Physical Society Colloquium

Inflation, String Theory, and Signatures in the CMB

Eva Silverstein

Stanford University & SLAC

Inflationary Cosmology — accelerated expansion driven by the potential energy of a scalar “inflaton” — is a very general framework for solving basic problems in primordial cosmology. The next generation of Cosmic Microwave Background (CMB) experiments promises to discriminate among very different possibilities for the mechanism behind inflation. These observables of primordial cosmology are sensitive to the short-distance completion of general relativity. For example, the observation of or constraint on primordial gravity waves — at the level accessible via upcoming measurements of CMB polarization — determines the ratio of the inflaton field strength and the Planck energy scale, while tests of the Gaussianity of the spectrum constrain microscopic interactions. This “UV sensitivity” motivates modeling inflation in string theory, as a candidate UV completion of particle physics and gravity. After reviewing these motivations, I will present basic classes of inflationary models within the framework of string theory, along with their signatures. In particular, I will explain a broad class of models descending from string theory — via a formal mechanism known as “monodromy” — which is falsifiable on the basis of its gravity wave signature.