Mixed Gauginos Sending Mixed Messages to the LHC

TL;DR

This paper explores how mixed gaugino masses, combining Dirac and Majorana types, affect squark production cross sections at the LHC, revealing nuanced impacts on collider search constraints.

Contribution

It generalizes the analysis of gaugino mass effects on squark production to mixed scenarios, highlighting how different mass configurations influence collider signals.

Findings

Majorana mass for gluino suppresses squark production

Majorana mass for adjoint fermion increases cross section

Electroweak gauginos can modestly enhance production when Majorana-like

Abstract

Supersymmetric models with a Dirac gluino have been shown to be considerably less constrained from LHC searches than models with a Majorana gluino. In this paper, we generalize this discussion to models with a "Mixed Gluino", that acquires both Dirac and Majorana masses, as well as models in which electroweak gauginos contribute to squark production. Our primary interest is the degree of suppression of the cross section for first generation squarks compared with a gluino with a pure Majorana mass. We find that not all Majorana masses are alike -- a Majorana mass for the gluino can suppress the squark production cross section, whereas a Majorana mass for the adjoint fermion partner leads to an increased cross section, compared with a pure Dirac gluino. In the presence of electroweak gauginos, squark production can increase by at most a factor of a few above the pure Dirac gluino case when the electroweak gauginos have purely Majorana masses near to the squark masses. This unusual set of gaugino masses is interesting since the usual Higgs quartic coupling would not be suppressed. When the electroweak gaugino masses are much lighter than the squarks, there is a negligible change to the squark production cross section. We explain both of these cases in detail by considering the various subprocesses for squark production at the LHC. Continued searches for squark production with cross sections much smaller than expected in the MSSM are absolutely warranted, and we suggest new simplified models to fully characterize the collider constraints.