title: Cages and anomalous diffusion in vibrated dense granular media.
abstract: A vertically shaken granular medium hosts a blade rotating around a fixed vertical axis, which acts as a mesorheological probe. At high densities, independently of the shaking intensity, the blade's dynamics shows strong caging effects, marked by transient subdiffusion and a maximum in the velocity power density spectrum, at a resonant frequency ~10 Hz. Interpreting the data through a diffusing harmonic cage model allows us to retrieve the elastic constant of the granular medium and its collective diffusion coefficient. For high frequencies f, a tail ~1/f in the velocity power density spectrum reveals nontrivial correlations in the intracage microdynamics. At very long times (larger than 10 s), a superdiffusive behavior emerges, ballistic in the most extreme cases. Consistently, the distribution of slow velocity inversion times τ displays a power-law decay, likely due to persistent collective fluctuations of the host medium.
authors.affiliation: Université de Lyon, Ecole Normale Supérieure de Lyon, Laboratoire de physique, 46 Allée d'Italie, 69364 Lyon, Cedex 07, France and Dipartimento di Fisica, Università "Sapienza", Piazzale Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Camille
authors.initials: C
authors.lastname: Scalliet
authors.affiliation: Istituto dei Sistemi Complessi-Consiglio Nazionale delle Ricerche, 00185 Rome, Italy and Dipartimento di Fisica, Università "Sapienza", Piazzale Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Gnoli
authors.affiliation: Istituto dei Sistemi Complessi-Consiglio Nazionale delle Ricerche, 00185 Rome, Italy and Dipartimento di Fisica, Università "Sapienza", Piazzale Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Puglisi
authors.affiliation: Dipartimento di Fisica, Università "Sapienza", Piazzale Aldo Moro 5, 00185 Rome, Italy and Istituto dei Sistemi Complessi-Consiglio Nazionale delle Ricerche, 00185 Rome, Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: Vulpiani