Extra-weakly interacting dark matter

We investigate a new type of dark matter with couplings to ordinary matter naturally suppressed by at least 1 order of magnitude compared to weak interactions. Despite the extra-weak interactions massive particles of this type (XWIMPs) can satisfy the Wilkinson Microwave Anisotropy Probe (WMAP) relic density constraints due to coannihilation if their masses are close to that of the lightest state of the minimal supersymmetric standard model (MSSM). The region in the parameter space of a suitably extended minimal supergravity model consistent with the WMAP3 constraints on XWIMPs is determined. Plots for sparticles’ masses are given which can be subject to test at the Large Hadron Collider. As an example for an explicit model we show that such a form of dark matter can arise in certain Z^′ extensions of the MSSM. Specifically, we consider an Abelian extension with spontaneous gauge symmetry breaking via Fayet-Iliopoulos D terms in the hidden sector. The lightest supersymmetric particle of the full model arises from the extra U(1)_X sector with extra-weak couplings to standard model particles due to experimental constraints. With R-parity conservation, the new XWIMP is a candidate for cold dark matter. In a certain limit the model reduces to the Stueckelberg extension of the MSSM without a Higgs mechanism, and wider ranges of models with similar characteristics are easy to construct.