Implications of the CMB power asymmetry for the early universe

Abstract

Observations of the microwave background fluctuations suggest a scale-dependent amplitude asymmetry of roughly 2.5 sigma significance. Inflationary explanations for this 'anomaly' require non-Gaussian fluctuations which couple observable modes to those on much larger scales. In this Letter we describe an analysis of such scenarios which significantly extends previous treatments. We identify the non-Gaussian 'response function' which characterizes the asymmetry, and show that it is non-trivial to construct a model which yields a sufficient amplitude: many independent fine tunings are required, often making such models appear less likely than the anomaly they seek to explain. We present an explicit model satisfying observational constraints and determine for the first time how large its bispectrum would appear to a Planck-like experiment. Although this model is merely illustrative, we expect it is a good proxy for the bispectrum in a sizeable class of models which generate a scale-dependent response using a large eta parameter.

5 pages. v2: Minor changes to match version published in Phys. Rev. D

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• Testing the scale-dependent hemispherical asymmetry with the 21-cm power spectrum from the epoch of reionization
• Primordial inhomogeneities from massive defects during inflation
• Closing in on the large-scale CMB power asymmetry
• CMB Polarization by the Asymmetric Template of Scalar Perturbations
• Testing cosmological models with large-scale power modulation using microwave background polarization observations
• Viable Curvaton Models from the $f_{NL}$ Parameter