by jsendak | Apr 16, 2025 | GR & QC Articles
arXiv:2504.10528v1 Announce Type: new
Abstract: This work explores the thermodynamic characteristics and geothermodynamics of a Bardeen black hole (BH) that interacts with a string cloud and is minimally connected to nonlinear electrodynamics. To avoid the singularities throughout the cosmic evolution, we consider an entropy function which comprises five parameters. In addition, by employing this entropy function for the specific range of parameters, we obtain the representations of BH entropy based on the holographic principle. Moreover, we employ this entropy function to investigate its impact on the thermodynamics of the BH by studying various thermodynamic properties like mass, temperature, heat capacity, and Gibbs free energy for numerous scalar charge and string cloud values. To support our investigation, we use various geothermodynamics formalisms to evaluate the stable behavior and identify different physical scenarios. Furthermore, in this analysis, we observe that only one entropy formalism provides us with better results regarding the thermodynamic behavior of the BH. Moreover, it is shown that one of the entropy models provides a thermodynamic geometric behavior compared to the other entropy models.
This work examines the thermodynamic characteristics and geothermodynamics of a Bardeen black hole (BH) interacting with a string cloud and connected to nonlinear electrodynamics. The study aims to avoid singularities throughout cosmic evolution by considering an entropy function with five parameters. This entropy function is then used to determine BH entropy based on the holographic principle and investigate its impact on various thermodynamic properties such as mass, temperature, heat capacity, and Gibbs free energy for different scalar charge and string cloud values.
To support the investigation, various geothermodynamics formalisms are employed to evaluate the stable behavior and identify different physical scenarios. The analysis reveals that only one entropy formalism yields better results concerning the BH’s thermodynamic behavior. Furthermore, one entropy model is found to provide a more thermodynamic geometric behavior compared to the other entropy models.
Roadmap for readers:
- Introduction: Provide an overview of the study’s objectives and the importance of exploring the thermodynamic characteristics and geothermodynamics of a Bardeen BH interacting with a string cloud.
- Entropy function: Explain the entropy function used in the study, highlighting its five parameters and the motivation behind its selection to avoid singularities.
- Holographic principle: Discuss how the entropy function is employed to determine BH entropy based on the holographic principle, emphasizing the significance of this approach.
- Thermodynamic properties: Present the investigation of various thermodynamic properties, including mass, temperature, heat capacity, and Gibbs free energy, for different scalar charge and string cloud values. Analyze the results and their implications.
- Geothermodynamics formalisms: Describe the utilization of different geothermodynamics formalisms to evaluate the stable behavior and identify physical scenarios. Compare the outcomes obtained from different entropy models.
- Conclusion: Summarize the main findings of the study, highlighting the entropy model that provides better results and a more thermodynamic geometric behavior. Discuss the implications and potential future directions.
Potential challenges:
- Understanding the technical aspects of thermodynamic characteristics and geothermodynamics for a BH interacting with a string cloud and connected to nonlinear electrodynamics.
- Grasping the mathematical representation and significance of the entropy function with five parameters and its role in avoiding singularities.
- Interpreting the results and implications of the investigation on various thermodynamic properties.
- Comprehending the different geothermodynamics formalisms used and their application in evaluating stable behavior and identifying physical scenarios.
Potential opportunities:
- Gaining insights into the thermodynamic behavior and characteristics of a BH interacting with a string cloud, which can contribute to our understanding of black holes and their evolution.
- Exploring the potential applications of the holographic principle in determining BH entropy and its implications.
- Identifying connections between different entropy models and their implications on the geometric behavior of the BH.
- Potential future collaborations and research to further explore the thermodynamics and geothermodynamics of BHs interacting with string clouds and connected to nonlinear electrodynamics.
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by jsendak | Apr 15, 2025 | GR & QC Articles
arXiv:2504.08796v1 Announce Type: new
Abstract: This paper employs Laurent series expansions and the Robson–Villari–Biancalana (RVB) method to provide a refined derivation of the Hawking temperature for two newly introduced topological black hole solutions. Previous calculations have demonstrated inconsistencies when applying traditional methods to such exotic horizons, prompting the need for a more thorough mathematical analysis. By systematically incorporating higher-order terms in the Laurent expansions of the metric functions near the horizon and leveraging the topological features characterized by the Euler characteristic, we reveal additional corrections to the Hawking temperature beyond standard approaches. These findings underscore the subtle interplay between local geometry, spacetime topology, and quantum effects. The results clarify discrepancies found in earlier works, present a more accurate representation of thermodynamic properties for the black holes in question, and suggest broader implications for topological structures in advanced gravitational theories.
