On quantifying and resolving the BICEP2/Planck tension over
  gravitational waves
  The recent BICEP2 measurement of primordial gravity waves (r =
0.2^{+0.07}_{-0.05}) appears to be in tension with the upper limit from WMAP
(r<0.13 at 95% CL) and Planck (r<0.11 at 95% CL). We carefully quantify the
level of tension and show that it is very significant (around 0.1% unlikely)
when the observed deficit of large-scale temperature power is taken into
account. We show that measurements of TE and EE power spectra in the near
future will discriminate between the hypotheses that this tension is either a
statistical fluke, or a sign of new physics. We also discuss extensions of the
standard cosmological model that relieve the tension, and some novel ways to
constrain them.
