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تسجيل مستخدم جديدEffective field theory approach to modified gravity including Horndeski theory and Hov{r}ava-Lifshitz gravity
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We review the effective field theory of modified gravity in which the Lagrangian involves three dimensional geometric quantities appearing in the 3+1 decomposition of space-time. On the flat isotropic cosmological background we expand a general action up to second order in the perturbations of geometric scalars, by taking into account spatial derivatives higher than two. Our analysis covers a wide range of gravitational theories-- including Horndeski theory/its recent generalizations and the projectable/non-projectab
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We investigate the Hamiltonian structure of linearized extended Hov{r}ava- Lifshitz gravity in a flat cosmological background following the Faddeev-Jackiws Hamiltonian reduction formalism. The Hamiltonian structure of extended Hov{r}ava-Lifshitz grav
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We investigate the linear cosmological perturbations in Hov{r}ava-Lifshitz gravity with a scalar field. Starting from the most general expressions of the metric perturbations as well as that of a canonical scalar field, we decompose the scalar, vecto
r and tensor parts of the perturbed action. By reducing the Hamiltonian, we find that there are two independent degrees of freedom for the tensor perturbations while none for the vector perturbations. For the scalar perturbations, the remaining number of degrees of freedom, which are all gauge invariant, depends on whether the projectable condition is applied or not. For both cases, we lose the time reparametrization symmetry of any kind.
We calculate the spectrum of the relic gravitational wave due to the trans-Planckian effect in which the standard linear dispersion relations may be modified. Of the modified dispersion relations suggested in literatures which have investigated the t
rans-Planckian effect, we especially use the Corley-Jacobson dispersion relations. The Corley-Jacobson type modified dispersion relations can be obtained from Hov{r}ava-Lifshitz gravity which is non-relativistic and UV complete. Although it is not clear how the transitions from Hov{r}ava-Lifshitz gravity in the UV regime to Einstein gravity in the IR limit occur, we assume Hov{r}ava-Lifshitz gravity regime is followed by the inflationary phase in Einstein gravity.
We investigate string-like solutions in four dimensions based on Hov{r}ava-Lifshitz gravity. For a restricted class of solutions where the Cotton tensor vanishes, we find that the string-like solutions in Einstein gravity including the BTZ black stri
ngs are solutions in Hov{r}ava-Lifshitz gravity as well. The geometry is warped in the same way as in Einstein gravity, but the conformal lapse function is not constrained in Hov{r}ava-Lifshitz gravity. It turns out that if $lambda e 1$, there exist no other solutions. For the value of model parameter with which Einstein gravity recovers in IR limit (i.e., $lambda=1$), there exists an additional solution of which the conformal lapse function is determined. Interestingly, this solution admits a uniform BTZ black string along the string direction, which is distinguished from the warped BTZ black string in Einstein gravity. Therefore, it is a good candidate for the test of the theory.
We present a detailed analysis of the construction of $z=2$ and $z eq2$ scale invariant Hov{r}ava-Lifshitz gravity. The construction procedure is based on the realization of Hov{r}ava-Lifshitz gravity as the dynamical Newton-Cartan geometry as well a
s a non-relativistic tensor calculus in the presence of the scale symmetry. An important consequence of this method is that it provides us the necessary mechanism to distinguish the local scale invariance from the local Schrodinger invariance. Based on this result we discuss the $z=2$ scale invariant Hov{r}ava-Lifshitz gravity and the symmetry enhancement to the full Schrodinger group.
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