arXiv subjects

Abhishek Chaudhuri

Publications and source records attributed to Abhishek Chaudhuri.

At least 19 recordsLinked to original sources

arXiv2026

Shape Transformations and Rupture of a Vesicle Driven by an Encapsulated Active Particle

Biological membranes are highly deformable structures that undergo shape transformations during numerous cellular processes. These transformations are often driven by active agents, including molecular motors, cytoskeletal machinery, and motile microorganisms, which consume energy and maintain biological systems far from equilibrium. Here, we investigate how a single active particle confined within a lipid vesicle drives membrane deformation. Using a lipid-resolved coarse-grained model, we examine how the activity and shape of an encapsulated self-propelled particle influence vesicle dynamics and morphology. Active particles generate persistent propulsion that exerts mechanical stresses on the enclosing membrane, thereby driving its deformation. Using particles of different shapes but identical surface area, we systematically investigate membrane morphologies as functions of activity and bending rigidity. We quantify membrane deformation through asphericity and excess bending energy relative to the equilibrium spherical state. Both measures exhibit a non-monotonic dependence on activity, peaking at intermediate activity. At sufficiently high activity, membrane rupture occurs before significant large-scale deformation can develop, limiting further remodeling. We further demonstrate that membrane surface tension plays a significant role in regulating activity-induced deformation dynamics.

cond-mat.soft↗

arXiv2026

Extreme Events in an Active Fluid Medium

We observe the emergence of extreme events in an active fluid involving two distinct chemical species that regulate active stress. One species is slow diffusing and the other is fast diffusing, and the growth of the fast-diffusing species is modelled using a nonlinear logistic term. We demonstrate the presence of extreme events in the temporal evolution of the concentrations, as well as in the spatial profile of the system,in regimes of merging-emerging soliton-like dynamics and spatio-temporal chaos, through analysis of the time-series, bifurcation diagrams, probability distribution functions of the concentration of the two species, return maps and distributions of inter-event intervals. Interestingly, we also find evidence of pronounced bunching of extreme events and super-extreme events in the slow chemical species in the soliton-like regime. We go on to systematically explore the dependence of the extreme event occurrences on the Péclet number and the strength of the nonlinear growth term, and find that the probability of extreme events increases after a critical Péclet number, while increasing the nonlinearity suppresses extreme events. Lastly, in order to gain further insight, we investigate a modified mode-truncated reduced order model comprising of coupled differential equations mimicking this active fluid system. We find that this reduced order model also exhibits extreme events whose emergence is correlated with a sudden expansion in attractor size due to a crisis arising from attractor collision.So these results demonstrate the existence of extreme events in an active fluid system, and are of potential relevance to biological phenomena where active transport plays an important role.

nlin.PS↗

arXiv2026

Intermittency Signatures in the Deformation of a Passive Droplet in Active Turbulence

We use fully resolved nematohydrodynamic simulations to study deformation statistics of a passive nematic droplet in two-dimensional extensile active-nematic turbulence. We find that the droplet aspect ratio serves as a scalar probe of the active bath. Its increments show heavy-tailed distributions with dependence on the time lag, scale-free burst statistics and multiscaling structure functions which establish temporal intermittency. While the mean deformation increases with activity, normalized intermittency is strongest at lower activity. This suggests slower and more coherent bath forcing. When compared with translational and forcing-side fluctuations, it reveals a hierarchy of intermittency: shape is more weakly intermittent than translation and active-stress fluctuations, consistent with filtering by interfacial restoring forces. Power spectra show an extended near-$1/ω$ regime for the maximal normal interface velocity, distinct from the steeper, approximately $1/ω^{2}$ spectrum of the interfacial active stress. Soft inclusions thus reveal how interfacial restoring forces convert active forcing into bursty, scale-rich deformation dynamics.

cond-mat.soft↗

arXiv2026

Semiflexible Ring Polymers on Active Motor Beds: Nonequilibrium Dynamics and Conformations

