DGP Specteroscopy

By C. Charmousis, R. Gregory, N. Kaloper, Antonio Padilla. 2006

146 citations recorded by the source corpus.

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 < m < 2H 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.

Subfields: Astronomy and Astrophysics, Epidemiology, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/41b5822ed8de9ba5f87d196752df171f5501a85a

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Citations in the corpus

A systematic approach to generalisations of General Relativity and their cosmological implications (2018, background): “However, it was quickly realised that this branch of solutions seems to be plagued by ghost-like instabilities [27, 28].”
Massive Gravity (2014, background): “Koyama in [360] (see also [263, 361] and [98]).”
Bi-galileon theory I: motivation and formulation (2010, background): “However, fluctuations about the self-accelerating vacuum were found to suffer from ghost-like instabilities, ruling out this sector of the theory [36–41].”
Modified Gravity and Cosmology (2011, background): “One can then readily calculate the 4D effective action [273], and derive the corresponding Hamiltonian [546].”
Brane-World Gravity (2004, methodology): “We also discuss the 5D DGP models, which modify general relativity at low energies, unlike the RS models; these models have become important examples in cosmology for achieving late-time acceleration of the universe without dark energy.”