The recent BICEP2 B-mode polarization determination of an inflationary tensor-scalar ratio r = 0.2 ^ { +0.07 } _ { -0.05 } is in tension with simple scale-free models of inflation due to a lack of a corresponding low multipole excess in the temperature power spectrum which places a limit of r _ { 0.002 } < 0.11 ( 95 % CL ) on such models .
Single-field inflationary models that reconcile these two observations , even those where the tilt runs substantially , introduce a scale into the scalar power spectrum .
To cancel the tensor excess , and simultaneously explain the excess already present in \Lambda CDM , ideally the model should introduce this scale as a relatively sharp transition in the tensor-scalar ratio around the horizon at recombination .
We consider models which generate such a step in this quantity and find that they can improve the joint fit to the temperature and polarization data by up to 2 \Delta \ln { \cal L } \approx - 14 without changing cosmological parameters .
Precision E-mode polarization measurements should be able to test this explanation .