Gravitational wave constraints on multi-brane inflation

Abstract

A class of non-canonical inflationary models is identified, where the leading-order contribution to the non-Gaussianity of the curvature perturbation is determined by the sound speed of the fluctuations in the inflaton field. Included in this class of models is the effective action for multiple coincident branes in the finite n limit. The action for this configuration is determined using a powerful iterative technique, based upon the fundamental representation of SU(2). In principle the upper bounds on the tensor–scalar ratio that arise in the standard, single-brane DBI inflationary scenario can be relaxed in such multi-brane configurations if a large and detectable non-Gaussianity is generated. Moreover models with a small number of coincident branes could generate a gravitational wave background that will be observable in future experiments.

Generalized DBI quintessence

“…26) but which simplifies in the limit α = β + 2. As before, the solution space splits into two disconnected sub-sets, therefore in the first instance where we take slices through z = 0, we find the following bound 27) which implies that α > β and so the brane tension should dominate the dynamics (in the large field regime).…”

Warped Wilson line DBI inflation

“…Here we have denoted f 0 = f (ϕ 0 ) with f (ϕ) given in (14) and χ n the Wilson line field, defined in (16) with e −φ 0 = g −1 s . V ϕ 0 is the potential for the position field(s), evaluated at the stable point ϕ 0 .…”

“…In this model, a probe D-brane propagates relativistically in a warped compactificationá la GKP [5,6] (that is, internal fluxes are switched on, such that most of the closed string moduli get stabilised [7] and a warped throat is formed). The brane dynamics is described by the DBI action, which contains non standard kinetic terms for the scalar fields associated to the brane's positions, acting as the inflaton(s) [4,[8][9][10][11][12][13][14]16,17]. A particular feature of the DBI scenario is that the sound speed of the fluctuations in the inflaton, can be much less that the speed of light, producing potentially large non-Gaussian signal in the density perturbations [4].…”

Cosmological perturbations in inflationary models with anisotropic space-time scaling in a Lifshitz background

“…Inflation in this picture ends when the brane and anti-brane annihilate each other resulting a copious productions of cosmic (super)strings which can be detected observationally [20][21][22][23][24]. DBI inflation [25,26] is another realization of inflation from string theory in which the mobile brane moves ultra-relativistically inside a warped throat [27][28][29][30][31][32][33]. A non-trivial predictions of DBI inflation is generating large equilateral type non-Gaussianities [34][35][36] which can be detected observationally [37].…”