Novel Topological Effects in Dense QCD in a Magnetic Field

TL;DR

This paper explores the topological electromagnetic effects in dense QCD with a magnetic dual chiral density wave, revealing phenomena like anomalous Hall currents, electric charge, and axion polaritons with implications for astrophysics and condensed matter.

Contribution

It introduces a novel topological phase in dense QCD characterized by an axion field coupling, leading to unique electromagnetic phenomena not previously described in this context.

Findings

Identification of a nontrivial topological phase in dense QCD

Prediction of anomalous Hall currents and electric charge

Proposal of axion polaritons in the phase

Abstract

We study the electromagnetic properties of dense QCD in the so-called Magnetic Dual Chiral Density Wave phase. This inhomogeneous phase exhibits a nontrivial topology that comes from the fermion sector due to the asymmetry of the lowest Landau level modes. The nontrivial topology manifests in the electromagnetic effective action via a chiral anomaly term $~\theta F^{\mu\nu}\tilde{F}_{\mu\nu}$, with a dynamic axion field $\theta$ given by the phase of the dual chiral density wave condensate. The coupling of the axion with the electromagnetic field leads to several macroscopic effects that include, among others, an anomalous, nondissipative Hall current, an anomalous electric charge, magnetoelectricity, and the formation of a hybridized propagating mode known as an axion polariton. Connection to topological insulators and Weyls semimetals, as well as possible implications for heavy-ion collisions and neutron stars are all highlighted.