Abstract
Following the 2001 paper of Loeb, we explore the imprint of the resonant 6708 A line opacity of neutral lithium on the temperature and polarization anisotropies of the cosmic microwave background (CMB) at observed wavelengths of 250-350 μm (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 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 ~ 500.
Highlights
The latest measurements of the anisotropies in the cosmic microwave background (CMB ; see Halverson et al 2001 ; Lee et al 2001 ; NetterÐeld et al 2001) imply that the days of ““ precision cosmology ÏÏ have already arrived.3 Future ground- and balloon-based experiments, in combination with the satellite missions Microwave Anisotropy Probe (MAP)4 in 2001 and Planck5 in 2007, will test current theoretical models to a subpercent precision at photon wavelengths Z500 km.at far-infrared wavelengths of [350 km, Loeb (2001) has recently shown that the drag force between photons and neutral lithium can strongly modify the CMB anisotropy maps through absorption and reemission at the resonant 6708 A transition of lithium from the ground state
The main difficulty in measuring the lithium imprint on the CMB anisotropies is the contamination by the farinfrared background (FIB)
We have shown that if more than half of the lithium ions recombine by z D 500, the temperature and polarization anisotropies of the CMB would be strongly altered at an observed wavelength of 335 km
Summary
The latest measurements of the anisotropies in the cosmic microwave background (CMB ; see Halverson et al 2001 ; Lee et al 2001 ; NetterÐeld et al 2001) imply that the days of ““ precision cosmology ÏÏ have already arrived. Future ground- and balloon-based experiments, in combination with the satellite missions Microwave Anisotropy Probe (MAP) in 2001 and Planck in 2007, will test current theoretical models to a subpercent precision at photon wavelengths Z500 km. At far-infrared wavelengths of [350 km, Loeb (2001) has recently shown that the drag force between photons and neutral lithium can strongly modify the CMB anisotropy maps through absorption and reemission at the resonant 6708 A transition of lithium from the ground state. We can solve the Boltzmann equation separately for each photon frequency by explicitly neglecting the transfer of momentum from the photons to the baryons due to lithium scattering. Ðed in this approach, the remaining correction is expected to be negligible. Tlithhiisufmollaotwoms f,raomphtohteonfawctiltlhlaikteqlLyi sI Dcat1te, ranwdhethnaittsfofrreqaugeivnecny is separated from the line center by less than the natural width (37 MHz/4n), which is much smaller than the frequency separation between these transitions (10 GHz)
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