Refining the Derivation of Hawking Temperature for Topological Black Holes
In this paper, we employ Laurent series expansions and the Robson-Villari-Biancalana (RVB) method to provide a refined derivation of the Hawking temperature for two recently discovered topological black hole solutions. Previous calculations have shown inconsistencies when using traditional methods on such exotic horizons, necessitating a more comprehensive mathematical analysis.
By incorporating higher-order terms in the Laurent expansions of the metric functions near the horizon and utilizing the topological attributes defined by the Euler characteristic, we uncover additional corrections to the Hawking temperature that go beyond standard approaches. These findings highlight the intricate interplay between local geometry, spacetime topology, and quantum effects.
The results of our study address the discrepancies identified in earlier works, offering a more precise depiction of the thermodynamic properties associated with the black holes under investigation. Moreover, these findings have broader implications for the understanding of topological structures in advanced gravitational theories.
The Future Roadmap
Potential Challenges
- Verification and Validation: As with any theoretical work, it is crucial to validate the results through experimental verification or comparison with other mathematical models.
- Generalization: The application and extension of this refined derivation to other topological black hole solutions will be a challenge, as each solution may have its distinct characteristics and complexities.
- Physical Interpretation: The interpretation of the additional corrections to the Hawking temperature and their implications for the black holes’ physical behavior will require further investigation and understanding.
Opportunities on the Horizon
- Advancements in Gravitational Theories: The refined derivation presented in this paper opens up new avenues for exploring the interplay between topology, geometry, and quantum effects in gravitational theories. It may lead to the development of more comprehensive theories or refine existing ones.
- Improved Understanding of Exotic Horizons: The insights gained from this study will contribute to a better understanding of the thermodynamic properties and behavior of topological black holes. This knowledge can lead to advancements in fields such as black hole thermodynamics and cosmology.
- Broader Implications: The implications of our findings extend beyond the specific topological black hole solutions examined in this study. They may have implications for other physical systems with topological structures and shed light on the connection between topology and quantum effects in various scientific domains.
Note: This paper is accompanied by extensive mathematical derivations, which are not included in this summary for brevity. Please refer to the full paper for a detailed analysis.
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by jsendak | Apr 14, 2025 | GR & QC Articles
arXiv:2504.08037v1 Announce Type: new
Abstract: We calculate the gravitational wave power spectrum from sound waves in a cosmological first order phase transition in the unexplored regime of large bubbles, by which we mean that the mean bubble spacing $R_*$ is a non-negligible fraction of the Hubble length $mathcal{H}_*^{-1}$, i.e. $R_*mathcal{H}_* lesssim mathcal{O}(1)$. Since the amplitude of the gravitational wave signal increases with $R_*mathcal{H}_*$, this is also the loud signal regime. In this regime the effects of gravity, hitherto neglected, become relevant. We carry out the calculation in cosmological perturbation theory expanding in the parameter $R_*mathcal{H}_*$, or bubble over Hubble radius. The leading order term is the standard result for acoustic production of gravitational waves. At next-to-leading order we find three novel contributions: two contributions arise from general relativistic corrections to the dynamics of both sound and gravitational waves. A third contribution comes from gravitational waves induced by curvature perturbations. These contributions suppress the gravitational wave peak amplitude. The suppression factor, with respect to the leading order contribution, scales as $(R_*mathcal{H}_*)^2$, and also depends on other transition parameters, such as the sound speed $c_s$, the duration of the acoustic source, and the peak wavenumber of the velocity field $k_p$. In a simplified model of the velocity field, we find that the suppression factor lies between $2%$ and $15%$ when $R_*mathcal{H}_* simeq 0.5$, but is independent of the root mean squared fluid velocity. We provide analytical approximations to the next-to-leading order corrections, and a recipe to join them smoothly across different frequency regimes. Our work improves the precision of the current estimations of the gravitational wave power spectrum in the relatively unexplored regime of phase transition with large bubbles.
