We explore the problem of braneworld black holes in the heterotic braneworld scenario of Lukas, Ovrut, Stelle and Waldram (LOSW). We show that black string solutions are unstable, and demonstrate some unusual asymptotics in the linearized metric. We also solve the fully coupled brane and bulk Einstein equations, finding an exact, though singular, solution which corresponds to a brane black hole...

In braneworld models coming from string theory one generally encounters massless scalar degrees of freedom –moduli– parameterizing the volume of small compact extra-dimensions. Here we discuss the effects of such moduli on Newton’s law for a fairly general 5-D supersymmetric braneworld scenario with a bulk scalar field φ . We show that the Newtonian potential describing the gravitational intera...

In recent years there has been much interest in braneworld scenarios [1, 2, 3], where our four dimensional universe could be a brane embedded in a higher dimensional bulk spacetime. The basic ingredient of braneworld scenarios is that while ordinary matter fields are confined to the brane, only gravitational interactions can propagate in the bulk. The second Randall-Sundrum model (RS II) [4] wi...

We calculate the bispectrum of single-field braneworld inflation, triggered by either an ordinary scalar field or a cosmological tachyon, by means of a gradient expansion of large-scale non-linear perturbations coupled to stochastic dynamics. The resulting effect is identical to that for single-field 4D standard inflation, the nonlinearity parameter being proportional to the scalar spectral ind...

One of the aims of braneworld cosmology is to identify a ‘smoking gun’ for the existence of large extra dimensions by means of observations of the early universe. Braneworld cosmology has succeeded in reproducing the conventional cosmology at late times in a higher-dimensional context, but finding a unique observational signature has proved elusive. Here we demonstrate that the recently propose...

We show how to construct consistent braneworld models which exhibit late time acceleration. Unlike self-acceleration, which has a de Sitter vacuum state, our models have the standard Minkowski vacuum and accelerate only in the presence of matter, which we dub “stealth-acceleration”. We use an effective action for the brane which includes an induced gravity term, and allow for an asymmetric set-...

In this work, we consider a graphene-like background in braneworld scenario which is one of the interesting models in cosmology and theoretical physics. Indeed, this paper is an application of holography in condense matter. We use the geometric form of potential which help to obtain field equations and solve it to obtain the energy spectrum. In that case we calculate superpotential and energy d...

We develop a parameterized post-Friedmann (PPF) framework which describes three regimes of modified gravity models that accelerate the expansion without dark energy. On large scales, the evolution of scalar metric and density perturbations must be compatible with the expansion history defined by distance measures. On intermediate scales in the linear regime, they form a scalar-tensor theory wit...

These lectures present some topics of string phenomenology and contain two parts. In the first part, I review the possibility of lowering the string scale in the TeV region, that provides a theoretical framework for solving the mass hierarchy problem and unifying all interactions. The apparent weakness of gravity can then be accounted by the existence of large internal dimensions, in the sub-mi...

We review various key issues in connection with the warped braneworld models which provide us with new insights and explanations of physical phenomena through interesting geometrical features of such extra dimensional theories. Starting from the original Randall-Sundrum two brane models, we have discussed the stability, hierarchy and other important issues in connection with such braneworld. Th...