DBI N-flation
John Ward
TL;DR
The paper investigates DBI inflation with a large number $N$ of coincident branes, showing an equivalence to a single wrapped $D5$-brane with flux and exploring the impact of $1/N$ corrections on observables. It derives how these corrections, computed via a symmetrised-trace expansion, alter the sound speed and non-Gaussianities in constant-warp and AdS backgrounds, revealing new phase-space structures and constraints on viable trajectories. A key contribution is the proposal of a representation-cascade inflation mechanism, where reducible to irreducible $SU(2)$ representations drive inflation, potentially yielding multiple e-folds via successive cascades or tunneling, though requiring careful handling of backreaction and reheating. Overall, the work highlights how subleading stringy corrections can qualitatively modify inflationary signatures and opens new avenues for string-theoretic, testable predictions in multi-brane DBI scenarios.
Abstract
We investigate DBI inflation using $N$ multiple branes and show how the configuration is equivalent to a single wrapped $D5$-brane with flux. We then show how 1/N corrections can be implemented, and we examine the sound speed and levels of non-Gaussianities in two distinct cases. For models with constant warping we find that the non-Gaussian amplitude is bounded from above (as a function of $γ$). For $AdS$ backgrounds we find that the signature is generally large and positive, although is no longer globally defined over the full phase space. We then investigate an inflationary mechanism using a representation cascade, whereby the transition from a reducible representation to the irrep drives inflation.