Low energy effective field theories of fermion liquids and mixed $U(1)\times \mathbb{R}^d$ anomaly

TL;DR

This paper develops low energy effective field theories for gapless fermionic and bosonic systems with $U(1) imes R^d$ symmetry, highlighting the role of mixed anomalies in constraining phases and properties like Fermi surface volume.

Contribution

It introduces a unified effective field theory framework incorporating mixed anomalies for systems with $U(1) imes R^d$ symmetry, including Fermi liquids with magnetic fields.

Findings

Mixed anomaly proportional to particle density can be measured via momentum distribution shifts.

Effective theories encode constraints on Fermi surface volume and low energy dynamics.

The framework applies to systems with real space and momentum space magnetic fields.

Abstract

In this paper we study gapless fermionic and bosonic systems in $d$-dimensional continuum space with $U(1)$ particle-number conservation and $\mathbb{R}^d$ translation symmetry. We write down low energy effective field theories for several gapless phases where $U(1)\times \mathbb{R}^d$ is viewed as internal symmetry. The $U(1)\times \mathbb{R}^d$ symmetry, when viewed as an internal symmetry, has a mixed anomaly, and the different effective field theories for different phases must have the same mixed anomaly. Such a mixed anomaly is proportional to the particle number density, and can be measured from the distribution of the total momentum $\boldsymbol{k}_\text{tot}$ for low energy many-body states (\ie how such a distribution is shifted by $U(1)$ symmetry twist $\boldsymbol{a}$), as well as some other low energy universal properties of the systems. In particular, we write down low energy effective field theory for Fermi liquid with infinite number of fields, in the presence of both real space magnetic field and $\boldsymbol{k}$-space "magnetic" field. The effective field theory also captures the mixed anomaly, which constraints the low energy dynamics, such as determine the volume of Fermi surface (which is another formulation of Luttinger-Ward-Oshikawa theorem).