In a D = 2+1 quantum critical system, the entanglement entropy across a boundary with a corner contains a subleading logarithmic scaling term with a universal coefficient. It has been conjectured that this coefficient is, to leading order, proportional to the number of field components N in the associated O(N ) continuum φ 4 field theory. Using density matrix renormalization group calculations combined with the powerful numerical linked cluster expansion technique, we confirm this scenario for the O(2) Wilson-Fisher fixed point in a striking way, through direct calculation at the quantum critical points of two very different microscopic models. The value of this corner coefficient is, to within our numerical precision, twice the coefficient of the Ising fixed point. Our results add to the growing body of evidence that this universal term in the Rényi entanglement entropy reflects the number of low-energy degrees of freedom in a system, even for strongly interacting theories.

We analyse vortex hair for charged rotating asymptotically AdS black holes in the abelian Higgs model. We give analytical and numerical arguments to show how the vortex interacts with the horizon of the black hole, and how the solution extends to the boundary. The solution is very close to the corresponding asymptotically flat vortex, once one transforms to a frame that is non-rotating at the boundary. We show that there is a Meissner effect for extremal black holes, with the vortex flux being expelled from sufficiently small black holes. The phase transition is shown to be first order in the presence of rotation, but second order without rotation. We comment on applications to holography.Comment: 24 pages, 7 figures, references adde

We report on the results of a study of the motion of a four particle non-relativistic one-dimensional self-gravitating system. We show that the system can be visualized in terms of a single particle moving within a potential whose equipotential surfaces are shaped like a box of pyramid-shaped sides. As such this is the largest N -body system that can be visualized in this way. We describe how to classify possible states of motion in terms of Braid Group operators, generalizing this to N bodies. We find that the structure of the phase space of each of these systems yields a large variety of interesting dynamics, containing regions of quasiperiodicity and chaos. Lyapunov exponents are calculated for many trajectories to measure stochasticity and previously unseen phenomena in the Lyapunov graphs are observed.

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