Theories with infinite extra dimensions open exciting opportunities for particle physics. We argued recently that along with attractive features there are phenomenological difficulties in this class of models. In fact, there is no graviton zeromode in this case and 4D gravity is obtained by means of continuum bulk modes. These modes have extra polarization degrees of freedom which do not decoup...

We suggest a mechanism by which four-dimensional Newtonian gravity emerges on a 3-brane in 5D Minkowski space with an infinite size extra dimension. The worldvolume theory gives rise to the correct 4D potential at short distances whereas at large distances the potential is that of a 5D theory. We discuss some phenomenological issues in this framework.

The key to membrane theory is to enlarge the diffeomorphism group until 4D gravity becomes almost topological. Just one ghost survives and its central charges can cancel against matter. A simple bosonic membrane emerges, but its flat D = 28 target space is unstable. Adding supersym-metry ought to give calculable (2,2) membranes in 12 target dimensions, but (2,1) membranes won't work.

In the present paper, we briefly review recent studies of second order gravitational perturbations in braneworld models. After we mention the possibility of pathological behavior of gravity in higher order perturbations, second order perturbations are discussed in RandallSundrum braneworld models. Since mass spectrums of each braneworld model are different, we analyze them by different approach...

We study the correlation functions in the branched polymer model. Although there are no correlations in the grand canonical ensemble, when looking at the canonical ensemble we find negative long range power like correlations. We propose that a similar mechanism explains the shape of recently measured correlation functions in the elongated phase of 4d simplicial gravity[1].

We construct a cosmological model with non-minimally coupled scalar field on the brane, where Gauss-Bonnet and Induced Gravity effects are taken into account. This model has 5D character at both high and low energy limits but reduces to 4D gravity in intermediate scales. While induced gravity is a manifestation of the IR limit of the model, Gauss-Bonnet term and non-minimal coupling of scalar f...

Using s-wave and large N approximation the one-loop effective action for 2d dilaton coupled scalars and spinors which are obtained by spherical reduction of 4d minimal matter is found. Quantum effective equations for reduced Einstein gravity are written. Their analytical solutions corresponding to 4d Kantowski-Sachs (KS) Universe are presented. For quantum-corrected Einstein gravity we get non-...

We explore an effective 4D cosmological model for the universe where the variable cosmological constant governs its evolution and the pressure remains negative along all the expansion. This model is introduced from a 5D vacuum state where the (space-like) extra coordinate is considered as noncompact. The expansion is produced by the inflaton field, which is considered as non-minimally coupled t...

We explore an effective 4D cosmological model for the universe where the variable cosmological constant governs its evolution and the pressure remains negative along all the expansion. This model is introduced from a 5D vacuum state where the (space-like) extra coordinate is considered as noncompact. The expansion is produced by the inflaton field, which is considered as non-minimally coupled t...

We discuss a model which gives rise to cosmic self-acceleration due to modified gravity. Improvements introduced by this approach are the following: In the coordinate system commonly used, the metric does not grow in the bulk, and no negative mass states are expected to appear. The spectrum of small perturbations contains a localized massless tensor mode, but does not admit dangerous localized ...