Inflation from wrapped branes

We show that the use of higher dimensional wrapped branes can significantly extend the inflaton field range compared to brane inflation models which use $D3$-branes. We construct a simple inflationary model in terms of 5-branes wrapping a 2-cycle and traveling towards the tip of the Klebanov-Strassler throat. Inflation ends when the branes reach the tip of the cone and self-annihilate. Assuming a quadratic potential for the brane it is possible to match the cosmic microwave background data in the Dirac-Born-Infeld regime, but we argue that the backreaction of the brane is important and cannot be neglected. This scenario predicts a strong non-Gaussian signal and possibly detectable gravitational waves.

Figure 1

A $D5$-brane wrapping a two-cycle $p$ times that shrinks to a point. We are showing here the system in Cartesian coordinates where the $D5$ is at a fixed radius ${\rho }_0$. Below ${\rho }_0$, there are $M-p$ units of $F_3$ while above it the original background $M$ units remain. When the radius reaches the (accordingly warped) string scale, a tachyon develops on the brane. One can think of this as brane-antibrane annihilation between antipodal part of the brane on the $S^2$ it wraps.

Figure 2

We show the $\rho$ direction together with the $S^2$ and $S^3$. There are $M$ units of $F_3$ threading through the $S^3$. We wrap the $D5$-brane on the $S^2$ at some fixed position on the $\rho$ axis. Below that value of $\rho$ (below the dark line in the picture) there is one less unit of $F_3$ threading through the $S^3$.