Toward a Simple, Accurate Lagrangian Hydrocode.

Lagrangian hydrocodes play an important role in the computation of transient, compressible, multi-material flows. This research was aimed at developing a simply constructed cell-centered Lagrangian method for the Euler equations that respects multidimensional physics while achieving second-order accuracy. Algorithms that can account for the multidimensional physics associated with acoustic wave propagation and vorticity transport are needed in order to increase accuracy and prevent mesh imprinting. Many of the building blocks of traditional finite volume schemes, such as Riemann solvers and spatial gradient limiters, have their foundations in one-dimensional ideas and so were not used here. Instead, multidimensional point estimates of the fluxes were computed with a Lax-Wendroff type procedure and then nonlinearly modified using a temporal flux limiting mechanism. The linear acoustic equations were used as a simplified test environment for the Lagrangian Euler system. Here Lax-Wendroff methods that exactly preserve vorticity were investigated and found to resist mesh imprinting. However, the dispersion properties of the schemes were poor and so third-order accurate vorticity preserving methods were developed to remedy the problem. The third-order methods guided the construction of a temporal limiting mechanism, which was then used in a vorticity preserving flux-corrected transport scheme. While the acoustic work was interesting in its own right, it also proved to be a useful stepping stone to Lagrangian hydrodynamics. The acoustics algorithms were extended to produce the Simple Lagrangian Method (SLaM). Standard test problems have shown that a first-order accurate version of the method is able to resist mesh imprinting and spurious vorticity despite its minimalistic structure. SLaM is capable of second-order accuracy with a simple parameter change and some preliminary work was done to extend the temporal flux limiting ideas from acoustics to the Lagrangian case. The limited SLaM method converges at second-order for smooth data and is able to capture shocks without producing large unphysical oscillations.PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113577/1/tblung_1.pd

Multi-messenger searches via IceCube’s high-energy neutrinos and gravitational-wave detections of LIGO/Virgo

We summarize initial results for high-energy neutrino counterpart searches coinciding with gravitational-wave events in LIGO/Virgo\u27s GWTC-2 catalog using IceCube\u27s neutrino triggers. We did not find any statistically significant high-energy neutrino counterpart and derived upper limits on the time-integrated neutrino emission on Earth as well as the isotropic equivalent energy emitted in high-energy neutrinos for each event

Non-standard neutrino interactions in IceCube

Non-standard neutrino interactions (NSI) may arise in various types of new physics. Their existence would change the potential that atmospheric neutrinos encounter when traversing Earth matter and hence alter their oscillation behavior. This imprint on coherent neutrino forward scattering can be probed using high-statistics neutrino experiments such as IceCube and its low-energy extension, DeepCore. Both provide extensive data samples that include all neutrino flavors, with oscillation baselines between tens of kilometers and the diameter of the Earth. DeepCore event energies reach from a few GeV up to the order of 100 GeV - which marks the lower threshold for higher energy IceCube atmospheric samples, ranging up to 10 TeV. In DeepCore data, the large sample size and energy range allow us to consider not only flavor-violating and flavor-nonuniversal NSI in the μ−τ sector, but also those involving electron flavor. The effective parameterization used in our analyses is independent of the underlying model and the new physics mass scale. In this way, competitive limits on several NSI parameters have been set in the past. The 8 years of data available now result in significantly improved sensitivities. This improvement stems not only from the increase in statistics but also from substantial improvement in the treatment of systematic uncertainties, background rejection and event reconstruction