arXiv subjects

Pablo Maynar

Publications and source records attributed to Pablo Maynar.

3 recordsLinked to original sources

arXiv2026

The Kovacs memory effect in a thin granular layer: experimental evidence and its physical origin

We report the experimental observation of memory effects in a vertically vibrated thin granular layer. Following a quench in the input acceleration, the granular temperature exhibits an anomalous Kovacs memory effect confined to the initial fast relaxation stage. This memory vanishes shortly thereafter, yielding a time-dependent memoryless regime governed solely by the instantaneous temperature before the system reaches its final steady state. We develop a kinetic theory framework that quantitatively captures these features by identifying the initial memory and subsequent memoryless regimes with the kinetic and hydrodynamic states, respectively (that are well established in kinetic theory). Our analysis reveals that memory emerges during fast transients through coupling between horizontal and vertical temperatures, a mechanism that fundamentally constrains the accessible memory phenomenology and precludes observation of the standard Kovacs effect in this system. Molecular dynamics simulations provide independent confirmation of all experimental and theoretical findings.

cond-mat.soft↗

arXiv2025

Cooling mechanism controls motility-induced phase separation in inertial active liquids

Motility-induced phase separation (MIPS) is a central collective phenomenon in active matter, theoretically established in the overdamped regime. We discover that the dynamical origin of MIPS is fundamentally altered by inertia, which induces a cooling mechanism absent in overdamped active matter. This conclusion is supported by an active variant of the direct simulation Monte Carlo method and by a kinetic theory for inertial self-propelled hard spheres derived from the microscopic dynamics. In contrast to the overdamped case, both analyses demonstrate that inertial MIPS does not rely on volume exclusion but on a cooling mechanism involving density, polarization, and temperature fields. This mechanism emerges from the competition between activity and a density dependent collision rate, arising from spatial correlations between colliding particles. These findings open a pathway to fundamentally connect inertial active matter with granular physics.

cond-mat.soft↗

arXiv2025

Self-diffusion in confined systems

The self-diffusion process of a hard sphere fluid confined by two parallel plates separated by a distance on the order of the particle diameter is studied. The starting point is a closed kinetic equation for the distribution function that takes into account the effects of the confinement and that is valid in the low-density limit. From it, the Boltzmann-Lorentz equation that describes the dynamics of some tagged particles when the whole system is in equilibrium is derived. An equation that describes the diffusion in the directions parallel to the walls is deduced by applying the Zwanzig-Mori projection technique to the Boltzmann-Lorentz equation, obtaining an explicit expression for the self-diffusion coefficient that depends on the height of the system. A very good agreement between its theoretical prediction and Molecular Dynamics simulation results is obtained for the whole range of heights.

cond-mat.stat-mech↗