Thermalization of the spectral function in strongly coupled two   dimensional conformal field theories
  Using Wigner transforms of Green functions, we discuss non-equilibrium generalizations of spectral functions and occupation numbers. We develop methods for computing time-dependent spectral functions in conformal field theories holographically dual to thin-shell AdS-Vaidya spacetimes. 
V. Balasubramanian, A. Bernamonti, B. Craps, V. Ker\"anen, E.   Keski-Vakkuri, B. M\"uller, L. Thorlacius, and J. Vanhoof
hep-th