Analytic Solutions of Ultra-High Energy Cosmic Ray Nuclei Revisited

The chemical composition of ultra-high energy cosmic rays is a key question in particle astrophysics. The measured composition, inferred from the elongation rates of cosmic ray showers, looks in general very different from the initial source composition: resonant photo-disintegration in the cosmic radiation background proceeds rapidly at the highest energies and the initial composition quickly becomes lighter during propagation. For a statistical analysis of continuously improving cosmic ray data it is desirable to know the secondary spectra as precisely as possible. Here, we discuss exact analytic solutions of the evolution equation of ultra-high energy cosmic ray nuclei. We introduce a diagrammatic formalism that leads to a systematic analytic expansion of the exact solution in terms of second order effects of the propagation. We show how the first order corrections of this expansion can improve the predictions of secondary spectra in a semi-analytical treatment.Comment: 10 figures, 1 tabl

Effect of a polymer additive on heat transport in turbulent Rayleigh-B\'enard convection

Measurements of heat transport, as expressed by the Nusselt number $Nu$, are reported for turbulent Rayleigh-B\'enard convection of water containing up to 120 ppm by weight of poly-[ethylene oxide] with a molecular weight of $4\times10^6$ g/mole. Over the Rayleigh number range 5\times 10^9 \alt Ra \alt 7 \times 10^{10} $Nu$ is smaller than it is for pure water by up to 10%.Comment: 3 pages, 2 figure

Quantum Decoherence of Photons in the Presence of Hidden U(1)s

Many extensions of the standard model predict the existence of hidden sectors that may contain unbroken abelian gauge groups. We argue that in the presence of quantum decoherence photons may convert into hidden photons on sufficiently long time scales and show that this effect is strongly constrained by CMB and supernova data. In particular, Planck-scale suppressed decoherence scales D ~ E^2/M_Pl (characteristic for non-critical string theories) are incompatible with the presence of even a single hidden U(1). The corresponding bounds on the decoherence scale are four orders of magnitude stronger than analogous bounds derived from solar and reactor neutrino data and complement other bounds derived from atmospheric neutrino data.Comment: 8 pages, 9 figure

Competition between Spiral-Defect Chaos and Rolls in Rayleigh-Benard Convection

We present experimental results for pattern formation in Rayleigh-Benard convection of a fluid with a Prandtl number, Pr~ 4. We find that the spiral-defect-chaos (SDC) attractor which exists for Pr~1 has become unstable. Gradually increasing the temperature difference from below to well above its critical value no longer leads to SDC. A sudden jump of temperature difference from below to above onset causes convection to grow from thermal fluctuations and does yield SDC. However, the SDC is a transient; it coarsens and forms a single cell-filling spiral which then drifts toward the cell wall and disappears.Comment: 9 pages(RevTeX), 5 jpg figures, To appear as Rapid Communication in PR

Revisiting the distance to the nearest UHECR source: Effects of extra-galactic magnetic fields

We update the constraints on the location of the nearest UHECR source. By analyzing recent data from the Pierre Auger Observatory using state-of-the-art CR propagation models, we reaffirm the need of local sources with a distance less than 25-100 Mpc, depending on mass composition. A new fast semi-analytical method for the propagation of UHECR in environments with turbulent magnetic fields is developed. The onset of an enhancement and a low-energy magnetic horizon of cosmic rays from sources located within a particular distance range is demonstrated. We investigate the distance to the nearest source, taking into account these magnetic field effects. The results obtained highlight the robustness of our constrained distances to the nearest source

Extensive Scaling and Nonuniformity of the Karhunen-Lo\`eve Decomposition for the Spiral-Defect Chaos State

By analyzing large-aspect-ratio spiral-defect-chaos (SDC) convection images, we show that the Karhunen-Lo\`eve decomposition (KLD) scales extensively for subsystem-sizes larger than 4d (d is the fluid depth), which strongly suggests that SDC is extensively chaotic. From this extensive scaling, the intensive length \xi_KLD is computed and found to have a different dependence on the Rayleigh number than the two-point correlation length \xi_2. Local computations of \xi_KLD reveal a substantial spatial nonuniformity of SDC that extends over radii 18d< r < 45d in a \Gamma=109 aspect-ratio cell.Comment: 10 pages single-spaced (total), 3 figues, 2 table