Berry's phase and chiral anomalies

TL;DR

This paper reviews Berry's phase and chiral anomalies, discussing their theoretical foundations, formalisms, and implications, including applications in nuclear physics, highlighting the differences between classical and quantum treatments.

Contribution

It provides a comprehensive survey of Berry's phase and chiral anomalies, comparing Lagrangian and Hamiltonian formalisms, and discusses lattice fermions and their anomalies.

Findings

Lagrangian formalism can incorporate both gauge symmetries but loses quantum properties.

Chiral fermions on the lattice do not exhibit anomalies at finite lattice spacing.

Ginsparg-Wilson fermions may be useful for anomaly-free lattice formulations.

Abstract

The basic materials of Berry's phase and chiral anomalies are presented to appreciate the phenomena related to those notions. As for Berry's phase, a general survey of the subject is presented using both Lagrangian and Hamiltonian formalisms. The canonical Hamiltonian formalism of the Born-Oppenheimer approximation, when applied to the anomalous Hall effect, can incorporate the gauge symmetry of Berry's connection but unable to incorporate the electromagnetic vector potential simultaneously. Transformed to the Lagrangian formalism with a time-derivative term allowed, the Born-Oppenheimer approximation can incorporate the electromagnetic vector potential simultaneously with Berry's connection, but the consistent canonical property is lost and thus becomes classical. The Lagrangian formalism can thus incorporate both gauge symmetries simultaneously but spoils the basic quantum symmetries, and thus results in classical anomalous Poisson brackets and the classical Nernst effect as in the conventional formalism. As for chiral anomalies, we present basic materials by the path integral formulation with an emphasis on fermions on the lattice. A chiral fermion defined by $\gamma_{5}$ on the lattice does not contain the chiral anomaly for the non-vanishing lattice spacing $a\neq0$. The idea of a spectral flow on the lattice does not lead to an anomaly for each species doubler separately but rather to a pair production in a general sense. We also mention that a specific construction called the Ginsparg-Wilson fermion, which is free of species doublers, may practically be useful. We discuss the representative applications of Berry's phase and chiral anomalies in nuclear physics and related fields to illustrate the use of these two basic notions.