This actually seems unlikely - first year PhD students publish papers in string theory all the time. My guess is that it would suffice for you to have the right conversations with the right people.

Whatever the field, there is probably a lot of perfectly do-able research problems that no-one has yet gotten round to doing. The problem being, of course, that it's pretty hard to recognise which these problems are without having the sort of in-depth knowledge that comes from years studying inside the field.