Chiral anomalous dispersion

Andrey Sadofyev,Srimoyee Sen

doi:10.1007/jhep02(2018)099

Abstract

The linearized Einstein equation describing graviton propagation through a chiral medium appears to be helicity dependent. We analyze features of the corresponding spectrum in a collision-less regime above a flat background. In the long wave-length limit, circularly polarized metric perturbations travel with a helicity dependent group velocity that can turn negative giving rise to a new type of an anomalous dispersion. We further show that this chiral anomalous dispersion is a general feature of polarized modes propagating through chiral plasmas extending our result to the electromagnetic sector.

Highlights

JHEP02(2018)099 may consider an anomalous response caused by a gravitational wave (GW) propagating through the medium
While it is theoretically motivated to study the back-reaction of a chiral medium to a propagating gravitational perturbation, in general, one could think about possible applications in the physics of early universe where chiral imbalance is often discussed in the context of axion dynamics and primordial magnetic field generation [2]
In this paper we study how circularly polarized electromagnetic and gravitational waves propagate through a chiral medium

Summary

Chiral matter in gravitational field

In order to understand the back-reaction of a chiral medium to a metric perturbation it is instructive to review the simpler case of the magnetic response. From (2.2) one expects a perturbation in h11 to result in a preferred orthogonal combination of spin and linear momentum leading to non-zero perturbation in T 12 according to (2.1) This effect cancels for two helicities of fermions in a P-even set-up but one may expect a response analogous to (1.2) if there is a chiral imbalance. Note that these simple arguments based on the spin-field interaction cannot serve as a rigorous derivation for massless fermions and should be supported by direct calculations in a chiral medium (as it is done for both magnetic [31, 34, 35] and gravitational [19] responses). We think that this picture can be helpful for understanding of the origin of CGE

Gravitational dispersion relation

Electromagnetic dispersion relation

Outlook and discussion