The Cosmic Microwave Background And Pseudo-Nambu-Goldstone Bosons:   Searching For Lorentz Violations In The Cosmos
  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. 
David Leon, Jonathan Kaufman, Brian Keating, Matthew Mewes
astro-ph.CO