Collaboration with other researchers except supervisors I am wondering if it is ethical and acceptable that a Ph.D. student receiving fund and RA from a university and a Prof collaborates on a topic with other researchers and professors (other universities)?
In this situation, should we inform our supervisors?
Yes, it's totally ethical and acceptable. Research doesn't happen in a vacuum, and collaborations are generally beneficial to all parties. I cannot imagine any funding body or person preventing you from collaborating with others. Talk to your supervisor first, of course, as they may want to be part of the collaboration too.