Ghosts, Instabilities, and Superluminal Propagation in Modified Gravity Models

De Felice, Antonio, Hindmarsh, Mark and Trodden, Mark (2006) Ghosts, Instabilities, and Superluminal Propagation in Modified Gravity Models. Journal of Cosmology and Astroparticle Physics (8). 005-15. ISSN 1475-7516

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We consider Modified Gravity models involving inverse powers of fourth-order curvature invariants. Using these models' equivalence to the theory of a scalar field coupled to a linear combination of the invariants, we investigate the properties of the propagating modes. Even in the case for which the fourth derivative terms in the field equations vanish, we find that the second derivative terms can give rise to ghosts, instabilities, and superluminal propagation speeds. We establish the conditions which the theories must satisfy in order to avoid these problems in Friedmann backgrounds, and show that the late-time attractor solutions are generically afflicted by superluminally propagating tensor or scalar modes.

Item Type: Article
Additional Information: Collaboration co-leader and supervisor of PDRA de Felice. We show that recently-proposed attempts to explain the cosmic acceleration by modifying gravity suffer from fundamental problems related to propagation instabilities of signals in the cosmos.
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Depositing User: Mark Hindmarsh
Date Deposited: 06 Feb 2012 18:23
Last Modified: 28 Mar 2012 15:21
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