Introduction:
One of the most exciting news of this year was the recent claim from the BICEP2 experiment of an indirect measurement of primordial gravitational waves. The experiment is based in the South Pole and designed to measure the polarization of the cosmic background radiation, focusing on the so-called B-modes. These modes can give insight on the physics of early stages of the Universe. In particular, inflationary theories predict the existence of a gravitational wave background which in turn can be seen nowadays as B-modes of polarized cosmic radiation. Unfortunately, there are other sources of B-modes, such as synchrotron radiation, gravitational lensing or polarized thermal emission from diffuse galactic dust.
In this paper, the Planck collaboration presents measurements of the polarized dust angular power spectra. Dust is considered the main background of B-modes at some of frequencies at which the BICEP2 experiment is operating (150 GHz). However, the BICEP2 collaboration found that the galactic dust cannot explain by itself their measurements, claiming therefore an observation of primordial B-modes.