On the Puzzle of Petitionary Prayer: Response to Daniel and Frances Howard-Snyder

I respond to Daniel and Frances Howard-Snyder’s criticisms of my arguments in another place for the conclusion that human supplicants would have little responsibility (if any) for the result of answered petitionary prayer, and criticize their defense of the claim that God would have good reasons for creating an institution of petitionary prayer

Dissecting holographic conductivities

The DC thermoelectric conductivities of holographic systems in which translational symmetry is broken can be efficiently computed in terms of the near-horizon data of the dual black hole. By calculating the frequency dependent conductivities to the first subleading order in the momentum relaxation rate, we give a physical explanation for these conductivities in the simplest such example, in the limit of slow momentum relaxation. Specifically, we decompose each conductivity into the sum of a coherent contribution due to momentum relaxation and an incoherent contribution, due to intrinsic current relaxation. This decomposition is different from those previously proposed, and is consistent with the known hydrodynamic properties in the translationally invariant limit. This is the first step towards constructing a consistent theory of charged hydrodynamics with slow momentum relaxation.Comment: v2: minor edits, matches published version. v1: 26 pages, 1 figur

Momentum dissipation and effective theories of coherent and incoherent transport

We study heat transport in two systems without momentum conservation: a hydrodynamic system, and a holographic system with spatially dependent, massless scalar fields. When momentum dissipates slowly, there is a well-defined, coherent collective excitation in the AC heat conductivity, and a crossover between sound-like and diffusive transport at small and large distance scales. When momentum dissipates quickly, there is no such excitation in the incoherent AC heat conductivity, and diffusion dominates at all distance scales. For a critical value of the momentum dissipation rate, we compute exact expressions for the Green's functions of our holographic system due to an emergent gravitational self-duality, similar to electric/magnetic duality, and SL(2,R) symmetries. We extend the coherent/incoherent classification to examples of charge transport in other holographic systems: probe brane theories and neutral theories with non-Maxwell actions.Comment: v1: 41 pages + appendices, 7 figures. v2: references and clarifications added. v3: reference adde

Incoherent transport in clean quantum critical metals

In a clean quantum critical metal, and in the absence of umklapp, most d.c. conductivities are formally infinite due to momentum conservation. However, there is a particular combination of the charge and heat currents which has a finite, universal conductivity. In this paper, we describe the physics of this conductivity $\sigma_Q$ in quantum critical metals obtained by charge doping a strongly interacting conformal field theory. We show that it satisfies an Einstein relation and controls the diffusivity of a conserved charge in the metal. We compute $\sigma_Q$ in a class of theories with holographic gravitational duals. Finally, we show how the temperature scaling of $\sigma_Q$ depends on certain critical exponents characterizing the quantum critical metal. The holographic results are found to be reproduced by the scaling analysis, with the charge density operator becoming marginal in the emergent low energy quantum critical theory.Comment: v1: 1 + 16 pages + reference

The agrarian economy of Romney Marsh and its hinterland, with special reference to the Knatchbull estate, c. 1730-90

This study explores the agrarian economy of Romney Marsh and its hinterland, c. 1730-90. It offers a fresh contribution to current knowledge in respect of landlord-tenant relations, landholding structures and farming practice. Some 60 years are covered, framed within a wider context embracing two distinct and contrasting economic phases that characterized the long eighteenth century. Special reference to the Knatchbull family affords in-depth insight into an eighteenth century Kentish landed estate, whose interests lay on the marsh and its hinterland. There is an appraisal of the character and values of Sir Wyndham Knatchbull in his official and unofficial roles at the head of the community. Aspects of the Home Farm economy of Mersham Hatch are explored. Particular attention is paid to landlord-tenant relations, and the multi-dimensional nature of negotiations for substantial holdings on Walland Marsh. The impact of a windfall inheritance is seen when, from 1763, the seventh baronet succeeded to the estate. Using early Land Tax evidence for the region, there is a comprehensive analysis of landownership and land occupation structures, c. 1746-90. An unusually large area is covered, for an exceptionally early period, adding substantially to current knowledge. Marsh tax evidence discloses landownership and land occupation structures on Walland/Denge, 1738-91. Used in tandem with the tax listings, the wider interests of ‘dual-regional’ farmers are more fully appreciated, and for whom knowledge has hitherto been confined to their operations on the marsh. These findings, together with the investigation of previously unexplored aspects of farming practice, offer fresh insight into the symbiotic relationship between the marsh and its hinterland. The influence of ties of social obligation and market-led considerations on landlord-tenant relations are recurring themes. On the marsh, tenant initiative and market demand are seen as the main driving forces that re-shaped patterns of landholding over the period

Statistical Modeling of Spatial Extremes

The areal modeling of the extremes of a natural process such as rainfall or temperature is important in environmental statistics; for example, understanding extreme areal rainfall is crucial in flood protection. This article reviews recent progress in the statistical modeling of spatial extremes, starting with sketches of the necessary elements of extreme value statistics and geostatistics. The main types of statistical models thus far proposed, based on latent variables, on copulas and on spatial max-stable processes, are described and then are compared by application to a data set on rainfall in Switzerland. Whereas latent variable modeling allows a better fit to marginal distributions, it fits the joint distributions of extremes poorly, so appropriately-chosen copula or max-stable models seem essential for successful spatial modeling of extremes.Comment: Published in at http://dx.doi.org/10.1214/11-STS376 the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

Rejoinder to "Statistical Modeling of Spatial Extremes"

Rejoinder to "Statistical Modeling of Spatial Extremes" by A. C. Davison, S. A. Padoan and M. Ribatet [arXiv:1208.3378].Comment: Published in at http://dx.doi.org/10.1214/12-STS376REJ the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

Hydrodynamic flows of non-Fermi liquids: magnetotransport and bilayer drag

We consider a hydrodynamic description of transport for generic two dimensional electron systems that lack Galilean invariance and do not fall into the category of Fermi liquids. We study magnetoresistance and show that it is governed only by the electronic viscosity provided that the wavelength of the underlying disorder potential is large compared to the microscopic equilibration length. We also derive the Coulomb drag transresistance for double-layer non-Fermi liquid systems in the hydrodynamic regime. As an example, we consider frictional drag between two quantum Hall states with half-filled lowest Landau levels, each described by a Fermi surface of composite fermions coupled to a $U(1)$ gauge field. We contrast our results to prior calculations of drag of Chern-Simons composite particles and place our findings in the context of available experimental data.Comment: 4 pages + references + supplementary information, 1 figur