• Publications
  • Influence
Avoiding dark energy with 1/r modifications of gravity
Scalar quintessence seems epicyclic because one can choose the potential to reproduce any cosmology (I review the construction) and because the properties of this scalar seem to raise more questionsExpand
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Nonlocal cosmology.
We explore nonlocally modified models of gravity, inspired by quantum loop corrections, as a mechanism for explaining current cosmic acceleration. These theories enjoy two major advantages: theyExpand
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The Problem of Nonlocality in String Theory
Abstract We discuss the problems associated with the essential nonlocality of all string field actions. Manifestly Poincare invariant theories are shown to be unstable and bereft of an initial valueExpand
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Observational viability and stability of nonlocal cosmology
We show that the nonlocal gravity models, proposed to explain current cosmic acceleration without dark energy, pass two essential tests: first, they can be defined so as not to alter the,Expand
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Ostrogradsky's theorem on Hamiltonian instability
  • R. Woodard
  • Mathematics, Computer Science
  • Scholarpedia
  • 6 June 2015
Ostrogradsky's Hamiltonian formalism for nondegenerate higher derivative Lagrangians is reviewed. Expand
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The Theorem of Ostrogradsky
Ostrogradsky’s construction of a Hamiltonian formalism for nondegenerate higher derivative Lagrangians is reviewed. The resulting instability imposes by far the most powerful restriction onExpand
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Nonlocal Models of Cosmic Acceleration
I review a class of nonlocally modified gravity models which were proposed to explain the current phase of cosmic acceleration without dark energy. Among the topics considered are deriving causal andExpand
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Maximally symmetric vector propagator
We derive the propagator for a massive vector field on a de Sitter background of arbitrary dimension. This propagator is de Sitter invariant and possesses the proper flat space-time and masslessExpand
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Reconstructing the Distortion Function for Nonlocal Cosmology
We consider the cosmology of modified gravity models in which Newton's constant is distorted by a function of the inverse d'Alembertian acting on the Ricci scalar. We derive a technique for choosingExpand
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Leading log solution for inflationary Yukawa theory
We generalize Starobinskii's stochastic technique to the theory of a massless, minimally coupled scalar interacting with a massless fermion in a locally de Sitter geometry. The scalar is an 'active'Expand
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