Constraints on Cosmological Parameters from the 500 deg$^2$ SPTpol
  Lensing Power Spectrum
  We present cosmological constraints based on the cosmic microwave background
(CMB) lensing potential power spectrum measurement from the recent 500 deg$^2$
SPTpol survey, the most precise CMB lensing measurement from the ground to
date. We fit a flat $\Lambda$CDM model to the reconstructed lensing power
spectrum alone and in addition with other data sets: baryon acoustic
oscillations (BAO) as well as primary CMB spectra from Planck and SPTpol. The
cosmological constraints based on SPTpol and Planck lensing band powers are in
good agreement when analysed alone and in combination with Planck full-sky
primary CMB data. With weak priors on the baryon density and other parameters,
the CMB lensing data alone provide a 4\% constraint on $\sigma_8\Omega_m^{0.25}
= 0.0593 \pm 0.025$.. Jointly fitting with BAO data, we find $\sigma_8=0.779
\pm 0.023$, $\Omega_m = 0.368^{+0.032}_{-0.037}$, and $H_0 =
72.0^{+2.1}_{-2.5}\,\text{km}\,\text{s}^{-1}\,\text{Mpc}^{-1} $, up to
$2\,\sigma$ away from the central values preferred by Planck lensing + BAO.
However, we recover good agreement between SPTpol and Planck when restricting
the analysis to similar scales. We also consider single-parameter extensions to
the flat $\Lambda$CDM model. The SPTpol lensing spectrum constrains the spatial
curvature to be $\Omega_K = -0.0007 \pm 0.0025$ and the sum of the neutrino
masses to be $\sum m_{\nu} < 0.23$ eV at 95\% C.L. (with Planck primary CMB and
BAO data), in good agreement with the Planck lensing results. With the
differences in the $S/N$ of the lensing modes and the angular scales covered in
the lensing spectra, this analysis represents an important independent check on
the full-sky Planck lensing measurement.
