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arxiv 0904.2092 v2 pith:UEEIWGF6 submitted 2009-04-14 astro-ph.CO gr-qchep-th

Vacuum structure for scalar cosmological perturbations in Modified Gravity Models

Antonio De Felice , Teruaki Suyama This is my paper
classification astro-ph.CO gr-qchep-th
keywords generalmodelsmodesscalarcosmologicalgravitymodifiedperturbations
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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We have found for the general class of Modified Gravity Models f(R,G) a new instability which can arise in vacuum for the scalar modes of the cosmological perturbations if the background is not de Sitter. In particular, the short-wavelength modes, if stable, in general have a group velocity which depends linearly in k, the wave number. Therefore these modes will be in general superluminal. We have also discussed the condition for which in general these scalar modes will be ghost-like. There is a subclass of these models, defined out of properties of the function f(R,G) and to which the f(R) and f(G) models belong, which however does not have this feature.

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Cited by 3 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Photon Sphere and Shadow of a Perturbative Black Hole in $f(R,\mathcal{G})$ Gravity

    gr-qc 2026-05 unverdicted novelty 4.0

    Perturbative f(R, G) corrections shift the photon-sphere radius and black-hole shadow size, with the Gauss-Bonnet sector contributing more than mixed terms.

  2. Photon Sphere and Shadow of a Perturbative Black Hole in $f(R,\mathcal{G})$ Gravity

    gr-qc 2026-05 unverdicted novelty 4.0

    Perturbative f(R,G) corrections shift the photon-sphere radius and shadow size, with the Gauss-Bonnet term dominating over mixed curvature contributions.

  3. Photon Sphere and Shadow of a Perturbative Black Hole in $f(R,\mathcal{G})$ Gravity

    gr-qc 2026-05 unverdicted novelty 3.0

    Perturbative higher-curvature corrections in f(R,G) gravity shift the photon-sphere radius and black-hole shadow size away from Schwarzschild values, with the Gauss-Bonnet sector contributing more than mixed terms.