Luneburg-lens-like universal structural Pauli attraction in nucleus-nucleus interactions: Origin of emergence of cluster structures and nuclear rainbows

The Pauli exclusion principle plays an important role in many-body fermion systems preventing them from collapsing by repulsion. For example, the Pauli principle causes a repulsive potential at short distances between two $\alpha$ particles. On the other hand, the existence of nuclear rainbows demonstrates that the inter-nuclear potential is sufficiently attractive in the internal region to cause refraction. The two concepts of repulsion and attraction are seemingly irreconcilable. Contrary to traditional understanding, it is shown that the Pauli principle causes a {\it universal structural Pauli attraction} between nuclei rather than a {\it structural repulsive core}. Through systematic studies of $\alpha$+$\alpha$, $\alpha$+$^{16}$O, $\alpha$+$^{40}$Ca and $^{16}$O+$^{16}$O systems, it is shown that the emergence of cluster structures near the threshold energy at low energies and nuclear rainbows at high energies is a direct consequence of the Pauli principle.