Nucleus-nucleus potentials in the scattering of tightly and weakly bound systems

\begin{description} \item[Background] Fusion reactions play an important role in nucleosynthesis and in applications to society. Yet they remain challenging to model. \item[Purpose] In this work, we investigate the features of the nucleus-nucleus potentials that describe fusion cross sections and compare with those needed for realistic calculations of elastic scattering and other direct-reaction cross sections. \item[Method] We perform coupled-channel calculations for studying elastic and fusion reactions around the Coulomb barrier with a tightly bound projectile ($^{16}$O+$^{144}$Sm). We also perform Continuum Discretized Coupled Channel calculations to study elastic ($^{8}$B+$^{58}$Ni) and fusion ($^{6}$Li+$^{198}$Pt) of loosely bound projectiles in the same energy regime. \item[Results] We contrast the coupled-channel results with those obtained in a single-channel solution with different assumptions for polarization potentials to shed light on the relevant absorption terms required for the two different reaction channels. \item[Conclusions] Our results suggest that different approximations may be required for modeling direct processes and for modeling fusion reactions. \end{description}