arXiv subjects

Giuseppe Fava

Publications and source records attributed to Giuseppe Fava.

4 recordsLinked to original sources

arXiv2026

Density-protected states in active matter under virtual confinement

We investigate photo-responsive structure formation in a minimal model of dry active nematics. Combining microscopic simulations with the analysis of the corresponding hydrodynamic theory, we show that the system generically self-assembles into a dense, nematically ordered ring at the boundary of compact illumination patterns. Remarkably, this boundary structure gives rise to a disordered core whose density is self-selected and independent of the global particle density. Our analysis reveals that these protected states emerge from a generic interplay between local nematic alignment and curvature-driven active currents. These results identify a robust route to boundary-induced structure formation in active matter and provide experimentally testable predictions.

cond-mat.soft↗

arXiv2024

Boundary symmetry breaking of flocking systems

We consider a flocking system confined transversally between two infinite reflecting parallel walls separated by a distance $L_\perp$. Infinite or periodic boundary conditions are assumed longitudinally to the direction of collective motion, defining a ring geometry typical of experimental realizations with flocking active colloids. Such a confinement selects a flocking state with its mean direction aligned parallel to the wall, thus breaking explicitly the rotational symmetry locally by a boundary effect. Finite size scaling analysis and numerical simulations show that confinement induces an effective mass term ${M_c} \sim L_\perp^{-\zeta}$ (with positive $\zeta$ being the dynamical scaling exponent of the free theory) suppressing scale free correlations at small wave-numbers. However, due to the finite system size in the transversal direction, this effect can only be detected for large enough longitudinal system sizes (i.e. narrow ring geometries). Furthermore, in the longitudinal direction, density correlations are characterized by an anomalous effective mass term. The effective mass term also enhances the global scalar order parameter and suppresses fluctuations of the mean flocking direction. These results suggest an equivalence between transversal confinement and driving by an homogeneous external field, which breaks the rotational symmetry at the global level.

cond-mat.soft↗

arXiv2023

Signatures of directed and spontaneous flocking

Collective motion - or flocking - is an emergent phenomena that underlies many biological processes of relevance, from cellular migrations to animal groups movement. In this work, we derive scaling relations for the fluctuations of the mean direction of motion and for the static density structure factor (which encodes static density fluctuations) in the presence of a homogeneous, small external field. This allows us to formulate two different and complementary criteria capable of detecting instances of directed motion exclusively from easily measurable dynamical and static signatures of the collective dynamics, without the need to detect correlations with environmental cues. The static one is informative in large enough systems, while the dynamical one requires large observation times to be effective. We believe these criteria may prove useful to detect or confirm the directed nature of collective motion in in vivo experimental observations, which are typically conducted in complex and not fully controlled environments.

cond-mat.soft↗

arXiv2022

Strong Casimir-like Forces in Flocking Active Matter

Confining in space the equilibrium fluctuations of statistical systems with long-range correlations is known to result into effective forces on the boundaries. Here we demonstrate the occurrence of Casimir-like forces in the non-equilibrium context provided by flocking active matter. In particular, we consider a system of aligning self-propelled particles in two spatial dimensions, which are transversally confined by reflecting or partially reflecting walls. We show that in the ordered flocking phase this confined active vectorial fluid is characterized by extensive boundary layers, as opposed to the finite ones usually observed in confined scalar active matter. Moreover, a finite-size,fluctuation-induced contribution to the pressure on the wall emerges, which decays slowly and algebraically upon increasing the distance between the walls. We explain our findings, which display a certain degree of universality, within a hydrodynamic description of the density and velocity fields.

cond-mat.soft↗