Abstract:We study the graviton scattering in the background of non-susy Dp branes of type II string theories consisting of a metric, a dilaton and a (p + 1) form gauge field. We show numerically that in these backgrounds graviton experiences a scattering potential which takes the form of an infinite barrier in the low energy (near brane) limit for p ≤ 5 and therefore is never able to reach the branes. This shows, contrary to what is known in the literature, that gravity indeed decouples from the non-susy Dp branes for p ≤ 5. For non-susy D6 brane, gravity couples as there is no such barrier for the potential. To give further credence to our claim we solve the scattering equation in some situation analytically and calculate the graviton absorption cross-sections on the non-susy branes and show that they vanish for p ≤ 4 in the low energy limit. This shows, as in the case of BPS branes, that gravity does decouple for non-susy Dp branes for p ≤ 4 but it does not decouple for D6 brane as the potential here is always attractive. We argue for the non-susy D5 brane that depending on one of the parameters of the solution gravity either always decouples (unlike the BPS D5 brane) or it decouples when the energy of the graviton is below certain critical value, otherwise it couples, very similar to BPS D5 brane.

In a previous work, we have shown that, like BPS Dp branes, bulk gravity gets decoupled from the brane even for the non-susy Dp branes of type II string theories indicating a possible extension of AdS/CFT correspondence for the non-supersymmetric case. In that work, the decoupling of gravity on the non-susy Dp branes has been shown numerically for the general case as well as analytically for some special case. Here we discuss the decoupling limit and the throat geometry of the non-susy D3 brane when the charge associated with the brane is very large. We show that in the decoupling limit the throat geometry of the non-susy D3 brane, under appropriate coordinate change, reduces to the Constable-Myers solution and thus confirming that this solution is indeed the holographic dual of a (non-gravitational) gauge theory discussed there. We also show that when one of the parameters of the solution takes a specific value, it reduces, under another coordinate change, to the five-dimensional solution obtained by Csaki and Reece, again confirming its gauge theory interpretation.Comment: 5 pages, no figures; v2: two-column ReVTeX format, shortened with more clarifications and references, version to appear in Phys Lett

Previously, two of the present authors obtained the decoupling limit and the corresponding throat geometry of non-supersymmetric D3 brane solution of type IIB string theory. In analogy with the supersymmetric case, it describes the gravity dual of a non-supersymmetric gauge theory with QCD-like properties such as running coupling and confinement (or mass gap) in certain range of its parameters. In this paper, we consider a 'black' version of the nonsupersymmetric D3 brane solution in the decoupling limit and use this gravity background to holographically compute the expectation value of a time-like Wilson loop which, in turn, is related to the potential of a heavy quark-antiquark pair. By boosting the gravity solution along one of the brane directions and placing the pair at an arbitrary orientation with this direction, we numerically obtain the variation of the screening length as well as the potential with velocity, its orientation with respect to the direction of motion and other parameters of the theory. Remarkably enough, our results are in qualitative agreement with those obtained holographically in supersymmetric gauge theories indicating that these features are quite robust and universal as they are insensitive to the presence of any supersymmetry in the theory. The physical interpretations of the variations with respect to the other parameters of the theory, not observed in supersymmetric theory, have also been given.

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Abstract:We consider the space-like Dp brane solutions of type II string theories having isometries ISO(p + 1) × SO(8 − p, 1). These are asymptotically flat solutions or in other words, the metrics become flat at the time scale τ ≫ τ 0 . On the other hand, when τ ∼ τ 0 , we get (p + 1) + 1 dimensional flat FLRW metrics upon compactification on a (8 − p) dimensional hyperbolic space with time dependent radii. We show that the resultant (p + 1) + 1 dimensional metrics describe transient accelerating cosmologies for all p from 1 to 6, i.e., from (2+1) to (7+1) space-time dimensions. We show how the accelerating phase changes with the interplay of the various parameters characterizing the solutions in (3 + 1) dimensions. Finally, for τ ≪ τ 0 , after compactification on (8 − p) dimensional hyperbolic space, the resultant metrics are shown to take the form of (p + 1) + 1 dimensional de Sitter spaces upto a conformal transformation. Cosmologies here are decelerating, but, only in a particular conformal frame we get eternal acceleration.