Magnetohydrodynamcis and Wave Dark Matter

• Main Authors: Ui-Han Zhang, 張瑋瀚
• Other Authors: Tzihong Chiueh
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/dmdcy2

博士 === 國立臺灣大學 === 物理學研究所 === 105 === GAMER, a Graphic-processing-unit-accelerated Adaptive-MEsh-Refinement Astrophysical code, is extended to support magnetohydrodynamics (MHD), where the solver features the corner-transport-upwind (CTU) scheme with the constraint transport (CT) technique. The divergent preserving operator for adaptive mesh refinement (AMR) is applied to reinforce the divergence-free constraint on the magnetic field. Numerical results show GAMER-MHD is as robust as those given by high-resolution uniform-grid runs. We explore a new 3D MHD test, where the magnetic field assumes the Arnold-Beltrami- Childress (ABC) configuration, temporarily becomes turbulent with current sheets and finally settles to a lowest-energy equilibrium state. This 3D problem is adopted for the performance test of GAMER-MHD. The single-GPU performance can reach 2×10^7 cell-updates/sec for K20X and is 25 times faster than a single 16-core CPU on the Blue Waters supercomputer. We also demonstrate a parallel efficiency of 70% using 1024 nodes on Blue Waters. Linear perturbations of the wave dark matter, or ψ dark matter ( ψ DM), in the radiation-dominant era are analyzed. We identify four phases of evolution for ψ DM perturbations. While in late stages after mass oscillation long-wave ψ DM perturbations are almost identical to cold dark matter (CDM) perturbations except that intermediate-to-short waves that bear no resemblance with those of CDM throughout the whole evolutionary history. We also discuss the axion model with a cosine field potential. The evolution of axion models are almost identical to those of ψ DM, but three new features are found in the extreme case where the initial axion angle is near the field potential top. A particularly novel new feature is the spectral excess relative to the CDM model in some wave number range, where the excess may be so large that landscapes of high-redshift universe beyond z = 10 can be significantly altered. The sub-horizon perturbations are accurately described by Mathieu''s equation and subjected to parametric instability, which explains this novel feature.