A framework for testing isotropy with the cosmic microwave background

Abstract

We present a new framework for testing the isotropy of the Universe using cosmic microwave background data, building on the nested-sampling ANICOSMO code. Uniquely, we are able to constrain the scalar, vector and tensor degrees of freedom alike; previous studies only considered the vector mode (linked to vorticity). We employ Bianchi type VII${}_h$ cosmologies to model the anisotropic Universe, from which other types may be obtained by taking suitable limits. In a separate development, we improve the statistical analysis by including the effect of Bianchi power in the high-$\ell$, as well as the low-$\ell$, likelihood. To understand the effect of all these changes, we apply our new techniques to WMAP data. We find no evidence for anisotropy, constraining shear in the vector mode to $({\sigma }_V/H{)}_0<1.7\times 10^{-10}$ (95% CL). For the first time, we place limits on the tensor mode; unlike other modes, the tensor shear can grow from a near-isotropic early Universe. The limit on this type of shear is $({\sigma }_{T,\mathrm{reg}}/H{)}_0<2.4\times 10^{-7}$ (95% CL).

11 pages, 6 figures, v3: minor modifications to match version accepted by MNRAS

References in corpus (5)

• Three Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Polarization Analysis
• Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Temperature Analysis
• Bianchi Model CMB Polarization and its Implications for CMB Anomalies
• Markov chain Monte Carlo analysis of Bianchi VII_h models
• Rogues' gallery: the full freedom of the Bianchi CMB anomalies

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• Anisotropic universe with anisotropic dark energy
• Redshift-space distortions from vector perturbations
• Bianchi spacetimes as super-curvature modes around isotropic cosmologies
• Spatially Homogeneous Universes with Late-Time Anisotropy
• Constraints on Bianchi-I type universe with SH0ES anchored Pantheon+ SNIa data
• Redshift-space distortions from vector perturbations II: Anisotropic signal
• Can cosmic rotation resolve the Hubble tension? Constraints from CMB and large-scale structure
• CMB line-of-sight integrators for nearly-isotropic cosmological models