Cargèse Lectures on Brane Induced Gravity

A brief introduction is given to the subject of brane induced gravity. The 5D example is discussed in detail. The 4D laws of gravity are obtained on a brane embedded in an infinite volume extra space, where the problem of stabilization of the volume modulus is absent. The theory has two classically disjoint branches of solutions – the conventional and self-accelerated one. The conventional branch is perturbatively stable, and gives rise to predictions that are potentially measurable within the Solar system. The self-accelerated branch, on the other hand, provides an existence proof for an idea that the accelerated expansion of the Universe could be due to modified gravity. This branch, however, exhibits negative mass states, suggesting that the self-accelerated solution may not be free of instabilities. A proposal to overcome this difficulty in an extension of the original model, that also allows for the quantum gravity scale to be unrestricted, is discussed.