Brane Inflation and Cosmic String Tension in Superstring Theory

TL;DR

This paper revisits D3-anti-D3 brane inflation in a multi-throat string-theory setup, showing that slow-roll can persist with moderate tuning of the conformal coupling parameter β rather than requiring extreme fine-tuning. A key result is that the cosmic string tension Gμ is highly sensitive to β, increasing rapidly and potentially saturating current observational bounds, which enhances the detectability of superstring-inspired strings. The authors explore slow-roll inflation in the A-throat as well as slow-roll in a separate B-throat, and also discuss a fast-roll (DBI) regime, highlighting how different throat dynamics yield distinct predictions for n_s, r, running, and Gμ. Overall, the multi-throat framework offers flexible inflationary scenarios with observable consequences in the cosmic string sector that can serve as windows into pre-inflationary string theory.

Abstract

In a simple reanalysis of the KKLMMT scenario, we argue that the slow roll condition in the D3-anti-D3-brane inflationary scenario in superstring theory requires no more than a moderate tuning. The cosmic string tension is very sensitive to the conformal coupling: with less fine-tuning, the cosmic string tension (as well as the ratio of tensor to scalar perturbation mode) increases rapidly and can easily saturate the present observational bound. In a multi-throat brane inflationary scenario, this feature substantially improves the chance of detecting and measuring the properties of the cosmic strings as a window to the superstring theory and our pre-inflationary universe.