Exact Friedmann Solutions in Higher-Order Gravity Theories
نویسنده
چکیده
We find the general behaviour of homogeneous and isotropic cosmological models in some fourth-order theories of gravity. Explicit, exact, general solutions are given for both empty universes and those filled with a perfect fluid. For the vacuum case, solutions are found with closed, open and flat geometries, whilst the perfect fluid solutions are all spatially flat. Both early and late-time limits are studied, and attractor behaviour towards simple power-law expansion is identified. Multiple solutions to the same theories, with the same matter content and topology are found. It is shown that these solutions exhibit great variety in their evolution. [email protected]
منابع مشابه
Curvature and Torsion Quintessence
The issues of quintessence and cosmic acceleration can be discussed in the framework of higher order curvature and torsion theories of gravity. We can define effective pressure and energy density directly connected to the curvature or to the torsion fields and then ask for the conditions to get an accelerated expansion. Exact accelerated expanding solutions can be achieved for several fourth or...
متن کاملar X iv : g r - qc / 0 60 11 18 v 1 2 7 Ja n 20 06 Further Exact Cosmological Solutions to Higher - Order Gravity Theories
We investigate the effect of deviations from general relativity on approach to the initial singularity by finding exact cosmological solutions to a wide class of fourth-order gravity theories. We present new anisotropic vacuum solutions of modified Kasner type and demonstrate the extent to which they are valid in the presence of non-comoving perfect-fluid matter fields. The infinite series of M...
متن کاملExact cosmological solutions of scale-invariant gravity theories
We have found new anisotropic vacuum solutions for the scale-invariant gravity theories which generalise Einstein’s general relativity to a theory derived from the Lagrangian R. These solutions are expanding universes of Kasner form with an initial spacetime singularity at t = 0 and exist for −1/2 < δ < 1/4 but possess different Kasner index relations to the classic Kasner solution of general r...
متن کاملBlack Holes, Cosmological Solutions, Future Singularities, and Their Thermodynamical Properties in Modified Gravity Theories
Along this review, we focus on the study of several properties of modified gravity theories, in particular on black-hole solutions and its comparison with those solutions in General Relativity, and on Friedmann–Lemaı̂tre–Robertson–Walker metrics. The thermodynamical properties of fourth order gravity theories are also a subject of this investigation with special attention on local and global sta...
متن کاملExact Solutions in Locally Anisotropic Gravity and Strings
In this Report we outline some basic results on generalized Finsler– Kaluza–Klein gravity and locally anisotropic strings. There are investigated exact solutions for locally anisotropic Friedmann–Robertson– Walker universes and three dimensional and string black holes with generic anisotropy. Devoted to the memory of Professor Ryszard Raczka (1931–1996)
متن کامل