We compute directly the entanglement entropy of spatial regions in ChernSimons gauge theories in 2 + 1 dimensions using surgery. We consider the possible dependence of the entanglement entropy on the topology of the spatial manifold and on the vacuum state on that manifold. The entanglement entropy of puncture insertions (quasiparticles) is discussed in detail for a few cases of interest. We show that quite generally the topological entanglement entropy is determined by the modular S-matrix of the associated rational conformal field theory as well as by the fusion rules and fusion coefficients. We use these results to determine the universal topological piece of the entanglement entropy for Abelian and non-Abelian quantum Hall fluids. As a byproduct we present the calculation of the modular S-matrix of two coset RCFTs of interest.

A holographic dual description of a 2+1 dimensional system of strongly interacting fermions at low temperature and finite charge density is given in terms of an electron cloud suspended over the horizon of a charged black hole in asymptotically AdS spacetime. The electron star of Hartnoll and Tavanfar is recovered in the limit of zero temperature, while at higher temperatures the fraction of charge carried by the electron cloud is reduced and at a critical temperature there is a second order phase transition to a configuration with only a charged black hole. The geometric structure implies that finite temperature transport coefficients, including the AC electrical conductivity, only receive contributions from bulk fermions within a finite band in the radial direction.Comment: LaTex 16 pages, 12 figures, v2: Added reference. Error in free energy corrected. Phase transition to AdS-RN black brane is third order rather than second order as was claimed previousl

We study vortex solutions in a holographic model of Herzog, Hartnoll, and Horowitz, with a vanishing external magnetic field on the boundary, as is appropriate for vortices in a superfluid. We study the relevant length scales related to the vortices and how the charge density inside the vortex core behaves as a function of temperature or chemical potential. We extract a critical superfluid velocity from the vortex solutions, study how it behaves as a function of the temperature, and compare it to earlier studies and to the Landau criterion. We also comment on the possibility of a Berezinskii-Kosterlitz-Thouless vortex confinement-deconfinement transition.