Several questions address the PhD. student/candidate issue. However, I stumbled upon the question of the correct abbreviation for a PhD. student. Indeed, one of my co-authors (technically an MSc., she is in the 1st year of her PhD.) asks to be listed as "PhD. student" on my paper. So is there an accepted way of doing that, or should I state "student" in full?
Other ideas would be "PhD. Stud.", "PhD. Stdt.", or something of that sort...
If this is common in your field, then you should imitate how you see it handled most often in other people's papers. I don't know of any standard abbreviation for "student" in this context, so I'd imagine you should write it out, but again you should imitate what other people do unless you see a good reason to do otherwise.
If it's not common in your field (and you therefore don't have many examples at hand to compare with), then I'd recommend not including this information. As MJeffryes points out in a comment, in much of academia papers don't list titles or positions at all. If that's the case in your field, then identifying the authors by title could look eccentric (or, depending on the title, pompous).
