= 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 ==
arXiv:1812.00380

== 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.