Future Roadmap for Readers
Introduction
This article presents a calculation of the gravitational wave power spectrum from sound waves in a cosmological first order phase transition. The focus is on the regime of large bubbles, where the mean bubble spacing is a non-negligible fraction of the Hubble length. The aim of this roadmap is to provide an overview of the conclusions of the study and outline potential challenges and opportunities on the horizon.
Calculation in Cosmological Perturbation Theory
The authors carry out the calculation using cosmological perturbation theory, expanding in the parameter $R_*mathcal{H}_*$, which represents the ratio of bubble spacing to Hubble length. The leading order term corresponds to the standard result for acoustic production of gravitational waves.
Novel Contributions at Next-to-Leading Order
At next-to-leading order, the authors find three novel contributions to the gravitational wave power spectrum. First, there are general relativistic corrections to the dynamics of both sound and gravitational waves. Second, there are gravitational waves induced by curvature perturbations. These contributions result in a suppression of the gravitational wave peak amplitude.
Suppression Factor
The suppression factor, compared to the leading order contribution, scales as $(R_*mathcal{H}_*)^2$ and depends on other transition parameters such as the sound speed, duration of the acoustic source, and peak wavenumber of the velocity field. In a simplified model, the authors find that the suppression factor ranges from 2% to 15% when $R_*mathcal{H}_* simeq 0.5$. Notably, the suppression factor is independent of the root mean squared fluid velocity.
Analytical Approximations and Smooth Frequency Regime Transition
The authors provide analytical approximations to the next-to-leading order corrections, allowing for more precise estimations of the gravitational wave power spectrum in the regime of phase transition with large bubbles. They also propose a recipe to smoothly join the corrections across different frequency regimes.
Conclusion
This study significantly improves the precision of estimations for the gravitational wave power spectrum in cosmological phase transitions with large bubbles. By considering both leading order and next-to-leading order contributions, the authors uncover novel gravitational wave effects and provide valuable insights for future research in this unexplored regime.
Potential Challenges and Opportunities
- Challenges may arise in extending the calculations and approximation techniques to more complex velocity field models.
- Further investigations are needed to explore the impact of additional transition parameters on the gravitational wave power spectrum.
- Opportunities exist for experimental validation of the predictions through gravitational wave observations by upcoming detectors.
- Future research can build upon this work to study the implications of these findings for cosmological models and the early universe.
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by jsendak | Apr 11, 2025 | GR & QC Articles
arXiv:2504.07130v1 Announce Type: new
Abstract: In this paper, we study the influence of the axion-plasmon medium, as proposed in [10.1103/PhysRevLett.120.181803]cite{Tercas:2018gxv}, on the optical properties of black holes in a Lorentz-violating spacetime containing a global monopole. Our primary aim is to provide a test for detecting the effects of a fixed axion-plasmon background within the framework of Ricci-coupled Kalb-Ramond bumblebee gravity. By extending the conventional Einstein-bumblebee model through a nonminimal coupling between the Kalb-Ramond field and the Ricci tensor, we demonstrate that the combined presence of a global monopole and Lorentz-violating effects induces significant modifications to the classical Schwarzschild lensing signature. Employing the Gauss-Bonnet theorem within an optical geometry approach, we derive an analytical expression for the deflection angle that incorporates both linear and quadratic contributions from the Lorentz-violating parameter and the monopole charge. Furthermore, we investigate how the axion-plasmon coupling alters light propagation, affecting key observable gravitational deflection angle. Our results indicate that these optical characteristics are notably sensitive to the axion-plasmon parameters, thereby offering promising observational signatures for probing new physics beyond standard general relativity.
Article Title: The Influence of Axion-Plasmon Medium on Black Hole Optics in a Lorentz-Violating Spacetime with a Global Monopole
Abstract
In this paper, the authors explore the effects of a fixed axion-plasmon background within the framework of Ricci-coupled Kalb-Ramond bumblebee gravity. They aim to detect the influence of the axion-plasmon medium on the optical properties of black holes in a Lorentz-violating spacetime containing a global monopole. By extending the conventional Einstein-bumblebee model, they demonstrate that the combined presence of a global monopole and Lorentz-violating effects leads to significant modifications in the classical Schwarzschild lensing signature. The authors utilize the Gauss-Bonnet theorem within an optical geometry approach to derive an analytical expression for the deflection angle, considering both linear and quadratic contributions from the Lorentz-violating parameter and the monopole charge. Additionally, they investigate the alteration of light propagation due to axion-plasmon coupling, which affects the gravitational deflection angle. The results suggest that the observed optical characteristics are highly sensitive to the axion-plasmon parameters, offering promising potential for observing new physics beyond standard general relativity.
