Anomalous electrodynamics of neutral pion matter in strong magnetic fields

Abstract

The ground state of quantum chromodynamics in sufficiently strong external magnetic fields and at moderate baryon chemical potential is a chiral soliton lattice (CSL) of neutral pions [1]. We investigate the interplay between the CSL structure and dynamical electromagnetic fields. Our main result is that in presence of the CSL background, the two physical photon polarizations and the neutral pion mix, giving rise to two gapped excitations and one gapless mode with a nonrelativistic dispersion relation. The nature of this mode depends on the direction of its propagation, interpolating between a circularly polarized electromagnetic wave [2] and a neutral pion surface wave, which in turn arises from the spontaneously broken translation invariance. Quite remarkably, there is a neutralpion-like mode that remains gapped even in the chiral limit, in seeming contradiction to the Goldstone theorem. Finally, we have a first look at the effect of thermal fluctuations of the CSL, showing that even the soft nonrelativistic excitation does not lead to the LandauPeierls instability. However, it leads to an anomalous contribution to pressure that scales with temperature and magnetic field as T 5/2 (B/f π ) 3/2 .

Global 3-group symmetry and ’t Hooft anomalies in axion electrodynamics

“…One is to analyze physics in the background magnetic field, spatially varying axion field, and so on. It has been shown that in non-trivial backgrounds, mass spectra of the axion and photon are deformed [26,54,55,116]. We may understand such deformations of the phase structure by using higher-form symmetries, 3group, and their 't Hooft anomalies (see e.g., ref.…”

Topological term, QCD anomaly, and the η′ chiral soliton lattice in rotating baryonic matter

“…To understand its possible realization in heavy ion collisions more realistically, it is necessary to take into account the finite-temperature effects on the η CSL; see also ref. [46] for the study on the low-temperature effects on the π 0 CSL in a magnetic field. Further studies in this direction will be reported elsewhere.…”

An Inhomogeneous Phase in Quark Matter without the Sign Problem

“…It is known that one-dimensional modulations in pion condensates [1] are unstable at finite temperatures (although quasi-long-range order may persist). On the other hand, CSL in QCD seems to be stable under quantum fluctuations [7] and the effects of finite temperature are subject of ongoing work.…”