Scientific Calendar Event

Abstract. We attempt an estimate for the distribution of the tensor-to-scalar ratio $r$ (the relative power of primordial gravitational waves from inflation) over the landscape of vacua in string theory. The dynamics of eternal inflation and quantum tunneling lead to a kind of democracy on the landscape, providing no bias towards large-field or small-field inflation regardless of the class of measure. The tensor mode fraction $r$ then follows the number frequency distributions of inflationary mechanisms of string theory over the landscape. We then determine the frequency of regions of small-field inflation in the Wigner landscape as an approximation to random supergravities/type IIB flux compactifications. We show that small-field inflation occurs exponentially more often than large-field inflation The tensor-to-scalar ratio $r$ is generically tied to the scale of inflation. For small-field models this is below current observational reach. However, we find small-field inflation to be dominated by the highest inflationary energy scales compatible with a sub-Planckian field range. Hence, we expect a typical $r\sim {\cal O}(10^{-3})$ currently undetectable in upcoming CMB measurements, but potentially detectable in a future dedicated B-mode space mission.
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