4 research outputs found
Accelerating cosmologies in Lovelock gravity with dilaton
For the description of the Universe expansion, compatible with observational
data, a model of modified gravity - Lovelock gravity with dilaton - is
investigated. D-dimensional space with 3- and (D-4)-dimensional maximally
symmetric subspaces is considered. Space without matter and space with perfect
fluid are under test. In various forms of the theory under way (third order
without dilaton and second order - Einstein-Gauss-Bonnet gravity - with dilaton
and without it) stationary, power-law, exponential and exponent-of-exponent
form cosmological solutions are obtained. Last two forms include solutions
which are clear to describe accelerating expansion of 3-dimensional subspace.
Also there is a set of solutions describing cosmological expansion which does
not tend to isotropization in the presence of matter.Comment: 23 page
Quadratic theory of gravity with a scalar field and type I Shapovalov wave spacetimes
For the quadratic theory of gravity with a scalar field, exact solutions are found for gravitational-wave models in Shapovalov I-type spacetimes, which do not arise in models of the general theory of relativity. The theory of gravity under consideration can effectively describe the early stages of the universe. Type I Shapovalov spaces are the most general forms of gravitational-wave Shapovalov spacetimes, whose metrics in privileged coordinate systems depend on three variables, including the wave variable. For Einstein vacuum spacetimes, these wave models degenerate into simpler types. The exact models of gravitational waves in the quadratic theory of gravity can be used to test the realism of such theories of gravity