POLARBEAR: The first measurement of non-zero B-mode angular power spectrum
The evolution of the universe is based on the idea of gravitational instability, whereby initial tiny fluctuations in the density of the Universe grew under the influence of gravity to form the large-scale gravitational structures we see around us today. The POLARBEAR team produced the first direct measurement of the cosmic polarization induced by structure in the universe. Dark matter twists the polarization into a 'B-mode' signal at arc minute scales on the sky. The measurement rejects the possibility of zero B-mode power from gravitational lensing at 97.5% confidence. This measurement was produced by the first year of POLARBEAR observations. This announcement came one week before the BICEP2 team announced their detection of B-mode power at degree scales, consistent with an energy scale for cosmic inflation of about 1016 GeV. This was an exciting week for Cosmology!
These remarkable results add to the compelling science case for precision characterization of the CMB B-mode angular power spectrum. POLARBEAR’s continued observations, and the POLARBEAR-2 and Simons Array upgrades, are on track to lead this detailed characterization. These instruments all have the angular resolution necessary to characterize the B-mode signal from gravitational lensing. This provides the opportunity to probe the physics of neutrinos and dark energy, and also allows the removal of the lensing “foreground” signal to enable the precision characterization of the primordial inflationary B-mode signal. With the ability to measure 80% of the sky from our Chilean site, we will be able to make precise measurements of inflationary physics, probing grand unified theory (GUT) energy scales.