Is there a need and another way to measure the Cosmic Microwave Background temperature more accurately?

TL;DR

Tiny uncertainties in the CMB temperature T_0 significantly impact the Universe's recombination history and power spectra, suggesting alternative measurement methods via low-frequency CMB spectrum distortions could improve accuracy.

Contribution

The paper proposes a novel approach to measure T_0 through low-frequency CMB spectrum distortions, potentially reducing uncertainties in cosmological parameters.

Findings

Current T_0 uncertainty causes over 0.1% uncertainty in power spectra.

Measuring low-frequency distortions can constrain T_0 without absolute calibration.

Sensitivity of ~30nK needed to detect the recombination spectrum signal.

Abstract

The recombination history of the Universe depends exponentially on the temperature, T_0, of the cosmic microwave background. Therefore tiny changes of T_0 are expected to lead to significant changes in the free electron fraction. Here we show that even the current 1sigma-uncertainty in the value of T_0 results in more than half a percent ambiguity in the ionization history, and more than 0.1% uncertainty in the TT and EE power spectra at small angular scales. We discuss how the value of T_0 affects the highly redshifted cosmological hydrogen recombination spectrum and demonstrate that T_0 could, in principle, be measured by looking at the low frequency distortions of the cosmic microwave background spectrum. For this no absolute measurements are necessary, but sensitivities on the level of ~30nK are required to extract the quasi-periodic frequency-dependent signal with typical Delta nu/nu~0.1 coming from cosmological recombination. We also briefly mention the possibility of obtaining additional information on the specific entropy of the Universe, and other cosmological parameters.