"The guy" was me. The medium you used to participate in here should never be an excuse to not providing the necessary information. And BTW, "the guy" is also a physicist and doesn't need a lesson in what a "theoretical physics" is, especially not from an entry in Wikipedia.
Then you should have been explicit with this from Post #1! What you want to do is go in "Cosmology and Astrophysics", and you prefer to do the theoretical part of this subject area. This area of study in physics, if you notice, is listed as a APS Division!
This makes zero sense. People tend to flock to the subject area, not "experimental" or "theoretical". Someone doing theoretical astrophysics tend to have less interest in someone doing theoretical condensed matter physics in topological insulator than someone doing experimental astrophysics. After all, as a theorist, you'd be MORE interested in seeing the experimental results in YOUR field that might confirm or contradict your ideas! Thus, conferences and workshops are all organized under the subject area rather than the broad and vague banner of theory or experiment.
Zz.