Probing Inflationary Physics with the South Pole Observatory

Cosmic inflation, an extension of the ΛCDM framework, proposes a brief exponential expansion of the early Universe to explain its observed initial conditions. A key prediction of inflationary models is a background of primordial gravitational waves, characterized by the tensor-to-scalar ratio r, which would imprint a distinct B-mode polarization pattern in the Cosmic Microwave Background (CMB). Measuring degree-scale B-mode polarization therefore provides a direct test of inflation and a window into physics near the Grand Unified Theory (GUT) energy scale.

The BICEP/Keck collaboration operates a series of telescopes at the Amundsen-Scott South Pole Station optimized for B-mode measurements. With broad frequency coverage to separate cosmological and Galactic foreground signals, a world-leading experimental uncertainty of σ(r) = 0.009 was achieved using data taken up to 2018. The South Pole Observatory (SPO), a joint effort between BICEP/Keck and the South Pole Telescope (SPT), aims to further tighten these limits by incorporating SPT data for delensing. In this talk, I will present performance-based forecasts for the SPO. With the planned deployment of a BICEP Array 90/150 GHz receiver in 2026/27 and an SPT-3G+ receiver in 2028/29, SPO is projected to reach σ(r) ≈ 0.001 by 2034.