Charmousis, C. and Gregory, R. and Kaloper, N. and Padilla, A. (2006) 'DGP specteroscopy.', Journal of high energy physics., 2006 (10). p. 66.
We systematically explore the spectrum of gravitational perturbations in codimension-1 DGP braneworlds, and find a 4D ghost on the self-accelerating branch of solutions. The ghost appears for any value of the brane tension, although depending on the sign of the tension it is either the helicity-0 component of the lightest localized massive tensor of mass 0<m2<2H2 for positive tension, the scalar `radion' for negative tension, or their admixture for vanishing tension. Because the ghost is gravitationally coupled to the brane-localized matter, the self-accelerating solutions are not a reliable benchmark for cosmic acceleration driven by gravity modified in the IR. In contrast, the normal branch of solutions is ghost-free, and so these solutions are perturbatively safe at large distance scales. We further find that when the Z2 orbifold symmetry is broken, new tachyonic instabilities, which are much milder than the ghosts, appear on the self-accelerating branch. Finally, using exact gravitational shock waves we analyze what happens if we relax boundary conditions at infinity. We find that non-normalizable bulk modes, if interpreted as 4D phenomena, may open the door to new ghost-like excitations.
|Keywords:||Large extra dimensions, Classical theories of gravity.|
|Full text:||(NA) Not Applicable |
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|Publisher Web site:||http://dx.doi.org/10.1088/1126-6708/2006/10/066|
|Publisher statement:||© SISSA 2006. Published by IOP Publishing for SISSA. This is an author-created, un-copyedited version of an article accepted for publication in Journal of high energy physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at 10.1088/1126-6708/2006/10/066.|
|Date accepted:||No date available|
|Date deposited:||No date available|
|Date of first online publication:||October 2006|
|Date first made open access:||No date available|
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