The classical dynamics of the tachyon scalar field of cubic string field theory is considered on a cosmological background. Starting from a nonlocal action with arbitrary tachyon potential, which encodes the bosonic and several supersymmetric cases, we study the equations of motion in the Hamilton–Jacobi formalism and with a generalized Friedmann equation, appliable in braneworld or modified gr...

The neutrino pulse from SN1987A provides one of the most rigourous constraints on models of extra dimensions. Previously, calculations have been done to bound the size of these extra dimensions in the case when the metric was factorizable. Here we consider the case of 2 ‘weakly warped’ extra dimensions. We find that even though weak warping seems only to affect the zero mode this can have a mea...

In a variant of the Randall-Sundrum braneworld model which has a charged black hole in an anti-de Sitter bulk, the 4D speed of gravity depends upon one’s location in the bulk, and in general differs from the speed of light on a given 3-brane. We apply phenomenological constraints on the difference in the speeds of light and gravity to models which use the warping to solve the hierarchy problem....

Massive gravity, galileon and braneworld models that modify gravity to explain cosmic acceleration utilize the nonlinear field interactions of the Vainshtein mechanism to screen fifth forces in high density regimes. These source-dependent interactions cause apparent equivalence principle violations. In the weakly-screened regime violations can be especially prominent since the fifth forces are ...

In these lectures notes, we will discuss a particular higher order gravity theory, Lovelock theory, that generalises in higher dimensions than 4, general relativity. After briefly motivating modifications of gravity, we will introduce the theory in question and we will argue that it is a unique, mathematically sensible, and physically interesting extension of general relativity. We will see, by...

Abstract Our review is devoted to three promising research lines in quantum cosmology and the physics of the early universe. The nonperturbative renormalization programme is making encouraging progress that we here assess from the point of view of cosmological applications: Lagrangian and Hamiltonian form of pure gravity with variable G and Λ; power-law inflation for pure gravity; an accelerati...

We study the slow-roll inflationary dynamics in a self-gravitating induced gravity braneworld model with bulk cosmological constant. For E ≫ M3 5 /M2 4 we find important corrections to the four-dimensional Friedmann equation which bring the standard chaotic inflationary scenario in closer agreement with recent observations. For M3 5 /M 2 P l ≪ E ≪ M3 5 /M2 4 we find five-dimensional corrections...

We extent our previous study on spherically symmetric braneworld solutions with induced gravity, including non-local bulk effects. We find the most general static four-dimensional black hole solutions with gtt = −g−1 rr . They satisfy a closed system of equations on the brane and represent the strong-gravity corrections to the Schwarzschild-(A)dS4 spacetime. These new solutions have extra terms...