Emission of photons through cavity mirrors in the absence of external   driving
  We present a mechanism of energy concentration in a system composed by an optical cavity and a large number of strongly confined atoms, which cannot be described in the rotating wave approximation. The mechanism consists in the emission of photons through the cavity mirrors even in the absence of external driving. 
Almut Beige, Antonio Capolupo, Andreas Kurcz, Emilio Del Giudice, and   Giuseppe Vitiello
quant-ph