Assisted inflation via tachyon condensation

TL;DR

This work investigates inflation driven by tachyon condensation on a stack of non-interacting unstable $\tilde{D4}$ branes, showing that a single tachyon is too steep for slow-roll, but collective dynamics of many tachyons can realize viable inflation along the familiar 3D spatial directions. By modeling the tachyon sector as a sum of independent fields with the potential $V_i(T_i)=T_i^2\ln T_i^2 + V_0$, the authors demonstrate that the slow-roll conditions $\epsilon_i,\eta_i \ll 1$ can be satisfied when the number of branes $n$ is sufficiently large (generally $n \gtrsim 10$), and that the tachyons follow a common attractor trajectory during inflation. They compute the density perturbation amplitude and show COBE normalization can be achieved for reasonable ratios of the string scale to the Planck scale, while outlining a reheating mechanism via kink formation into stable $D3$ branes and gauge-field production, which may imply a potentially high reheating temperature. The results embed inflation within a string-theoretic D-brane framework, highlighting how multi-field tachyon dynamics can drive early-universe expansion and generate observable perturbations, with caveats about post-inflationary thermal histories.

Abstract

In this paper we propose a new mechanism of inflating the Universe with non-BPS $D4$ branes which decay into stable $D3$ branes via tachyon condensation. In a single brane scenario the tachyon potential is very steep and unable to support inflation. However if the universe lives in a stack of branes produced by a set of non-interacting unstable $\tilde {D4}$ branes, then the associated set of tachyons may drive inflation along our 3 spatial dimensions. After tachyon condensation the Universe is imagined to be filled with a set of parallel stable $D3$ branes. We study the scalar density perturbations and reheating within this setup.

Figures (3)

• Figure 1: The shape of the symmetric potential in Eq. (\ref{['pot']}). The height is given by $V_0=e^{-1}$, while the minimum occurs for $T_0=1/\sqrt{e}$.
• Figure 2: The two slow-roll parameters; $\epsilon$, and $\eta$, plotted with respect to the tachyon field $T$. Notice that the slow-roll conditions in Eq. (\ref{['slowroll1']}) are not simultaneously satisfied as the field rolls down from top of the potential to the global minimum.
• Figure 3: The two slow-roll parameters; $\epsilon_{i}$, and $\eta_{i}$ are plotted with respect to a single tachyon field $T_{i}$ when the total number of tachyons is taken to be $n=10$. Notice, now the slow-roll conditions can be satisfied concurrently in the region where the tachyonic fields are rolling down their respective potentials.