A semiflexible ring polymer on a motor-protein bed exhibits activity- and processivity-dependent rotational and conformational dynamics that are not captured by linear-chain behavior. Using coarse-grained Langevin simulations with bending elasticity, excluded-volume interactions, and stochastic motor attachment, stepping, and detachment, we vary activity (Peclet number), motor processivity, and chain stiffness to map the nonequilibrium response. The mean-squared displacement shows crossover dynamics, with semiflexible rings displaying subdiffusive-to-diffusive behavior at low activity and an intermediate ballistic regime at higher activity, while increasing flexibility shifts the short-time response toward a Rouse-like limit. Diameter autocorrelations exhibit damped oscillations associated with coherent rotation; the rotational frequency increases with activity and processivity, whereas the decorrelation time is non-monotonic at high processivity. Fourier mode analysis identifies competition between the radius (k=0) and elliptic (k=2) modes as the origin of the non-monotonic asphericity.

cond-mat.soft↗

arXiv2026

Spectral Signatures of Active Fluctuations in Semiflexible Polymers

We study how an active bath is transduced into the internal fluctuation spectrum of a semiflexible polymer. Starting from the statistics of active forces exerted by an explicit bath of active Brownian particles, we derive an effective description in terms of temporally persistent and spatially correlated noise, and test it against simulations of both explicit-bath and implicit-noise models. We find that activity reorganizes polymer fluctuations spectrally rather than uniformly: increasing the active force predominantly enhances the lowest modes, while increasing persistence shifts the spectral weight toward progressively longer wavelengths. The theory captures this mode-level reorganization well and explains the strong qualitative correspondence between explicit and implicit active baths over a broad parameter range. In contrast, global size measures such as the radius of gyration are systematically underestimated, which we trace to activity-induced bond stretching and contour-length renormalization absent from the present fixed-contour theory. Our results show that a semiflexible polymer acts as a multiscale probe of active matter, resolving the temporal and spatial structure of nonequilibrium forcing through its mode spectrum.

cond-mat.soft↗

arXiv2026

Characterizing exact dynamics of a trapped active Brownian particle under torque in two and three dimensions

The interplay of chirality, self-propulsion, and spatial confinement generates striking non-equilibrium fluctuations whose higher-order statistics carry information about the dynamics and shape of the position distribution. Here, we present an exact analytical framework, based on a Laplace-transform solution of the Fokker-Planck equation, for the transient dynamics of a chiral active Brownian particle in a harmonic trap, in both two and three dimensions. We obtain closed-form expressions for all time-dependent moments up to fourth order, enabling a complete characterization of the excess kurtosis throughout the transient and steady-state regimes. In two dimensions, the excess kurtosis exhibits a damped oscillatory response with multiple re-entrant crossovers, evolving from negative values that reflect active off-centered ring-like position distributions to positive values characteristic of heavy-tailed fluctuations. This damped oscillatory excess kurtosis appears both for free and harmonic confinement, although increasing the trapping stiffness progressively suppresses it, and the positive excess kurtosis eventually vanishes at sufficiently high stiffness. In contrast, in three dimensions, the excess kurtosis remains negative, indicating a robustly active non-Gaussian state characterized by half-ring-like to band-like position distributions in the two-dimensional plane spanned by the torque axis and its normal radial direction. Our results demonstrate how chirality, propulsion, and confinement, together with dimensionality, shape transient dynamics, while providing experimentally accessible signatures of confined chiral active dynamics.

cond-mat.soft↗

arXiv2026

Polymer translocation through extended patterned pores in two dimensions: scaling of the total translocation time

We study the translocation of a flexible polymer through extended patterned pores using molecular dynamics (MD) simulations. We consider cylindrical and conical pore geometries that can be controlled by the angle of the pore apex $α$. We obtained the average translocation time $\langle τ\rangle$ for various chain lengths $N$ and the length of the pores $L_p$ for various values $α$ and found that $\langle τ\rangle$ scales as $\langle τ\rangle \sim N^γ\mathcal{F}\left( L_p N^ϕ\right)$ with exponents $γ= 3.00\pm0.05$ and $ϕ= 1.50\pm0.05$ for both patterned and unpatterned pores.

cond-mat.soft↗

arXiv2026

Non-reciprocal visual perception and polar alignment drive collective states in chiral active particles

