Classical emergence of the quantum-backreacted BTZ black hole from exponential electrodynamics

In this work, we revisit a recently reported generalization of the Bañados-Teitelboim-Zanelli black hole arising in New Massive Gravity sourced by the quantum fluctuations of scalar matter, now examined through the lens of a purely classical framework. We show that the same geometry, distinguished by its logarithmic asymptotic structure, emerges as the unique static solution of Einstein gravity coupled to an exponential nonlinear electrodynamics. We trace the origin of this correspondence and prove that this geometry belongs to a unique class of metrics constituting the intersection of the moduli spaces of the static and circularly symmetric sectors of the two theories, thereby revealing a dynamical equivalence between them. An explicit mapping is established between the global charges of the nonlinearly charged black holes and the parameters governing the quantum backreaction in New Massive Gravity, allowing for a natural reinterpretation of the quantum imprints in terms of classical charges. A detailed analysis of the horizon structure of these spacetimes is presented. In addition, the full thermodynamics of the more general configurations is constructed using the Iyer-Wald formalism, from which we derive the first law and the associated Smarr relation. Altogether, our results provide a classical realization of a semiclassical spacetime and point toward a broader correspondence between higher-curvature corrections in quantum gravity and nonlinear effects in self-gravitating electrodynamics in three dimensions.

💡 Research Summary

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In this paper the authors revisit a recently discovered quantum‑backreacted BTZ black‑hole solution that arises in New Massive Gravity (NMG) when a large number of conformally coupled scalar fields are quantized on the BTZ background. In the semiclassical treatment the renormalized expectation value of the scalar stress‑tensor ⟨T_{μν}⟩ sources the higher‑curvature terms of NMG, leading to a static metric that deviates from the usual AdS₃ asymptotics by a logarithmic term. The metric reads

ds² = –f(r)dt² + dr²/f(r) + r²dφ²,

f(r) = r²/ℓ² – M + 2Nℓ_p F(M) M/ℓ²