Monodromy in the CMB: Gravity Waves and String Inflation

TL;DR

This paper proposes a string theory-based mechanism for large-field inflation involving monodromy, predicting observable gravitational waves and spectral tilt, using twisted tori compactifications.

Contribution

It introduces a novel large-field inflation model from string theory with specific potential forms and discusses the generality of the monodromy mechanism in compactifications.

Findings

Predicted spectral index n_s ≈ 0.98

Tensor-to-scalar ratio r ≈ 0.04

Potential forms proportional to phi^(2/3) and phi^(2/5)

Abstract

We present a simple mechanism for obtaining large-field inflation, and hence a gravitational wave signature, from string theory compactified on twisted tori. For Nil manifolds, we obtain a leading inflationary potential proportional to phi^(2/3) in terms of the canonically normalized field phi, yielding predictions for the tilt of the power spectrum and the tensor-to-scalar ratio, $n_s\approx 0.98$ and $r\approx 0.04$ with 60 e-foldings of inflation; we note also the possibility of a variant with a candidate inflaton potential proportional to phi^(2/5). The basic mechanism involved in extending the field range -- monodromy in D-branes as they move in circles on the manifold -- arises in a more general class of compactifications, though our methods for controlling the corrections to the slow-roll parameters require additional symmetries.