Cosmological Recombination of Lithium and Its Effect on the Microwave Background Anisotropies

The cosmological recombination history of lithium, produced during Big--Bangnucleosynthesis, is presented using updated chemistry and cosmologicalparameters consistent with recent cosmic microwave background (CMB)measurements. For the popular set of cosmological parameters, about a fifth ofthe lithium ions recombine into neutral atoms by a redshift $z\sim 400$. Theneutral lithium atoms scatter resonantly the CMB at 6708 \AA and distort itsintensity and polarization anisotropies at observed wavelengths around $\sim300 \mu$m, as originally suggested by Loeb (2001). The modified anistropiesresulting from the lithium recombination history are calculated for a varietyof cosmological models and found to result primarily in a suppression of thepower spectrum amplitude. Significant modification of the power spectrum occursfor models which assume a large primordial abundance of lithium. Whiledetection of the lithium signal might prove difficult, if offers thepossibility of inferring the lithium primordial abundance and is the only probeproposed to date of the large-scale structure of the Universe for $z\sim500-100$.Comment: 20 pages, 7 figure