After getting a PhD in high energy theoretical physics at one institution, could you apply and go to another institution (perhaps with higher prestige) for a second PhD in theoretical physics? Or is this technically disallowed? I suppose this will infuriate your first PhD advisor, and would probably not write a letter of recommendation for you. Any other problems? The reason I am asking this is because 1. My portfolio of published papers is not at all indicative of my interests. 2. I would like more time to learn, which I think is implicitly discouraged as a post-doc. 3. I am at a 2nd class institution, and would like to obtain a PhD from a top-tier institution to improve chances at getting tenure-track.