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GRIFFIN: A C++ library for electroweak radiative corrections in fermion scattering and decay processes

by Lisong Chen, Ayres Freitas

Submission summary

Authors (as registered SciPost users): Lisong Chen · Ayres Freitas
Submission information
Preprint Link: scipost_202304_00009v3  (pdf)
Code repository:
Date accepted: 2023-09-13
Date submitted: 2023-06-08 00:06
Submitted by: Freitas, Ayres
Submitted to: SciPost Physics Codebases
Ontological classification
Academic field: Physics
  • High-Energy Physics - Phenomenology
Approaches: Theoretical, Computational, Phenomenological


This paper describes a modular framework for the description of electroweak scattering and decay processes, including but not limited to Z-resonance physics. The framework consistently combines a complex-pole expansion near a s-channel resonance with a regular fixed-order perturbative description away from the resonance, in a manifestly gauge-invariant scheme. Leading vertex correction contributions are encapsulated in form factors that can be predicted or treated as numerical fit parameters. This framework has been implemented in the publicly available object-oriented C++ library GRIFFIN. Version 1.0 of this library provides Standard Model predictions for the process $f\bar{f} \to f'\bar{f}'$ with full NNLO and leading higher-order contributions on the Z-resonance, and with NLO corrections off resonance. The library can straightforwardly be extended to include higher-order corrections, should they become available, or predictions for new physics models. It can be interfaced with Monte-Carlo programs to account for QED and QCD initial-state and final-state radiation.

Author comments upon resubmission

Response to report 1:

We thank the referee for the positive response. We have added the suggested reference when we talk about the full NLO corrections in the paragraph after (36).

Response to report 2:

We thank the referee for the careful review of our manuscript. In response to the comments we have made several changes. In the following, we address the comments individually:

1) Thank you for the additional suggestions for references related to computer codes for four-fermion processes. We have included them.

2)+4) We have added the suggested references [D,E] on the gauge invariance of the complex propagator pole, as well as the review [I].

3) We have added the clarification that the scattering angle is defined in the center-of-mass frame.

5) We thank the referee for reminding us that one needs to clarify what variables are kept fixed in the expansion. We have added a statement below eq.(7) that we parametrize the matrix element in terms of s and the scattering angle \theta, and the latter is kept constant in the expansion.

6)+8) We have added the suggested references on the cancellation of leading IFI logs and on the complex-mass scheme.

7) In footnote 5 in the revised version ( we explicitly explain that the combination in (36) does not exactly reproduce all terms of the full matrix element, but that the mismatch is beyond the order of accuracy considered in our work. We agree that it is appropriate to cite the suggested reference [C], which is similar but not identical to our approach. At NLO, both approaches should lead to identical results, but our approach allows for a systematic extension to NNLO.

9) In response to the comments by the original three referee reports we have already added additional explanations on the IR subtraction in v2 (page 5 in The manuscript contains explicit formulae for the definition, as well as references where explicit results for the factorized QED/QCD contributions can be found. We believe this description is adequate for all practical purposes.

10) We believe that our added explanations at the end of section 5 in v2 of our manuscript ( provide a satisfactory clarification of this situation (also see comment 1.8 in our response to the first round of referee reports, If the relative NLO corrections are at the level of 20-30% (and this magnitude is observed both in GRIFFIN and DIZET), NNLO contributions of O(1-2%) are perfectly reasonable to expect. We wish to reiterate that the size of the relative NLO/NNLO corrections is due to the smallness of the Born matrix element in this kinematical region, not due to any special feature of the corrections.

List of changes

Please see author comments for the list of changes.

Published as SciPost Phys. Codebases 18 (2023) , SciPost Phys. Codebases 18-r1.0 (2023)

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