Stability and hyperfine structure of the 4- and 5-body muon-atomic clusters a+b+μ-e- and a+b+μ-e-e-

Based on the results of accurate variational calculations we demonstrate stability of the five-body negatively charged ions a+b+μ-e-e-. Each of these five-body ions contains two electrons e-, one negatively charged muon μ- and two nuclei of the hydrogen isotopes a,b = (p,d,t). The bound state properties of these five-body ions, including their hyperfine structure, are briefly discussed. We also investigate the hyperfine structure of the ground states of the four-body muonic quasi-atoms a+b+μ-e-. In particular, we determine the hyperfine structure splittings for the ground state of the four-body muonic quasi-atoms: p+d+μ-e- and p+t+μ-e- and predict the results of possible future experiments. (authors)