Self-propelled particles rarely move in straight lines; environmental interactions, shape asymmetry, and intrinsic torques generically induce curved or fluctuating trajectories. In biological and synthetic systems, this curvature often coexists with directional sensing and non-reciprocal interactions. Motivated by this, we explore the collective dynamics of chiral intelligent active Brownian particles (iABPs) that combine polar alignment with vision-based sensing. By varying the ratio of alignment to visual maneuverability, the vision angle, and the reduced chirality $(ω/D_r)$, we construct a phase diagram exhibiting diverse collective states: spinners, vortices, ripples, worm-like swarms, rotary clusters, and irregular aggregates. Chirality critically governs their morphology: high chirality yields dilute phases, while moderate to low chirality produces cohesive yet dynamic patterns. Ripple loops emerge as a distinct state, characterized by expanding ring-like motion driven by outward torques and sustained only when both particle number and visual maneuverability are large. Structural and dynamical measures, including polarization, pair correlations, mean-square displacement, and orientation correlations, reveal clear signatures distinguishing these phases. Overall, our results show how chirality, non-reciprocal perception, and alignment together generate collective states inaccessible to non-chiral systems, with implications for chiral active matter in biological and synthetic contexts.

cond-mat.soft↗

arXiv2025

Chirality, confinement and dimensionality govern re-entrant transitions in active matter

The non-equilibrium dynamics of individual chiral active particles underpin the complex behavior of chiral active matter. Here we present an exact analytical framework, supported by simulations, to characterize the steady states of two-dimensional chiral active Brownian particles and three-dimensional torque-driven counterparts in a harmonic trap. Using a Laplace-transform approach of the Fokker-Planck equation, we derive closed-form expressions for displacement moments and excess kurtosis, providing a precise probe of non-Gaussian statistics. Our analysis reveals three distinct regimes: bimodal active states with off-center peaks, Gaussian-like passive states, and weakly heavy-tailed distributions unique to two dimensions. We show that dimensionality plays a decisive role: in two dimensions, increasing chirality suppresses activity and restores passive behavior, while in three dimensions torque preserves activity along the torque axis, producing anisotropic steady states. These behaviors are captured by simple active length-scale arguments that map the boundaries between passive and active phases. Our results offer concrete experimental signatures - including kurtosis crossovers, off-center peaks, and torque-induced anisotropy - that establish confinement as a powerful tool to probe and control chiral and torque-driven active matter.

cond-mat.soft↗

arXiv2025

Inertia-chirality interplay in active Brownian motion: exact dynamics and phase maps

We present an exact, time-resolved theory for a two-dimensional chiral active Brownian particle (cABP) with translational inertia. Using a Laplace-transform moment hierarchy, we derive closed-form expressions for the mean velocity, velocity-orientation projections, velocity autocorrelation, mean-squared velocity, mean-squared displacement, and the fourth moment of velocity. These results agree quantitatively with simulations over all masses, activities, and chiralities. We show that the velocity autocorrelation factorizes into an inertial envelope and a chiral envelope. Despite rich transients in the velocity sector, the long-time positional diffusion equals the overdamped cABP value, independent of mass. From the steady mean-squared velocity, we define a kinetic temperature and a modified fluctuation-dissipation relation whose violation vanishes in two limits: large mass or large chirality, identifying chirality as an additional route to equilibrium-like behavior. The steady-state velocity excess kurtosis gives a phase map that exhibits a (Gaussian-like)-active(bimodal)-(Gaussian-like) re-entrance with mass; chirality confines activity and shrinks the active sector. A narrow positive-kurtosis window emerges at large mass and intermediate chirality, with analytic boundaries consistent with the heavy-mass asymptote.

cond-mat.stat-mech↗

arXiv2025

From spirals to flagellar beating: How pivot-like defects control semiflexible filament dynamics in motility assays

