What do you think about Gravitational wave physics and numerical relativity ? Will it expand much in future? Now few universities are giving research facilities on these two. Why ? But i really like these two.
A (presumable) lesser known university I know of would be the Rochester Institute of Technology (ccrg(DOT)rit(DOT)edu) in New York. Although they lack a grad program in physics as well as a PhD program in mathematics (MS only) they seem to be ramping up a PhD in "Astrophysical Sciences and Technology."