arXiv subjects

M. Alakhras

Publications and source records attributed to M. Alakhras.

2 recordsLinked to original sources

arXiv2025

Graph-based Summary Statistics for Revealing the Stochastic Gravitational Wave Background in Pulsar Timing Arrays

In this work, we propose a graph-based method implemented on the pulsar timing residuals (PTRs) for stochastic gravitational wave background (SGWB) detection within the nano-Hertz frequency regime and examining uncertainties of its parameters. We construct a correlation graph with pulsars as its nodes, and analyze the graph-based summary statistics, including structural characteristics of complex network, for identifying SGWB in the real and synthetic datasets. The effect of the number of pulsars, the observation time span, and the strength of the SGWB on the graph-based feature vector is evaluated. Our results demonstrate that the Discriminative Summary Statistics for common signal detection consists of the average clustering coefficient and the edge weight fluctuation. The SGWB detection conducted after the observation of a common signal and then exclusion of non-Hellings \& Downs templates is performed by the second cumulant of edge weight for angular separation thresholds $\bar{\zeta}\gtrsim 40^{\circ}$. The lowest detectable value of SGWB strain amplitude utilizing our graph-based measures at the current PTAs sensitivity is $A_{\rm SGWB}\gtrsim 1.2\times 10^{-15}$. Fisher forecasts confirmed that the uncertainty levels of $\log_{10} A_{\rm SGWB}$ and spectral index reach $1.5\%$ and $19.5\%$, respectively, at $2\sigma$ confidence interval. A weak evidence for an SGWB at $\sim 2.3\sigma$ level is obtained by applying our graph-based method to the NANOGrav 15-year dataset.

astro-ph.CO↗

arXiv2025

Cosmic Strings-induced CMB anisotropies in light of Weighted Morphology

Motivated by the morphological measures in assessing the geometrical and topological properties of a generic cosmological stochastic field, we propose an extension of the weighted morphological measures, specifically the $n$th conditional moments of derivative (cmd-$n$). This criterion assigns a distinct weight to each excursion set point based on the associated field. We apply the cmd-$n$ on the Cosmic Microwave Background (CMB) to identify the cosmic string networks (CSs) through their unique Gott-Kaiser-Stebbins effect on the temperature anisotropies. We also formulate the perturbative expansion of cmd-$n$ for the weak non-Gaussian regime up to $\mathcal{O}(\sigma_0^3)$. We propose a comprehensive pipeline designed to analyze the morphological properties of string-induced CMB maps within the flat sky approximation. To evaluate the robustness of our proposed criteria, we employ string-induced high-resolution flat-sky CMB simulated patches of $7.2$ deg$^2$ size with a resolution of $0.42$ arc-minutes. Our results demonstrate that the minimum detectable value of cosmic string tension is $G\mu\gtrsim 1.9\times 10^{-7}$ when a noise-free map is analyzed with normalized cmd-$n$. Whereas for the ACT, CMB-S4, and Planck-like experiments at 95.45\% confidence level, the normalized cmd-$n$ can distinguish the CSs network for $G\mu\gtrsim2.9 \times 10^{-7}$, $G\mu\gtrsim 2.4\times 10^{-7}$ and $G\mu\gtrsim 5.8\times 10^{-7}$, respectively. The normalized cmd-$n$ exhibits a significantly enhanced capability in detecting CSs relative to the Minkowski Functionals.

astro-ph.CO↗