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| Format: | Preprint |
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2022
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| Online Access: | https://arxiv.org/abs/2209.11995 |
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| _version_ | 1866914708337983488 |
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| author | Chakraborty, Tanmoy Pradhan, Punyabrata |
| author_facet | Chakraborty, Tanmoy Pradhan, Punyabrata |
| contents | We characterize collective diffusion of hardcore run-and-tumble particles (RTPs) by explicitly calculating the bulk-diffusion coefficient $D(ρ, γ)$ in two minimal models on a $d$ dimensional periodic lattice for arbitrary density $ρ$ and tumbling rate $γ$. We focus on two models: Model I is the standard version of hardcore RTPs [Phys. Rev. E \textbf{89}, 012706 (2014)], whereas model II is a long-ranged lattice gas (LLG) with hardcore exclusion - an analytically tractable variant of model I; notably, both models are found to have qualitatively similar features. In the strong-persistence limit $γ\rightarrow 0$ (i.e., dimensionless $r_0 γ/v \rightarrow 0$), with $v$ and $r_{0}$ being the self-propulsion speed and particle diameter, respectively, the fascinating interplay between persistence and interaction is quantified in terms of two length scales - mean gap, or "mean free path", and persistence length $l_{p}=v/ γ$. Indeed, for a small tumbling rate, the bulk-diffusion coefficient varies as a power law in a wide range of density: $D \propto ρ^{-α}$, with exponent $α$ gradually crossing over from $α= 2$ at high densities to $α= 0$ at low densities. Thus, the density relaxation is governed by a nonlinear diffusion equation with anomalous spatiotemporal scaling. Moreover, in the thermodynamic limit, we show that the bulk-diffusion coefficient - for $ρ,γ\rightarrow 0$ with $ρ/γ$ fixed - has a scaling form $D(ρ, γ) = D^{(0)}\mathcal{F}(ψ=ρa v/γ)$, where $a\sim r_{0}^{d-1}$ is particle cross-section and $D^{(0)}$ is proportional to the diffusivity of noninteracting particles; the scaling function $\mathcal{F}(ψ)$ is calculated analytically for model I and numerically for model II. Our arguments are independent of dimensions and microscopic details. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2209_11995 |
| institution | arXiv |
| publishDate | 2022 |
| record_format | arxiv |
| spellingShingle | Time-dependent properties of run-and-tumble particles: Density relaxation Chakraborty, Tanmoy Pradhan, Punyabrata Statistical Mechanics Soft Condensed Matter We characterize collective diffusion of hardcore run-and-tumble particles (RTPs) by explicitly calculating the bulk-diffusion coefficient $D(ρ, γ)$ in two minimal models on a $d$ dimensional periodic lattice for arbitrary density $ρ$ and tumbling rate $γ$. We focus on two models: Model I is the standard version of hardcore RTPs [Phys. Rev. E \textbf{89}, 012706 (2014)], whereas model II is a long-ranged lattice gas (LLG) with hardcore exclusion - an analytically tractable variant of model I; notably, both models are found to have qualitatively similar features. In the strong-persistence limit $γ\rightarrow 0$ (i.e., dimensionless $r_0 γ/v \rightarrow 0$), with $v$ and $r_{0}$ being the self-propulsion speed and particle diameter, respectively, the fascinating interplay between persistence and interaction is quantified in terms of two length scales - mean gap, or "mean free path", and persistence length $l_{p}=v/ γ$. Indeed, for a small tumbling rate, the bulk-diffusion coefficient varies as a power law in a wide range of density: $D \propto ρ^{-α}$, with exponent $α$ gradually crossing over from $α= 2$ at high densities to $α= 0$ at low densities. Thus, the density relaxation is governed by a nonlinear diffusion equation with anomalous spatiotemporal scaling. Moreover, in the thermodynamic limit, we show that the bulk-diffusion coefficient - for $ρ,γ\rightarrow 0$ with $ρ/γ$ fixed - has a scaling form $D(ρ, γ) = D^{(0)}\mathcal{F}(ψ=ρa v/γ)$, where $a\sim r_{0}^{d-1}$ is particle cross-section and $D^{(0)}$ is proportional to the diffusivity of noninteracting particles; the scaling function $\mathcal{F}(ψ)$ is calculated analytically for model I and numerically for model II. Our arguments are independent of dimensions and microscopic details. |
| title | Time-dependent properties of run-and-tumble particles: Density relaxation |
| topic | Statistical Mechanics Soft Condensed Matter |
| url | https://arxiv.org/abs/2209.11995 |