Flavor corrections to the entanglement entropy

We consider the holographic entanglement entropy in N=4 SYM coupled to massive flavor degrees of freedom. The flavors are introduced by putting D7 branes in AdS_5. The resulting geometry including the backreaction of the branes is known in a perturbation expansion in the ratio N_f/N_c. We consider the expansion to first order, and compute the entanglement entropy of a region of the boundary. We consider two different cases for the geometry of the region: a slab and a ball. We find analytic solutions for the minimal surfaces in the bulk whose area gives the entropy, and analyze the structure of the UV divergence and the dependence on the masses. Our results confirm the general structure that was predicted by free field theory calculations, but with coefficients that depend on the coupling.Comment: 17 pages, 1 figure, references adde

Circuit Complexity and 2D Bosonisation

We consider the circuit complexity of free bosons, or equivalently free fermions, in 1+1 dimensions. Motivated by the results of [1] and [2, 3] who found different behavior in the complexity of free bosons and fermions, in any dimension, we consider the 1+1 dimensional case where, thanks to the bosonisation equivalence, we can consider the same state from both the bosonic and the fermionic perspectives. In this way the discrepancy can be attributed to a different choice of the set of gates allowed in the circuit. We study the effect in two classes of states: i) bosonic-coherent / fermionic-gaussian states; ii) states that are both bosonic- and fermionic-gaussian. We consider the complexity relative to the ground state. In the first class, the different results can be reconciled admitting a mode-dependent cost function in one of the descriptions. The differences in the second class are more important, in terms of the cutoff-dependence and the overall behavior of the complexity.Comment: Fix typos and add reference

Phenomenological characterisation of semi-holographic non-Fermi liquids

We analyse some phenomenological implications of the most general semi-holographic models for non-Fermi liquids that have emerged with inputs from the holographic correspondence. We find generalizations of Landau-Silin equations with few parameters governing thermodynamics, low energy response and collective excitations. We show that even when there is a Fermi surface with well-defined quasi-particle excitations, the collective excitations can behave very differently from Landau's theory.Comment: 5+5 pages, 3 figures, expanded supplementary material, published versio

Dressing the Electron Star in a Holographic Superconductor

We construct new asymptotically AdS_4 solutions dual to 2+1 CFTs at finite density and zero temperature by combining the ingredients of the electron star and the holographic superconductor. The solutions, which we call "compact electron stars", contain both a fermionic fluid and charged scalar hair in the bulk. We show that the new solutions are thermodynamically favoured in the region of parameter space where they exist. Along the boundary of this region, we find evidence for a continuous phase transition between the holographic superconductor and the compact star solution.Comment: 31 pages, 10 figures; added reference

Conformal Blocks and Negativity at Large Central Charge

We consider entanglement negativity for two disjoint intervals in 1+1 dimensional CFT in the limit of large central charge. As the two intervals get close, the leading behavior of negativity is given by the logarithm of the conformal block where a set of approximately null descendants appears in the intermediate channel. We compute this quantity numerically and compare with existing analytic methods which provide perturbative expansion in powers of the cross-ratio.Comment: harvmac, 30 pages, 2 figures, references added, accepted for publication in JHE

The Super-Higgs Mechanism in Fluids

Supersymmetry is spontaneously broken when the field theory stress-energy tensor has a non-zero vacuum expectation value. In local supersymmetric field theories the massless gravitino and goldstino combine via the super-Higgs mechanism to a massive gravitino. We study this mechanism in four-dimensional fluids, where the vacuum expectation value of the stress-energy tensor breaks spontaneously both supersymmetry and Lorentz symmetry. We consider both constant as well as space-time dependent ideal fluids. We derive a formula for the gravitino mass in terms of the fluid velocity, energy density and pressure. We discuss some of the phenomenological implications.Comment: 16 page

Late time behavior of non-conformal plasmas

We determine analytically the dependence of the approach to thermal equilibrium of strongly coupled plasmas on the breaking of scale invariance. The theories we consider are the holographic duals to Einstein gravity coupled to a scalar with an exponential potential. The coefficient in the exponent, $X$, is the parameter that controls the deviation from the conformally invariant case. For these models we obtain analytic solutions for the plasma expansion in the late-time limit, under the assumption of boost-invariance, and we determine the scaling behaviour of the energy density, pressure, and temperature as a function of time. We find that the temperature decays as a function of proper time as $T\sim \tau^{-s/4}$ with $s$ determined in terms of the non-conformality parameter $X$ as $s=4(1-4X^2)/3$. This agrees with the result of Janik and Peschanski, $s=4/3$, for the conformal plasmas and generalizes it to non-conformal plasmas with $X\neq 0$. We also consider more realistic potentials where the exponential is supplemented by power-law terms. Even though in this case we cannot have exact solutions, we are able under certain assumptions to determine the scaling of the energy, that receives logarithmic corrections.Comment: 31 page