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National Aeronautics and Space Administration

Goddard Space Flight Center

Astrophysics Science Division | Sciences and Exploration

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Upper Limits to Distorted Spectra

Distortions in the cosmic microwave background away from a perfect blackbody curve are an expected part of all viable cosmological models. Detecting these distortions or showing that they do not exist is an important step for understanding the early universe. The plot below shows current 95% confidence upper limits to distorted spectra. The purple curves show the upper limit and predicted signal resulting from free-free emission from ionized gas at the epoch of reionization and structure formation. The predicted signal from the formation of observed structure lies well below the current upper limit, set by ground-based measurements at centimeter wavelengths. Detecting this signal requires mK precision at wavelengths longer than 10 cm, well within the capabilities of ARCADE.
CMB Data vs expected signals
The green curve shows the chemical potential distortion from the decay or annihilation of massive particles in the early universe. Recent analyses of gamma ray emission hint at a signal from annihilating dark matter toward the Galactic center. Since the annihilation rate varies as z^6, annihilation in the early universe could produce a measurable energy input, resulting in a detectable distortion. Measurements of the CMB spectrum can provide important constraints on dark matter properties and high-energy physics.

The gray box shows the ARCADE frequency range and the anticipated 1 mK error budget. ARCADE will measure the CMB spectrum at wavelengths 15 cm to 3 mm (3 GHz to 90 GHz frequency) where these cosmological signals are largest.