Abstract
Geometry- and gravity-induced effective photon mass is known to arise in many cases,
such as various optical waveguides, Kaluza–Klein theories, and many
other optical and general relativity situations. Here we study the
appearance of effective photon mass in the Newtonian limit due to the
presence of a gravity gradient emulated by an electromagnetic medium.
The effective photon mass squared appears to be proportional to the
local gravity gradient, and it becomes negative in an optical
anti-waveguide around the unstable equilibrium location. A similar
effect is observed in the emulated Kottler–Møller spacetime where the
absolute value of the gravity-induced effective photon mass appears to
coincide with the Unruh temperature. We demonstrate that similar to
the Unruh effect, a bath of thermal radiation should be observed in an
optical anti-waveguide near the unstable equilibrium, whose
temperature is defined by the emulated local gravity gradient, and
which remains unchanged in the c→∞ limit.