One-particle reducible contribution to the one-loop scalar propagator in a constant field

Recently, Gies and Karbstein showed that the two-loop Euler-Heisenberg Lagrangian receives a finite one-particle reducible contribution in addition to the well-known one-particle irreducible one. Here, we demonstrate that a similar contribution exists for the propagator in a constant field already at the one-loop level, and we calculate this contribution for the scalar QED case. We also present an independent derivation of the Gies-Karbstein result using the worldline formalism, treating the scalar and spinor QED cases in a unified manner.Comment: 13 pages, 4 figures. Minor corrections mad

Uncovering the Hidden Conflicts in Securities Class Action Litigation: Lessons from the State Street Case

Courts, Congress, and commentators have long worried that stockholder plaintiffs in securities and M&A litigation and their counsel may pursue suits that benefit themselves rather than absent stockholders or the corporations in which they invest. Following congressional reforms that encouraged the appointment of institutional stockholders as lead plaintiffs in securities actions, significant academic commentary has focused on the problem of “pay to play”—the possibility that class action law firms encourage litigation by making donations to politicians with influence over institutional stockholders, particularly public sector pension funds. A recent federal securities class action in the District of Massachusetts, however, suggests that the networks of influence between class plaintiffs and their counsel are much more complex and difficult to detect. After appointing a special master to look into fee issues, the court discovered that a large class action firm had paid over $4 million in “bare referral” fees to an attorney who did little work on the case but had recommended the larger firm to a public sector pension fund “after considerable favors, political activity, money spent and time dedicated in Arkansas.” This is only one of the less-visible ways that class counsel may route benefits to class plaintiffs. Current class action processes do not routinely identify these potential conflicts of interest. Instead, they tend to surface when nonlitigants bring them to public attention. Because neither the lead plaintiff nor the defendants have a strong incentive to voluntarily address these conflicts, we propose revisions to the class certification process that would require class plaintiffs to disclose more information regarding their relationships with class counsel. We also propose that courts routinely appoint special masters or class guardians as part of the settlement approval process to ensure that class plaintiffs’ statements are subject to discovery and adversarial review

Mixed symmetry tensors in the worldline formalism

We consider the first quantised approach to quantum field theory coupled to a non-Abelian gauge field. Representing the colour degrees of freedom with a single family of auxiliary variables the matter field transforms in a reducible representation of the gauge group which - by adding a suitable Chern-Simons term to the particle action - can be projected onto a chosen fully (anti-)symmetric representation. By considering F families of auxiliary variables, we describe how to extend the model to arbitrary tensor products of F reducible representations, which realises a U(F) "flavour" symmetry on the worldline particle model. Gauging this symmetry allows the introduction of constraints on the Hilbert space of the colour fields which can be used to project onto an arbitrary irreducible representation, specified by a certain Young Tableau. In particular the occupation numbers of the wavefunction - i.e. the lengths of the columns (rows) of the Young Tableau - are fixed through the introduction of Chern-Simons terms. We verify this projection by calculating the number of colour degrees of freedom associated to the matter field. We suggest that, using the worldline approach to quantum field theory, this mechanism will allow the calculation of one-loop scattering amplitudes with the virtual particle in an arbitrary representation of the gauge group.Comment: 1+32 page

Changes in fish populations in the Lower Canyons of the Rio Grande

The Lower Canyons of the Rio Grande suffer from environmental degradation that has negatively impacted native fish populations and their distributions. Macrhybopsis aestivalis (speckled chub), Notropis jemezanus (Rio Grande shiner), Rhinichthys cataractae (longnose dace) and Cycleptus elongatus (blue sucker) populations appear to have suffered recent declines. Although diminished water quantity is likely an important factor in these declines, related changes in channel morphology precipitated by massive stands of Arundo donax (giant reed) and Tamarix sp. (salt cedar) may also be responsible. These invasive exotics have essentially channelized the river, disrupted normal sediment distribution and reduced shallow, low-velocity habitats. Much of the Lower Canyons of the Rio Grande are devoid of sandy sediment and most riffles are now composed of gravel and cobble.Integrative Biolog

A Fresh Approach to Forecasting in Astroparticle Physics and Dark Matter Searches

We present a toolbox of new techniques and concepts for the efficient forecasting of experimental sensitivities. These are applicable to a large range of scenarios in (astro-)particle physics, and based on the Fisher information formalism. Fisher information provides an answer to the question what is the maximum extractable information from a given observation?. It is a common tool for the forecasting of experimental sensitivities in many branches of science, but rarely used in astroparticle physics or searches for particle dark matter. After briefly reviewing the Fisher information matrix of general Poisson likelihoods, we propose very compact expressions for estimating expected exclusion and discovery limits (equivalent counts method). We demonstrate by comparison with Monte Carlo results that they remain surprisingly accurate even deep in the Poisson regime. We show how correlated background systematics can be efficiently accounted for by a treatment based on Gaussian random fields. Finally, we introduce the novel concept of Fisher information flux. It can be thought of as a generalization of the commonly used signal-to-noise ratio, while accounting for the non-local properties and saturation effects of background and instrumental uncertainties. It is a powerful and flexible tool ready to be used as core concept for informed strategy development in astroparticle physics and searches for particle dark matter.Comment: 33 pages, 12 figure

Concept for controlled transverse emittance transfer within a linac ion beam

For injection of beams into circular machines with different horizontal and vertical emittance acceptance, the injection efficiency can be increased if these beams are flat, i.e. if they feature unequal transverse emittances. Generation of flat electron beams is well known and has been demonstrated already in beam experiments. It was proposed also for ion beams that were generated in an Electron Cyclotron-Resonance (ECR) source. We introduce an extension of the method to beams that underwent charge state stripping without requiring their generation inside an ECR source. Results from multi-particle simulations are presented to demonstrate the validity of the method.Comment: 23 pages (preprint style), 14 Figures, submitted to PRST-A

X-ray laser pulses at the Fourier transform limit

The temporal output of a Ni-like Ag x-ray laser of wavelength 13.9 nm has been recorded using a streak camera with ultrashort (700 fs) temporal resolution. We present a model to calculate the degree of coherence and Fourier transform limit of x-ray laser pulses produced by amplified spontaneous emission and relate the results from the model to previous interferometric measurements of the coherence length of the same Ni-like Ag x-ray laser and our measured duration of temporal output. Our modeling shows that the interferometer and streak camera results are consistent and close to the Fourier transform limit at longer gain medium lengths