Last modified 4 years ago Last modified on 01/06/14 11:58:34

Top FCNC Model


  • Mathieu Buchkremer
    • Université catholique de Louvain (CP3)
  • Giacomo Cacciapaglia
    • Université de Lyon (CNRS/IN2P3)
  • Aldo Deandrea
    • Université de Lyon (CNRS/IN2P3)
  • Luca Panizzi
    • University of Southampton (School of Physics and Astronomy)


This model is an extension of the Standard Model (SM), intended for the study of flavor-changing neutral Higgs interactions in the framework of two Higgs doublet models [1]. More general parametrizations can be found in the context of effective field theories [2]. As a generic framework, the following interactions are added to the SM Lagrangian where H is a generic CP-even scalar boson, and the real parameters K_utH and K_cTH denote the flavor-changing couplings of H to up-type quarks. The scenario K_utH = K_ctH = 0 corresponds to the SM case with H being the physical Higgs boson. We highlight that this parametrisation does not include the possiblity for off-shell decays of the H boson, potentially allowing for large values of the associated decay rates due to three-body decays. The H boson default mass and width are set to 125 GeV and 5.75 MeV, respectively. Caution should be exercised when considering the decay width of the top quark, which value in the parameter cards should be adjusted depending on the values of the new flavor-changing couplings. The new user-defined parameters consist of the FCNC block, containing the new flavor-changing couplings of the Higgs boson and top quark to the up and charm quarks (set to 0 and 1, respectively).


The model files have been cross-checked analytically and numerically against the results presented in [1] and [3] for the top quark decay rates and the same-sign top pair production cross-sections, respectively. The UFO model was generated with FeynRules 2.0, and validation has been performed using MG5_aMC 2.0.0. Below we provide the tarballs containing the main input files. The model implementation is also known to work with the CalcHEP/CompHEP interfaces, which can be generated from the TFCNC.nb Mathematica notebook. To import the model into MadGraph?, it is enough to copy the UFO directory into the /models/ subdirectory of MadGraph?, and load the model using the "import model TFCNC_UFO" command.


[1] C. Kao, H.-Y. Cheng, W.-S. Hou, J. Sayre, Top Decays with Flavor Changing Neutral Higgs Interactions at the LHC , Phys. Lett. B716 (2012) 225-230 hep-ph/1112.1707.

[2] C. Degrande, J.-M. Gerard, C. Grojean, F. Maltoni, G. Servant, An effective approach to same sign top pair production at the LHC and the forward-backward asymmetry at the Tevatron, Phys. Lett. B703 (2011) 306-309 hep-ph/1104.1798.

[3] M. Buchkremer, G. Cacciapaglia, A. Deandrea, L. Panizzi, Model Independent Framework for Searches of Top Partners, Nucl.Phys. B876 (2013) 376-417 hep-ph/1305.4172.