We demonstrate that internal pivot-like defects, arising from rigor mutant motor proteins that bind without stepping, fundamentally reshape the dynamics of semiflexible filaments in two-dimensional motility assays. Using large-scale numerical simulations, we show that such internal pivots establish a previously unrecognized boundary condition, intermediate between free and clamped filaments, that decisively governs filament behavior. Strikingly, by tuning the pivot position, motor activity, and processivity, filaments undergo sharp transitions from tightly wound spiral states to extended, flagella-like beating. Spiral formation is stabilized by a balance between motor-driven forces and bending rigidity, with intermediate stiffness yielding the most robust spirals. Unlike generic active polymer models, our framework isolates the distinct role of rigor-bound motor proteins, revealing how they function as internal control elements governing the transition between spiral and flagellar dynamics. This minimal yet physically grounded model yields experimentally testable predictions and reveals how localized defects can act as key regulators of cytoskeletal organization and dynamics.

physics.bio-ph↗

arXiv2025

Confinement and Activity-Driven Dynamics of Semiflexible Polymers in Motility Assays

We investigate the nonequilibrium dynamics of semiflexible polymers driven by motor proteins (MPs) in two-dimensional motility assays under harmonic confinement. Using a coarse-grained agent-based model that incorporates stochastic motor attachment, detachment, and force generation, we study how activity, filament rigidity, and confinement interact to control polymer behavior. We construct dynamical behavior maps as a function of Péclet number, motor processivity, and trap strength. We find a two-state transition from a trapped to a free polymer, with an intermediate coexistence region, and obtain a scaling relation for the critical Péclet number, which is supported by simulation data across a range of parameters. Polymer flexibility strongly influences confinement: flexible filaments are more easily trapped, while increasing rigidity destabilizes confinement. Processivity of MPs can also induce a change in the effective rigidity of the polymer and, therefore, influence confinement by the trap. Under moderate confinement and activity, we observe the emergence of stable spiral conformations. The center-of-mass dynamics is analyzed through the mean square displacement, showing diffusive, ballistic, and diffusive regimes that depend on the trap strength and activity. Additionally, time series analysis of the excess kurtosis shows the variation of the non-Gaussian fluctuations with trap strength and activity. Our results provide a minimal physical framework to understand the dynamic organization of active filaments under confinement, with relevance to in vitro motility assays, cytoskeletal filament manipulation by optical traps, and synthetic active polymer systems.

cond-mat.soft↗

arXiv2025

From Order to Chimeras: Unraveling Dynamic Patterns in Active Fluids with Nonlinear Growth

We explore pattern formation in an active fluid system involving two chemical species that regulate active stress: a fast-diffusing species ($A$) and a slow-diffusing species ($I$). The growth of species $A$ is modelled using a nonlinear logistic term. Through linear stability analysis, we derive phase diagrams illustrating the various dynamical regimes in parameter space. Our findings indicate that an increase in the Péclet number results in the destabilisation of the uniform steady state. In contrast, counter-intuitively, an increase in the nonlinear growth parameter of $A$ actually stabilises the homogeneous steady-state regime. Additionally, we observe that greater asymmetry between the species leads to three distinct dynamical phases, while low asymmetry fails to produce oscillatory instability. Numerical simulations conducted in instability regimes show patterns that range from irregular, arrhythmic configurations at high Péclet numbers to both transient and robust symmetry-breaking chimera states. Notably, these chimera patterns are more prevalent in the oscillatory instability regime, and our stability analysis indicates that this regime is the most extensive for high nonlinear growth parameters and moderately high Péclet numbers. Further, we also find soliton-like structures where aggregations of species $A$ merge, and new aggregations spontaneously emerge, and these patterns are prevalent in the phase of stationary instability. Overall, our study illustrates that a diverse array of patterns can emerge in active matter influenced by nonlinear growth in a chemical species, with chimeras being particularly dominant when the nonlinear growth parameter is elevated.

nlin.PS↗

arXiv2025

Spatial organisation of multiple species of active particles interacting with an interface

We investigate the steady-state organisation of active particles residing on an interface. Particle activity induces interface deformations, while the local shape of the interface guides particle movement. We consider multiple species of particles which can locally pull on the interface or push it. This coupled system exhibits a wide variety of behaviours, including clustering, anti-clustering, diffusion, mixing, demixing, and localisation. Our findings suggest that one can control surface properties by strategically adding or removing specific particle types. Furthermore, by adjusting particle activity levels, we can selectively disperse particle types, enabling precise manipulation of surface movement and geometry.

