Brane Inflation : String Theory viewed from the Cosmos

TL;DR

Brane inflation, a string theory-based early universe model, predicts observable signatures like cosmic strings and non-Gaussianities, with current data constraining its parameters and offering potential validation of string theory.

Contribution

This paper discusses the naturalness, robustness, and cosmological predictions of brane inflation within string theory, highlighting potential observable signatures and current constraints.

Findings

Potential detection of cosmic superstrings via gravitational waves.

Stringy features like non-Gaussianity and tensor modes could be observed.

Cosmological data constrains brane inflation parameters.

Abstract

Brane inflation is a specific realization of the inflationary universe scenario in the early universe within the brane world framework in string theory. The naturalness and robustness of this realistic scenario is explained. Its predictions on the cosmological observables in the cosmic microwave background radiation, especially possible distinct stringy features, such as large non-Gaussianity or large tensor mode that deviates from that predicted in the slow roll scenario, are discussed. Stringy KK modes as hidden dark matter is also a possibility. Another generic consequence of brane inflation is the production of cosmic strings towards the end of inflation. These cosmic strings are nothing but superstrings stretched to cosmological sizes. The properties of these cosmic superstrings and their subsequent cosmological evolution into a scaling network open up their possible detections in the near future, via cosmological, astronomical and/or gravitational wave measurements. At the moment, cosmological data is already imposing strong constraints on the details of the scenario. Finding distinctive stringy signatures in cosmological observations will go a long way in revealing the specific brane inflationary scenario and validating string theory as well as the brane world picture. Precision measurements may even reveal the structures of the flux compactification. Irrespective of the final outcome, we see that string theory is confronting data and making predictions.