Directed and elliptic flow in $^{197}$Au+$^{197}$Au at intermediate energies

Directed and elliptic flow for the $^{197}$Au+$^{197}$Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4$\pi$ multi-detector. For semi-central collisions, the excitation function of elliptic flow shows a transition from in-plane to out-of-plane emission at around 100 MeV per nucleon. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. Molecular dynamics calculations (CHIMERA) indicate sensitivity of the global squeeze-out transition on the $\sigma$ and demonstrate the importance of angular momentum conservation in transport codes at low energies. The conditions for the appearance and possible origins of negative flow are discussed.