arXiv subjects

Nathan O. Silvano

Publications and source records attributed to Nathan O. Silvano.

6 recordsLinked to original sources

arXiv2026

Impact of fluctuations on particle systems described by Dean-Kawasaki-type equations

We study the role of fluctuations in particle systems modeled by Dean-Kawasaki-type equations, which describe the evolution of particle densities in systems with Brownian motion. By comparing microscopic simulations, stochastic partial differential equations, and their deterministic counterparts, we analyze four models of increasing complexity. Our results identify macroscopic quantities that can be altered by the conserved multiplicative noise that typically appears in the Dean-Kawasaki-type description. We find that this noise enhances front propagation speed in systems with density-dependent diffusivity, accelerates the onset of pattern formation in particle systems with nonlocal interactions, and reduces hysteresis in systems interacting via repulsive forces. In some cases, it accelerates transitions or induces structures absent in deterministic models. These findings illustrate that (conservative) fluctuations can have constructive and nontrivial effects, emphasizing the importance of stochastic modeling in understanding collective particle dynamics.

cond-mat.stat-mech↗

arXiv2025

Flow spatial structure determines pattern instabilities in nonlocal models of population dynamics

We investigate how environmental flows influence spatial pattern formation and population dynamics using two nonlocal models of population dynamics, which we couple to two different stationary flows. Combining numerical simulations and analytical approximations, we show that the spatial structure of the flow's velocity field determines the pattern formation instability. For a simple shear flow, where one of the primary axes of the population pattern can become aligned with the flow, the onset of pattern formation remains unaffected. In contrast, a vortex flow delays the pattern instability relative to the no-flow case. The velocity field, therefore, interacts with the spatial feedbacks responsible for pattern formation in complex ways, which also leads to different oscillatory time series of population abundance. In some cases, the population undergoes regular oscillations with a characteristic frequency, while in others, the dynamics exhibits long erratic transients with no well-defined period before settling into a more regular behavior.

q-bio.PE↗

arXiv2024

Laser induced $\mathcal{PT}$-symmetry breaking in the fluctuations of electronic fluids

Electronic fluids can display exciting dynamical properties. In particular, due to Landau damping, the collective modes spectrum of an electronic system with multipolar interactions is non-hermitian, and can present non-hermitian degeneracies called $\textit{exceptional points}$. In this work, we want to explore the dynamical properties of these degeneracies using laser control. We show that by using a light pulse, we can control the collective mode spectrum and tune a non-hermitian $\mathcal{PT}$ phase transition in which two exceptional points anhilate each other. At this transition, the gap closes with a cubic root signature, what defines a third order exceptional point.

cond-mat.str-el↗

arXiv2024

Emergent Gauge Symmetry in Active Brownian Matter

We investigate a two-dimensional system of interacting Active Brownian Particles. Using the Martin-Siggia-Rose-Janssen-de Dominicis formalism, we built up the generating functional for correlation functions. We study in detail the hydrodynamic regime with a constant density stationary state. Our findings reveal that, within a small density fluctuations regime, an emergent $U(1)$ gauge symmetry arises, originated from the conservation of fluid vorticity. Consequently, the interaction between the orientational order parameter and density fluctuations can be cast into a gauge theory, where the concept of ``electric charge density" aligns with the local vorticity of the original fluid. We study in detail the case of a microscopic local two-body interaction. We show that, upon integrating out the gauge fields, the stationary states of the rotational degrees of freedom satisfy a non-local Frank free energy for a nematic fluid. We give explicit expressions for the splay and bend elastic constants as a function of the Péclet number (${\rm Pe}$) and the diffusion interaction constant ($k_d$).

cond-mat.stat-mech↗

arXiv2023

The role of multiplicative noise in critical dynamics

We study the role of multiplicative stochastic processes in the description of the dynamics of an order parameter near a critical point. We study equilibrium, as well as, out-of-equilibrium properties. By means of a functional formalism, we built the Dynamical Renormalization Group equations for a real scalar order parameter with $Z_2$ symmetry, driven by a class o multiplicative stochastic processes with the same symmetry. We have computed the flux diagram, using a controlled $ε$-expansion, up to order $ε^2$. We have found that, for dimensions $d=4-ε$, the additive dynamic fixed point is unstable. The flux runs to a {\em multiplicative fixed point} driven by a diffusion function $G(ϕ)=1+g^*ϕ^2({\bf x})/2$, where $ϕ$ is the order parameter and $g^*=ε^2/18$ is the fixed point value of the multiplicative noise coupling constant. We show that, even though the position of the fixed point depends on the stochastic prescription, the critical exponents do not. Therefore, different dynamics driven by different stochastic prescriptions (such as Itô, Stratonovich, anti-Itô and so on) are in the same universality class.

cond-mat.stat-mech↗

arXiv2021

Critical Dynamics: multiplicative noise fixed point in two dimensional systems

We study the critical dynamics of a real scalar field in two dimensions near a continuous phase transition. We have built up and solved Dynamical Renormalization Group equations at one-loop approximation. We have found that, different form the case $d\lesssim 4$, characterized by a Wilson-Fisher fixed point with dynamical critical exponent $z=2+ O(ε^2)$, the critical dynamics is dominated by a novel multiplicative noise fixed point. The zeroes of the beta function depend on the stochastic prescription used to define the Wiener integrals. However, the critical exponents and the anomalous dimension do not depend on the prescription used. Thus, even though each stochastic prescription produces different dynamical evolutions, all of them are in the same universality class.

cond-mat.stat-mech↗