Faster Dark Matter Calculations Using the GPU

Abstract: We have investigated the use of the graphical processing unit to accelerate the software package DarkSUSY. DarkSUSY is, among other things, used for calculating the dark matter relic density -- an measurable quantity -- given the supersymmetric neutralino, χ, as a dark matter candidate. Supersymmetric theories have many free parameters and we want to calculate the relic density for large areas of the parameter space. The results can then be compared with observations and to constrain the parameters. A faster DarkSUSY would allow for larger searches in the parameter space. We modified DarkSUSY using Nvidia's CUDA platform and wrote a program that, by using the GPU, calculates the χ + χ <-> W+ + W- contribution to the annihilation cross-section. Our initial try was only negligible faster than our non-CUDA program due to under-utilization of the GPU, but solving that the program was 47 times faster than the reference program. We also report on difficulties we faced, both solved and unsolved so the reader can make an informed decision on the worth of rewriting so that the heavy calculations in DarkSUSY use the GPU.