Galileon as a local modification of gravity
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- 31 March 2009
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review D
- Vol. 79 (6), 064036
- https://doi.org/10.1103/physrevd.79.064036
Abstract
In the Dvali-Gabadadze-Porrati (DGP) model, the “self-accelerating” solution is plagued by a ghost instability, which makes the solution untenable. This fact, as well as all interesting departures from general relativity (GR), are fully captured by a four-dimensional effective Lagrangian, valid at distances smaller than the present Hubble scale. The 4D effective theory involves a relativistic scalar , universally coupled to matter and with peculiar derivative self-interactions. In this paper, we study the connection between self-acceleration and the presence of ghosts for a quite generic class of theories that modify gravity in the infrared. These theories are defined as those that at distances shorter than cosmological, reduce to a certain generalization of the DGP 4D effective theory. We argue that for infrared modifications of GR locally due to a universally coupled scalar, our generalization is the only one that allows for a robust implementation of the Vainshtein effect—the decoupling of the scalar from matter in gravitationally bound systems—necessary to recover agreement with solar-system tests. Our generalization involves an internal Galilean invariance, under which ’s gradient shifts by a constant. This symmetry constrains the structure of the Lagrangian so much so that in 4D there exist only five terms that can yield sizable nonlinearities without introducing ghosts. We show that for such theories in fact there are “self-accelerating” de Sitter solutions with no ghostlike instabilities. In the presence of compact sources, these solutions can support spherically symmetric, Vainshtein-like nonlinear perturbations that are also stable against small fluctuations. We investigate a possible infrared completion of these theories at scales of order of the Hubble horizon, and larger. There are however some features of our theories that may constitute a problem at the theoretical or phenomenological level: the presence of superluminal excitations; the extreme subluminality of other excitations, which makes the quasistatic approximation for certain solar-system observables unreliable due to Cherenkov emission; the very low strong-interaction scale for scatterings.
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This publication has 32 references indexed in Scilit:
- Null energy condition and superluminal propagationJournal of High Energy Physics, 2006
- Phases of massive gravityJournal of High Energy Physics, 2004
- Ghost Condensation and a Consistent IR Modification of GravityJournal of High Energy Physics, 2004
- Diluting the cosmological constant in infinite volume extra dimensionsPhysical Review D, 2003
- Cosmology on a brane in Minkowski bulkPhysics Letters B, 2001
- 4D gravity on a brane in 5D Minkowski spacePhysics Letters B, 2000
- Measurements of Ω and Λ from 42 High‐Redshift SupernovaeThe Astrophysical Journal, 1999
- Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological ConstantThe Astronomical Journal, 1998
- Anthropic Bound on the Cosmological ConstantPhysical Review Letters, 1987
- Extra space-time dimensions: Towards a solution to the cosmological constant problemPhysics Letters B, 1983