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Topological odd-parity superconductors

In this letter, we investigate topological phases of full-gapped odd-parity superconductors, which are distinguished by the bulk topological invariants and the topologically protected gapless boundary states. Using the particle-hole symmetry, we introduce Z_2 invariants characterizing topological odd-parity superconductors without or with time-reversal invariance. For odd-parity superconductors, a combination of the inversion and the U(1) gauge symmetry is manifestly preserved, and the combined symmetry enables us to evaluate the Z_2 invariants from the knowledge of the Fermi surface structure. Relating the Z_2 invariants to other topological invariants, we establish characterization of topological odd-parity superconductors in terms of the Fermi surface topology. Simple criteria for topological odd-parity superconductors in various dimensions are provided. Implications of our formulas for nodal odd-parity superconductors are also discussed.