Architectures and assessment of next-generation CMB polarization instruments

Cosmological inflation predicts a background of gravitational waves that imprint a characteristic polarized pattern on the CMB. This signal is degraded by "foreground" emission from our galaxy, and by non-ideal aspects of the instrument. Future missions must be motivated by end-to-end pipelines that include systematics and sophisticated representations of astrophysical foregrounds and cleaning. We plan to write a pipeline that will quickly close the loop between design choices and projected scientific outcomes.

The curl-like component of the polarization field, or “B-mode” is the primary target of the next generation of cosmic microwave background polarization experiments. B-modes can be sourced by gravitational waves produced during cosmological inflation, subsequent gravitational lensing of CMB polarization, or by astrophysical “foreground” polarized emission. The inflationary component of the B-modes is of greatest scientific interest because it would reflect energy scales and physics significantly beyond the reach of terrestrial accelerators. To secure a clear statement on inflation as the correct interpretation, the other sources of B-modes must be cleanly removed or ruled out. The new experimental burden is now not on detecting B-modes but showing convincingly that they are inflationary.

Basic decisions about focal plane arrangements, optical design, frequency bands, sensitivity, and survey strategy all interact and drive mission costs. There is not a simple analytic expression relating design parameters to scientific output. Instead, these questions must be addressed using an end-to-end simulation that can quickly close the loop and evaluate design decisions.