Bound and resonant states of muonic few-body Coulomb systems: Extended stochastic variational approach

We compute the bound and resonant states of hydrogen-like muonic ions ($μμp$, $μμd$, $μμt$) and three-body muonic molecular ions ($ppμ$, $pdμ$, $ptμ$, $ddμ$, $dtμ$, $ttμ$), and the four-body double-muonic hydrogen molecule ($μμpp$) using an extended stochastic variational method combined with complex scaling. The approach provides a unified treatment of bound and quasibound states and achieves an energy accuracy better than $0.1~\mathrm{eV}$ across all systems studied. Complete spectra below the corresponding $n=2$ atomic thresholds are obtained, including several previously unresolved shallow resonances in both three- and four-body sectors.