The Atacama Cosmology Telescope: Delensed Power Spectra and Parameters
  We present LCDM cosmological parameter constraints obtained from delensed
microwave background power spectra. Lensing maps from a subset of DR4 data from
the Atacama Cosmology Telescope (ACT) are used to undo the lensing effect in
ACT spectra observed at 150 and 98 GHz. At 150 GHz, we remove the lensing
distortion with an effective efficiency of 30% (TT), 30% (EE), 26% (TE) and 20%
(BB); this results in detections of the delensing effect at 8.7 sigma (TT), 5.1
sigma (EE), 2.6 sigma (TE), and 2.4 sigma (BB) significance. The combination of
150 and 98 GHz TT, EE, and TE delensed spectra is well fit by a standard LCDM
model. We also measure the shift in best-fit parameters when fitting delensed
versus lensed spectra; while this shift does not inform our ability to measure
cosmological parameters, it does provide a three-way consistency check among
the lensing inferred from the best-fit parameters, the lensing in the CMB power
spectrum, and the reconstructed lensing map. This shift is predicted to be zero
when fitting with the correct model since both lensed and delensed spectra
originate from the same region of sky. Fitting with a LCDM model and
marginalizing over foregrounds, we find that the shift in cosmological
parameters is consistent with zero. Our results show that gravitational lensing
of the microwave background is internally consistent within the framework of
the standard cosmological model.
