Extra-weakly interacting dark matter

We investigate a new type of dark matter with couplings to ordinary matternaturally suppressed by at least one order of magnitude compared to weakinteractions. Despite the extra-weak interactions massive particles of thistype (XWIMPs) can satisfy the WMAP relic density constraints due tocoannihilation if their masses are close to that of the lightest state of theMSSM. The region in the parameter space of a suitably extended mSUGRA modelconsistent with the WMAP3 constraints on XWIMPs is determined. Plots forsparticles masses are given which can be subject to test at the LHC. We alsodiscuss the sensitivity of the analysis to the top mass. As an example for anexplicit 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 withspontaneous gauge symmetry breaking via Fayet-Iliopoulos D-terms in the hiddensector. The LSP of the full model arises from the extra $U(1)_X$ sector withextra-weak couplings to Standard Model particles due to experimentalconstraints. With R-parity conservation the new XWIMP is a candidate for colddark matter. In a certain limit the model reduces to the \st extension of theMSSM without a Higgs mechanism, and wider ranges of models with similarcharacteristics are easy to construct.Comment: 25 pages, 7 figures, Version to appear in Physical Review