Highly correlated exponential variational method applied to the system
Phys. Rev. C 114, 034009 – Published 21 September, 2026
DOI: https://doi.org/10.1103/hlmx-6x21
Abstract
Recent calculations based on the same HAL QCD Collaboration lattice-QCD potential have reached conflicting conclusions on whether the system supports a bound state. The problem is reexamined here with a highly correlated exponential variational method. The near-threshold state is directly evaluated without coupling-constant extrapolation, and the Coulomb interaction is treated through analytically exact matrix elements. Without Coulomb, the variational energy lies below the threshold, indicating a shallow bound state with a binding energy of about 0.025 MeV. The resulting bound state is spatially extended, with fm, consistent with the near-threshold scale fm (rms fm). When Coulomb repulsion is included, the variational energy approaches the threshold from above while the rms separation grows strongly and remains unconverged; no binding signal is found within the explored basis sizes. Complex-scaling calculations likewise yield no -stable resonance pole. In the Coulomb-free model, a survey of the nine spin-channel/time-slice combinations finds only the , case below threshold.