Last year I met a professor from another university and approached him about writing a journal article together on a topic that is not that similar to my main research. In fact, I suspect this research will prove a point that is contrary to the beliefs of my supervisor. Should I mention the article/research at all to my supervisor? In general, if the supervisor is paying me, should his name go on everything I publish during my PhD? It's a tough call. Thanks everyone!

personally, if the article is nothing to do with your thesis topic, then i cant see a good reason to put your supervisors name on the article - presumably they wont have contributed anything, so why would they be on it? However, i would mention that you're doing it, out of courtesy really - if anything, they should be pleased that you're getting involved in stuff and making yourself a more well-rounded academic!

Definately mention it - you don't want your sup finding out by reading the article after its published!