A note on the primordial abundance of stau NLSPs
  In scenarios with a gravitino LSP, there exist strong BBN constraints on the abundance of a possible stau NLSP. We find that in settings with substantial left-right mixing of the stau mass eigenstates these constraints can be evaded even for very long-lived staus. 
Michael Ratz, Kai Schmidt-Hoberg, Martin Wolfgang Winkler