonrelativistic Hamiltonian of p_x+ip_y superconductor in
two dimensions can be derived from the relativistic Jackiw-Rossi model by
taking the limit of large Zeeman magnetic field and chemical potential. In
particular, the existence of a fermion zero mode bound to a vortex in the
p_x+ip_y superconductor can be understood as a remnant of that in the
Jackiw-Rossi model. In three dimensions, the nonrelativistic limit of the
Jackiw-Rebbi model leads to a "p+is" superconductor in which spin-triplet
p-wave and spin-singlet s-wave pairings coexist. The resulting Hamiltonian
supports a fermion zero mode when the pairing gaps form a hedgehoglike
structure. Our findings provide a unified view of fermion zero modes in
relativistic (Dirac-type) and nonrelativistic (Schr\"odinger-type)
superconductors.
