arXiv subjects

Lucas Sigaud

Publications and source records attributed to Lucas Sigaud.

5 recordsLinked to original sources

arXiv2026

Nonequilibrium phase transitions in a racism-spreading model with interaction-driven dynamics

Racism remains a persistent societal issue, increasingly amplified by the structure and dynamics of online social networks. In this work, we propose a three-state compartmental model to study the spreading and suppression of racist content, drawing from epidemic-like dynamics and interaction-driven transitions. We analyze the model on fully-connected (homogeneous mixing) networks using a set of coupled differential equations, and on Barab\'asi-Albert (BA) scale-free and Watts-Strogatz (WS) small-world networks through agent-based simulations. The system exhibits three distinct stationary regimes: two racism-free absorbing states and one active phase with persistent racist content. We identify and characterize the phase transitions between these regimes, discuss the role of network topology, and highlight the emergence of absorbing states. Our findings illustrate how statistical physics tools can help uncover the macroscopic consequences of microscopic social interactions in digital environments.

physics.soc-ph↗

arXiv2025

A Statistical Physics perspective on fairness in shared expenses: The bar bill analogy

In social contexts where individuals consume varying amounts, such as shared meals or bar gatherings, splitting the total bill equally often yields surprisingly fair outcomes. In this work, we develop a statistical physics framework to explain this emergent fairness by modeling individual consumption as stochastic variables drawn from a realistic distribution, specifically the gamma distribution. Introducing a Boltzmann-like weighting factor, we derive exact analytical expressions for the partition function, average consumption, variance, and entropy under economic or social penalization constraints. Numerical simulations, performed using the Marsaglia-Tsang algorithm, confirm the analytical results with high precision. Drawing a direct parallel between individual consumption and ideal gas particle energy in the canonical ensemble, we show how the law of large numbers, mutual compensation, and the effective ordering induced by penalization combine to make equal cost-sharing statistically robust and predictable. These findings reveal that what appears to be an informal social convention is, in fact, grounded in the same fundamental principles that govern the collective behavior of particles in thermodynamic systems, highlighting the interdisciplinary power of statistical physics.

physics.soc-ph↗

arXiv2022

Role of inflexible minorities in the evolution of alcohol consumption

In this work we study a simple contagion model for drinking behavior evolution, but including the presence of inflexible or zealot agents, i.e., individuals that never change their behavior (never drink or always drink a lot). We analyze the impact of such special agents in the evolution of drinking behavior in the population. Our analytical and numerical results indicate that the presence of only one class of inflexible agents destroys one of the two possible absorbing phases that are observed in the model without such inflexibles. In the presence of the both kinds of inflexible agents simultaneously, there are no absorbing states anymore. Since absorbing states are collective macroscopic states with the presence of only one kind of individuals in the population, we argue that the inclusion of inflexible agents in the population makes the model more realistic. Furthermore, the presence of inflexible agents are similar to the introduction of quenched disorder in the model, and here we observe the suppression of a nonequilibrium phase transition to absorbing states, which had not been reported before.

physics.soc-ph↗

arXiv2021

Crime and COVID-19 in Rio de Janeiro: How does organized crime shape the disease evolution?

The city of Rio de Janeiro is one of the biggest cities in Brazil. Drug gangs and paramilitary groups called \textit{milícias} control some regions of the city where the government is not present, specially in the slums. Due to the characteristics of such two distinct groups, it was observed that the evolution of COVID-19 is different in those two regions, in comparison with the regions controlled by the government. In order to understand qualitatively those observations, we divided the city in three regions controlled by the government, by the drug gangs and by the \textit{milícias}, respectively, and we consider a SIRD-like epidemic model where the three regions are coupled. Considering different levels of exposure, the model is capable to reproduce qualitatively the distinct evolution of the COVID-19 disease in the three regions, suggesting that the organized crime shapes the COVID-19 evolution in the city of Rio de Janeiro. This case study suggests that the model can be used in general for any metropolitan region with groups of people that can be categorized by their level of exposure.

physics.soc-ph↗

arXiv2021

Modeling the evolution of drinking behavior: A Statistical Physics perspective

In this work we study a simple compartmental model for drinking behavior evolution. The population is divided in 3 compartments regarding their alcohol consumption, namely Susceptible individuals $S$ (nonconsumers), Moderate drinkers $M$ and Risk drinkers $R$. The transitions among those states are ruled by probabilities. Despite the simplicity of the model, we observed the occurrence of two distinct nonequilibrium phase transitions to absorbing states. One of these states is composed only by Susceptible individuals $S$, with no drinkers ($M=R=0$). On the other hand, the other absorbing state is composed only by Risk drinkers $R$ ($S=M=0$). Between these two steady states, we have the coexistence of the three subpopulations $S$, $M$ and $R$. Comparison with abusive alcohol consumption data for Brazil shows a good agreement between the model's results and the database.

physics.soc-ph↗