The accretion disk and neutrino pair annihilation process of Barrow-modified Black Hole

This paper attempts to clarify the deep consequences of Barrow fractal black hole spacetime configurations caused by quantum gravity on neutrino pair annihilation and accretion disk dynamics. We systematically derive the analytical expression for the innermost stable circular orbit (ISCO) radius ($r_{\text{ISCO}}\propto M^{2/(2+\Delta)}$) by building a Barrow-modified static spherically symmetric metric ($r\rightarrow r^{1+\Delta/2}$), and we find that increasing $\Delta$ significantly shifts the ISCO inward. We numerically solve the radiation flux, effective temperature, and differential luminosity distribution under the modified metric based on the Novikov-Thorne relativistic thin accretion disk model. For $\Delta=1$, the results show that the temperature increases by $62.5\%$, the peak disk radiation flux increases by $22.5\%$, and the spectral radiance increases by around $50\%$. Fractal horizons enhance neutrino trajectory bending effects, according to further study of neutrino pair annihilation ($\nu\bar{\nu}\rightarrow e^+e^-$) energy deposition processes using local Lorentz transformations and null geodesic equations. The energy deposition rate for $\Delta=1$ is $8-28$ times higher than classical estimates when the black hole radius is $R/M\sim3-4$. This work provides important theoretical insights into the influence of quantum spacetime geometry on high-energy astrophysical phenomena in extreme gravitational fields by establishing, for the first time, quantitative relationships between the Barrow parameter $\Delta$ and neutrino pair annihilation energy and accretion disk radiative efficiency.