Toponium Spectrum in the Complex-Energy Plane

The electroweak decay width of the top quark of ~2 GeV is comparable to binding energies expected for the toponium system, raising the long-standing question of whether top and antitop quarks can sustain meaningful bound states. This issue has been been reignited by recent discoveries of a cross section enhancement near the t-tbar threshold by the CMS and ATLAS collaborations in pp collisions at the LHC. Here, we deploy a T-matrix approach with an underlying Cornell potential to study the properties of the toponium system by varying the top-quark widths in the intermediate propagators. In particular, we carry out a complex-energy analysis of the T-matrix to assess how its poles, as a rigorous criterion for bound-state formation, develop from the limit of small widths to realistic ones. We also revisit the impact of the confining force in the potential on the toponium T-matrix.