Les Houches lectures on inflationary observables and string theory

TL;DR

This paper provides an overview of inflationary mechanisms, emphasizing the role of string theory in generating observable signatures and discussing the importance of ultraviolet completion for understanding inflation.

Contribution

It introduces novel string theory-based inflation mechanisms and explores their phenomenological implications, including observational tests and the role of UV sensitivity.

Findings

String theory offers new inflation models with testable predictions.

Tensor mode measurements are highly sensitive to UV physics.

Systematic analysis of low energy theories informs data searches for non-Gaussianity.

Abstract

These lectures cover the theoretical structure and phenomenology of some basic mechanisms for inflation. A full treatment of the problem requires `ultraviolet completion' because of the sensitivity of inflation to quantum gravity effects, while the observables are elegantly parameterized using low energy field theory. String theory provides novel mechanisms for inflation, some subject to significant observational tests, with highly UV-sensitive tensor mode measurements being a prime example. Although the ultraviolet completion is not directly accessible experimentally, some of these mechanisms have helped stimulate a more systematic analysis of the space of low energy theories and signatures relevant for data analysis, including searches for non-Gaussianity and additional structure in the power spectrum. We include a pedagogical overview of string compactifications, with a focus on candidate inflatons and their symmetry structure. In the last lecture we attack the problem of thought-experimental observables in inflation, developing a generalization of gauge-gravity duality that relies on the structure of the scalar potential in string theory.