Cosmic-Ray Signatures of Dark Matter Decay

In light of recent observations of an anomalous excess of high-energy positrons and electrons by the PAMELA and Fermi LAT experiments, we investigate exotic cosmic-ray signatures in scenarios with unstable dark matter that decays with an extremely long lifetime. We identify decay modes capable of explaining the observed anomalies and mention constraints arising from measurements of antiprotons and gamma rays. We also discuss complementary tests by measurements of anisotropies in diffuse gamma rays which should be accessible to Fermi.Comment: 4 pages, 1 figure. To appear in the proceedings of SUSY 2009, June 5 - 10, Northeastern University, Boston, M

Impeded inverse energy transfer in the Charney--Hasegawa--Mima model of quasi-geostrophic flows

The behaviour of turbulent flows within the single-layer quasi-geostrophic (Charney--Hasegawa--Mima) model is shown to be strongly dependent on the Rossby deformation wavenumber $\lambda$ (or free-surface elasticity). Herein, we derive a bound on the inverse energy transfer, specifically on the growth rate \d\ell/\dt of the characteristic length scale $\ell$ representing the energy centroid. It is found that \d\ell/\dt\le2\norm q_\infty/(\ell_s\lambda^2), where \norm q_\infty is the supremum of the potential vorticity and $\ell_s$ represents the potential enstrophy centroid of the reservoir, both invariant. This result implies that in the potential energy dominated regime ($\ell\ge\ell_s\gg\lambda^{-1}$), the inverse energy transfer is strongly impeded, in the sense that under the usual time scale no significant transfer of energy to larger scales occurs. The physical implication is that the elasticity of the free surface impedes turbulent energy transfer in wavenumber space, effectively rendering large-scale vortices long-lived and inactive. Results from numerical simulations of forced-dissipative turbulence confirm this prediction.Comment: 8 pages, 2 figures, accepted for publication in JF

Indirect Searches for Decaying Dark Matter

Numerous observations point towards the existence of an unknown elementary particle with no electromagnetic interactions, a large population of which was presumably produced in the early stages of the history of the Universe. This so-called dark matter has survived until the present day, accounting for the 26% of the present energy budget of the Universe. It remains an open question whether the particles comprising the dark matter are absolutely stable or whether they have a finite but very long lifetime, which is a possibility since there is no known general principle guaranteeing perfect stability. In this article we review the observational limits on the lifetime of dark matter particles with mass in the GeV-TeV range using observations of the cosmic fluxes of antimatter, gamma-rays and neutrinos. We also examine some theoretically motivated scenarios that provide decaying dark matter candidates.Comment: 47 pages, 11 figures, 6 tables. Invited review for the International Journal of Modern Physics A. Matches published versio

Impeded inverse energy transfer in the Charney--Hasegawa--Mima model of quasi-geostrophic flows

The behaviour of turbulent flows within the single-layer quasi-geostrophic (Charney-Hasegawa-Mima) model is shown to be strongly dependent on the Rossby deformation wavenumber lambda (or free-surface elasticity). Herein, we derive a bound oil the inverse energy transfer, specifically on the growth rate dl/dt of the characteristic length scale e representing the energy centroid. It is found that dl/dt = l(s) >> lambda(-1)) the inverse energy transfer is strongly impeded, in the sense that under the usual time scale no significant transfer of energy to larger scales occurs. The physical implication is that the elasticity of the free surface impedes turbulent energy transfer in wavenumber space, effectively rendering large-scale vortices long-lived and inactive. Results from numerical simulations of forced-dissipative turbulence confirm this prediction.Publisher PDFPeer reviewe

Impact on a water filled cylinder

The computational and experimental results of impact loading a water filled cylinder with a high speed piston are presented. Computational simulation of the impact process is performed by means of DIANA, a commercial finite element software package. In this simulation, water is modeled as a solid with very small shear modulus compared to the bulk modulus of water. The efficiency of the simulated impact is evaluated by the time dependent water pressure in the vicinity of the cylinder. Also, the shock pressure resulting from impact is detected by using a pressure transducer located in the middle of the water tube. Comparison of the computational and experimental results shows that the impact process on a water filled cylinder is well modeled. It is shown that the best way to increase the pressure peaks of the pressure profile curve is to increase the piston’s impact velocity

The Viet Cong

After the loss of his father, Eddie Nguyen – an English teacher – travels to Vietnam to fulfill his father’s dying wish, which is to have his remains returned to his village of origin, but the problem is that Eddie can’t seem to locate it. In an attempt to generate funds and solicit more information about the whereabouts of the mysterious village, Eddie tries to find work as an English teacher in Saigon, but he quickly discovers no school will hire him based off his Vietnamese heritage. Frustrated, Eddie goes to a local bar and befriends a bartender named Nykky, who then passes his information to a “friend” named Tony who might be able to help him. Instead of a face-to-face meeting, Tony – a gangster – tests Eddie’s English skills by sending him on an errand with his hired muscle, Big Baby, to collect an outstanding debt from an American expat. After the frightening ordeal, Eddie meets Tony in his club. Tony, impressed with the results, offers him a job – the details he withholds until Eddie agrees to his terms – and the payment being the location of mysterious village and the sum of three million dollars