BSFfast is a lightweight numerical tool providing precomputed effective bound-state formation (BSF) cross sections for annihilation processes in the early Universe.
This repository accompanies the paper:
BSFfast: Rapid computation of bound-state effects on annihilation in the early Universe arXiv:2512.23812
The code provides tabulated effective BSF cross sections and interpolation routines for use in Boltzmann solvers.
If you use BSFfast in a publication, please cite the paper above.
For scientific questions, usage issues, or bug reports, please contact:
- Stefan Lederer stefan.lederer@tum.de
- Jan Heisig heisig@physik.rwth-aachen.de
Place the directory BSFfast_DataCSV/ next to BSFfast.py, then:
from BSFfast import fastXS
# choose model parameters
x = 200.0
m = 1000.0 # GeV
# rescaled models (require coupling strength alpha)
xs = fastXS("dQCD-S", x, m, alpha=0.1)
# SM QCD tables support "cutoff" (default) and "plateau"
xs_cut = fastXS("QCD-SU", x, m)
xs_plat = fastXS("QCD-SU", x, m, "plateau")A more comprehensive Python example is provided in example_use.py.
Corresponding example files are also provided for:
- Mathematica:
example_use.nb - C:
example_use.c