cond-mat.soft↗

arXiv2025

Self-organized fractal architectures driven by motility-dependent chemotactic feedback

Complex spatial patterns in biological systems often arise through self-organization without a central coordination, guided by local interactions and chemical signaling. In this study, we explore how motility-dependent chemical deposition and concentration-sensitive feedback can give rise to fractal-like networks, using a minimal agent-based model. Agents deposit chemicals only while moving, and their future motion is biased by local chemical gradients. This interaction generates a rich variety of self-organized structures resembling those seen in processes like early vasculogenesis and epithelial cell dispersal. We identify a diverse phase diagram governed by the rates of chemical deposition and decay, revealing transitions from uniform distributions to sparse and dense networks, and ultimately to full phase separation. At low chemical decay rates, agents form stable, system-spanning networks; further reduction leads to re-entry into a uniform state. A continuum model capturing the co-evolution of agent density and chemical fields confirms these transitions and reveals how linear stability criteria determine the observed phases. At low chemical concentrations, diffusion dominates and promotes fractal growth, while higher concentrations favor nucleation and compact clustering. These findings unify a range of biological phenomena - such as chemotaxis, tissue remodeling, and self-generated gradient navigation - within a simple, physically grounded framework. Our results also offer insights into designing artificial systems with emergent collective behavior, including robotic swarms or synthetic active matter.

physics.bio-ph↗

arXiv2024

Packing and ejection dynamics of polymers: Role of confinement, polymer stiffness and activity

The translocation of biopolymers, such as DNA and proteins, across cellular or nuclear membranes is essential for numerous biological processes. The translocation dynamics are influenced by the properties of the polymers, such as polymer stiffness, and the geometry of the capsid. In our study, we aim to investigate the impact of polymer stiffness, activity, and different capsid geometries on the packing and ejection dynamics of both passive and active polymers. We employ Langevin dynamics simulations for a systematic investigation. We observe that flexible polymers exhibit packing times that are faster than those of their semi-flexible counterparts. Interestingly, for large polymers compared to the capsid size, sphere facilitates faster packing and unpacking compared to ellipsoid, mimicking the cell nucleus and suggesting a geometrical advantage for biopolymer translocation. In summary, we observe that increasing activity accelerates both the packing and ejection processes for both flexible and semi-flexible polymers. However, the effect is significantly more pronounced for semi-flexible polymers, highlighting the crucial role of polymer flexibility in these dynamics. These findings deepen our understanding of the intricate interplay between polymer flexibility, capsid geometry, and activity, providing valuable insight into the dynamics of polymer packing and ejection processes.

cond-mat.soft↗

arXiv2024

Inertia and Activity: Spiral transitions in semi-flexible, self-avoiding polymers

We consider a two-dimensional, tangentially active, semi-flexible, self-avoiding polymer to find a dynamical re-entrant transition between motile open chains and spinning achiral spirals with increasing activity. Utilizing probability distributions of the turning number, we ascertain the comparative stability of the spiral structure and present a detailed phase diagram within the activity inertia plane. The onset of spiral formation at low activity levels is governed by a torque balance and is independent of inertia. At higher activities, however, inertial effects lead to spiral destabilization, an effect absent in the overdamped limit. We further delineate alterations in size and shape by analyzing the end-to-end distance distribution and the radius of gyration tensor. The Kullback-Leibler divergence from equilibrium distributions exhibits a non-monotonic relationship with activity, reaching a peak at the most compact spirals characterized by the most persistent spinning. As inertia increases, this divergence from equilibrium diminishes.

cond-mat.soft↗

arXiv2024

Impact of chirality on active Brownian particle: Exact moments in two and three dimensions

In this work, we investigate the effects of chirality, accounting for translational diffusion, on active Brownian particles in two and three dimensions. Despite the inherent complexity in solving the Fokker-Planck equation, we demonstrate a Laplace transform method for precisely calculating the temporal evolution of various dynamic moments. Our analysis yields explicit expressions for multiple moments, such as the second and fourth moments of displacement, revealing the impact of persistence and chirality. These moments exhibit oscillatory behaviour, and excess kurtosis indicates deviations from the Gaussian distribution during intermediate time intervals.

cond-mat.stat-mech↗