Optimal escapes in active matter

The out-of-equilibrium character of active particles, responsible for accumulation at boundaries in confining domains, determines not-trivial effects when considering escape processes. Non-monotonous behavior of exit times with respect to tumbling rate (inverse of mean persistent time) appears, as a consequence of the competing processes of exploring the bulk and accumulate at boundaries. By using both 1D analytical results and 2D numerical simulations of run-and-tumble particles with different behaviours at boundaries, we scrutinize this very general phenomenon of active matter, evidencing the role of accumulation at walls for the existence of optimal tumbling rates for fast escapes.Comment: 9 pages, 4 figure

Configurational entropy of hard spheres

We numerically calculate the configurational entropy S_conf of a binary mixture of hard spheres, by using a perturbed Hamiltonian method trapping the system inside a given state, which requires less assumptions than the previous methods [R.J. Speedy, Mol. Phys. 95, 169 (1998)]. We find that S_conf is a decreasing function of packing fraction f and extrapolates to zero at the Kauzmann packing fraction f_K = 0.62, suggesting the possibility of an ideal glass-transition for hard spheres system. Finally, the Adam-Gibbs relation is found to hold.Comment: 10 pages, 6 figure

Generalized energy equipartition in harmonic oscillators driven by active baths

We study experimentally and numerically the dynamics of colloidal beads confined by a harmonic potential in a bath of swimming E. coli bacteria. The resulting dynamics is well approximated by a Langevin equation for an overdamped oscillator driven by the combination of a white thermal noise and an exponentially correlated active noise. This scenario leads to a simple generalization of the equipartition theorem resulting in the coexistence of two different effective temperatures that govern dynamics along the flat and the curved directions in the potential landscape.Comment: 4 pages, 3 figure

Probing the non-Debye low frequency excitations in glasses through random pinning

We investigate the properties of the low-frequency spectrum in the density of states $D(\omega)$ of a three-dimensional model glass former. To magnify the Non-Debye sector of the spectrum, we introduce a random pinning field that freezes a finite particle fraction in order to break the translational invariance and shifts all the vibrational frequencies of the extended modes towards higher frequencies. We show that Non-Debye soft localized modes progressively emerge as the fraction $p$ of pinned particles increases. Moreover, the low-frequency tail of $D(\omega)$ goes to zero as a power law $\omega^{\delta(p)}$, with $2 \!\leq \! \delta(p) \!\leq\!4$ and $\delta\!=\!4$ above a threshold fraction $p_{th}$.Comment: 4 Figures, submitted to PNA