If you like Mathematics, you will probably like Theoretical Physics too. Theoretical Physics is about manipulating very complex equations to describe something in the Nature. Derivation of one equation from another can take a very long way, often 10 pages or more. Sometimes it can take so long on the paper so one better to use Computer Algebra programs like Maple. Theoretical Physics is a vast field, in our group we work on the Theoretical Physics of Complex fluids, and self-organization and pattern formation in Soft and Active Matter.
Example of research
Ratushnaya V.I., Bedeaux D., Kulinskii V.L., Zvelindovsky A.V. “Stability properties of the collective stationary motion of self-propelling particles with conservative kinematic constraints” J. of Physics A: Mathematical and Theoretical 40 (2007) 2573-2581.