Multiple Inflation, Cosmic String Networks and the String Landscape

TL;DR

This paper explores a two-step inflationary model motivated by the string landscape, analyzing how cosmic string networks influence the required number of e-foldings for successful cosmological inflation.

Contribution

It introduces a scenario where a short initial inflation followed by a longer low-energy inflation is viable, emphasizing the role of cosmic string networks in the inter-inflationary epoch.

Findings

First inflation can be as short as 12 e-foldings.

Cosmic string networks can dominate the inter-inflationary period.

An additional 20 e-foldings are needed at lower energies for flatness and horizon problems.

Abstract

Motivated by the string landscape we examine scenarios for which inflation is a two-step process, with a comparatively short inflationary epoch near the string scale and a longer period at a much lower energy (like the TeV scale). We quantify the number of $e$-foldings of inflation which are required to yield successful inflation within this picture. The constraints are very sensitive to the equation of state during the epoch between the two inflationary periods, as the extra-horizon modes can come back inside the horizon and become reprocessed. We find that the number of $e$-foldings during the first inflationary epoch can be as small as 12, but only if the inter-inflationary period is dominated by a network of cosmic strings (such as might be produced if the initial inflationary period is due to the brane-antibrane mechanism). In this case a further 20 $e$-foldings of inflation would be required at lower energies to solve the late universe's flatness and horizon problems.