Title: Precision Calibration for 21 cm Cosmology
21 cm cosmology has great potential for revealing the structure and dynamics of the early universe, but recent experiments have struggled to achieve the necessary measurement precision. One of the principal challenges is overcoming calibration error. Established calibration approaches in the field require an exquisitely accurate sky model, and low-level sky model errors introduce calibration errors that corrupt the cosmological signal. We discuss recent advances in precision calibration, namely the development of an approach called Delay-Weighted Calibration, or DWCal. DWCal enables precise calibration even in the presence of sky model error. Sky model error does not affect all power spectrum modes equally, and DWCal fits calibration solutions preferentially from error-free modes. We present results from simulated data, showing that it substantially reduces calibration error in the presence of realistic levels of sky model error and can improve 21 cm power spectrum sensitivity by approximately 2 orders of magnitude.