The Imprint of Lithium Recombination on the Microwave Background Anisotropies

Abstract

Following the 2001 paper of Loeb, we explore the imprint of the resonant 6708 Angstrom line opacity of neutral lithium on the temperature and polarization anisotropies of the cosmic microwave background (CMB) at observed wavelengths of 250-350 mum (0.9-1.2 THz). We show that if lithium recombines in the redshift range of z = 400-500 as expected, then the standard CMB temperature and polarization anisotropies would be significantly modified in this wavelength band. The lithium signal may be difficult to separate from the contamination by the far-infrared background and galactic foregrounds. We show that in polarization, the signal could be comparable to the expected polarization anisotropies of the far-infrared background on subdegree angular scales (l greater than or similar to 100). Detection of the predicted signal can be used to infer the primordial abundance of lithium, and to probe structure in the universe at z similar to 500.