arXiv subjects

Reza Jafari

Publications and source records attributed to Reza Jafari.

5 recordsLinked to original sources

arXiv2026

Impact of Higher-Order Interactions on Collective Motion

Collective motion in self-propelled particle systems has been widely studied using the Vicsek model, which relies on pairwise alignment interactions. We introduce a generalized Vicsek model that incorporates higher-order (triadic) alignment interactions. Using agent-based simulations and mean-field theory, we demonstrate that pure triadic alignment induces a discontinuous phase transition, evidenced by hysteresis, a double-well free-energy landscape, and a Binder cumulant minimum that deepens with system size, whereas the standard pairwise model exhibits a continuous transition at the same system sizes. We further show that higher-order interactions require higher particle densities to sustain collective order and produce sharper fluctuation peaks near the transition with lower critical noise. These results establish that the microscopic structure of the alignment interaction, whether pairwise or many-body, is an independent control parameter for the order of the phase transition in active matter, with implications for understanding collective behavior in biological and synthetic systems.

physics.bio-ph↗

arXiv2025

Solving the MIT Inverse Problem by Considering Skin and Proximity Effects in Coils

This paper presents an improved technique for solving the inverse problem in magnetic induction tomography (MIT) by considering skin and proximity effects in coils. MIT is a non-contact, noninvasive, and low-cost imaging modality for obtaining the distribution of conductivity inside an object. Reconstruction of low conductivity distribution by MIT requires more accurate techniques since measured signals are inherently weak and the reconstruction problem is highly nonlinear and ill-posed. Previous MIT inverse problem studies have ignored skin and proximity effects inside coils in the forward method. In this article, the improved technique incorporates these effects in the forward method. Furthermore, it employs the regularized Gauss-Newton algorithm to reconstruct the conductivity distribution. The regularization parameter is obtained by an adaptive method using the two input parameters: a coefficient and an initial conductivity distribution. The new Jacobian matrix is computed based on a standard technique. To compare the early and improved forward methods in possible medical and industrial applications with low conductivity regions, a 2D 8-coil MIT system is modeled, and image reconstruction is performed for synthetic phantoms. Results show that it is crucial to use the improved forward method for the reconstruction of the absolute conductivity values.

physics.med-ph↗

arXiv2024

Stability of Brain Functional Network During Working Memory Using Structural Balance Theory

Working memory plays a crucial role in various aspects of human life. Therefore, it has been an area of interest in different research studies, especially neuroscience. The neuroscientists investigating working memory have primarily emphasized the brain's functional modularity. At the same time, a holistic perspective is still required to investigate the brain as an integrated and unified system. We hypothesized that the brain should shift towards a more stable state during working memory than the resting state. Therefore, based on the Structural Balance Theory (SBT), we aimed to address this process. To achieve this, we examined triadic associations in signed fMRI networks in healthy individuals using the N-back as the working memory task. We demonstrated that the number of balanced triads increased during the working memory task compared to the resting state, while the opposite is true for imbalanced triads. The increase of balanced triads forced the network to a more stable state with a lower balance energy level. The increase of balanced triads was crucially related to changes in anti-synchrony to synchronous activities between the Temporal Cortex, the Prefrontal Cortex, and the Parietal Cortex, which are known to be involved in various aspects of working memory, during the working memory process. We hope these findings pave the way to a better understanding the working memory process.

q-bio.NC↗

arXiv2024

Exploring non-standard $Hb\bar{b}$ interactions at future electron-proton colliders

In this paper, we use the charged-current Higgs boson production process at future electron-proton colliders, $e^-p \to H j ν_e$, with the subsequent decay of the Higgs boson into a $b\bar{b}$ pair, to probe the Standard Model effective field theory with dimension-six operators involving the Higgs boson and the bottom quark. The study is performed for two proposed future high-energy electron-proton colliders, the Large Hadron Electron Collider (LHeC) and the Future Circular Collider (FCC-he) at the center-of-mass energies of 1.3 TeV and 3.46 TeV, respectively. Constraints on the CP-even and CP-odd $Hb\bar{b}$ couplings are derived by analyzing the simulated signal and background samples. A realistic detector simulation is performed and a multivariate technique using the gradient Boosted Decision Trees algorithm is employed to discriminate the signal from background. Expected limits are obtained at $95\%$ Confidence Level for the LHeC and FCC-he assuming the integrated luminosities of 1, 2 and 10 ab$^{-1}$. We find that using 1 ab$^{-1}$ of data, the CP-even and CP-odd $Hb\bar{b}$ couplings can be constrained with accuracies of the order of $10^{-3}$ and $10^{-2}$, respectively, and a significant region of the unprobed parameter space becomes accessible.

hep-ph↗

arXiv2020

Constraining the top quark effective field theory using the top quark pair production in association with a jet at future lepton colliders

Our main aim in this paper is to constrain the effective field theory describing the top quark couplings through the $e^{-} e^{+} \rightarrow t \bar{t}+$jet process. The analysis is carried out considering two different center-of-mass energies of 500 and 3000 GeV including a realistic simulation of the detector response and the main sources of background processes. The expected limits at 95\% CL are derived on the new physics couplings such as $t \bar t γ$, $t \bar t Z$, and $t \bar t g$ for each benchmark scenario using the dileptonic $t \bar{t}$ final state. We show that the 95\% CL limits on dimensionless Wilson coefficients $\bar{c}_i$ considered in this analysis could be probed down to $10^{-4}$.

hep-ph↗