The Effect of Gravitational Tidal Forces on Vacuum Polarization: How to Undress a Photon

Understand

The effect of gravitational tidal forces on photon propagation in curved spacetime is investigated.

• It is found that the imaginary part of the local refractive index Im n(u;w) may be negative as well as positive, corresponding to a local amplification as well as attenuation of the amplitude of the renormalized photon field.
• This is interpreted in terms of the effect of tidal forces on the virtual e^+e^- cloud surrounding the bare photon field---a positive/negative Im n(u;w) corresponds to an increased dressing/undressing of the bare photon.
• Below threshold decays of the photon to e^+e^- pairs can occur.