Regge-plus-resonance predictions for neutral-kaon photoproduction from the deuteron

We present a Regge-inspired effective-Lagrangian framework for neutral-kaon photoproduction from the deuteron. Quasi-free kaon production is investigated using the Regge-plus-resonance elementary operator within the relativistic plane-wave impulse approximation. The Regge-plus-resonance model was developed to describe photoinduced and electroinduced charged-kaon production off protons. We show how this elementary operator can be transformed to account for the production of neutral kaons from both protons and neutrons. Our results compare favourably to the sole 2H(gamma,K0)YN dataset published to date.Comment: 4 pages, 1 figure; Proceedings 12th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon, Williamsburg VA, May 31-June 4, 201

Creating conditions of anomalous self-diffusion in a liquid with molecular dynamics

We propose a computational method to simulate anomalous self-diffusion in a simple liquid. The method is based on a molecular dynamics simulation on which we impose the following two conditions: firstly, the inter-particle interaction is described by a soft-core potential and secondly, the system is forced out of equilibrium. The latter can be achieved by subjecting the system to changes in the length scale at intermittent times. In many respects, our simulation system bears resemblance to slowly driven sandpile models displaying self-organised criticality. We find non-Gaussian single time step displacement distributions during the out-of-equilibrium time periods of the simulation.Comment: Extended version: 12 pages, 9 figure

The Regge-plus-resonance model for kaon production on the proton and the neutron

The Regge-plus-resonance (RPR) framework for kaon photoproduction on the proton and the neutron is an economical single-channel model with very few parameters. Not only does the RPR model allow one to extract resonance information from the data, it has predictive power. As an example we show that the RPR model makes fair predictions for the $p(e,e'K^{+})\Lambda$ and the $n(\gamma,K^{+})\Sigma ^{-}$ observables starting from amplitudes optimized for the reaction $p(\gamma, K ^{+})\Lambda$ and $p(\gamma,K^{+})\Sigma ^{0}$ respectively

The p(γ,K+)Λp(\gamma,K^+)\Lambda reaction: consistent high-spin interactions and Bayesian inference of its resonance content

A Bayesian analysis of the world's $p(\gamma,K^+)\Lambda$ data is presented. We adopt a Regge-plus-resonance framework featuring consistent interactions for nucleon resonances up to spin $J = 5/2$. The power of the momentum dependence of the consistent interaction structure rises with the spin of the resonance. This leads to unphysical structures in the energy dependence of the computed cross sections when the short-distance physics is cut off with standard hadronic form factors. A plausible, spin-dependent modification of the hadronic form factor is proposed which suppresses the unphysical artifacts. Next, we evaluate all possible combinations of 11 candidate resonances. The best model is selected from the 2048 model variants by calculating the Bayesian evidence values against the world's $p(\gamma,K^+)\Lambda$ data. From the proposed selection of 11 resonances, we find that the following nucleon resonances have the highest probability of contributing to the reaction: $S_{11}(1535)$, $S_{11}(1650)$, $F_{15}(1680)$, $P_{13}(1720)$, $D_{13}(1900)$, $P_{13}(1900)$, $P_{11}(1900)$, and $F_{15}(2000)$.Comment: 5 pages, 4 figure

Consistent interactions for high-spin fermion fields

We address the issue of consistent interactions for off-shell fermion fields of arbitrary spin. These interactions play a crucial role in the quantum hadrodynamical description of high-spin baryon resonances in hadronic processes. The Rarita-Schwinger description of high-spin fermion fields involves unphysical degrees of freedom, associated with their lower-spin content. These enter the interaction if not eliminated outright. The invariance condition of the interaction under the unconstrained Rarita-Schwinger gauge removes the lower-spin content of the fermion propagator and leads to a consistent description of the interaction. We develop the most general, consistent interaction structure for high-spin fermions. We find that the power of the momentum dependence of a consistent interaction rises with the spin of the fermion field. This leads to unphysical structures in the energy dependence of the computed cross sections when the short-distance physics is cut off with standard hadronic form factors. A novel, spin-dependent hadronic form factor is proposed that suppresses the unphysical artifacts.Comment: 17 pages, 10 figure

Low-frequency variability and heat transport in a low-order nonlinear coupled ocean-atmosphere model

