In natural inflation models, the inflaton is a pseudo Nambu-Goldstone boson and the flatness of the potential is protected by shift symmetries. In this framework, a successful inflation requires the global symmetry to be spontaneously broken at a scale close to the Planck mass. Such a high value of the spontaneous breaking scale may not be legitimate in an effective field theory. On the other h...

We construct an eternally inflating spacelike brane world model. If the space dimension of the brane is three (SM2) or six (SM5) for M theory or four (SD3) for superstring theory, a time-dependent n-form field would supply a constant energy density and cause exponentially expansion of the spacelike brane. In these cases, the hyperbolic space perpendicular to the brane would keep its scale facto...

In a Randall–Sundrum type II inflationary scenario we compute perturbation amplitudes and spectral indices up to next-to-lowest order in the slowroll parameters, starting from the well-known lowest-order result for a de Sitter brane. Using two different prescriptions for the tensor amplitude, we show that the braneworld consistency equations are not degenerate with respect to the standard relat...

We find an exact solution of Kerr-Newman-de Sitter type on the braneworld(4D) of the DGP model. When a constant 4D Ricci scalar is assumed, only zero(flat) and a positive(deSitter) values satisfy the Hamiltonian constraint equation coming from the extra dimension. With a Z2-symmetry across the brane and a stationary and axisymmetric metric ansatz on the brane, we solve the constraint equation e...

We consider a magnetic Bianchi I braneworld, embedded in between two SchwarzschildAdS spacetimes, boosted equal amounts in opposite directions and compare them to the analagous solution in four-dimensional General Relativity. The efficient dissipation of anisotropy on the brane is explicitly demonstrated, a process we dub braneworld isotropization. From the bulk point of view, we attribute this...

It has been believed that topology and signature change of the universe can only happen accompanied by singularities in classical or instantons in quantum gravity. In this note, we point out however that in the braneworld context, such an event can be understood as a classical, smooth event. We supply some explicit examples of such cases, starting from the Dirac-Born-Infeld action. Topology cha...

We study the braneworld effective action in the two-brane RandallSundrum model. In the framework of this essentially-nonlocal action we reveal the origin of an infinite sequence of gravitational wave modes — the usual massless one as well as the tower of Kaluza-Klein massive ones. Mixing of the modes, which parametrically depends on the background value of the modulus of the extra dimension, ca...

Abstract Braneworld models with induced gravity exhibit phantom-like behavior of the effective equation state dark energy. They can, therefore, naturally accommodate higher values H 0 , preferred by recent local measurements while satisfying cosmic microwave background constraints. We test evolution in such phantom braneworld scenarios current observational data sets. find that prefers a value ...

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 ...

The brane cosmology scenario is based on the idea that our Universe is a 3−brane embedded in a five-dimensional bulk. In this work, a general class of braneworld wormholes is explored with R 6= 0, where R is the four dimensional Ricci scalar, and specific solutions are further analyzed. A fundamental ingredient of traversable wormholes is the violation of the null energy condition (NEC). Howeve...