István Csabai PhD (2018.08.01-2018.12.31)

ELTE, The Department of Physics of Complex Systems

Publication: StePS: A Multi-GPU Cosmological N-body Code for Compactified Simulations

Abstract: Although the LCDM model has achieved remarkable success, however, in recent years the accuracy of the measurements has reached the limit where parameter estimates from various observations, such as the Hubble constant determined from both CMB and supernovae, are incompatible with it. Recently we have developed a model, based on N-body simulations, which is able to resolve this tension by taking better account of complex structure formation and without introducing dark energy. During the project we will develop a new type of \(N\)-body simulation algorithm ,,StePS" that overcomes limitations of current methods through mapping the infinite spatial extent of the universe onto a compact manifold. Specifically, we use stereographic projection onto the surface of a four dimensional sphere. The discretization of this surface leads to a systematic multi-resolution simulation with unprecedented dynamic range for given computational resources and perfect consistency with the Newtonian force law. Our approach retains the best features of multipole solvers and AMR simulations through a continuous, mathematically consistent refinement of scales toward the center of the simulations and constant angular resolution of distant fluctuations. The algorithm is ideal for GPUs, harnessing a recent cost effective numerical hardware revolution. A prototype of our algorithm has been successfully tested against GADGET, the early version of the code is open source, and available on GitHub, and the paper on the preliminary results R\'acz et al. (2018) has been submitted to MNRAS.