Date:
19. February 2016 - 11:30
Speaker:
Daniela Saadeh (UCL)
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.
I will present a new search for signatures of highly generalised models in Planck and WMAP data. 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. We don’t find any evidence for anisotropy.