Title: Unexpected topology of the cosmic microwave background
Authors: Pratyush Pranav - Ecole Normale Superieure de Lyon (France) [presenting]
Abstract: The aim is to study the topology generated by the temperature fluctuations of the Cosmic Microwave Background (CMB) radiation, as quantified by the number of components and holes in the growing excursion sets. We compare CMB maps observed by the Planck satellite with a thousand simulated maps generated according to the LCDM paradigm with Gaussian distributed fluctuations. The comparison is multi-scale, being performed on a sequence of degraded maps with mean pixel separation ranging from 0.05 to 7.33 degrees. The parametric $\chi^2$-test shows differences between observations and simulations, yielding $p$-values at per-cent to less than per-mil levels roughly between 2 and 7 degrees, with the difference in the number of components and holes peaking at more than $3\sigma$ sporadically at these scales. There are reports of mildly unusual behaviour of the Euler characteristic at 3.66 degrees, which is phenomenologically related to the strongly anomalous behaviour of components and holes. It is also the scale at which the observed maps exhibit low variance compared to the simulations, and approximately the range of scales at which the power spectrum exhibits a dip with respect to the theoretical model. Non-parametric tests show even stronger differences at almost all scales. The results motivate a closer look at the standard cosmological paradigm, including primordial non-Gaussianity.