English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We propose the most general modified first-order Ho\v{r}ava-Lifshitz (HL)gravity, whose action does not contain time derivatives higher than the secondorder. The Hamiltonian structure of this theory is studied in all the detailsin the case of the spatially-flat FRW space-time, demonstrating many of thefeatures of the general theory. It is shown that, with some plausibleassumptions, including the projectability of the lapse function, this model isconsistent. As a large class of such theories, the modified HL $F(R)$ gravityis introduced. The study of its ultraviolet properties shows that its $z=3$version seems to be renormalizable in the same way as the original HL proposal.The Hamiltonian analysis of the modified HL $F(R)$ gravity shows that it is ingeneral a consistent theory. The $F(R)$ gravity action is also studied in thefixed-gauge form, where the appearance of a scalar field is particularlyillustrative. Then the spatially-flat FRW cosmology for this $F(R)$ gravity isinvestigated. It is shown that a special choice of parameters for this theoryleads to the same equations of motion as in the case of traditional $F(R)$gravity. Nevertheless, the cosmological structure of the modified HL $F(R)$gravity turns out to be much richer than for its traditional counterpart. Theemergence of multiple de Sitter solutions indicates to the possibility ofunification of early-time inflation with late-time acceleration within the samemodel. Power-law $F(R)$ theories are investigated in detail. It is analyticallyshown that they have a quite rich cosmological structure: early/late-timecosmic acceleration of quintessence, as well as of phantom types. Also it isdemonstrated that all the four known types of finite-time future singularitiesmay occur in the power-law HL $F(R)$ gravity. Finally, a covariant proposal for(renormalizable) $F(R)$ gravity within the HL spirit is presented.

Modified first-order Horava-Lifshitz gravity: Hamiltonian analysis of the general theory and accelerating FRW cosmology in power-law F(R) model