Novel higher-dimensional regular black holes in general relativity coupled to nonlinear electrodynamics
We present a formalism for constructing higher-dimensional regular black holes in general relativity coupled to nonlinear electrodynamics, and propose a new class of electrically charged solutions that unifies the Bardeen and Hayward models in a single analytic form valid for any $D\geq4$. The Bardeen and Hayward solutions are shown to have a correct Maxwellian weak-field limit in five and six dimensions, respectively. The matter sector is written as a Hamiltonian density $\mathcal{H}(P)$ containing only fixed coupling constants, so that the mass and the charge enter as integration constants. The resulting theory has a two-parameter family of solutions, of which a one-parameter subfamily is regular, with the mass tied to the charge. We locate the radius at which the Lagrangian $Ł(F)$ splits into two branches and show that it is always hidden inside the horizon for $D=4$ but can lie outside it near extremality for $D\geq5$. The null and weak energy conditions hold everywhere, while the strong energy condition is violated near the core. Building on our recent result that the first law holds in its standard form once the theory is fixed, we derive the horizon potential in closed form, the extended first law with the couplings as thermodynamic variables, and a generalized Smarr formula.