Fluctuation, dissipation, and thermalization in non-equilibrium AdS_5 black hole geometries

We give a simple recipe for computing dissipation and fluctuations (commutator and anti-commutator correlation functions) for non-equilibrium black hole geometries. The recipe formulates Hawking radiation as an initial value problem, and is suitable for numerical work. We show how to package the fluctuation and dissipation near the event horizon into correlators on the stretched horizon. These horizon correlators determine the bulk and boundary field theory correlation functions. In addition, the horizon correlators are the components of a horizon effective action which provides a quantum generalization of the membrane paradigm. In equilibrium, the analysis reproduces previous results on the Brownian motion of a heavy quark. Out of equilibrium, Wigner transforms of commutator and anti-commutator correlation functions obey a fluctuation-dissipation relation at high frequency.Comment: 28 pages, 6 figure

New Representations of the Perturbative S-Matrix

We propose a new framework to represent the perturbative S-matrix which is well-defined for all quantum field theories of massless particles, constructed from tree-level amplitudes and integrable term-by-term. This representation is derived from the Feynman expansion through a series of partial fraction identities, discarding terms that vanish upon integration. Loop integrands are expressed in terms of "Q-cuts" that involve both off-shell and on-shell loop-momenta, defined with a precise contour prescription that can be evaluated by ordinary methods. This framework implies recent results found in the scattering equation formalism at one-loop, and it has a natural extension to all orders---even non-planar theories without well-defined forward limits or good ultraviolet behavior.Comment: 4+1 pages, 4 figure

Colour-electric spectral function at next-to-leading order

The spectral function related to the correlator of two colour-electric fields along a Polyakov loop determines the momentum diffusion coefficient of a heavy quark near rest with respect to a heat bath. We compute this spectral function at next-to-leading order, O(alpha_s^2), in the weak-coupling expansion. The high-frequency part of our result (omega >> T), which is shown to be temperature-independent, is accurately determined thanks to asymptotic freedom; the low-frequency part of our result (omega << T), in which Hard Thermal Loop resummation is needed in order to cure infrared divergences, agrees with a previously determined expression. Our result may help to calibrate the overall normalization of a lattice-extracted spectral function in a perturbative frequency domain T << omega << 1/a, paving the way for a non-perturbative estimate of the momentum diffusion coefficient at omega -> 0. We also evaluate the colour-electric Euclidean correlator, which could be directly compared with lattice simulations. As an aside we determine the Euclidean correlator in the lattice strong-coupling expansion, showing that through a limiting procedure it can in principle be defined also in the confined phase of pure Yang-Mills theory, even if a practical measurement could be very noisy there.Comment: 38 page

Twistors, Harmonics and Holomorphic Chern-Simons

We show that the off-shell N=3 action of N=4 super Yang-Mills can be written as a holomorphic Chern-Simons action whose Dolbeault operator is constructed from a complex-real (CR) structure of harmonic space. We also show that the local space-time operators can be written as a Penrose transform on the coset SU(3)/(U(1) \times U(1)). We observe a strong similarity to ambitwistor space constructions.Comment: 34 pages, 3 figures, v2: replaced with published version, v3: Added referenc

The new Mars climate database

Not available

Holographic dilepton production in a thermalizing plasma

We determine the out-of-equilibrium production rate of dileptons at rest in strongly coupled N=4 Super Yang-Mills plasma using the AdS/CFT correspondence. Thermalization is achieved via the gravitational collapse of a thin shell of matter in AdS_5 space and the subsequent formation of a black hole, which we describe in a quasistatic approximation. Prior to thermalization, the dilepton spectral function is observed to oscillate as a function of frequency, but the amplitude of the oscillations decreases when thermal equilibrium is approached. At the same time, we follow the flow of the quasinormal spectrum of the corresponding U(1) vector field towards its equilibrium limit.Comment: 21 pages, 7 figures. v2: Version accepted for publication in JHEP; minor modifications, added reference

Heavy flavor diffusion in weakly coupled N=4 Super Yang-Mills theory

We use perturbation theory to compute the diffusion coefficient of a heavy quark or scalar moving in N=4 SU(N_c) Super Yang-Mills plasma to leading order in the coupling and the ratio T/M<<1. The result is compared both to recent strong coupling calculations in the same theory and to the corresponding weak coupling result in QCD. Finally, we present a compact and simple formulation of the Lagrangian of our theory, N=4 SYM coupled to a massive fundamental N=2 hypermultiplet, which is well-suited for weak coupling expansions.Comment: 22 pages, 4 figures; v3: error corrected in calculations, figures and discussion modified accordingl

The latest (version 4.3) Mars Climate Database

Introduction: The Mars Climate Database (MCD) is a database of meteorological fields derived from General Circulation Model (GCM) numerical simulations of the Martian atmosphere and validated using available observational data. The MCD includes complementary post-processing schemes such as high spatial resolution interpolation of environmental data and means of reconstructing the variability thereof. The GCM is developed at Laboratoire de Météorologie Dynamique du CNRS (Paris, France) [1,2] in collaboration with the Open University (UK), the Oxford University (UK) and the Instituto de Astrofisica de Andalucia (Spain) with support from the European Space Agency (ESA) and the Centre National d'Etudes Spatiales (CNES)

The Effect of Display Size on Ultrasound Interpretation

Purpose: To assess how display size affects providers’ abilities to accurately interpret ultrasound (U/S) videos. U/S has become essential for patient evaluation in the emergency setting. Although newer devices that are smaller in size and affordable place the technology within the pockets of practitioners, it is necessary to assess how smaller size may impact image quality. Methods: The target learner population for this study includes all practitioners who perform point of care U/S. A prospective convenience sample of emergency providers were randomized to begin on either a phone-sized screen or a laptop-sized screen. Participants answered Yes or No in response to whether they identified free fluid, above and/or below the diaphragm on each of 50 unique right upper quadrant U/S videos, with 25 displayed per device. Researchers collected data on the speed of interpretation and participants\u27 experiences. Results and Conclusions: Prior to study initiation, 50% of participants felt display size would affect accuracy, 42.3% were unsure, and 7.7% felt it would not (n=52). The accuracy of interpretation for phone versus laptop display was 87.3% and 87.6%, respectively (p=0.84). Mean time spent with phone versus laptop display was 293s and 290s, respectively (p=0.66). Upon study completion, 48.1% of participants believed display size affected their ability to interpret the videos, 38.5% felt it did not, and 13.5% were unsure. The results of this study show no significant statistical difference in the accuracy of interpretation between screen sizes