Two novel topological black hole exact solutions with unusual shapes of
horizons in the simplest holographic axions model, the four-dimensional
Einstein-Maxwell-axions theory, are constructed. We draw embedding diagrams in
various situations to display unusual shapes of novel black holes. To
understand their thermodynamics from the quasi-local aspect, we re-derive the
unified first law and the Misner-Sharp mass from the Einstein equations for the
spacetime as a warped product $M2 times Mco2$. The Ricci scalar $Rhat$ of
the sub-manifold $Mco2$ can be a non-constant. We further improve the
thermodynamics method based on the unified first law. Such a method simplifies
constructing solutions and hints at generalization to higher dimensions.
Moreover, we apply the unified first law to discuss black hole thermodynamics.

Examine the conclusions of the following text and outline a future roadmap for readers, indicating potential challenges and opportunities on the horizon.

Two novel topological black hole exact solutions with unusual shapes of horizons have been constructed in the simplest holographic axions model, specifically in the four-dimensional Einstein-Maxwell-axions theory. The article presents embedding diagrams in various situations to display the unusual shapes of these novel black holes. Additionally, the thermodynamics of these black holes is explored from a quasi-local aspect, involving the re-derivation of the unified first law and the Misner-Sharp mass from the Einstein equations for the spacetime as a warped product $M2 times Mco2$. Notably, it is observed that the Ricci scalar $Rhat$ of the sub-manifold $Mco2$ can be non-constant. Furthermore, an improved thermodynamics method is proposed based on the unified first law, demonstrating its potential to simplify the construction of solutions and suggesting its applicability to higher dimensions. Lastly, the unified first law is applied to discuss black hole thermodynamics.

Future Roadmap

As we look to the future, there are several potential challenges and opportunities on the horizon. Here is a suggested roadmap for readers:

  1. Further Study of Novel Black Hole Solutions: Researchers should conduct further study and exploration of the constructed novel black hole solutions. Analyzing their properties, behavior, and implications could provide valuable insights into the nature of black holes and their role in the holographic axions model.
  2. Investigation of Unusual Horizon Shapes: The unusual shapes of the black hole horizons presented in this article warrant further investigation. Researchers can delve deeper into understanding the factors influencing these shapes and their significance in the context of black hole physics and the holographic axions model. Exploring the connection between horizon shapes and other physical properties could be a promising avenue of research.
  3. Refinement of Thermodynamics Method: The proposed improved thermodynamics method based on the unified first law presents an opportunity for refinement and enhancement. Researchers can fine-tune and optimize the method to make it even more effective in constructing solutions and analyzing black hole thermodynamics. Additionally, applying this method to other models and dimensions could provide valuable comparisons and insights.
  4. Generalization to Higher Dimensions: The hint at generalization to higher dimensions opens up a new dimension of research. Investigating the applicability and implications of the unified first law and the constructed solutions in higher-dimensional spacetimes could contribute to the understanding of black holes in a broader context.
  5. Exploration of Non-constant Ricci Scalar: The observation that the Ricci scalar $Rhat$ of the sub-manifold $Mco2$ can be non-constant raises intriguing questions. Future research should aim to understand the implications and consequences of this non-constancy, exploring its relationship with other geometric and physical properties. Investigating whether this phenomenon exists in other models or scenarios could shed further light on its significance.
  6. Application to Other Areas: Building upon the insights gained from studying these novel black hole solutions and the improved thermodynamics method, researchers can explore potential applications in other areas of physics. Investigating whether similar techniques and concepts can be applied to different phenomena or theories could open up new avenues of research and discovery.

In conclusion, this article presents two novel black hole solutions with unusual horizon shapes, along with an improved thermodynamics method based on the unified first law. The roadmap outlined above outlines potential future directions for research, including further studying the black hole solutions, refining the thermodynamics method, exploring higher dimensions and non-constant Ricci scalars, and seeking applications in other physics domains.

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