Energy Extraction via Magnetic Reconnection from a Rotating Dyonic Black Hole in $N=2,U(1{)}^2$ Gauged Supergravity

Abstract

We study energy extraction via magnetic reconnection from a rotating dyonic black hole in four-dimensional $N=2$, $U(1{)}^2$ gauged supergravity. Using the Comisso-Asenjo mechanism in the ZAMO frame, we derive the asymptotic hydrodynamic energy per unit enthalpy ${\epsilon }_{\pm }^{\infty }$ and determine when reconnection outflows attained negative energy at infinity. By varying the spin $a$, electric and magnetic charges, NUT parameter $N_g$, and gauge coupling $g$, we compute the cutoff magnetization ${\sigma }_0^{\mathrm{cutoff}}$ and map the region of parameter space that admits ${\epsilon }_{-}^{\infty }<0$. We find that ${\sigma }_0^{\mathrm{cutoff}}$ and the very existence of Comisso-Asenjo extraction are tightly controlled by $g$ and the dyonic charges: increasing $g$ or pushing the charges toward extremality raises ${\sigma }_0^{\mathrm{cutoff}}$ and shrinks the CA-active part of the ergoregion. Unlike Kerr, the spin enters through the normalization factor $\Xi$, and the quartic horizon function ${\Delta }_g$, so geometric effects from the AdS/NUT deformation dominate the usual frame-dragging enhancement. As a result, the extracted power and efficiency are non-monotonic in $a$ and peak at intermediate spin ($a\sim 0.8$); near-extremal rotation is not required for high efficiency, provided $g$ is small and $Q$ is moderate. Efficient extraction further demands extreme magnetization and nearly radial outflows, confining the active reconnection layer to a thin shell, just outside the horizon.

25 pages, 14 figures