By Dawn's Early Light: CMB Polarization Impact on Cosmological
  Constraints
  Cosmic microwave background polarization encodes information not only on the
early universe but also dark energy, neutrino mass, and gravity in the late
universe through CMB lensing. Ground based surveys such as ACTpol, PolarBear,
SPTpol significantly complement cosmological constraints from the Planck
satellite, strengthening the CMB dark energy figure of merit and neutrino mass
constraints by factors of 3-4. This changes the dark energy probe landscape. We
evaluate the state of knowledge in 2017 from ongoing experiments including dark
energy surveys (supernovae, weak lensing, galaxy clustering), fitting for
dynamical dark energy, neutrino mass, and a modified gravitational growth
index. Adding a modest strong lensing time delay survey improves those dark
energy constraints by a further 32%, and an enhanced low redshift supernova
program improves them by 26%.
