Energy's and amplitudes' positivity
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In this paper, an effective field theory that allows for stable null energy conditions with exactly luminal excitations only is presented, and it is shown that if the relevant null energy condition is inside the effective theory, then other solutions allow for superluminal signal propagation.Abstract:
In QFT, the null energy condition (NEC) for a classical field configuration is usually associated with that configuration's stability against small perturbations, and with the sub-luminality of these. Here, we exhibit an effective field theory that allows for stable NEC-violating solutions with exactly luminal excitations only. The model is the recently introduced `galileon', or more precisely its conformally invariant version. We show that the theory's low-energy S-matrix obeys standard positivity as implied by dispersion relations. However we also show that if the relevant NEC-violating solution is inside the effective theory, then other (generic) solutions allow for superluminal signal propagation. While the usual association between sub-luminality and positivity is not obeyed by our example, that between NEC and sub-luminality is, albeit in a less direct way than usual.read more
Citations
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DBI and the Galileon reunited
Claudia de Rham,Andrew J. Tolley +1 more
TL;DR: In this paper, the relativistic generalization of the Covariant Galileon was derived by studying the brane position modulus of a probe brane embedded in a five-dimensional bulk.
Journal ArticleDOI
DBI and the Galileon reunited
Claudia de Rham,Andrew J. Tolley +1 more
TL;DR: In this paper, the relativistic generalization of the Galileon was derived by studying the brane position modulus of a probe brane embedded in a five-dimensional bulk in the appropriate Galilean contraction limit.
Journal ArticleDOI
Quantum Gravity Constraints from Unitarity and Analyticity
TL;DR: In this article, the authors derived rigorous bounds on corrections to Einstein gravity using unitarity and analyticity of graviton scattering amplitudes in D≥4 spacetime dimensions, and systematically enumerated all such positivity bounds in D=4 and D=5 before extending to D ≥6.
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Consistent null-energy-condition violation: Towards creating a universe in the laboratory
TL;DR: The null energy condition (NEC) can be violated in a consistent way in models with unconventional kinetic terms, notably in Galileon theories and their generalizations as mentioned in this paper, and the scale-invariant kinetic braiding model is used to discuss whether a universe can in principle be created by manmade processes.
Journal ArticleDOI
Gravitational properties of the Proca field
TL;DR: In this article, the effects of a Proca field coupled to gravity through minimal and quadrupole interactions were studied, described by a two-parameter family of Lagrangians.
References
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Galileon as a local modification of gravity
TL;DR: In this article, the authors study the connection between self-acceleration and the presence of ghosts for a quite generic class of theories that modify gravity in the infrared, defined as those that at distances shorter than cosmological, reduce to a certain generalization of the Dvali-Gabadadze-Porrati (DGP) effective theory.
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Causality, analyticity and an IR obstruction to UV completion
Allan Adams,Nima Arkani-Hamed,Sergei Dubovsky,Sergei Dubovsky,Sergei Dubovsky,Alberto Nicolis,Riccardo Rattazzi +6 more
TL;DR: In this paper, it was shown that low-energy effective field theories described by local, Lorentz invariant Lagrangians, secretly exhibit macroscopic non-locality and cannot be embedded in any UV theory whose S-matrix satisfies canonical analyticity constraints.
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Ghost condensation and a consistent infrared modification of gravity
Nima Arkani-Hamed,Hsin-Chia Cheng,Markus A. Luty,Markus A. Luty,Markus A. Luty,Shinji Mukohyama +5 more
TL;DR: In this article, the authors proposed a theoretically consistent modification of gravity in the infrared, which is compatible with all current experimental observations and opens up a number of new avenues for attacking cosmological problems, including inflation, dark matter and dark energy.
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Strong Interactions and Stability in the DGP Model
TL;DR: The model of Dvali, Gabadadze and Porrati (DGP) as mentioned in this paper gives a simple geometrical setup in which gravity becomes 5-dimensional at distances larger than a length scale lambda(DGP).