Constraints on Holographic Multifield Inflation and Models Based on the Hamilton-Jacobi Formalism.

In holographic inflation, the 4D cosmological dynamics is postulated to be dual to the renormalization group flow of a 3D Euclidean conformal field theory with marginally relevant operators. The scalar potential of the 4D theory-in which inflation is realized-is highly constrained, with use of the Hamilton-Jacobi equations. In multifield holographic realizations of inflation, fields additional to the inflaton cannot display underdamped oscillations (that is, their wave functions contain no oscillatory phases independent of the momenta).

Active galactic nuclei shed light on axionlike particles.

We demonstrate that the scatter in the luminosity relations of astrophysical objects can be used to search for axionlike particles. This analysis is applied to observations of active galactic nuclei, where we find evidence highly suggestive of the existence of a very light axionlike particle.

Brane inflation and defect formation.

Brane inflation and the production of topological defects at the end of the inflationary phase are discussed. After a description of the inflationary set-up, we discuss the properties of the cosmic strings produced at the end of inflation. Specific examples of brane inflation are described, such as D-D , D3/D7 and modular inflations.

Compatibility of the chameleon-field model with fifth-force experiments, cosmology, and PVLAS and CAST results.

We analyze the PVLAS results using a chameleon field whose properties depend on the environment. We find that, assuming a runaway bare potential V(phi) and a universal coupling to matter, the chameleon potential is such that the scalar field can act as dark energy. Moreover, the chameleon-field model is compatible with the CERN Axion Solar Telescope results, fifth-force experiments, and cosmology.