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  • Heather Logan's Web Page - Research - GMCALC

    A calculator for the Georgi-Machacek model

    The Georgi-Machacek model adds scalar triplets to the Standard Model Higgs sector in such a way as to preserve custodial SU(2) symmetry in the scalar potential. This allows the triplets to have a non-negligible vacuum expectation value while satisfying constraints from the rho parameter. Depending on the parameters, the 125 GeV neutral Higgs particle can have couplings to WW and ZZ larger than in the Standard Model due to mixing with the triplets. The model also contains singly- and doubly-charged Higgs particles that couple to vector boson pairs at tree level (WZ and like-sign WW, respectively).

    GMCALC is a FORTRAN program that, given a set of input parameters, calculates the particle spectrum and tree-level couplings, checks theoretical and indirect constraints on the model, and computes the branching ratios and total widths of the scalars. It also generates a param_card.dat file for MadGraph5 (LO, NLO, and an EFT version) to be used with the corresponding FeynRules model implementations.

    The full functionality of GMCALC v1.3.0 and higher requires an installation of the LoopTools package. There is an option to compile GMCALC v1.3.0 and higher without LoopTools; if this is done then the loop-induced decay widths of H_5^0 to Z gamma and H_3^+, H_5^+ to W^+ gamma will be set to zero.

    GMCALC v1.5.0 and higher includes an interface to HiggsBounds/HiggsSignals (HB/HS). GMCALC's interface supports HiggsBounds 5.3.2 and HiggsSignals 2.2.3 (later versions of HB/HS are not yet supported). Proper compilation of the HB/HS interface requires gfortran version 5 or later.

    • Ameen Ismail, Ben Keeshan, Heather E. Logan, and Yongcheng Wu (v.1.5.x) and all authors of previous versions
    • Celine Degrande, Katy Hartling, Kunal Kumar, Heather E. Logan, Andrea D. Peterson, Mark B. Reimer, and Yongcheng Wu (v1.4.x)
    • Celine Degrande, Katy Hartling, Kunal Kumar, Heather E. Logan, and Andrea D. Peterson (v1.3.x)
    • Katy Hartling, Kunal Kumar, Heather E. Logan, and Andrea D. Peterson (v1.2.x)
    • Katy Hartling, Kunal Kumar, and Heather E. Logan (v1.0.x, 1.1.x)

    If you use this program to write a paper, please cite:
    The physics that went into this code is described in more detail in the following references:
    Requests and bug reports:

    Contact Heather Logan at

    Older versions:

    Last updated 2021-02-08 by