USAP-DC

The theory of the "Big Bang" provides a well-established cosmological model for the Universe from its earliest known periods through its subsequent large-scale evolution. The model traces the expansion of the Universe, starting from initial conditions of a very high density and temperature state which is almost but not perfectly smooth, and it offers a comprehensive explanation for a broad range of now-known phenomena, including the abundance of light elements, the cosmic microwave background radiation, and the distribution of large scale structures. While the established "Big Bang" theory leaves open the question of explaining the initial conditions, current evidence is consistent with the entire observable Universe being spawned in a dramatic, exponential "inflation" of a sub-nuclear volume that lasted about one trillionth of a trillionth of a trillionth of a second. Following this short inflationary period, the Universe continues to expand, but at a less rapid rate. While the basic "inflationary paradigm" is accepted by most scientists, the detailed particle physics mechanism responsible for inflation is still not known. 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 will address one of the oldest questions ever posed by mankind, "How did the Universe begin?", and it does so via observations made at one of the most intriguing places on Earth, South Pole Station in Antarctica.

The community-driven Astro2010 Decadal Survey described the search for the CGB as "the most exciting quest of all", emphasizing that "mid-term investment is needed for systems aimed at detecting the (B-mode) polarization of the CMB". In 2005, the NASA/DOE/NSF Task Force on CMB Research identified this topic as the highest priority for the field and established a target sensitivity for the ratio of gravitational waves to density fluctuations of r ~ 0.01. Such measurements promise a definitive test of slow-roll models of inflation, which generally predict a gravitational-wave signal around r~0.01 or above, producing CMB B-modes fluctuations that peak on degree angular scales. The ongoing BICEP series of experiments is dedicated to this science goal. The experiment began operating at South Pole in 2006 and has been relentlessly mapping an 800 square degree region of the sky in a region of low in Galactic foregrounds known as the Southern Hole. This award will support science observations and analysis for the CMB "Stage 3" science with the BICEP Array program that will measure the polarized sky in five frequency bands. It is projected to reach an ultimate sensitivity to the amplitude of inflationary gravitational waves of "sigma r" < 0.005, extrapolating from achieved performance and after conservatively accounting for the Galactic dust, Galactic synchrotron radiation, and CMB lensing foregrounds. This measurement will offer a definitive test of most slow-roll models of Inflation, and will realize or exceed the goals set by the Task Force in 2005 for sensitivity. The project will continue to provide excellent training for undergraduate and graduate students and postdoctoral fellows (including those from underrepresented groups) in laboratories that have exceptional track records in this regard. Cosmology and research in Antarctica both capture the public imagination, making this combination a remarkably effective vehicle for stimulating interest in science.

Person	Role
Kovac, John	Investigator and contact
Pryke, Clem	Co-Investigator

Antarctic Astrophysics and Geospace Sciences	Award # 1638957
Antarctic Instrumentation and Support	Award # 1638957

USAP-1638957_1

Deployment	Type
many members of BICEP/Keck team deployed to South Pole	general deployment

None in the Database

Repository	Title (link)	Format(s)	Status
Project website	BICEP/Keck data products	None	exist

1. Zhang, C., Ade, P. A. R., Ahmed, Z., Amiri, M., Barkats, D., Thakur, R. B., … Bullock, E. (2020). Characterizing the Sensitivity of 40 GHz TES Bolometers for BICEP Array. Journal of Low Temperature Physics. (doi:10.1007/s10909-020-02411-8)
2. St Germaine, T., Ade, P. A. R., Ahmed, Z., Amiri, M., Barkats, D., Basu Thakur, R., … Bullock, E. (2020). Optical Characterization of the Keck Array and BICEP3 CMB Polarimeters from 2016 to 2019. Journal of Low Temperature Physics. (doi:10.1007/s10909-020-02392-8)
3. Schillaci, A., Ade, P. A. R., Ahmed, Z., Amiri, M., Barkats, D., Thakur, R. B., … Bullock, E. (2020). Design and Performance of the First BICEP Array Receiver. Journal of Low Temperature Physics. (doi:10.1007/s10909-020-02394-6)
4. Ade, P. A. R., Ahmed, Z., Aikin, R. W., Alexander, K. D., Barkats, D., Benton, S. J., … Brevik, J. A. (2018). Constraints on Primordial Gravitational Waves Using Planck , WMAP, and New BICEP2/ Keck Observations through the 2015 Season. Physical Review Letters, 121(22). (doi:10.1103/physrevlett.121.221301)
5. Ade, P. A. R., Ahmed, Z., Amiri, M., Anderson, A. J., Austermann, J. E., Avva, J. S., … Bender, A. N. (2021). A demonstration of improved constraints on primordial gravitational waves with delensing. Physical Review D, 103(2). (doi:10.1103/physrevd.103.022004)
6. Ade, P. A. R., Ahmed, Z., Amiri, M., Barkats, D., Basu Thakur, R., Bischoff, C. A., … Buza, V. (2021). BICEP/Keck  XII: Constraints on axionlike polarization oscillations in the cosmic microwave background. Physical Review D, 103(4). (doi:10.1103/physrevd.103.042002)
7. Ade, P. A. R., Ahmed, Z., Amiri, M., Barkats, D., Thakur, R. B., Bischoff, C. A., … Bullock, E. (2021). Improved Constraints on Primordial Gravitational Waves using Planck, WMAP, and BICEP/Keck Observations through the 2018 Observing Season. Physical Review Letters, 127(15). (doi:10.1103/physrevlett.127.151301)
8. Ade, Ahmed, Z., Amiri, M., Barkats, D., Basu Thakur, R., Bischoff, C. A., Beck, D., Bock, J. J., Boenish, H., Bullock, E., Buza, V., Cheshire, J. R., Connors, J., Cornelison, J., Crumrine, M., Cukierman, A., Denison, E. V., Dierickx, M., Duband, L., … Fliescher, S. (2022). BICEP/Keck XIV: Improved constraints on axionlike polarization oscillations in the cosmic microwave background. Physical Review D, 105(2). (doi:10.1103/physrevd.105.022006)
9. Ade, P. A. R., Ahmed, Z., Amiri, M., Barkats, D., Thakur, R. B., Bischoff, C. A., Beck, D., Bock, J. J., Boenish, H., Bullock, E., Buza, V., Cheshire, J. R., Clark, S. E., Connors, J., Cornelison, J., Crumrine, M., Cukierman, A., Denison, E. V., Dierickx, M., … Zhang, S. (2023). BICEP/Keck. XVI. Characterizing Dust Polarization through Correlations with Neutral Hydrogen. The Astrophysical Journal, 945(1), 72. (doi:10.3847/1538-4357/acb64c)