A note on the Esscher transform of affine Markov processes
  In affine models, both the martingale property of stochastic exponentials and non-explosion of affine processes is characterized in terms of minimality of solutions to a system of generalized Riccati differential equations. This is the final improvement of previous results by Duffie, Filipovic and Schachermayer (2003), Mayerhofer, Muhle-Karbe and Smirnov (2011) and Keller-Ressel and Mayerhofer (2015) for processes on canonical state spaces. 
Eberhard Mayerhofer
math.PR