String theory as it has developed is not a field theory. It has more in common with Schroedinger's or Dirac's particle theories than with QED or the Standard Model. There is a real string field theory, and papers about it sometime appear on the arxiv. It started with Sen's conjectures about the role of tachyons and has developed over a number of years. I am interested that Kaku claims an interest here. I don't know of any thread in the research I have seen that goes back to him, but of course that doesn't mean it isn't there. Does anyone else have any information on this?