  Systems with long-range interactions display a short-time relaxation towards
Quasi Stationary States (QSSs) whose lifetime increases with system size. With
reference to the Hamiltonian Mean Field (HMF) model, we here show that a
maximum entropy principle, based on Lynden-Bell's pioneering idea of "violent
relaxation", predicts the presence of out-of-equilibrium phase transitions
separating the relaxation towards homogeneous (zero magnetization) or
inhomogeneous (non zero magnetization) QSSs. When varying the initial condition
within a family of "water-bags" with different initial magnetization and
energy, first and second order phase transition lines are found that merge at
an out--of--equilibrium tricritical point. Metastability is theoretically
predicted and numerically checked around the first-order phase transition line.
