Consistency of a Causal Theory of Radiative Reaction with the Optical Theorem

The Abraham-Lorentz-Dirac equation for a point electron, while suffering from runaway solutions and an acausal response to external forces, is compatible with the optical theorem. We show that a theory of radiative reaction that allows for a finite charge distribution is not only causal and free of runaway solutions, but is also consistent with the optical theorem and the standard formula for the Rayleigh scattering cross section.Comment: 4 pages, 2 figure

A multi-layer extension of the stochastic heat equation

Motivated by recent developments on solvable directed polymer models, we define a 'multi-layer' extension of the stochastic heat equation involving non-intersecting Brownian motions.Comment: v4: substantially extended and revised versio

Continuum-particle hybrid coupling for mass, momentum and energy transfers in unsteady fluid flow

The aim of hybrid methods in simulations is to communicate regions with disparate time and length scales. Here, a fluid described at the atomistic level within an inner region P is coupled to an outer region C described by continuum fluid dynamics. The matching of both descriptions of matter is made across an overlapping region and, in general, consists of a two-way coupling scheme (C->P and P->C) which conveys mass, momentum and energy fluxes. The contribution of the hybrid scheme hereby presented is two-fold: first it treats unsteady flows and, more importantly, it handles energy exchange between both C and P regions. The implementation of the C->P coupling is tested here using steady and unsteady flows with different rates of mass, momentum and energy exchange. In particular, relaxing flows described by linear hydrodynamics (transversal and longitudinal waves) are most enlightening as they comprise the whole set of hydrodynamic modes. Applying the hybrid coupling scheme after the onset of an initial perturbation, the cell-averaged Fourier components of the flow variables in the P region (velocity, density, internal energy, temperature and pressure) evolve in excellent agreement with the hydrodynamic trends. It is also shown that the scheme preserves the correct rate of entropy production. We discuss some general requirements on the coarse-grained length and time scales arising from both the characteristic microscopic and hydrodynamic scales.Comment: LaTex, 12 pages, 9 figure

Drivers of intrapopulation variation in resource use in a generalist predator, the macaroni penguin

Intrapopulation variation in resource use occurs in many populations of generalist predators with important community and evolutionary implications. One of the hypothesised mechanisms for such widespread variation is ecological opportunity, i.e. resource availability determined by intrinsic constraints and extrinsic conditions. We combined tracking data and stable isotope analysis to examine how breeding constraints and prey conditions influenced intrapopulation variation in resource use among macaroni penguins Eudyptes chrysolophus. Isotopic variation was also examined as a function of breeding success, individual traits and individual specialisation. Variation in isotope ratios was greatest across multiple tissue types when birds were able to undertake mid-range foraging trips (i.e. during incubation and pre-moult). This variation was highly consistent between years that spanned a 3-fold difference in local krill Euphausia superba density and was also highly consistent at the individual level between 2 years that had similar krill densities. However, by comparing our results with previous work on the same population, it appeared that a decrease in local prey availability can increase intrapopulation variation in resource use during periods with more restricted foraging ranges (i.e. during brood-guard and crèche). This study highlights the importance of considering ecological interactions that operate on multiple spatio-temporal scales when examining the drivers of resource use in populations of generalist predators

Vector meson dominance and the rho meson

We discuss the properties of vector mesons, in particular the rho^0, in the context of the Hidden Local Symmetry (HLS) model. This provides a unified framework to study several aspects of the low energy QCD sector. Firstly, we show that in the HLS model the physical photon is massless, without requiring off field diagonalization. We then demonstrate the equivalence of HLS and the two existing representations of vector meson dominance, VMD1 and VMD2, at both tree level and one loop order. Finally the S matrix pole position is shown to provide a model and process independent means of specifying the rho mass and width, in contrast to the real axis prescription currently used in the Particle Data Group tables.Comment: 18 pages, REVTE