Ditauonium spectroscopy

We examine the properties of ditauonium, an exotic atom consisting a pair opposite-sign $\tau$ leptons bound together by quantum electrodynamics (QED) interaction in hydrogen-like state. The energy levels, decay modes and associated partial widths, as well total widths lifetimes ortho- para-ditauonium states are calculated. Higher-order QED effects -- including Lamb shifts, hyperfine splitting structure, corrections incorporated up to approximately next-to-next-to-leading-order (NNLO) accuracy. Beyond dominant diphoton difermion decays, rates rare channels Dalitz, radiative, triple-photon, double-Dalitz, four-fermion, neutrinos final determined.