Understanding the index theorems with massive fermions

Abstract

The index theorems relate the gauge field and metric on a manifold to the solution of the Dirac equation on it. In the standard approach, the Dirac operator must be massless in order to make the chirality operator well-defined. In physics, however, the index theorem appears as a consequence of chiral anomaly, which is an explicit breaking of the symmetry. It is then natural to ask if we can understand the index theorems in a massive fermion system which does not have chiral symmetry. In this review, we discuss how to reformulate the chiral anomaly and index theorems with massive Dirac operators, where we find nontrivial mathematical relations between massless and massive fermions. A special focus is placed on the Atiyah-Patodi-Singer index, whose original formulation requires a physicist-unfriendly boundary condition, while the corresponding massive domain-wall fermion reformulation does not. The massive formulation provides a natural understanding of the anomaly inflow between the bulk and edge in particle and condensed matter physics.

31 pages, 3 figures, invited review in IJMPA, references added

References in corpus (6)

• Dai-Freed theorem and topological phases of matter
• Atiyah-Patodi-Singer index from the domain-wall fermion Dirac operator
• The Schrödinger functional in lattice QCD with exact chiral symmetry
• Bulk-edge correspondence, spectral flow and Atiyah-Patodi-Singer theorem for the Z2-invariant in topological insulators
• Anomaly and Superconnection
• Mod-two APS index and domain-wall fermion