Brane Interaction as the Origin of Inflation

TL;DR

This work argues that inflation can originate from brane interactions in string theory, treating the inflaton as the inter-brane separation and the potential as arising from brane-brane forces and tachyon dynamics. By combining branes at angles with compactification effects, the authors show that slow-roll inflation is generic for small angles, with the COBE normalization $\delta_H \approx 1.9\times10^{-5}$ constraining the string scale to be near the GUT scale ($M_s \sim M_{\rm GUT}$). The analysis covers hypercubic and generic compactifications, quantifies the probability of achieving sufficient inflation, and discusses reheating and defect production, notably the possible formation of cosmic strings. The results link string-scale physics to observable cosmology, offering a robust, less-tuned path to inflation and predicting observational signatures that could test brane-world scenarios.

Abstract

We reanalyze brane inflation with brane-brane interactions at an angle, which include the special case of brane-anti-brane interaction. If nature is described by a stringy realization of the brane world scenario today (with arbitrary compactification), and if some additional branes were present in the early universe, we find that an inflationary epoch is generically quite natural, ending with a big bang when the last branes collide. In an interesting brane inflationary scenario suggested by generic string model-building, we use the density perturbation observed in the cosmic microwave background and the coupling unification to find that the string scale is comparable to the GUT scale.