Thermodynamics, topology and non-Abelian instability of the five-dimensional Einstein--Yang--Mills black hole with exponential entropy correction

Abstract

The five-dimensional Einstein--Yang--Mills black hole obtained from the higher-dimensional Wu--Yang ansatz carries a logarithmic non-Abelian contribution to the metric function, making it an analytically tractable setting for studying how gauge charge reshapes horizon thermodynamics beyond four dimensions. We derive expressions for the mass--radius relation, the Hawking temperature, the entropy, the Yang--Mills potential and the first law, and record the curvature invariants, which show that the logarithm sharpens the central singularity rather than smoothing it. A non-perturbative exponential entropy correction is then added, and the corrected heat capacity and free energies are obtained analytically. The geometry is extremal at $r_h=|Q|$ and the heat capacity diverges at $r_h=\sqrt{3}|Q|$, a Davies-type point. The correction moves that point inward, $r_{\mathrm{tr}}/|Q|\simeq \sqrt{3}-9\lambda \alpha \eta e^{-3\sqrt{3}\lambda }$. Using the generalized off-shell free energy we find a conserved topological charge $W=0$ carried by a stable--unstable defect pair whose inner member alone responds to the correction. We then solve the spherically symmetric magnetic Yang--Mills perturbation sector, which probes the gauge field itself rather than a test scalar. Two independent numerical schemes agree to better than $1.2\times 10^{-7}$ and give a purely imaginary unstable mode whose growth rate falls monotonically from ${\Gamma }_0{r}_h=0.414753$ at $Q/r_h\to 0$ to $0.317520$ at $Q/r_h=0.99$, passing through the Davies scale without any feature. Because the effective potential decays as $-9/(4r_{\ast }^2)$, with a coefficient above the critical value $1/4$, the sector supports an infinite geometric tower of unstable modes accumulating at $\Gamma \to 0$ with the charge-independent ratio ${\Gamma }_{n+1}/{\Gamma }_n\to e^{-\pi /\sqrt{2}}\simeq 0.108453$, which we confirm numerically.