Hi guys, I need an advise. I would like to start a Phd in physics, but I have not decided in which field yet. My curriculum is in theoretical physics, and my thesis was in cosmology, but I want to change the research field. I am looking for something theoretical that: 1)Still has conceptual problems open, 2)Requires skillness in math, 3)Has an effective contact with experiments, 4)Gives good chance to find career opportunities. What do you think could be suitable for me? Thanks! p.s. Excuse me for my atrocious english!