  In this work we study interacting spinless fermions on a two-chain ladder
with inter-chain pair tunneling while single-particle tunneling is suppressed
at low energy. The model embodies a $\mathbb{Z}_2$ symmetry associated with the
fermion parity on each chain. We find that when the system is driven to the
strong-coupling phase by the pair tunneling, Majorana excitations appear on the
boundary. Such Majorana edge states correspond to two-fold degeneracy of ground
states distinguished by different fermion parity on each chain, thus
representing a generalization of one-dimensional topological superconductors.
We also characterize the stability of the ground state degeneracy against local
perturbations. Lattice fermion models realizing such effective field theory are
discussed.
