Assisted Inflation from Geometric Tachyon

TL;DR

This work demonstrates that a stack of N D3-branes falling into an NS5-brane throat can realize slow-roll assisted inflation via a geometric tachyon, when coupled to four-dimensional gravity. By formulating the DBI-like geometric-tachyon action and deriving an effective potential $V_{\rm eff}$ for a rescaled field, the authors obtain slow-roll parameters $\epsilon$ and $\eta$ and identify bounds on $\tilde{N}$ to achieve viable inflation and perturbation amplitudes. They show that the model yields approximately Planck-suppressed density perturbations and can produce ~100 e-folds of inflation before transitioning to a radion-dominated phase, with the large-$N$ requirement balanced against COBE constraints. This provides a string-theoretic realization of multi-field assisted inflation via a geometric tachyon, extending open-string tachyon inflation ideas to D-brane/NS5-brane systems and offering concrete observationally relevant constraints. The work highlights a concrete mechanism by which multi-brane dynamics in curved backgrounds can yield viable early-universe cosmology within a controlled string-theory framework.

Abstract

We study the effect of rolling of N D3-branes in the vicinity of NS5-branes. We find out that this system coupled with the four dimensional gravity gives the slow roll assisted inflation of the scalar field theory. Once again this expectation is exactly similar to that of N-tachyon assisted inflation on unstable D-branes.

Figures (3)

• Figure 1: Plot of $V(R)$ as a function of R for $k=2$. It has a large flat region and is suitable for eternal inflation.
• Figure 2: Plot of $H(t)$ as a function of time. Area under the curve is roughly 100.
• Figure 3: The quantities $X\equiv R/4$ and $Y\equiv |\sqrt{h}\dot R|$.