Complementing the ground-based CMB Stage-4 experiment on large scales   with the PIXIE satellite
  We present forecasts for cosmological parameters from future Cosmic Microwave Background (CMB) data measured by the Stage-4 (S4) generation of ground-based experiments in combination with large-scale anisotropy data from the PIXIE satellite. We demonstrate the complementarity of the two experiments and focus on science targets that benefit from their combination. We show that a cosmic-variance-limited measurement of the optical depth to reionization provided by PIXIE, with error $\sigma(\tau)=0.002$, is vital for enabling a 5$\sigma$ detection of the sum of the neutrino masses when combined with a CMB-S4 lensing measurement, and with lower-redshift constraints on the growth of structure and the distance-redshift relation. Parameters characterizing the epoch of reionization will also be tightly constrained; PIXIE's $\tau$ constraint converts into $\sigma(\rm{z_{re}})=0.2$ for the mean time of reionization, and a kinematic Sunyaev-Zel'dovich measurement from S4 gives $\sigma(\Delta \rm{z_{re}})=0.03$ for the duration of reionization. Both PIXIE and S4 will put strong constraints on primordial tensor fluctuations, vital for testing early-universe models, and will do so at distinct angular scales. We forecast $\sigma(r)\approx 5\times10^{-4}$ for a signal with a tensor-to-scalar ratio $r=10^{-3}$, after accounting for diffuse foreground removal and de-lensing. The wide and dense frequency coverage of PIXIE results in an expected foreground-degradation factor on $r$ of only $\approx$25%. By measuring large and small scales PIXIE and S4 will together better limit the energy injection at recombination from dark matter annihilation, with $p_{\rm ann}<0.09 \times 10^{-6} \ {\rm m^3/s/Kg}$ projected at 95% confidence. Cosmological parameters measured from the damping tail with S4 will be best constrained by polarization, which has the advantage of minimal contamination from extragalactic emission. 
Erminia Calabrese, David Alonso, and Jo Dunkley
astro-ph.CO