Positivity in the presence of initial system-environment correlation
  The constraints imposed by the initial system-environment correlation can lead to nonpositive Dynamical maps. We find the conditions for positivity and complete positivity of such dynamical maps by using the concept of an assignment map. Any initial system-environment correlations make the assignment map nonpositive, while the positivity of the dynamical map depends on the interplay between the assignment map and the system-environment coupling. We show how this interplay can reveal or hide the nonpositivity of the assignment map. We discuss the role of this interplay in Markovian models. 
Kavan Modi, and C\'esar A. Rodr\'iguez-Rosario, and Al\'an   Aspuru-Guzik
quant-ph