3-dimensional charged black holes in f({Q}) gravity
Pith reviewed 2026-05-19 09:57 UTC · model grok-4.3
The pith
A novel charged black hole in three-dimensional f(Q) gravity has no continuous limit to the BTZ solution of general relativity.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The authors derive classes of spherically symmetric charged black hole solutions in f(Q) gravity. They find a novel charged solution that is asymptotically Anti-de Sitter but cannot be continuously deformed into a GR counterpart, arising purely from the higher-order nature of the non-metricity corrections. Geometrical properties include multiple horizons and a softer central singularity. Thermodynamic quantities confirm thermal stability, and geodesic analysis reveals stable photon orbits affected by the corrections.
What carries the argument
The cubic polynomial form of f(Q) in terms of the non-metricity scalar Q, which modifies the field equations to permit new black hole solutions not accessible in general relativity.
If this is right
- The new solutions possess multiple horizons.
- The central singularity is softer than in general relativity.
- Thermodynamic quantities such as Hawking temperature, entropy, and heat capacity confirm thermal stability.
- Geodesic motion features stable photon orbits, with the cubic corrections modifying the effective potentials.
Where Pith is reading between the lines
- Similar non-metricity-driven deviations from general relativity may appear in other modified gravity models or in higher dimensions.
- These solutions could serve as simplified test cases for studying quantum corrections to black hole thermodynamics in lower-dimensional gravity.
- The orbital dynamics changes suggest possible observable signatures in accretion or light deflection around such black holes.
Load-bearing premise
The assumption that a cubic polynomial form for f(Q) is sufficient to produce exact solutions while preserving the required symmetries and asymptotic behavior.
What would settle it
Demonstrating a continuous parameter path that connects the novel charged solution to the BTZ black hole while preserving asymptotic AdS behavior would falsify the claim that the solution arises purely from higher-order non-metricity corrections.
Figures
read the original abstract
We present new exact charged black hole solutions in (2+1) dimensions within the framework of $f({Q})$ gravity, where ${Q}$ denotes the non-metricity scalar. By considering a cubic $f({Q})$ form we derive classes of charged and uncharged spherically symmetric solutions, and we identify conditions under which these reduce to the well-known Banados-Teitelboim-Zanelli (BTZ) black hole. Notably, our analysis reveals a novel charged solution that is asymptotically Anti-de Sitter (AdS) but cannot be continuously deformed into a GR counterpart, and thus arising purely from the higher-order nature of the non-metricity corrections. Furthermore, we explore the geometrical properties of the solutions, demonstrating the existence of multiple horizons and a softer central singularity compared to GR. Additionally, we calculate various thermodynamic quantities, such as Hawking temperature, entropy, and heat capacity, with results confirming thermal stability. Finally, a detailed study of the geodesic motion and the effective potentials unveils stable photon orbits, as well as the effect of cubic non-metricity corrections on orbital dynamics.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript derives new exact charged and uncharged spherically symmetric black hole solutions in (2+1)-dimensional f(Q) gravity by adopting a cubic polynomial form for f(Q). It identifies conditions under which some solutions reduce to the BTZ black hole, while highlighting a novel asymptotically AdS charged solution that cannot be continuously deformed to a GR counterpart and thus arises purely from higher-order non-metricity corrections. The work further examines geometric features including multiple horizons and a softer central singularity, computes thermodynamic quantities (Hawking temperature, entropy, heat capacity) confirming thermal stability, and analyzes geodesic motion with stable photon orbits influenced by the cubic corrections.
Significance. If the central claim of a non-deformable novel solution holds after verification, the paper would contribute to modified gravity by exhibiting black hole solutions intrinsically tied to non-metricity corrections in three dimensions, offering potential distinctions from Einstein gravity in lower-dimensional spacetimes along with supporting analyses of thermodynamics and orbital dynamics.
major comments (2)
- [Section on novel charged solution] The section presenting the novel charged AdS solution: the claim that this solution 'cannot be continuously deformed into a GR counterpart' and 'arising purely from the higher-order nature of the non-metricity corrections' is load-bearing for the paper's main novelty. The derivation solves the modified equations for nonzero cubic coefficients and notes the solution vanishes at c=0, but without explicitly substituting the limiting metric functions into the f(Q)=Q (or 3D Einstein) equations and showing they fail to hold for any choice of mass/charge parameters, it remains possible that the limit recovers a BTZ solution with adjusted parameters. This explicit check is required to support the central assertion.
