Cherenkov radiation in a strong magnetic field

Cheng-Yang Lee

doi:10.1016/j.physletb.2020.135794

Abstract

According to quantum electrodynamics, in a strong magnetic field that is constant and spatially uniform, the vacuum becomes polarized with a refractive index greater than unity. As a result, ultra-relativistic charged particles travelling in such media can emit Cherenkov radiation with a power spectrum directly proportional to the photon frequency ω. Therefore, by extrapolating ω beyond the critical synchrotron frequency ωc, the Cherenkov radiation will eventually dominate over its synchrotron counterpart. However, such an extrapolation is not possible. We show that in the framework of effective field theory, the maximal attainable photon frequency ωmax is about four order of magnitude less than ωc. At ω=ωmax, given the γe-factor of an electron travelling normal to a constant and spatially uniform magnetic field B, the spectrum of Cherenkov radiation becomes dominant when γe(|B|/Gauss)≳4.32×1019. Nevertheless, detecting the Cherenkov radiation in astrophysical environments remains challenging since its spectral flux density is about three orders of magnitude less than the synchrotron radiation.

Highlights

According to quantum electrodynamics, in a strong magnetic field that is constant and spatially uniform, the vacuum becomes polarized with a refractive index greater than unity
In order to discover new physics from astronomical observations, it is important to understand the mechanisms in which electromagnetic radiation are produced by the astrophysical sources
According to quantum electrodynamics (QED), as the electromagnetic fields approach the critical value |B|c = m2e/e = 4.42 × 1013 Gauss where me is the electron mass and e the electric charge 1, the vacuum becomes polarized with a refractive index greater than unity Bialynicka-Birula and Bialynicki-Birula (1970); Adler (1971); Brezin and Itzykson (1971); Tsai and Erber (1975); Latorre et al (1995); Dittrich and Gies (1998); Gies and Dittrich (1998); Dittrich and Gies (2000); Marklund and Shukla (2006)

Summary

Introduction

In a strong magnetic field that is constant and spatially uniform, the vacuum becomes polarized with a refractive index greater than unity. In order to discover new physics from astronomical observations, it is important to understand the mechanisms in which electromagnetic radiation are produced by the astrophysical sources. For ultra-relativistic charged particles travelling in such media, the emission of Cherenkov radiation becomes a real possibility. Taking into account the effects of non-linear QED, in the presence of a constant and spatially uniform magnetic field, the Cherenkov power spectrum is given by Macleod et al (2019)

Results

Conclusion