1) Nathan Hook: Identities at Play. Available here.
Nathan presents some really nice points on in-play identities, in a rather abrupt manner. Some typos disrupt the flow, but all in all, good work. (Nathan has severely misunderstood my ilinx idea, but I see now that it's my own wording's fault). Nathan is in strong contact with other researchers, so no surprise that he's well informed. Clever ideas.
2) Kivinen, Sari: Spin-Fold-Spill : a textual investigation about role-play, narrative, and fictitious truths. Available here.
Coming from a theatre studies angle, Kivinen presents a game/artpiece design, and its theoretical framing. Some ideas I liked a lot, as I did her permutations on what the medium allows, but the fact remains some very relevant key works (at least one of Harviainen, 2008, or 2010, or Lampo, 2011, or Stenros, 2010, should have been there...) were not at all mentioned. So: nice, but lots of unused potential because of a limited frame of reference. If you're into the larp-theatre angle at all, however, do check it out. Valuable.
3) Mosley, Ian: Beyond the 4th Wall: Exploring Identity in Live Action Role Players. For this one, you need to contact Ian personally.
Mosley looks at larps from a sociological viewpoint, especially with serious leisure as a concept in mind. Sadly, his reference base is strangely limited (rumor has it, at least partially due to supervisor bias), and key works like Brenne, Balzer and Stenros aren't used - nor is the absolutely seminal Fine. Some important others are there, however, as are some surprising texts, and the arguments are mostly well presented, so I get a very mixed reaction from it all. In any case, the author shows obvious talent that in my opinion just needs a bit of more reading to get into full bloom. Larp sociologists, do ask him for a copy.