Thank you for your interest in our research program at xxx University.
Usually our theory students are accepted into the departmental graduate program,
and begin the core curriculum before starting research. Once you have passed
the qualifying exam, then you can start work with a PhD advisor.
However, there is usually financial support for students when they arrive via a
teaching assistantship.
Your credentials look very good and I strongly encourage you apply!
You can find the
graduate school online application details at the University website.