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# Beyond Positivity Bounds and the Fate of Massive Gravity

Physical Review Letters

American Physical Society (APS)

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### Most cited references66

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### To the problem of nonvanishing gravitation mass

(1972)
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### The galileon as a local modification of gravity

In the 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 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 \pi, 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 \pi's gradient shifts by a constant. This symmetry constrains the structure of the \pi Lagrangian so much so that in 4D there exist only five terms that can yield sizable non-linearities without introducing ghosts. We show that for such theories in fact there are self-accelerating'' deSitter solutions with no ghost-like instabilities. In the presence of compact sources, these solutions can support spherically symmetric, Vainshtein-like non-linear perturbations that are also stable against small fluctuations. [Short version for arxiv]
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### Topologically massive gauge theories

(1982)
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### Author and article information

###### Journal
PRLTAO
Physical Review Letters
Phys. Rev. Lett.
American Physical Society (APS)
0031-9007
1079-7114
April 2018
April 17 2018
: 120
: 16
10.1103/PhysRevLett.120.161101