ULYSSES the Third: An Odyssey Towards a Unified Python Toolkit for Leptogenesis
Abstract
We present the third release of ULYSSES, a Python package for the numerical evaluation of the baryon asymmetry generated through leptogenesis. This version includes code implementing state-of-the-art density matrix equations for low-scale leptogenesis with three quasi-degenerate right-handed neutrinos. We extend the validity of the code in this scenario beyond the 100 GeV right-handed neutrino mass scale, into the regime of resonant leptogenesis, by including neutrino production rates valid in both the relativistic and non-relativistic regimes. In addition, in the high-scale vanilla scenario, we provide routines for computing ΔL = 1 scattering processes, enabling full phase-space evolution of the right-handed neutrino and lepton asymmetry. A new −−extended parameter interface allows users to pass model-specific inputs beyond the standard leptogenesis runcard without modifying the core infrastructure and demonstrate its use with a toy module that simultaneously solves the vanilla leptogenesis equations and the freeze-in production of dark matter. On top of these improvements, we introduce an alternative parametrisation of the Casas-Ibarra matrix, update the default neutrino oscillation parameters and report cross-checks of the new low-scale leptogenesis module against published benchmarks and independent codes. ULYSSES is publicly available on hrefhttps://github.com/earlyuniverse/ulyssesGitHub and pip-installable from PyPI.
Versions
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BibTeX
@misc{granelli2026ulysses,
title = {{ULYSSES the Third: An Odyssey Towards a Unified Python Toolkit for Leptogenesis}},
author = {Alessandro Granelli and Juraj Klarić and Dhruv Pasari and Yuber F. Perez-Gonzalez and Jessica Turner},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2605.16540},
eprint = {2605.16540},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.16540},
}
RIS
TY - UNPB
TI - ULYSSES the Third: An Odyssey Towards a Unified Python Toolkit for Leptogenesis
AU - Alessandro Granelli
AU - Juraj Klarić
AU - Dhruv Pasari
AU - Yuber F. Perez-Gonzalez
AU - Jessica Turner
PY - 2026
DA - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2605.16540
UR - https://arxiv.org/abs/2605.16540
AB - We present the third release of ULYSSES, a Python package for the numerical evaluation of the baryon asymmetry generated through leptogenesis. This version includes code implementing state-of-the-art density matrix equations for low-scale leptogenesis with three quasi-degenerate right-handed neutrinos. We extend the validity of the code in this scenario beyond the 100 GeV right-handed neutrino mass scale, into the regime of resonant leptogenesis, by including neutrino production rates valid in both the relativistic and non-relativistic regimes. In addition, in the high-scale vanilla scenario, we provide routines for computing ΔL = 1 scattering processes, enabling full phase-space evolution of the right-handed neutrino and lepton asymmetry. A new −−extended parameter interface allows users to pass model-specific inputs beyond the standard leptogenesis runcard without modifying the core infrastructure and demonstrate its use with a toy module that simultaneously solves the vanilla leptogenesis equations and the freeze-in production of dark matter. On top of these improvements, we introduce an alternative parametrisation of the Casas-Ibarra matrix, update the default neutrino oscillation parameters and report cross-checks of the new low-scale leptogenesis module against published benchmarks and independent codes. ULYSSES is publicly available on hrefhttps://github.com/earlyuniverse/ulyssesGitHub and pip-installable from PyPI.
ER -