Dec 13 – 18, 2015
International Conference Centre Geneva
Europe/Zurich timezone

Is there evidence for anisotropy in CMB data?

Dec 14, 2015, 4:35 PM
Level 0, Room 4 (International Conference Centre Geneva)

Level 0, Room 4

International Conference Centre Geneva

17 Rue de Varembé, 1211 Geneva


Ms Daniela Saadeh (University College London)


Large scales in the Cosmic Microwave Background (CMB) may break statistical isotropy. Bianchi models are often invoked as a possible explanation for these low-\ell features: they provide an anisotropic underlying pattern over which the usual stochastic fluctuations are superimposed. However, the Bianchi models generally employed in the analysis of CMB data — despite mimicking the anomalies in the CMB temperature map — overproduce B-mode polarisation due to the very specific way in which they break isotropy. In this work, we consider the most general way to break Friedmann-Robertson-Walker isotropy that still preserves homogeneity and test for its signatures in Planck temperature and polarisation map; WMAP data are also analysed for comparison. In addition to the well-known Bianchi models that are more commonly employed in the literature, we consider more physical and untested-for Bianchi models that comply with polarisation constraints. We also show that improved constraints on anisotropy may be obtained by extending the likelihood to high \ell. Nested sampling techniques are employed to determine whether the Bayesian evidence favours anisotropic universes over the standard Lambda-CDM scenario.

Primary author

Ms Daniela Saadeh (University College London)


Dr Andrew Pontzen (University College London) Prof. Hiranya Peiris (University College London) Dr Jason McEwen (Mullard Space Science Laboratory, University College London) Dr Stephen Feeney (Imperial College London)

Presentation materials