Improvedd+4He potentials by inversion: The tensor force and validity of the double folding model

Improved potential solutions are presented for the inverse scattering problem for ${d+}^4$He data. The input for the inversions includes both the data of recent phase shift analyses and phase shifts from RGM coupled-channel calculations based on the $\mathrm{NN}$ Minnesota force. The combined calculations provide a more reliable estimate of the odd-even splitting of the potentials than previously found, suggesting a rather moderate role for this splitting in deuteron-nucleus scattering generally. The approximate parity-independence of the deuteron optical potentials is shown to arise from the nontrivial interference between antisymmetrization and channel coupling to the deuteron breakup channels. A further comparison of the empirical potentials established here and the double folding potential derived from the M3Y effective $\mathrm{NN}$ force (with the appropriate normalization factor) reveals strong similarities. This result supports the application of the double folding model, combined with a small Majorana component, to the description even of such a loosely bound projectile as the deuteron. In turn, support is given for the application of iterative-perturbative inversion in combination with the double folding model to study fine details of the nucleus-nucleus potential. A $d{-}^4$He tensor potential is also derived to reproduce correctly the negative ${}^6$Li quadrupole moment and the $D$-state asymptotic constant.