Inflation After False Vacuum Decay: New Evidence from BICEP2
  Last year we argued that if slow-roll inflation followed the decay of a false vacuum in a large landscape, the steepening of the scalar potential between the inflationary plateau and the barrier generically leads to a potentially observable suppression of the scalar power spectrum at large distances. Here we revisit this analysis in light of the recent BICEP2 results. Assuming that both the BICEP2 B-mode signal and the Planck analysis of temperature fluctuations hold up, we find that the data now discriminate more sharply between our scenario and $\Lambda$CDM. Nonzero tensor modes exclude standard $\Lambda$CDM with notable but not yet conclusive confidence: at $\sim 3.8\,\sigma$ if $r\approx0.2$, or at $\sim 3.5\,\sigma$ if $r=0.15$. Of the two steepening models of our previous work, one is now ruled out by existing bounds on spatial curvature. The other entirely reconciles the tension between BICEP2 and Planck. Upcoming $EE$ polarization measurements have the potential to rule out unmodified $\Lambda$CDM decisively. Next generation Large Scale Structure surveys can further increase the significance. More precise measurements of $BB$ at low $\ell$ will help distinguish our scenario from other explanations. If steepening is confirmed, the prospects for detecting open curvature increase but need not be large. 
Raphael Bousso, Daniel Harlow, Leonardo Senatore
astro-ph.CO gr-qc hep-ph hep-th