Brane-Bulk Interaction in Topological Theory

In this letter we address the problem of inducing boundary degrees of freedom from a bulk theory whose action contains higher-derivative corrections. As a model example we consider a topological theory with an action that has only a ``higher-derivative'' term. By choosing specific coupling of the brane to the bulk we show that the boundary action contains gravity action along with some higher-derivative corrections. The co-dimension of the brane is more than one. In this sense the boundary is singular.Comment: 10 pages, minor corrections, references added, to appear in Phys. Lett.

On automorphisms of certain free nilpotent-by-abelian Lie algebras

For a positive integer $n$, with $n \geq 4$, let $R_{n}$ be a free (nilpotent of class 2)-by-abelian and abelian-by-(nilpotent of class 2) Lie algebra of rank $n$. We show that the subgroup of Aut$(R_{n})$ generated by the tame automorphisms and a countably infinite set of explicitly given automorphisms of $R_{n}$ is dense in Aut$(R_{n})$ with respect to the formal power series topology

Induced Gravity on RS Branes

It is shown that a localized four-dimensional Einstein term, induced by quantum corrections, modifies significantly the law of gravity in a Randall-Sundrum brane world. In particular, the short-distance behavior of gravity changes from five- to four-dimensional, while, depending on the values of parameters, there can be an intermediate range where gravity behaves as in five dimensions. The spectrum of graviton fluctuations around the brane, their relative importance for the gravitational force, and the relevance of their emission in the bulk for the brane cosmology are analysed. Finally, constraints on parameters are derived from energy loss in astrophysical and particle physics processes.Comment: 20 pages, 1 figure, JHEP.cl

Gauss-Bonnet gravity renders negative tension braneworlds unstable

We show that the Gauss-Bonnet correction to Einstein gravity induces a gravitational tachyon mode, namely an unstable spin 2 fluctuation, in the Randall-Sundrum I model. We demonstrate that this instability is generically related to the presence of a negative tension brane in the set-up, with or without $Z_2$-symmetry across it. Indeed it is shown that the tachyon mode is a bound state localised on any negative tension brane of co-dimension one, embedded in anti-de Sitter background. We discuss the possible resolution of this instability by the inclusion of induced gravity terms on the branes or by an effective four-dimensional cosmological constant.Comment: published versio

Gravitational Leakage into Extra Dimensions: Probing Dark Energy Using Local Gravity

The braneworld model of Dvali-Gabadadze-Porrati (DGP) is a theory where gravity is modified at large distances by the arrested leakage of gravitons off our four-dimensional universe. Cosmology in this model has been shown to support both "conventional" and exotic explanations of the dark energy responsible for today's cosmic acceleration. We present new results for the gravitational field of a clustered matter source on the background of an accelerating universe in DGP braneworld gravity, and articulate how these results differ from those of general relativity. In particular, we show that orbits nearby a mass source suffer a universal anomalous precession as large as 5 microarcseconds/year, dependent only on the graviton's effective linewidth and the global geometry of the full, five-dimensional universe. Thus, this theory offers a local gravity correction sensitive to factors that dictate cosmological history.Comment: 18 pages, 1 figure, revtex. Reference updated. Footnote change

Non-uniform Braneworld Stars: an Exact Solution

The first exact interior solution to Einstein's field equations for a static and non-uniform braneworld star with local and non-local bulk terms is presented. It is shown that the bulk Weyl scalar ${\cal U}(r)$ is always negative inside the stellar distribution, in consequence it reduces both the effective density and the effective pressure. It is found that the anisotropy generated by bulk gravity effect has an acceptable physical behaviour inside the distribution. Using a Reissner-N\"{o}rdstrom-like exterior solution, the effects of bulk gravity on pressure and density are found through matching conditions.Comment: 22 pages, 3 figures, version to be published in International Journal of Modern Physics D (IJMPD

Thermodynamics of Friedmann Equation and Masslike Function in General Braneworld

Using the generalized procedure proposed by \emph{Wu et al}\cite{wu} recently, we construct the first law of thermodynamics on apparent horizon in a general braneworld model with curvature correction terms on the brane and in the bulk, respectively. The explicit entropy formulary of apparent horizon in the general braneworld is worked out. We also discuss the masslike function which associated with a new type first law of thermodynamics of the general braneworld in detail. We analyze the difference between the conventional thermodynamics and the new type thermodynamics on apparent horizon. At last, the discussions about the physical meanings of the masslike function have also been given.Comment: 14 pages, revtex form, no figure, english writing improved and some discussions expanded. Accepted for publication in Int.J.Mod.Phys.