Largescale anomalies in the cosmic microwave background as signatures of nonGaussianity
Abstract
We derive a general expression for the probability of observing deviations from statistical isotropy in the cosmic microwave background (CMB) if the primordial fluctuations are nonGaussian and extend to superhorizon scales. The primary motivation is to properly characterize the monopole and dipole modulations of the primordial power spectrum that are generated by the coupling between superhorizon and subhorizon perturbations. Unlike previous proposals for generating the hemispherical power asymmetry, we do not assume that the power asymmetry results from a single large superhorizon mode. Instead, we extrapolate the observed power spectrum to superhorizon scales and compute the power asymmetry that would result from a specific realization of nonGaussian perturbations on scales larger than the observable universe. Our study encompasses many of the scenarios that have been put forward as possible explanations for the CMB hemispherical power asymmetry. We confirm our analytic predictions for the probability of a given power asymmetry by comparing them to numerical realizations of CMB maps. We find that nonlocal models of nonGaussianity and scaledependent local nonGaussianity produce scaledependent modulations of the power spectrum, thereby potentially producing both a monopolar and a dipolar power modulation on large scales. We then provide simple examples of finding the posterior distributions for the parameters of the bispectrum from the observed monopole and dipole modulations.
 Publication:

Physical Review D
 Pub Date:
 January 2016
 DOI:
 10.1103/PhysRevD.93.023524
 arXiv:
 arXiv:1508.06489
 Bibcode:
 2016PhRvD..93b3524A
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 21 pages, 11 figures