arXiv subjects

Youness Diouane

Publications and source records attributed to Youness Diouane.

6 recordsLinked to original sources

arXiv2026

Modeling Perpetrators' Fate-to-Fate Contagion in Public Mass Shootings In The United States Using Bivariate Hawkes Processes

This study examines how the fate of a perpetrator in a public mass shooting influences the fate of subsequent perpetrators. Using data from 1966 to 2024, we classify incidents according to whether the perpetrator died at the scene or survived the attack. Using a bivariate Hawkes process, we quantify the cross-excitation effect, which is the triggering effect that each event type exerts on the other, i.e., "die at the scene"$\rightarrow$ "live" and "live"$\rightarrow$ "die at the scene", as well as the self-excitation effects, i.e., "die at the scene"$\rightarrow$ "die at the scene" and "live"$\rightarrow$ "live". Our results show that the strongest spillover was from "live" incidents to "die at the scene", where we estimate that 0.34 (0.09, 0.80) of "die at the scene" incidents are triggered by a prior event in which the offender survived the attack. This pathway also exhibits the longest estimated contagion timescale: approximately 20 days. In contrast, the reverse influence, that is, "die at the scene"$\rightarrow$"live", is not statistically significant, with the lower bound of its 95% confidence interval nearly equal to zero. We also find that "die at the scene" events can only cause their own type, where 0.139 (0.01, 0.52) of such incidents are caused by previous "die at the scene" events, with the shortest contagion timescale of roughly 20 hours.

cs.SI↗

arXiv2023

Critical points in coupled Potts models and correlated percolation

We use scale invariant scattering theory to exactly determine the renormalization group fixed points of a $q$-state Potts model coupled to an $r$-state Potts model in two dimensions. For integer values of $q$ and $r$ the fixed point equations are very constraining and show in particular that scale invariance in coupled Potts ferromagnets is limited to the Ashkin-Teller case ($q=r=2$). Since our results extend to continuous values of the number of states, we can access the limit $r\to 1$ corresponding to correlated percolation, and show that the critical properties of Potts spin clusters cannot in general be obtained from those of Fortuin-Kasteleyn clusters by analytical continuation.

cond-mat.stat-mech↗

arXiv2022

On the $RP^{N-1}$ and $CP^{N-1}$ universality classes

We recently determined the exact fixed point equations and the spaces of solutions of the two-dimensional $RP^{N-1}$ and $CP^{N-1}$ models using scale invariant scattering theory. Here we discuss subtleties hidden in some solutions and related to the difference between ferromagnetic and antiferromagnetic interaction.

cond-mat.stat-mech↗

arXiv2021

Critical points in the $CP^{N-1}$ model

We use scale invariant scattering theory to obtain the exact equations determining the renormalization group fixed points of the two-dimensional $CP^{N-1}$ model, for $N$ real. Also due to special degeneracies at $N=2$ and 3, the space of solutions for $N\geq 2$ reduces to that of the $O(N^2-1)$ model, and accounts for a zero temperature critical point. For $N<2$ the space of solutions becomes larger than that of the $O(N^2-1)$ model, with the appearance of new branches of fixed points relevant for criticality in gases of intersecting loops.

cond-mat.stat-mech↗

arXiv2021

Critical points in the $RP^{N-1}$ model

The space of solutions of the exact renormalization group fixed point equations of the two-dimensional $RP^{N-1}$ model, which we recently obtained within the scale invariant scattering framework, is explored for continuous values of $N\geq 0$. Quasi-long-range order occurs only for $N=2$, and allows for several lines of fixed points meeting at the BKT transition point. A rich pattern of fixed points is present below $N^*=2.24421..$, while only zero temperature criticality in the $O(N(N+1)/2-1)$ universality class can occur above this value. The interpretation of an extra solution at $N=3$ requires the identitication of a path to criticality specific to this value of $N$.

cond-mat.stat-mech↗

arXiv2021

Absence of nematic quasi-long-range order in two-dimensional liquid crystals with three director components

The Lebwohl-Lasher model describes the isotropic-nematic transition in liquid crystals. In two dimensions, where its continuous symmetry cannot break spontaneously, it is investigated numerically since decades to verify, in particular, the conjecture of a topological transition leading to a nematic phase with quasi-long-range order. We use scale invariant scattering theory to exactly determine the renormalization group fixed points in the general case of $N$ director components ($RP^{N-1}$ model), which yields the Lebwohl-Lasher model for $N=3$. For $N>2$ we show the absence of quasi-long-range order and the presence of a zero temperature critical point in the universality class of the $O(N(N+1)/2-1)$ model. For $N=2$ the fixed point equations yield the Berezinskii-Kosterlitz-Thouless transition required by the correspondence $RP^1\sim O(2)$.

cond-mat.stat-mech↗