Holographic Checkerboards

We construct cohomogeneity-three, finite temperature stationary black brane solutions dual to a field theory exhibiting checkerboard order. The checkerboards form a backreacted part of the bulk solution, and are obtained numerically from the coupled Einstein-Maxwell-scalar PDE system. They arise spontaneously and without the inclusion of an explicit lattice. The phase exhibits both charge and global U(1)-current modulation, which are periodic in two spatial directions. The current circulates within each checkerboard plaquette. We explore the competition with striped phases, finding first-order checkerboard to stripe phase transitions. We also detail spatially modulated instabilities of asymptotically AdS black brane backgrounds with neutral scalar profiles, including those with an hyperscaling violating IR geometry at zero temperature.Comment: 26 pages, 11 figures. v2: Published versio

Short-lived modes from hydrodynamic dispersion relations

We consider the dispersion relation of the shear-diffusion mode in relativistic hydrodynamics, which we generate to high order as a series in spatial momentum q for a holographic model. We demonstrate that the hydrodynamic series can be summed in a way that extends through branch cuts present in the complex q plane, resulting in the accurate description of multiple sheets. Each additional sheet corresponds to the dispersion relation of a different non-hydrodynamic mode. As an example we extract the frequencies of a pair of oscillatory non-hydrodynamic black hole quasinormal modes from the hydrodynamic series. The analytic structure of this model points to the possibility that the complete spectrum of gravitational quasinormal modes may be accessible from the hydrodynamic derivative expansion.Comment: 17 pages, 6 figures. Matches published versio

Enterprising women: independence, finance and Virago Press, c.1976-1993

Virago Press were established in 1972 and became one of the twentieth century’s most enduring publishing brands. As a women-led enterprise, articulations of independence have defined key moments in Virago’s history. This article explores two moments when the company re-structured as independent, in 1976 and 1987. To become successful, Virago had to overcome barriers that have historically hindered women’s participation in business, namely limited social capital and difficulties accessing finance. Virago founder Carmen Callil’s friendships with publisher Paul Hamlyn and printing entrepreneur Robert Gavron embedded Virago in networks of male entrepreneurial knowledge that helped shape the evolution of the company. Such networks were vital to Virago securing investment from Rothschilds Ventures Limited in 1987 who were, at that time, leading figures in the UK’s growing private equity industry. This article contributes to growing historical understanding of the synergies between financial, arts and culture industries in the 80s. It argues that while this era offered new opportunities for women to participate in business, such participation was tempered by new forms of legal and financial discipline that re-calibrated existing gender inequalities within business cultures. Due to the time periods under consideration, this article also analyses how entrepreneurial practices and opportunities for women changed dramatically with the onset of Thatcher’s ‘Enterprise Culture’

Robinson-Trautman spacetimes and gauge/gravity duality

We study far-from-equilibrium field theory dynamics using gauge/gravity duality applied to the Robinson-Trautman (RT) class of spacetimes and we present a number of new results. First, we assess the applicability of the hydrodynamic approximation to inhomogeneous plasma dynamics dual to RT spacetimes. We prove that to any order in a late time expansion it is possible to identify variables corresponding to the local energy density and fluid velocity. However, we show using numerical examples that this does not hold at the non-perturbative level; for sufficiently inhomogeneous initial data a local rest frame does not exist. Second, we preset a new class of holographic inhomogeneous plasma flows on the plane. The corresponding spacetimes are not of the RT type but they can be obtained from RT spacetimes with spatially compact boundaries by coordinate transformations which generate Poincar\'e patch-like coordinates with planar boundaries. We demonstrate the application of this procedure using numerical examples.Comment: Proceedings prepared for the "Workshop on Geometry and Physics" in memoriam of Ioannis Bakas, November 2016, Ringberg Castle, Germany. v2: Minor changes, added discussion of isotropisation tim

Bay Scallops, Argopecten irradians, in the Northwestern Gulf of Mexico (Alabama, Mississippi, Louisiana, and Texas)

There is no evidence that a commercial bay scallop fishery exists anywhere in the northwestern Gulf of Mexico. No data concerning scallop abundance or distribution was found for Alabama, Mississippi, and Louisiana. Texas is the only state west of Florida where bay scallop populations have been documented. These records come from a variety of literature sources and the fisheries-independent data collected by Texas Parks and Wildlife Department (1982–2005). Although common in the diet of prehistoric peoples living on the Texas coast, recent (last ~50 years) bay scallop population densities tend to be low and exhibit “boom–bust” cycles of about 10–15 years. The Laguna Madre, is the only place on the Texas coast where scallops are relatively abundant; this is likely due to extensive seagrasses cover (>70%) and salinities that typically exceed 35 psu. The lack of bay scallop fishery development in the northwestern Gulf of Mexico is probably due to variable but generally low densities of the species combined with a limited amount of suitable (i.e. seagras

A gravity derivation of the Tisza-Landau Model in AdS/CFT

We derive the fully backreacted bulk solution dual to a boundary superfluid with finite supercurrent density in AdS/CFT. The non-linear boundary hydrodynamical description of this solution is shown to be governed by a relativistic version of the Tisza-Landau two-fluid model to non-dissipative order. As previously noted, the phase transition can be both first order and second order, but in the strongly-backreacted regime at low charge q we find that the transition remains second order for all allowed fractions of superfluid density.Comment: 27 pages, 6 figures, 1 appendix; version published in PR

Invariant graphs of a family of non-uniformly expanding skew products over Markov maps

We consider a family of skew-products of the form $(Tx, g_x(t)) : X \times \mathbb{R} \to X \times \mathbb{R}$ where $T$ is a continuous expanding Markov map and $g_x : \mathbb{R} \to \mathbb{R}$ is a family of homeomorphisms of $\mathbb{R}$. A function $u: X \to \mathbb{R}$ is said to be an invariant graph if $\mathrm{graph}(u) = \{(x,u(x)) \mid x\in X\}$ is an invariant set for the skew-product; equivalently if $u(T(x)) = g_x(u(x))$. A well-studied problem is to consider the existence, regularity and dimension-theoretic properties of such functions, usually under strong contraction or expansion conditions (in terms of Lyapunov exponents or partial hyperbolicity) in the fibre direction. Here we consider such problems in a setting where the Lyapunov exponent in the fibre direction is zero on a set of periodic orbits. We prove that $u$ either has the structure of a `quasi-graph' (or `bony graph') or is as smooth as the dynamics, and we give a criteria for this to happen.Comment: 21 pages, 2 figure