Roadmap
1. Introduction
– Provide a brief overview of the study’s focus on the influence of the axion-plasmon medium on black hole optics in a Lorentz-violating spacetime with a global monopole.
– Highlight the significance of this research in probing new physics beyond standard general relativity.
2. Theoretical Framework
– Explain the Ricci-coupled Kalb-Ramond bumblebee gravity model and its extension from the conventional Einstein-bumblebee model through a nonminimal coupling between the Kalb-Ramond field and the Ricci tensor.
– Discuss the role of Lorentz-violating effects and the presence of a global monopole in inducing modifications to the classical Schwarzschild lensing signature.
3. Derivation of Deflection Angle
– Describe the utilization of the Gauss-Bonnet theorem within an optical geometry approach to derive an analytical expression for the deflection angle.
– Consider the linear and quadratic contributions from the Lorentz-violating parameter and the monopole charge in the expression.
4. Effects of Axion-Plasmon Coupling
– Investigate how the axion-plasmon coupling alters light propagation and affects the gravitational deflection angle.
– Emphasize the sensitivity of the observed optical characteristics to the axion-plasmon parameters.
5. Conclusion
– Summarize the key findings of the study, highlighting the significant modifications to the classical Schwarzschild lensing signature caused by the combined presence of a global monopole and Lorentz-violating effects.
– Discuss the potential of utilizing the observed optical characteristics as promising signatures for probing new physics beyond standard general relativity.
Challenges and Opportunities
- Challenges:
- – Understanding and quantifying the effects of the axion-plasmon medium on the black hole optics in a Lorentz-violating spacetime.
- – Overcoming the complexity of the extended Ricci-coupled Kalb-Ramond bumblebee gravity model to derive analytical expressions and make accurate predictions.
- Opportunities:
- – Potential for detecting and observing new physics beyond standard general relativity by studying the optical properties of black holes.
- – Promising observational signatures provided by the sensitivity of the optical characteristics to the axion-plasmon parameters.
- – Advancement in understanding the interplay between axion-plasmon coupling, Lorentz violation, and global monopoles in modifying the classical Schwarzschild lensing signature.
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by jsendak | Apr 10, 2025 | GR & QC Articles
arXiv:2504.06427v1 Announce Type: new
Abstract: This paper presents an improvement to the four-dimensional spinfoam model with cosmological constant ($Lambda$-SF model) in loop quantum gravity. The original $Lambda$-SF model, defined via ${rm SL}(2,mathbb{C})$ Chern-Simons theory on graph-complement 3-manifolds, produces finite amplitudes and reproduces curved 4-simplex geometries in the semi-classical limit. However, extending the model to general simplicial complexes necessitated ad hoc, non-universal phase factors in face amplitudes, complicating systematic constructions. We resolve this issue by redefining the vertex amplitude using a novel set of phase space coordinates that eliminate the extraneous phase factor, yielding a universally defined face amplitude. Key results include: (1) The vertex amplitude is rigorously shown to be well-defined for Chern-Simons levels $k in 8mathbb{N}$, compatible with semi-classical analysis ($k to infty$). (2) The symplectic structure of the Chern-Simons phase space is modified to accommodate ${rm SL}(2,mathbb{C})$ holonomies, relaxing quantization constraints to $mathrm{Sp}(2r,mathbb{Z}/4)$. (3) Edge amplitudes are simplified using constraints aligned with colored tensor models, enabling systematic gluing of 4-simplices into complexes dual to colored graphs. (4) Stationary phase analysis confirms consistency of critical points with prior work, recovering Regge geometries with curvature determined by $Lambda$. These advancements streamline the spinfoam amplitude definition, facilitating future studies of colored group field theories and continuum limits of quantum gravity. The results establish a robust framework for 4D quantum gravity with non-zero $Lambda$, free of previous ambiguities in face amplitudes.
