Chaotic Brane Inflation

TL;DR

The paper proposes a UV completion of large-field chaotic/natural inflation in string theory by embedding the inflaton as the position of a mobile D3-brane and generating its potential through flux monodromies around a nontrivial 1-cycle. In the probe limit, the winding of Ramond-Ramond flux yields an exactly quadratic potential $V(\phi)=\frac{\phi^2}{M_P L^3}$, with backreaction capable of flattening to a sinusoidal form $V(\phi)\approx\Lambda^4\left[1-\cos\left(\frac{\phi}{N f_\phi}\right)\right]$, where $f_\phi=\frac{\sqrt{M_P}}{2\pi\sqrt{L}}$ and $\Lambda=\frac{\sqrt{N}}{\sqrt[4]{2\pi^2}\,L}$. Realizing this requires a compactification with $H^1({\cal M}^6)=\mathbb{Z}$ or $\mathbb{Z}_N$ and a large number of windings $N\gtrsim 2\times 10^3$, together with robust moduli stabilization to avoid backreaction that would spoil slow-roll. The framework provides a UV perspective on large-field inflation via brane monodromies, predicting potentially observable tensor modes in the CMB, but faces challenges related to stabilization, backreaction control, and sustaining a long, flat trajectory.

Abstract

We illustrate a framework for constructing models of chaotic inflation where the inflaton is the position of a D3 brane along the universal cover of a string compactification. In our scenario, a brane rolls many times around a non-trivial one-cycle, thereby unwinding a Ramond-Ramond flux. These "flux monodromies" are similar in spirit to the monodromies of Silverstein, Westphal, and McAllister, and their four-dimensional description is that of Kaloper and Sorbo. Assuming moduli stabilization is rigid enough, the large-field inflationary potential is protected from radiative corrections by a discrete shift symmetry.