Statistical anisotropy of CMB as a probe of conformal rolling scenario

TL;DR

This paper investigates statistical anisotropy in the CMB as a test for the conformal rolling early Universe scenario, using WMAP data to constrain model parameters and identify potential anisotropic signatures.

Contribution

It applies a quadratic maximum likelihood method to WMAP data to constrain anisotropy parameters in conformal rolling models, including scenarios with an intermediate stage.

Findings

Confirmed large quadrupole anisotropy likely due to systematics.

Set an upper limit h^2 < 0.045 for models with an intermediate stage.

Found weaker constraints for models without the intermediate stage.

Abstract

Search for the statistical anisotropy in the CMB data is a powerful tool for constraining models of the early Universe. In this paper we focus on the recently proposed cosmological scenario with conformal rolling. We consider two sub-scenarios, one of which involves a long intermediate stage between conformal rolling and conventional hot epoch. Primordial scalar perturbations generated within these sub-scenarios have different direction-dependent power spectra, both characterized by a single parameter h^2. We search for the signatures of this anisotropy in the seven-year WMAP data using quadratic maximum likelihood method, first applied for similar purposes by Hanson and Lewis. We confirm the large quadrupole anisotropy detected in V and W bands, which has been argued to originate from systematic effects rather than from cosmology. We construct an estimator for the parameter h^2. In the case of the sub-scenario with the intermediate stage we set an upper limit h^2 < 0.045 at the 95% confidence level. The constraint on h^2 is much weaker in the case of another sub-scenario, where the intermediate stage is absent.