Until you are truly Happy it will be quite difficult to pretend to be.
There really isn’t any research you need to confirm this. However, if you truly need it conduct one yourself. Try to be Happy about something that you have never been Happy about before. It is probably going to be a lot more difficult to imagine Being something you have never experienced.
So you see, it not about pretending to be Happy. You truly have to be present in order to be Happy.