arXiv subjects

Chandraniva Guha Ray

Publications and source records attributed to Chandraniva Guha Ray.

5 recordsLinked to original sources

arXiv2026

Towards a Matrix Product Ansatz in Two Dimensions

Matrix product ansatz (MPA) is a powerful framework for constructing exact steady state weights of one dimensional non-equilibrium stochastic processes; but its generalization to higher dimensions is limited. Here, we introduce the MPA formalism for two dimensions (2D). As a concrete application, we introduce and exactly solve a non-conserved assisted exclusion model (NAEM) in one and two dimensions with constrained hopping and local birth-death dynamics: a particle can hop to a neighbouring site only when exactly one of its neighbouring sites is vacant, while creation and annihilation occur exclusively at sites whose neighbours are all occupied. The MPA yields exact steady-state weights and provides a systematic method to compute observables such as density moments and particle currents. In the particle-conserving limit, the system undergoes an absorbing phase transition at the critical density $\rho_c=\frac12$ with order-parameter exponent $\beta=3$. We further show that the steady state of the NAEM maps exactly onto the well-studied hard-square lattice gas with nearest-neighbour exclusion, thereby providing a nonequilibrium dynamical route to realizing equilibrium states of constrained lattice gases. Our work generalizes matrix-product methods beyond one dimension, establishing a systematic approach to exact solutions of interacting stochastic systems in 2D.

cond-mat.stat-mech↗

arXiv2026

Minority-Triggered Reorientations Yield Macroscopic Cascades and Enhanced Responsiveness in Swarms

Collective motion in animals and cells often exhibits rapid reorientations and scale-free velocity correlations. This allows information to spread rapidly through the group, allowing an adequate collective response to environmental changes and threats such as predators. To explain this phenomenon, we introduce a simple, biologically plausible mechanism: a minority-triggered reorientation rule. When local order is high, agents sometimes follow a strongly deviating neighbor instead of the majority. This rule qualitatively changes the macroscopic system behavior compared to traditional flocking models, as it generates heavy-tailed cascades of reorientations over broad parameter ranges. Our mechanism preserves cohesion while markedly enhancing collective responsiveness because localized directional cues elicit amplified group-level reorientation. Our results provide a parsimonious, biologically interpretable route to critical-like fluctuations and high responsiveness during flocking.

q-bio.QM↗

arXiv2025

Control of lumen morphology by lateral and basal cell surfaces

Across development, the morphology of fluid-filled lumina enclosed by epithelial tissues arises from an interplay of lumen pressure, mechanics of the cell cortex, and cell-cell adhesion. Here, we explore the mechanical basis for the control of this interplay using the shape space of MDCK cysts and the instability of their apical surfaces under tight junction perturbations [Mukenhirn et al., Dev. Cell 59, 2886 (2024)]. We discover that the cysts respond to these perturbations by significantly modulating their lateral and basal tensions, in addition to the known modulations of pressure and apical belt tension. We develop a mean-field three-dimensional vertex model of these cysts that reproduces the experimental shape instability quantitatively. This reveals that the observed increase of lateral contractility is a cellular response that counters the instability. Our work thus shows how regulation of the mechanics of all cell surfaces conspires to control lumen morphology.

cond-mat.soft↗

arXiv2024

How motility affects Ising transitions

We study a lattice gas model of hard-core particles on a square lattice experiencing nearest neighbour attraction $J$. Each particle has an internal orientation, independent of the others, that point towards one of the four nearest neighbour and it can move to the neighbouring site along that direction with the usual Metropolis rate if the target site is vacant. The internal orientation of the particle can also change to any of the other three with a constant rate $ω.$ The dynamics of the model in $ω\to \infty$ reduces to that of the Lattice Gas (LG) which exhibits a phase separation transition at particle density $ρ=\frac12$ and temperature $T=1,$ when the strength of attraction $J$ crosses a threshold value $\ln(1+ \sqrt{2}).$ This transition belongs to Ising universality class. For any finite $ω>0,$ the particles can be considered as attractive run-and-tumble particles (RTPs) in two dimensions with motility $ω^{-1}.$ We find that RTPs also exhibit a phase separation transition, but the critical interaction required is $J_c(ω)$ which increases monotonically with increased motility $ω^{-1}.$ It appears that the transition belongs to Ising universality class. Surprisingly, in these models, motility impedes cluster formation process necessitating higher interaction to stabilize microscopic clusters. Moreover, MIPS like phases are not found when $J=0.$

cond-mat.stat-mech↗

arXiv2024

(Un)buckling mechanics of epithelial monolayers under compression

When cell sheets fold during development, their apical or basal surfaces constrict and cell shapes approach the geometric singularity in which these surfaces vanish. Here, we reveal the mechanical consequences of this geometric singularity for tissue folding in a minimal vertex model of an epithelial monolayer. In simulations of the buckling of the epithelium under compression and numerical solutions of the corresponding continuum model, we discover an "unbuckling" bifurcation: At large compression, the buckling amplitude can decrease with increasing compression. By asymptotic solution of the continuum equations, we reveal that this bifurcation comes with a large stiffening of the epithelium. Our results thus provide the mechanical basis for absorption of compressive stresses by tissue folds such as the cephalic furrow during germband extension in Drosophila.

cond-mat.soft↗