Second PhD vs PostDoc - Math vs Theoretical Physics I'm about to complete my PhD in mathematics. I've been working with Group theory (Representations). Besides the PhD I also did a master's in theoretical physics (I took much more courses than necessary to earn the degree and all of them were in advanced level, and did really well). The thing is: I would like to work in Theoretical Physics, and I'd like to use my Math background and apply it to theoretical physics. I love both subjects and I think they are like brothers in a sense. So my question is:

1) Should I apply for a second PhD (In physics)? For me it would be the worst option, since I'd have to spent a lot of time in things that I already know, and I don't see the point of writing another thesis. I heard that in Europe some universities "hire" PhD students as Research Assistants, so maybe this wouldn't be so bad. What you think?

2) Apply for a PostDoc position in theoretical physics? This is the best option in my opnion, but I don't know if physics departments welcomes mathematicians applying for PostDocs positions, Do they?

Observe that this question is not answered in another post, my question is specific to math/theoretical physics research. Besides I'm not thinking in getting a second PhD to "learn" physics, I am asking about what is more reasonable when considering to do research both in math and in physics.
Anyone will hire you provided you can convince them you are better than the other candidates. You already have a PhD in Maths, you have to show them you have the skills and knowledge to complement their baggage and help solve their problems.

In the Mathematical Physics department in my undergrad university (Spain), there is at least one postdoc that is mathematician with a PhD in Economy, and two physicist readerers that works in Applied Mathematics.