Implications of heavy neutralino dark matter: The underlying structure in the hidden sector

The possibility of heavy neutralino dark matter (DM) in the gravity-mediation mechanism is explored. The appearance of the heavy lightest supersymmetric particle is seemingly suggested by Large Hadron Collider runs, which have not provided evidence of superparticles around the TeV region. On the basis of the so-called WIMPZILLA scenario, it is understood that the nonthermally produced DM has the larger mass than the reheating temperature. Hence, the expected DM mass should be more than 10(9) GeV so that thermal leptogenesis successfully occurs. In this paper, we first examine the generation of the Higgsino mass parameter (mu) in the context of gravity mediation, postulating that the resolution of the strong CP problem should be the criterion for arriving at a valid hypothesis for heavy neutralino DM. Accordingly, we address how the Peccei-Quinn (PQ) symmetry could influence dynamical supersymmetry breaking (DSB) models. It is found that as long as A(SUSY) (the SUSY-breaking scale) approximately coincides with A(PQ) (the PQ-breaking scale), no DSB models can naturally account for the existence of the heavy neutralino DM, based upon the supersymmetric Dine-Fischler-Srednicki-Zhitinitski (DFSZ)-like mechanism. Thus, we attempt to construct a new model wherein hierarchical SUSY breakings occur. For this purpose, we propose gauge coupling unification in the hidden-sector dynamics at some high-energy scale, and we show that such a class of models can achieve Asusy >> A(PQ) through renormalization flow. As a consequence, the nonthermal neutralino, practically the wino -like one in our model, is shown to be a rather natural and viable DM candidate. Moreover, we argue that on the basis of Kac-Moody algebra, multiple breakdowns of supersymmetry may entail unified gauge dynamics. We also present a possible unified model. Finally, the heavy wino -like neutralino may be a DM candidate that will favor future direct DM detection experiments, mainly because its scattering on nuclei well conserves isospin symmetry.