Anisotropic singularities in modified gravity models

Abstract

We show that the common singularities present in generic modified gravity models governed by actions of the type $S=\int d^{4}x\sqrt{-g}f(R,\varphi ,X)$, with $X=-1/2g^{ab}{\partial }_a\varphi {\partial }_b\varphi$, are essentially the same anisotropic instabilities associated to the hypersurface $F(\varphi )=0$ in the case of a non-minimal coupling of the type $F(\varphi )R$, enlightening the physical origin of such singularities that typically arise in rather complex and cumbersome inhomogeneous perturbation analyses. We show, moreover, that such anisotropic instabilities typically give rise to dynamically unavoidable singularities, precluding completely the possibility of having physically viable models for which the hypersurface $\frac{\partial f}{\partial R}=0$ exists. Some examples are explicitly discussed.

6 pages, final version to appear in PRD

References in corpus (11)

• Models of f(R) Cosmic Acceleration that Evade Solar-System Tests
• Class of viable modified $f(R)$ gravities describing inflation and the onset of accelerated expansion
• Future of the universe in modified gravitational theories: Approaching to the finite-time future singularity
• The future evolution and finite-time singularities in $F(R)$-gravity unifying the inflation and cosmic acceleration
• A Singularity Problem with f(R) Dark Energy
• Perturbations in generalized multi-field inflation
• The phase space view of f(R) gravity
• Can higher curvature corrections cure the singularity problem in f(R) gravity?
• Primordial Non-Gaussianities of General Multiple Field Inflation
• Curvature and Entropy Perturbations in Generalized Gravity
• Homogeneous cosmologies and the Maupertuis-Jacobi principle