FSD: Frequency Space Differential measurement of CMB spectral distortions

TL;DR

The paper introduces Frequency Space Differential (FSD), a novel method for detecting CMB spectral distortions by analyzing inter-frequency brightness temperature differences, potentially enabling measurements without internal calibrators.

Contribution

It proposes the FSD technique to measure CMB spectral distortions through inter-frequency differences, offering an alternative approach for future CMB missions.

Findings

FSD can model known spectral distortions like y and μ.

Method allows distortion detection without internal blackbody calibrator.

Potential for improved spectral distortion measurements in future missions.

Abstract

Although the Cosmic Microwave Background agrees with a perfect blackbody spectrum within the current experimental limits, it is expected to exhibit certain spectral distortions with known spectral properties. We propose a new method, Frequency Space Differential (FSD) to measure the spectral distortions in the CMB spectrum by using the inter-frequency differences of the brightness temperature. The difference between the observed CMB temperature at different frequencies must agree with the frequency derivative of the blackbody spectrum, in the absence of any distortion. However, in the presence of spectral distortions, the measured inter-frequency differences would also exhibit deviations from blackbody which can be modeled for known sources of spectral distortions like $y\,\&\,\mu$. Our technique uses FSD information for the CMB blackbody, $y$, $\mu$ or any other sources of spectral distortions to model the observed signal. Successful application of this method in future CMB missions can provide an alternative method to extract spectral distortion signals and can potentially make it feasible to measure spectral distortions without an internal blackbody calibrator.