Density perturbations in general modified gravitational theories

Antonio De Felice*, Shinji Mukohyama, Shinji Tsujikawa

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

97 Citations (Scopus)


We derive the equations of linear cosmological perturbations for the general Lagrangian density f(R,φ,X)/2+Lc, where R is a Ricci scalar, φ is a scalar field, and X=-∂μφ∂μφ/2 is a field kinetic energy. We take into account a nonlinear self-interaction term Lc=ξ(φ)□φ(∂μφ∂μφ) recently studied in the context of "Galileon" cosmology, which keeps the field equations at second order. Taking into account a scalar-field mass explicitly, the equations of matter density perturbations and gravitational potentials are obtained under a quasistatic approximation on subhorizon scales. We also derive conditions for the avoidance of ghosts and Laplacian instabilities associated with propagation speeds. Our analysis includes most of modified gravity models of dark energy proposed in literature; and thus it is convenient to test the viability of such models from both theoretical and observational points of view.

Original languageEnglish
Article number023524
JournalPhysical Review D - Particles, Fields, Gravitation and Cosmology
Issue number2
Publication statusPublished - 2010 Jul 26
Externally publishedYes

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Physics and Astronomy (miscellaneous)


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