[Paper] To *b or not to *b: Proto-Indo-European *b in a phylogenetic perspective

Fun scientific paper talking about the odd rarity of *b in the current Proto-Indo-European reconstructions. It doesn't propose why this happens, but it claims that most PIE instances of *b might be actually from a later stage of the language, that the author calls "Indo-Celtic" (the common ancestor of all IE languages minus Anatolian and Tocharian; also known in the literature as "core PIE").