Limits on anisotropic inflation from the Planck data

Abstract

Temperature anisotropy of the cosmic microwave background offers a test of the fundamental symmetry of spacetime during cosmic inflation. Violation of rotational symmetry yields a distinct signature in the power spectrum of primordial fluctuations as P(k)=P₀(k)[1+g_*(k^·E^_cl)²], where E^_cl is a preferred direction in space and g_* is an amplitude. Using the Planck 2013 temperature maps, we find no evidence for violation of rotational symmetry, g_*=0.002±0.016 (68% C.L.), once the known effects of asymmetry of the Planck beams and Galactic foreground emission are removed. (Based on observations obtained with the Planck Collaboration, a ESA science mission with instruments and contributions directly funded by ESA Member States, NASA, and Canada.)