ALOHA: Automatic Libraries Of Helicity Amplitudes for Feynman diagram computations

TL;DR

ALOHA automates the generation of helicity amplitude routines from arbitrary Lagrangians by consuming UFO-formatted models and producing language-specific code (Fortran, C++, Python) that integrates with MadGraph5. The method contracts Lorentz structures with wavefunctions to yield analytic expressions for amplitudes, supports conjugate and multi-coupling routines, and validates results against the established HELAS library across SM, MSSM, RS-I and beyond-HELAS cases. Validation uses phase-space-point comparisons with a defined DeltaD metric, demonstrating high precision and broad coverage, while speed comparisons show generated routines are nearly as fast as optimized HELAS code. The work substantially extends event-generation automation from the Lagrangian level and outlines practical future extensions (complex-mass schemes, dimensional generalizations, R2 rules, GPUs, and broader generator compatibility).

Abstract

We present an application that automatically writes the Helas library corresponding to the Feynman rules of any Lagrangian, renormalizable or not, in quantum field theory. The code, written in Python, takes the Universal FeynRules Output as an input and produces the complete set of routines (wave-functions and amplitudes) that are needed for the computation of Feynman diagrams at leading as well as at higher orders. The representation is language independent and outputs in Fortran, C++, Python are currently available. A few key sample applications implemented in the MadGraph5 framework are presented.

Figures (2)

• Figure 1: $W^+W^-\to t\bar{t}$ via $Z$ exchange
• Figure 2: Interactions induced by the chromomagnetic operator.