Foreground Scaling in the BICEP/Keck 2018 Likelihood

When studying B-mode polarization in the Cosmic Microwave Background, there is foreground emission from the Milky Way that obscures our view of the CMB. This foreground consists of dust and synchrotron radiation, where the foreground power spectra scales with angular scale. While this power-law is empirically supported when analyzing small patches of the sky, there is no theory to support this scaling. The baseline likelihood used in in the BK18 analysis uses data from multiple different telescopes, including the BICEP/Keck collaboration, WMAP, and Planck through the 2018 observation season. By using this data and separating dust and synchrotron radiation into bins based on angular scale, ι, and changing the likelihood calculation, we make the foreground model more flexible. The new likelihood follows the initial power-law likelihood within 1σ for both dust and synchrotron.