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On the evolution of universes in quadratic theories of gravity
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We use a dynamical systems approach to investigate Bianchi type I and II universes in quadratic theories of gravity. Due to the complicated nature of the equations of motion we focus on the stability of exact solutions and find that there exists an isotropic FRW universe acting as a past attractor. This may indicate that there is an isotropisation mechanism at early times for these kind of theories. We also discuss the Kasner universes, elucidate the associated centre manifold structure, and show that there exists a set of non-zero measure which has the Kasner solutions as a past attractor. Regarding the late-time behaviour, the stability shows a dependence of the parameters of the theory. We give the conditions under which the de Sitter solution is stable and also show that for certain values of the parameters there is a possible late-time behaviour with phantom-like behaviour. New types of anisotropic inflationary behaviour are found which do not have counterparts in general relativity.
Forward citations
Cited by 5 Pith papers
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Unstable de Sitter inflationary solution in sixth-order gravity
For the sixth-order gravity action (2.1), the exact FLRW de Sitter solution is unstable whenever 3γ1+γ2<0, while the second-order limit admits a stable de Sitter attractor.
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Initial conditions for Starobinsky inflation in general quadratic gravity
In general quadratic gravity with alpha = -10 beta, Starobinsky inflation remains reachable from a nonzero band of initial conditions, though the basin shifts from expanding to contracting starts as shear increases.
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Thermodynamics of FLRW universe in Quadratic Gravity
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Effect of $R^2$ on the stability of de Sitter solution of the generalized Einsteinian cubic gravity
Generalized Einsteinian cubic gravity admits a de Sitter solution from the P cubic term alone; stability analysis is incomplete until the R^2 term is added, which leaves the solution value unchanged.
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On the stability of de Sitter inflationary solution in the Starobinsky-Bel-Robinson gravity
The exact de Sitter solution of Starobinsky-Bel-Robinson gravity is fixed by the quartic Bel-Robinson coupling alone and is an unstable saddle point for the physically allowed positive sign of the R^2 coefficient.
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