Thermodynamic Topology, Photon Spheres, and Evidence for Weak Gravity Conjecture in Charged Black Holes with Perfect Fluid within Rastall Theory

Abstract: In this paper, we explore the Weak Gravity Conjecture (WGC) within the context of photon spheres in charged black holes, framed by Perfect Fluid in Rastall Theory. We aim to validate the WGC by identifying the extremality states of these black holes. We highlight the interplay between quantum dynamics and gravitational forces, opening new avenues in high-energy physics and quantum gravity. Our analysis reveals significant system changes with varying perfect fluid intensity $(\alpha)$ and Rastall parameters ( $k$ and $\lambda$ ). For dust field $(\omega=0)$, the WGC is met in extremality $(T=0)$ with $(Q / M)_{\text {ext }}>1$, indicating a black hole due to the presence of photon spheres (PS) with a total charge-1. However, further increases in $k$ and $\lambda$ or decreases $(\alpha)$ lead to $P S=0$ that determines a singularity, not a black hole. We observed that the radiation field $(\omega=1 / 3)$, quintessence field ( $\omega=-2 / 3$ ), and phantom fields field ( $\omega=-4 / 3$ ) also confirmed the WGC and maintaining a total charge of $P S=-1$ in some regions of the free parameters. Our numerical solutions identify points satisfying the WGC, establishing a bridge between quantum and cosmic realms. The results are summarized in Table (I). We also examine Duans topological current $\phi$-mapping theory by analyzing generalized Helmholtz free energy methods to study the topological classes of our black hole. We reveal that for given values of the free parameters, the total topological numbers $(W=0)$ exist for the generalized Helmholtz free energy method for $\omega=0,1 / 3,-2 / 3,-4 / 3$.