It is suggested [1] that current cosmic acceleration arises due to modification of General Relativity by the terms with negative powers of curvature. We argue that time-dependent (hyperbolic) compactifications of 4 + n-dimensional gravity ( string/M-theory) lead to the effective 4d gravity which naturally contains such terms. The same may be achieved in the braneworld by the proper choice of th...

We investigate a formulation of continuum 4d gravity in terms of a constrained topological (BF) theory, in the spirit of the Plebanski formulation, but involving only linear constraints, of the type used recently in the spin foam approach to quantum gravity. We identify both the continuum version of the linear simplicity constraints used in the quantum discrete context and a linear version of t...

The induced 4d gravity on a brane world is analyzed. The case of a thick brane is considered and the unexpected appearance of a new threshold scale, much larger than the thickness scale is found. In cases of phenomenological interest, this new length scale turns out to be in the submillimeter range. The effect of R corrections, both in the bulk and on the brane, is also studied. It is shown tha...

Models with extra dimensions postulate the existence of δ additional spatial dimensions of size R where gravity and perhaps other fields freely propagate while the SM degrees of freedom are confined to (3+1)-dimensional wall (4D) of the higher dimensional space. The true scale of gravity, or fundamental Planck scale M∗, of the (4 + δ)D space time is related to the reduced 4D Planck scale MP l, ...

In the present paper, we briefly review recent studies of second-order gravitational perturbations in braneworld models. After we consider the possibility of pathological behavior of gravity at higher orders of perturbation, second-order perturbations are discussed in Randall-Sundrum braneworld models. Because the mass spectra in these braneworld models are different, we analyze them using diff...

We address the localization of gravity on the Friedmann-Robertson-Walker type brane embedded in either AdS5 or dS5 bulk space, and derive two definite limits between which the value of the bulk cosmological constant has to lie in order to localize the graviton on the brane. The lower limit implies that the brane should be either dS4 or 4d Minkowski in the AdS5 bulk. The positive upper limit ind...

Abstract The existence of strange matter in compact stars may give rise to striking outcomes the various physical phenomena. As an alternative neutron stars, a new class called should exist if hypothesis is true. In this paper, we investigate possible construction quark phases based on MIT bag model. We consider scenarios which have no crusts. Then apply two types equations state quantify mass–...