The impact of high-speed jets -- dynamic pressure enhancements in the magnetosheath -- on the Earths magnetopause has been observed to trigger local magnetic reconnection. We perform a three-dimensional hybrid simulation to study the magnetosheath an
d magnetopause under turbulent conditions using a quasi-radial southward interplanetary magnetic field (IMF). In contrast to quasi-steady reconnection with a strong southward IMF, we show that after the impact of a jet on the magnetopause, the magnetopause moves inwards, the current sheet is compressed and intensified and signatures of local magnetic reconnection are observed, showing similarities to spacecraft measurements
The integration of kinetic effects in fluid models is important for global simulations of the Earths magnetosphere. We use a two-fluid ten moment model, which includes the pressure tensor and has been used to study reconnection, to study the drift ki
nk and lower hybrid drift instabilities. Using a nonlocal linear eigenmode analysis, we find that for the kink mode, the ten moment model shows good agreement with kinetic calculations with the same closure model used in reconnection simulations, while the electromagnetic and electrostatic lower hybrid instabilities require modeling the effects of the ion resonance using a Landau fluid closure. Comparisons with kinetic simulations and the implications of the results for global magnetospheric simulations are discussed.
The Magnetospheric Multiscale (MMS) mission has given us unprecedented access to high cadence particle and field data of magnetic reconnection at Earths magnetopause. MMS first passed very near an X-line on 16 October 2015, the Burch event, and has s
ince observed multiple X-line crossings. Subsequent 3D particle-in-cell (PIC) modeling efforts of and comparison with the Burch event have revealed a host of novel physical insights concerning magnetic reconnection, turbulence induced particle mixing, and secondary instabilities. In this study, we employ the Gkeyll simulation framework to study the Burch event with different classes of extended, multi-fluid magnetohydrodynamics (MHD), including models that incorporate important kinetic effects, such as the electron pressure tensor, with physics-based closure relations designed to capture linear Landau damping. Such fluid modeling approaches are able to capture different levels of kinetic physics in global simulations and are generally less costly than fully kinetic PIC. We focus on the additional physics one can capture with increasing levels of fluid closure refinement via comparison with MMS data and existing PIC simulations.
The boundary element method is applied to investigate the optical forces when whispering gallery modes (WGMs) are excited by a total internally reflected wave. Such evanescent wave is particularly effective in exciting the high-$Q$ WGM, while the low
angular or high radial order modes are suppressed relatively. This results in a large contrast between the forces on and off resonance, and thus allows for high size-selectivity. We fully incorporate the prism-particle interaction and found that the optical force behaves differently at different separations. Optimal separation is found which corresponds to a compromise between intensity and $Q$ factor.
The electromagnetic box diagram for the leptonic decays of pseudoscalar mesons in the quark model is evaluated to all orders in ${bf p} / m_q$, where ${bf p}$ is the relative three-momentum of the quark-antiquark pair and $m_q$ is the quark mass. We
compute $B_P equiv Gamma(eta to l^+ l^-) / Gamma(eta to gammagamma)$ using a popular nonrelativistic (NR) harmonic oscillator wave function, and with a relativistic momentum space wave function that we derive from the MIT bag model. We also compare with a calculation in the limit of extreme NR binding due to Bergstrom. Numerical calculations of $B_P$ using these three parameterizations of the wave function agree to within a few percent over a wide kinematical range. We find that the quark model leads in a natural way to a negligible value for the ratio of dispersive to absorptive parts of the electromagnetic amplitude for $eta to mu^+ mu^-$ (unitary bound). However we find substantial deviations from the unitary bound in other kinematical regions, such as $eta,pi^0 to e^+ e^-$. These quark models yield $B(eta to mu^+mu^-) approx 4.3 times 10^{-6}$, within errors of the recent SATURNE measurement of $5.1 pm 0.8 times 10^{-6}$, $B(eta to e^+ e^-) approx 6.3 times 10^{-9}$, and $B(pi^0 to e^+ e^-) approx 1.0 times 10^{-7}$.
