Cherenkov Radiation from the Quantum Vacuum

A charged particle moving through a medium emits Cherenkov radiation when its velocity exceeds the phase velocity of light in that medium. Under the influence of a strong electromagnetic field, quantum fluctuations can become polarized, imbuing the vacuum with an effective anisotropic refractive index and allowing the possibility of Cherenkov radiation from the quantum vacuum. We analyze the properties of this vacuum Cherenkov radiation in strong laser pulses and the magnetic field around a pulsar, finding regimes in which it is the dominant radiation mechanism. This radiation process may be relevant to the excess signals of high energy photons in astrophysical observations.

Figure 1

Radiated power from the interaction of an electron with $\gamma ={10}^5$ and a crossed field with field strength $E=E_S\times {10}^{-3}$, due to: Synchrotron radiation (red line); total Cherenkov radiation (blue, solid line); Cherenkov $+$ mode (blue, dashed line); Cherenkov $-$ mode (blue, dotted line). The cutoff energy (black, dashed line) is $\hslash {\omega }_{\max }\simeq 0.25\mathrm{GeV}$.

Figure 2

Power radiated via synchrotron, pion, and Cherenkov emission, by protons in a magnetic field $B={10}^4\mathrm{T}$, with Lorentz factor $\gamma =5\times {10}^7$ (upper panel) and $\gamma =5\times {10}^9$ (lower panel). The cutoff energy is $\hslash {\omega }_{\max }\simeq 225\mathrm{GeV}$.