@article {1805.08764, archivePrefix = {arXiv}, eprint = {1805.08764}, primaryClass = {gr-qc}, author = {Mihalis Dafermos and Yakov Shlapentokh-Rothman}, title = {Rough initial data and the strength of the blue-shift instability on cosmological black holes with $Λ> 0$}, year = {2018}, url = {http://arxiv.org/abs/1805.08764} }