title: Non-mean-field critical exponent in a mean-field model: dynamics versus statistical mechanics.
abstract: Mean-field theory tells us that the classical critical exponent of susceptibility is twice that of magnetization. However, linear response theory based on the Vlasov equation, which is naturally introduced by the mean-field nature, makes the former exponent half of the latter for families of quasistationary states having second order phase transitions in the Hamiltonian mean-field model and its variances, in the low-energy phase. We clarify that this strange exponent is due to the existence of Casimir invariants which trap the system in a quasistationary state for a time scale diverging with the system size. The theoretical prediction is numerically confirmed by N-body simulations for the equilibrium states and a family of quasistationary states.
authors.affiliation: Department of Applied Mathematics and Physics, Graduate School of Informatics, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Shun
authors.initials: S
authors.lastname: Ogawa
authors.affiliation: Dipartimento di Fisica e Astronomia, Universitá di Firenze and INFN, Via Sansone 1, IT-50019 Sesto Fiorentino, Italy.
authors.forename: Aurelio
authors.initials: A
authors.lastname: Patelli
authors.affiliation: Department of Applied Mathematics and Physics, Graduate School of Informatics, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Yoshiyuki Y
authors.initials: YY
authors.lastname: Yamaguchi