MSSMD Model

Author

Wei Shi

Rice University, weishi[at]rice.edu

Model Description

The model is based on MSSM from the model database, but adding a dark sector, U(1)D. The dark sector is broken, giving rise to light dark photon, ad, that weakly couples to the SM particles via a small kinetic mixing with photons. The lightest neutralino in MSSM, n1, is no longer stable and can decay via processes such as n1 → nd + ad, where nd is a light dark neutralino. In this model, ad is mediated by very weak interactions with the SM, and can decay to muon pairs.

References

To be updated: CMS HIG-18-003.

Model Files

MSSMD implementation: http://feynrules.irmp.ucl.ac.be/attachment/wiki/MSSMD/MSSMD.fr; Main changes compared to MSSM .fr file are

Line 30-31: U1D gauge group 
Line 41-43: New Physics (NP) interaction order
Line 63: Superfield related to the U1D gauge group
Line 93-95: Physics field for the dark photon, “ad”
Line 106-107: Gaugino for the new U1D gauge boson
Line 136-138: Physics field for dark neutralino, “nd"
Line 348-349: U1D gauge group coupling constant, “gd"
Line 567-568: Vertice for “n1 > ad nd”
Line 569-570: Vertice for “ad > mu+ mu-”
Line 573: Added vertices to the Lagrangian 

Parameter file: http://feynrules.irmp.ucl.ac.be/attachment/wiki/MSSMD/sps1a.dat

Example of a notebook to produce UFO model: http://feynrules.irmp.ucl.ac.be/attachment/wiki/MSSMD/MSSMD.nb

UFO model: http://feynrules.irmp.ucl.ac.be/attachment/wiki/MSSMD/MSSMD_UFO.zip

Validation

The model is validated by checking kinematic distribution plots from the LHE file generated by MadGraph5 for two dark photon (ad) mass points. Also the distributions are consistent with those from MadGraph4.

m(ad)=0.25 GeV: ​https://github.com/weishi10141993/DarkSUSY_MC_MG5/tree/master/MSSMDarkSector/MG5_0p25_cT_100_LHE

m(ad)=8.5 GeV: ​https://github.com/weishi10141993/DarkSUSY_MC_MG5/tree/master/MSSMDarkSector/MG5_8p5_cT_100_LHE

An example instruction for LHE generation using the model is here: ​https://github.com/weishi10141993/DarkSUSY_MC_MG5/blob/master/README.md#private-darksusy-mc-in-mg5

Acknowledgement

The author would like to thank M. Abdullah and F. Elahi for insightful discussions. Thanks to B. Fuks for help in the implementation. Thanks to O. Mattelaer for help interface between UFO and MadGraph5. Any suggestions for improving this model implementation are always welcome by the author.