CMB as a Probe of New Physics: The Story of Cosmic Birefringence

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birefringence is a postulated rotation of the linear polarization of photons
that arises due to a Chern-Simons coupling of a new scalar field to
electromagnetism. In particular, it appears as a generic feature of simple
quintessence models for Dark Energy, and therefore, should it be detected,
could provide insight into the microphysics of cosmic acceleration. Prior work
has sought this rotation, assuming the rotation angle to be uniform across the
sky, by looking for the parity-violating TB and EB correlations in the CMB
temperature/polarization. However, if the scalar field that gives rise to
cosmological birefringence has spatial fluctuations, then the rotation angle
may vary across the sky. In this talk, I will present the results of the first
CMB-based search for direction-dependent cosmological birefringence, using
WMAP-7 data, and report the constraint on the rotation-angle power spectrum for
all multipoles up to the resolution of the instrument. I will discuss the
implications for a specific models for rotation, and show forecasts for Planck
and future experiments. I will then conclude with a brief discussion of other
exotic physical models, such as chiral gravity, and astrophysical scenarios,
such as inhomogeneous reionization, that can be probed using the same analysis.