DBI Genesis: An Improved Violation of the Null Energy Condition

TL;DR

It is shown that the Dirac-Born-Infeld conformal galileons, derived from the world-volume theory of a 3-brane moving in an anti-de Sitter bulk, admit a background, stable under quantum corrections, which violates the null energy condition.

Abstract

We show that the DBI conformal galileons, derived from the world-volume theory of a 3-brane moving in an AdS bulk, admit a background, stable under quantum corrections, which violates the Null Energy Condition (NEC). The perturbations around this background are stable and propagate subluminally. Unlike other known examples of NEC violation, such as ghost condensation and conformal galileons, this theory also admits a stable, Poincare-invariant vacuum, with a Lorentz-invariant S-matrix satisfying standard analyticity conditions. Like conformal galileons, perturbations around deformations of the Poincare invariant vacuum propagate superluminally.

Figures (1)

• Figure 1: Allowed (white) region of $(C_3,C_4)$ parameter space satisfying all of our conditions, with $C_1 = C_5 = 0$ and $C_2 = 1$. In the allowed region, $\beta \simeq -C_3/C_4$ for $|C_3| \gg 1$. On the solid curve, $\beta$ grows without bound as $C_3 \rightarrow -\infty$, showing that all constraints can be satisfied for arbitrarily large $\beta$.