Nonequilibrium tricritical point in a system with long-range interactions.
Systems with long-range interactions display a short-time relaxation towards quasistationary states whose lifetime increases with system size. With reference to the Hamiltonian mean field 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 (nonzero magnetization) quasistationary states. 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.
Dipartimento di Energetica and CSDC, Università di Firenze, and INFN, via S. Marta, 3, 50139 Firenze, Italy.
Andrea
A
Antoniazzi
Duccio
D
Fanelli
Stefano
S
Ruffo
Yoshiyuki Y
YY
Yamaguchi