Quantifying discordance in the 2015 Planck CMB spectrum
  We examine the internal consistency of the Planck 2015 cosmic microwave
background (CMB) temperature anisotropy power spectrum. We show that tension
exists between cosmological constant cold dark matter (LCDM) model parameters
inferred from multipoles l<1000 (roughly those accessible to Wilkinson
Microwave Anisotropy Probe), and from l>=1000, particularly the CDM density,
Omega_ch^2, which is discrepant at 2.5 sigma for a Planck-motivated prior on
the optical depth, tau=0.07+/-0.02. We find some parameter tensions to be
larger than previously reported because of inaccuracy in the code used by the
Planck Collaboration to generate model spectra. The Planck l>=1000 constraints
are also in tension with low-redshift data sets, including Planck's own
measurement of the CMB lensing power spectrum (2.4 sigma), and the most precise
baryon acoustic oscillation (BAO) scale determination (2.5 sigma). The Hubble
constant predicted by Planck from l>=1000, H_0=64.1+/-1.7 km/s/Mpc, disagrees
with the most precise local distance ladder measurement of 73.0+/-2.4 km/s/Mpc
at the 3.0 sigma level, while the Planck value from l<1000, 69.7+/-1.7
km/s/Mpc, is consistent within 1 sigma. A discrepancy between the Planck and
South Pole Telescope (SPT) high-multipole CMB spectra disfavors interpreting
these tensions as evidence for new physics. We conclude that the parameters
from the Planck high-multipole spectrum probably differ from the underlying
values due to either an unlikely statistical fluctuation or unaccounted-for
systematics persisting in the Planck data.
