Pitt Seal University of Pittsburgh

Homepage of Ayres Freitas

Research page

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   → Computer codes

My working area is theoretical high energy elementary particle physics. Currently, most results both from low and high energy experiments are well described by a theory called the Standard Model. This model is larglely defined by a few symmetries, some of which must be broken. However, the Standard Model contains only an unsatisfactory explanation for these broken symmetries. In particular, the Standard Model fails to describe the origion of ordinary matter as well as dark matter in the universe. These shortcomings have spawned many new ideas like supersymmetry, extra dimensions, technicolor and little Higgs models, which all predict many new heavy particles.

My research mostly deals with the phenomenology of these new particles and their interactions at current and future colliders, most notably at the Large Hadron Collider (LHC). Furthermore, models for physics beyond the Standard Model can be constrained by existing precision data and possibly could be discovered at future experiments, most notably at the Large Hadron Collider (LHC). Of special interest to me are precision analyses that would allow to reconstruct the underlying framework of a model from experimental data. I am working on methods to determine the spin and couplings of newly discovered particles, as well as ideas to detect particles that would be particularly eluvise. One main focus has been on supersymmetric models, but also on models with extra dimensions, extended gauge groups and little Higgs models.

Some of the new physics models quite naturally could explain the origin of ordinary matter and/or dark matter in the universe. This opens up striking connections between collider physics and astrophysics and cosmology.

On the technical side, development of loop calculation techniques and Monte-Carlo tools are very important for the interpretation of the flood of new data expected from the LHC. Recently there has been much progress in both areas, leading to automated computer programs. I have been working on methods for electroweak one- and two-loop calculations, as well as implementation of new models in Monte-Carlo generators.

Recent projects and publications:

Probing dark sector fermions in Higgs precision studies and direct searches
A. Freitas, Q. Song,   arXiv:2308.13030

Fermionic electroweak NNLO corrections to e+e→ZH with polarized beams and different renormalization schemes
A. Freitas, Q. Song, K. Xie,   Phys. Rev. D 108, 053006 (2023)

GRIFFIN: A C++ library for electroweak radiative corrections in fermion scattering and decay processes
L. Chen, A. Freitas,   SciPost Phys. Codeb. 8 (2023)

Two-Loop Electroweak Corrections with Fermion Loops to e+e→ZH
A. Freitas, Q. Song,   Phys. Rev. Lett. 130, 031801 (2023)

Report of the Topical Group on Electroweak Precision Physics and Constraining New Physics for Snowmass 2021
A. Belloni, A. Freitas, J. Tian (eds.), Report of the EF04 topical group for Snowmass 2021

Hadronic effects in Møller scattering at NNLO
J. Erler, R. Ferro-Hernández, A. Freitas,   JHEP 2208, 183 (2022)

Evaluation of multiloop multiscale Feynman integrals for precision physics
I. Dubovyk, A. Freitas, J. Gluza, K. Grzanka, M. Hidding, J. Usovitsch,   Phys. Rev. D 106, L111301 (2022)

Renormalizable models of flavor-specific scalars
B. Batell, A. Freitas, A. Ismail, D. McKeen, M. Rai,   Phys. Rev. D 104, 115032 (2021)

Parity-Violating Møller Scattering at NNLO: Closed Fermion Loops
Y. Du, A. Freitas, H. Patel, M. Ramsey-Musolf,   Phys. Rev. Lett. 126, 131801 (2021)

    Complete list of publications (from INSPIRE HEP database)

Computer codes:


A C++ library for the description of fermion scattering processes with a consistent description of the Z resonance.

GitHub repository


A Mathematica/C++ package for the evaluation of 3-loop integrals.

Version 2.2 (December 2020)

Version 2.1 (August 2020)

Version 2.0 (August 2019)     [Paper and manual]

Version 1.1 (August 2018)

Version 1.0 (December 2016)     [Manual]


A Mathematica/Fortran package for the numerical computation of loop integrals using subtraction terms.

  Version 1.2 (August 2014)
  Version 1.1 (August 2012)
  Version 1.0 (May 2012)

Slepton production at lepton colliders:

NLO corrections to R-smuon production, e+e → μR+μR (Installation and user's guide)
NLO corrections to L-smuon production, e+e → μL+μL (Installation and user's guide)
NLO corrections to R-selectron production, e+e → eR+eR (Installation and user's guide)
NLO corrections to R-selectron production
in e-e- collisions
ee → eReR (Installation and user's guide)
NLO corrections to muon-sneutrino production, e+e → νμνμ* (Installation and user's guide)
NLO corrections to electron-sneutrino production, e+e → νeνe* (Installation and user's guide)

Littlest Higgs model with T-parity broken by WZW term:

CalcHEP model file