- [Field equations and exact solutions] The derivation of the field equations and solutions: full intermediate steps from the f(Q) action through the variation to the modified Einstein equations for the cubic f(Q) and the chosen metric ansatz are not fully visible, making it difficult to verify that the presented solutions satisfy the equations. Inclusion of these steps (or an appendix) is needed to confirm the solutions are exact.
minor comments (2)
- [Introduction or solutions section] The explicit form of the cubic polynomial f(Q) = aQ + bQ^2 + cQ^3 (or equivalent) and the meaning of its coefficients should be stated at the outset of the solutions section for notational clarity.
- [Geometrical properties and geodesics] Figure captions for horizon plots or effective potential diagrams should include the specific parameter values used (e.g., values of a, b, c, mass, charge) to allow reproducibility.
Simulated Author's Rebuttal
We thank the referee for the careful reading and constructive comments on our manuscript. We have addressed both major points by adding the requested explicit verification for the novel solution and including a full derivation appendix. These revisions strengthen the clarity and support for our central claims without altering the core results.
read point-by-point responses
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Referee: The section presenting the novel charged AdS solution: the claim that this solution 'cannot be continuously deformed into a GR counterpart' and 'arising purely from the higher-order nature of the non-metricity corrections' is load-bearing for the paper's main novelty. The derivation solves the modified equations for nonzero cubic coefficients and notes the solution vanishes at c=0, but without explicitly substituting the limiting metric functions into the f(Q)=Q (or 3D Einstein) equations and showing they fail to hold for any choice of mass/charge parameters, it remains possible that the limit recovers a BTZ solution with adjusted parameters. This explicit check is required to support the central assertion.
Authors: We agree that an explicit check is necessary to rigorously support the novelty claim. We have now substituted the c=0 limit of the metric functions into the 3D Einstein equations (equivalent to f(Q)=Q) and explicitly verified that no choice of mass and charge parameters satisfies the equations, as the resulting curvature terms do not balance for the given asymptotic AdS behavior. This calculation is added as a new paragraph in the relevant section, with full algebraic details placed in Appendix B. The solution remains intrinsically tied to the cubic non-metricity corrections. revision: yes
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Referee: The derivation of the field equations and solutions: full intermediate steps from the f(Q) action through the variation to the modified Einstein equations for the cubic f(Q) and the chosen metric ansatz are not fully visible, making it difficult to verify that the presented solutions satisfy the equations. Inclusion of these steps (or an appendix) is needed to confirm the solutions are exact.
Authors: We acknowledge that the intermediate steps were not fully expanded in the main text. To address this, we have added a comprehensive Appendix A that details the variation of the f(Q) action, the resulting modified field equations for the cubic polynomial form, the substitution of the spherically symmetric metric ansatz, and all algebraic manipulations leading to the exact solutions. This appendix confirms that the presented metrics satisfy the equations identically. revision: yes
Circularity Check
Derivation is self-contained from action to exact solutions
full rationale
The paper obtains its charged black hole solutions by direct substitution of a cubic f(Q) ansatz and a spherically symmetric metric into the field equations derived from the f(Q) action. The novel AdS solution and its non-deformability to the BTZ case are identified by solving these modified equations and inspecting the c→0 limit of the resulting metric functions. No step reduces a central prediction to a fitted input, self-citation chain, or definitional equivalence; the derivation remains independent of the target result and is self-contained against the modified gravity equations.
Axiom & Free-Parameter Ledger
free parameters (1)
- coefficients in cubic f(Q)
axioms (1)
- domain assumption The gravitational action is an arbitrary function f of the non-metricity scalar Q in three dimensions.
Lean theorems connected to this paper
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IndisputableMonolith/Foundation/AlexanderDuality.leanalexander_duality_circle_linking unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
By considering a cubic f(Q) form we derive classes of charged and uncharged spherically symmetric solutions... novel charged solution that is asymptotically Anti-de Sitter (AdS) but cannot be continuously deformed into a GR counterpart
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IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
f(Q) = −2Λ − Q + ½αQ² + ⅓βQ³ ... α and β are dimensional constants
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
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discussion (0)
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