Gravitational Waves from the Big Bang - Inflation in String Theory after BICEP2

Alexander Westphal (DESY)
DESY Auditorium, 16.45 h

BICEP2 from Antarctica has given us the first clear evidence for primordial gravitational waves causing B-mode polarization at degree angular scales l < 100. If interpreted in the context of inflation, their signal corresponds to a tensor-to-scalar ratio , which disfavors r < 0.01 at about 5σ. We will discuss the implications of this result for models of single-field slow-roll inflation. Due to the Lyth bound, the new data represent strong evidence against virtually all small-field models of inflation. We will discuss the need for protective symmetries such as shift symmetries in large-field inflation models which are now favored, and review the situation of string inflation and its large-field version of (axion) monodromy.

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