Mixed Higgsino Dark Matter from a reduced SU(3) gaugino mass: consequences for dark matter and collider searches

Abstract

In gravity-mediated SUSY breaking models with non-universal gaugino masses, lowering the SU(3) gaugino mass |M3| leads to a reduction in the squark and gluino masses. Lower third generation squark masses, in turn, diminish the effect of a large top quark Yukawa coupling in the running of the higgs mass parameter mHu2, leading to a reduction in the magnitude of the superpotential μ parameter (relative to M1 and M2). A low |μ| parameter gives rise to mixed higgsino dark matter (MHDM), which can efficiently annihilate in the early universe to give a dark matter relic density in accord with WMAP measurements. We explore the phenomenology of the low |M3| scenario, and find for the case of MHDM increased rates for direct and indirect detection of neutralino dark matter relative to the mSUGRA model. The sparticle mass spectrum is characterized by relatively light gluinos, frequently with mtilde g << mtilde q. If scalar masses are large, then gluinos can be very light, with tilde g→tilde zig loop decays dominating the gluino branching fraction. Top squarks can be much lighter than sbottom and first/second generation squarks. The presence of low mass higgsino-like charginos and neutralinos is expected at the CERN LHC. The small mtilde z2-mtilde z1 mass gap should give rise to a visible opposite-sign/same flavor dilepton mass edge. At a TeV scale linear e+e- collider, the region of MHDM will mean that the entire spectrum of charginos and neutralinos are amongst the lightest sparticles, and are most likely to be produced at observable rates, allowing for a complete reconstruction of the gaugino-higgsino sector.