Inflation near a metastable de Sitter vacuum from moduli stabilisation

TL;DR

This paper explores a string theory-based model of inflation near a metastable de Sitter vacuum, demonstrating successful small-field inflation with a very low tensor-to-scalar ratio and analyzing the vacuum's stability and decay mechanisms.

Contribution

It introduces a novel inflationary scenario within type IIB flux compactifications with moduli stabilization, incorporating quantum corrections and analyzing vacuum stability and decay.

Findings

Achieves small-field inflation with $r \, \sim 4 \times 10^{-4}$.

Shows the metastable vacuum is practically stable with decay only via Hawking-Moss instanton.

Suggests additional physics, like a waterfall field, is needed to end inflation.

Abstract

We study the cosmological properties of a metastable de Sitter vacuum obtained recently in the framework of type IIB flux compactifications in the presence of three D7-brane stacks, based on perturbative quantum corrections at both world-sheet and string loop level that are dominant at large volume and weak coupling. In the simplest case, the model has one effective parameter controlling the shape of the potential of the inflaton which is identified with the volume modulus. The model provides a phenomenological successful small-field inflation for a value of the parameter that makes the minimum very shallow and near the maximum. The horizon exit is close to the inflection point while most of the required e-folds of the Universe expansion are generated near the minimum, with a prediction for the ratio of tensor-to-scalar primordial fluctuations $r \sim 4 \times 10^{-4}$. Despite its shallowness, the minimum turns out to be practically stable. We show that it can decay only through the Hawking-Moss instanton leading to an extremely long decay rate. Obviously, in order to end inflation and obtain a realistic model, new low-energy physics is needed around the minimum, at intermediate energy scales of order $10^{12}$ GeV. An attractive possibility is by introducing a "waterfall"' field within the framework of hybrid inflation.