Astrophysics

An update is given on AdS/CFT models of cosmological singularities, in particular on models in which a big crunch instability of the bulk theory is induced by an unstable multi-trace deformation of the dual field theory.

Certain classes of cosmological backgrounds in asymptotically anti-de-Sitter space-times have hologropically dual descriptions in terms of gauge theories. We analyse such backgrounds with smooth initial conditions, where curvatures become strong in a finite time and the gravity equations break down. We will show how the dual gauge theory can be used to continue time evolution in this singular region and speculate on the nature of space-time at late times.

The standard theorist's model for the dynamics of galaxies is the limit of a Newtonian N-body system at fixed mass as the number of particles goes to infinity - i.e a phase space fluid After going over conventional wisdom, some interesting open issues which remain will be highlighted, and their relation to real galaxies explored.

It has been shown by Hertog and Horowitz that certain AdS boundary conditions allow non-singular initial conditions to evolve into a Big Crunch. To study this kind of cosmological singularities, one can use the dual quantum field theory, where the singularity is manifested by the presence of a multi-trace potential unbounded below. Recently, Craps, Hertog and Turok have proposed two specific models of this type to study the possibility of a Big Crunch/Big Bang transition. For both models, I will provide a D-brane interpretation of the unbounded potential. In particular, I will show that the AdS boundary conditions of interest cause spherical D-branes to be pushed to the boundary of AdS, and that the corresponding potential agrees with the multi-trace deformation of the boundary field theory

I discuss the basic model of Higgs inflation, with a large non-minimal curvature coupling, from the point of view of effective field theory. It is pointed out that the effective cutoff scale is uncomfortably low compared to the inflation scale, thus rendering these models extremely sensitive to the details of the ultraviolet completion.