Calculation of HELAS amplitudes for QCD processes using graphics processing unit (GPU)

TL;DR

This paper develops GPU-accelerated algorithms for calculating helicity amplitudes in massless QCD processes, significantly speeding up computations compared to CPU-based methods, especially for multi-jet final states.

Contribution

The authors introduce HEGET codes for gluon self-interactions and a C++ conversion program from MadGraph, enabling efficient GPU-based calculations of QCD scattering amplitudes.

Findings

GPU implementation achieves 60-100x speedup over CPU

Maximum final state jets evaluated: 4 for gluons, 5 with quarks

Performance gain varies with process complexity

Abstract

We use a graphics processing unit (GPU) for fast calculations of helicity amplitudes of quark and gluon scattering processes in massless QCD. New HEGET ({\bf H}ELAS {\bf E}valuation with {\bf G}PU {\bf E}nhanced {\bf T}echnology) codes for gluon self-interactions are introduced, and a C++ program to convert the MadGraph generated FORTRAN codes into HEGET codes in CUDA (a C-platform for general purpose computing on GPU) is created. Because of the proliferation of the number of Feynman diagrams and the number of independent color amplitudes, the maximum number of final state jets we can evaluate on a GPU is limited to 4 for pure gluon processes ($gg\to 4g$), or 5 for processes with one or more quark lines such as $q\bar{q}\to 5g$ and $qq\to qq+3g$. Compared with the usual CPU-based programs, we obtain 60-100 times better performance on the GPU, except for 5-jet production processes and the $gg\to 4g$ processes for which the GPU gain over the CPU is about 20.