We formulate and study a low-order nonlinear coupled ocean-atmosphere model with an emphasis on the impact of radiative and heat fluxes and of the frictional coupling between the two components. This model version extends a previous 24-variable version by adding a dynamical equation for the passive advection of temperature in the ocean, together with an energy balance model. The bifurcation analysis and the numerical integration of the model reveal the presence of low-frequency variability (LFV) concentrated on and near a long-periodic, attracting orbit. This orbit combines atmospheric and oceanic modes, and it arises for large values of the meridional gradient of radiative input and of frictional coupling. Chaotic behavior develops around this orbit as it loses its stability; this behavior is still dominated by the LFV on decadal and multi-decadal time scales that is typical of oceanic processes. Atmospheric diagnostics also reveals the presence of predominant low- and high-pressure zones, as well as of a subtropical jet; these features recall realistic climatological properties of the oceanic atmosphere. Finally, a predictability analysis is performed. Once the decadal-scale periodic orbits develop, the coupled system's short-term instabilities --- as measured by its Lyapunov exponents --- are drastically reduced, indicating the ocean's stabilizing role on the atmospheric dynamics. On decadal time scales, the recurrence of the solution in a certain region of the invariant subspace associated with slow modes displays some extended predictability, as reflected by the oscillatory behavior of the error for the atmospheric variables at long lead times.Comment: v1: 41 pages, 17 figures; v2-: 42 pages, 15 figure

Regge-plus-resonance predictions for charged-kaon photoproduction from the deuteron

We present a Regge-inspired effective-Lagrangian framework for charged-kaon photoproduction from the deuteron. Quasi-free kaon production is investigated using the Regge-plus-resonance elementary operator within the non-relativistic plane-wave impulse approximation. The Regge-plus-resonance model was developed to describe photoinduced and electroinduced kaon production off protons and can be extended to strangeness production off neutrons. The non-resonant contributions to the amplitude are modelled in terms of K+(494) and K*+(892) Regge-trajectory exchange in the t-channel. This amplitude is supplemented with a selection of s-channel resonance-exchange diagrams. We investigate several sources of theoretical uncertainties on the semi-inclusive charged-kaon production cross section. The experimental error bars on the photocoupling helicity amplitudes turn out to put severe limits on the predictive power when considering quasi-free kaon production on a bound neutron.Comment: 5 pages, 2 figures; Proceedings 19th International IUPAP Conference on Few-Body Problems in Physics, Bonn, 200

Regge-plus-resonance predictions for kaon photoproduction from the neutron

We present predictions for n(gamma,K+)Sigma- differential cross sections and photon-beam asymmetries and compare them to recent LEPS data. We adapt a Regge-plus-resonance (RPR) model developed to describe photoinduced and electroinduced kaon production off protons. The non-resonant contributions to the amplitude are modelled in terms of K+(494) and K*+(892) Regge-trajectory exchange. This amplitude is supplemented with a selection of s-channel resonance diagrams. The three Regge-model parameters of the n(gamma,K+)Sigma- amplitude are derived from the ones fitted to proton data through SU(2) isospin considerations. A fair description of the n(gamma,K+)Sigma- data is realized, which demonstrates the Regge model's robustness and predictive power. Conversion of the resonances' couplings from the proton to the neutron is more challenging, as it requires knowledge of the photocoupling helicity amplitudes. We illustrate how the uncertainties of the helicity amplitudes propagate and heavily restrain the predictive power of the RPR and isobar models for kaon production off neutron targets.Comment: 14 pages, 4 figures; Minor revisions; Published in Physics Letters

Bayesian model selection for electromagnetic kaon production in the Regge-plus-resonance framework

A long-standing goal of hadronic physics is to obtain a detailed map of the nucleon's resonance spectrum. This would help bridge the gap between hadrodynamical models on the one hand and constituent quark models on the other hand. Some quark models predict so-called "missing resonances" that have not been found in analyses of pion-nucleon scattering data. Input from non-pionic reactions such as open-strangeness photoproduction is key to resolve the status of these missing resonances, as some are predicted to couple more strongly to non-pionic channels. Despite the increasing availability of experimental data for p(gamma,K^+)Lambda, different hadrodynamical models reach contradictory conclusions with respect to the contributing resonances. The cause of this disparity is twofold. First, the important role played by the non-resonant dynamics makes the precise parametrisation of the background amplitude a great source of model dependence. Second, the criterion to determine whether a resonance contributes significantly or insignificantly varies among different analyses. This work aims to address these two issues so as to unambiguously determine the resonance content of p(gamma,K^+)Lambda. The reaction p(gamma,K^+)Lambda is described by the Regge-plus-resonance (RPR) model. The RPR model combines Regge theory and elements from the isobar approach into an economical model for kaon photo- and electroproduction in and above the resonance region. In the RPR approach, the parameters of the reggeised background are constrained to high-energy data. This approach allows for a clear separation between the non-resonant background and the s-channel resonance contributions. The second issue boils down to the question: "How probable is resonance R, given experimental data?" Adding resonances improves a model's description of the data, but does not necessarily represent the correct dynamics. Bayesian inference provides a statistically solid way to do model selection, that naturally includes the principle of Occam's razor. The conditional probability of a model given data is quantified by its Bayesian evidence Z. This dissertation presents a method to compute the evidence and to evaluate the probabilities of a proposed set of resonances. Using this method, we find that the resonances S11(1535), S11(1650), F15(1680), P13(1720), D13(1900), P13(1900), P11(1900), and F15(2000) have the highest probability of contributing to p(gamma,K^+)Lambda