  One of the most powerful probes of new physics is the polarized Cosmic
Microwave Background (CMB). The detection of a nonzero polarization angle
rotation between the CMB surface of last scattering and today could provide
evidence of Lorentz-violating physics. The purpose of this paper is twofold.
First we review one popular mechanism for polarization rotation of CMB photons:
the pseudo-Nambu-Goldstone boson. Second, we propose a method to use the
Polarbear experiment to constrain Lorentz-violating physics in the context of
the Standard-Model Extension, a framework to standardize a large class of
potential Lorentz-violating terms in particle physics.
