Abstract

We derive quantum field theory Ward identities based on linear area preserving and conformal transformations in 2+1 dimensions. The identities relate Hall viscosities, Hall conductivities and the angular momentum. They apply both for relativistic and non relativistic systems, at zero and at finite temperature. We consider systems with or without translation invariance, and introduce an external magnetic field and viscous drag terms. A special case of the identities yields the well known relation between the Hall conductivity and half the angular momentum density.

Highlights

  • Quantum field theory Ward identities are relations among correlators that are derived using the symmetry generators

  • We derive quantum field theory Ward identities based on linear area preserving and conformal transformations in 2+1 dimensions

  • Ward identities introduce constraints among transport coefficients, which should be valid in holographic models that have quantum field theory dual descriptions

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Summary

Introduction

Quantum field theory Ward identities are relations among correlators that are derived using the symmetry generators. In [10] it has been shown that Ward identities of non-relativistic systems lead to a non-trivial relation between Hall viscosity and conductivities, and between Hall viscosity and angular momentum density. In this paper we will derive such identities for general relativistic or non-relativistic 2 + 1 dimensional quantum field theories, at zero and at finite temperature. For convenience we introduced in table 1 all the notations that will be used in the paper, and highlighted the main results in the different sections

Ward identities from linear transformations
Systems with conserved momentum
Systems with a magnetic field
Adding dissipative terms
Relation between Hall viscosity and conductivities
Galilean invariant theories
Relation to angular momentum density
Systems with magnetic field
Spectral representation
Conformal transformations on the plane
Conformal Ward identity
Discussion
A Details of the calculation of Ward identities
Relation to conductivities
Coefficients of second derivatives of delta function
B Alternative derivation in systems with translation invariance
C Shear generators for free fermions in a magnetic field
D Spectral decomposition and retarded correlators
Finite temperature At finite temperature T the correlators are
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