Most major graduate institutions, including Cornell, have extensive written materials that lay out how some of these things are done in a specific program. For example, waiting 1 year to join a research group sounds like a long time for me, but apparently it is normal for your institution (maybe normal for physics in general).
For Cornell Physics, see their handbook at http://physics.cornell.edu/sites/physics/files/Yellow-Book-Revised-July-2013.pdf and the rest of their graduate website at http://physics.cornell.edu/graduate
Verbatim from the 'yellow book':
As to research, students should, during the first year of graduate work, spur themselves (and be
encouraged by the faculty) to find out about some of the Cornell research going on around them.
By the summer following the first year they should associate themselves personally with the
research of some professor or research group, even if this association is only temporary. The
normal time for a reasonably firm commitment for a Ph.D. thesis area, and for such an
understanding with a supervising professor, is at about the end of the second year.
You may certainly approach professors who you may want to work with during and after acceptance into the program. I am not sure what the funding norms are in physics in terms of how far in advance professors know they will be able to take on a student, but I see no reason why it would hurt to contact professors you are interested in working with as part of the application process and decision to accept admission if granted.
Cornell offers visits to prospective Ph.D students: http://physics.cornell.edu/prospective-graduate-students#plan-a-visit which includes meeting with professors, presumably who you would be interested in working with.
It doesn't seem like a visit is necessary just based on what I see on their website (and I would expect this sort of thing is normally done before acceptance, maybe you have even already done this), but you could certainly manage a more informal visit via email, particularly if travel is a hardship.