Astrophysics

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.

The holographic duality gives a one-to-one mapping between consistent theories of gravity with AdS_d ground state, and conformal field theories in d-1 dimensions. Since the latter are unambiguously well-defined, we can use their defining properties to prove rigorous, model-independent theorems covering all quantum gravity theories with negative cosmological constant. Taking d=3, I will prove in this talk that every two-dimensional CFT contains a primary perator of weight less than C /12 + 0.473695, where C is the sum of right- and left-moving central charges. Using the AdS/CFT dictionary, this establishes that every theory of quantum gravity in asymptotically AdS space contains some state of mass less than 1 / (4 G), above and beyond the universal sector of boundary metric excitations.