The current established cosmological model for a theory of the Big Bang leaves open the question of explaining how the entire observable Universe being spawned in a dramatic, exponential "inflation" of a sub-nuclear volume. Following this short inflationary period, the Universe continues to expand, but at a less rapid rate. It is believed that this violent space-time expansion would have produced primordial gravitational waves now propagating through the expanding universe, thus forming a cosmic gravitational-wave background (CGB) the amplitude of which measures the energy scale of inflation. The CGB imprints a faint signature in the polarization of the Cosmic Microwave Background (CMB), and detecting this polarization signature is arguably the most important goal in cosmology today.
This award supports the development of a 150 GHz wide-field receiver for studying the CMB polarization as part of the BICEP Array multi-institutional experiment. The BICEP Array continues the BICEP program of CMB polarization measurements and will ultimately operate in six frequency bands at 30, 40, 95, 150, 220 and 270 GHz to measure and remove polarized emission from the Milky Way Galaxy and detect the long-sought primordial gravitational waves signal. The proposed MRI effort will: (a) provide a large leap in measurement capability at the critical 150 GHz frequency band as the new 150 GHz receiver will make CMB measurements 15 times more rapidly than a single Keck Array receiver in this band, representing the leading measurement capability at this frequency when fielded; (b) leverage NSF's current investment in developing the BICEP Array telescope mount, and its commitment to supporting BICEP Array logistics, fielding, operations, and data analysis through 2021; and (c) leverage existing private funding to construct 30/40 and 95 GHz receivers that will place tight constraints on galactic synchrotron emission at the appropriate level of sensitivity for the proposed 150 GHz instrument. This development is low-risk and incorporates significant technological advances reached recently with fabrication of larger detector arrays. The proposed BICEP Array program is a pathfinder towards the CMB-S4 initiative to build ultimate CMB polarization experiments, which will combine many (up to 5-10) CMB telescopes deployed at different locations.
