I have been working on problems where there are various scales, such as disparate masses. I have formulated theoretical framework to deal with such problems in general.
I am also very interested in the issue of masses, which is a window into the extension of the Standard Model. This is very much tied up with effective field theory and in turn with what I described in the last paragraph.
Anticipating new precision experimental results from b-factories and other facilities, I have developed with a post-doctoral fellow a general way to evaluate two-loop Feynman diagrams, which fully respects the mass structure and the kinematics of the process under consideration.