Future Roadmap for Readers: Challenges and Opportunities on the Horizon
Introduction
In this paper, we present an improvement to the four-dimensional spinfoam model with cosmological constant ($Lambda$-SF model) in loop quantum gravity. The original $Lambda$-SF model had some complications when it came to extending the model to general simplicial complexes, requiring ad hoc phase factors in face amplitudes. However, we have resolved this issue by redefining the vertex amplitude using a new set of phase space coordinates, eliminating the extraneous phase factor and yielding a universally defined face amplitude. This paper outlines the key results and establishes a robust framework for 4D quantum gravity with non-zero $Lambda$.
Roadmap
- Redefining the Vertex Amplitude
We redefine the vertex amplitude using a novel set of phase space coordinates, eliminating the non-universal phase factor. This improvement allows for a universally defined face amplitude in the $Lambda$-SF model.
- Well-Defined Vertex Amplitude
We rigorously show that the vertex amplitude is well-defined for Chern-Simons levels $k in 8mathbb{N}$, which is compatible with semi-classical analysis ($k to infty$). This result provides reassurance that the model is consistent in the limit where classical gravity is recovered.
- Modification of the Symplectic Structure
We modify the symplectic structure of the Chern-Simons phase space to accommodate ${rm SL}(2,mathbb{C})$ holonomies. This relaxation of quantization constraints to $mathrm{Sp}(2r,mathbb{Z}/4)$ allows for a more flexible and general framework.
- Simplification of Edge Amplitudes
We simplify edge amplitudes using constraints aligned with colored tensor models. This enables a systematic gluing of 4-simplices into complexes dual to colored graphs, expanding the applicability of the model.
- Confirmation of Consistency with Prior Work
Through stationary phase analysis, we confirm the consistency of critical points with prior work. We recover Regge geometries with curvature determined by $Lambda$, validating our advancements in the spinfoam amplitude definition.
- Potential Future Studies
These advancements in the $Lambda$-SF model open up new avenues for future research. Some potential areas of exploration include:
- Colored Group Field Theories: The improved spinfoam amplitude definition facilitates further studies of colored group field theories, potentially leading to new insights and applications.
- Continuum Limits of Quantum Gravity: With the robust framework established by our results, investigations into the continuum limits of quantum gravity become more accessible.
- Conclusion
We have addressed the complications in the $Lambda$-SF model by redefining the vertex amplitude and eliminating non-universal phase factors. Our results provide a robust framework for 4D quantum gravity with non-zero $Lambda$, free of previous ambiguities in face amplitudes. This advancement opens up exciting possibilities for future research in colored group field theories and the continuum limits of quantum gravity.
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by jsendak | Apr 9, 2025 | GR & QC Articles
arXiv:2504.05432v1 Announce Type: new
Abstract: Motivated by the recent results published by the DESI DR2 Collaboration and its compelling results in obtaining statistical preference for dynamical dark energy models over the standard {Lambda}CDM model, this study presents an MCMC fit for all currently viable f (R) models using this dataset, along with a corresponding Bayesian analysis. The findings reveal very strong evidence in favor of f (R) models compared to {Lambda}CDM model. The analysis also includes data from cosmic chronometers and the latest Pantheon Plus + SH0ES supernova compilation.
Examining the Conclusions of the Study: MCMC Fit for f (R) Models
The study discussed in this article is motivated by the recent results published by the DESI DR2 Collaboration. This collaboration has provided compelling evidence for dynamical dark energy models over the standard {Lambda}CDM model. In response to these results, the study presents a Markov Chain Monte Carlo (MCMC) fit for all currently viable f (R) models.
An MCMC fit is a statistical technique used to estimate the parameters of a model by exploring the parameter space using a Markov Chain Monte Carlo algorithm. In this case, the goal is to determine the parameters of the f (R) models that best fit the data provided by the DESI DR2 Collaboration, cosmic chronometers, and the Pantheon Plus + SH0ES supernova compilation.
Key Findings: Strong Evidence in favor of f (R) Models
The findings of the study reveal very strong evidence in favor of f (R) models when compared to the standard {Lambda}CDM model. This suggests that f (R) models provide a better explanation for the observed data and should be considered as viable alternatives to the current standard model.
This is a significant development in our understanding of dark energy and cosmology as it challenges the prevailing {Lambda}CDM model. With the DESI DR2 Collaboration’s results and the support from this study, there is a growing consensus that f (R) models have strong theoretical and observational support.
Roadmap for the Future: Challenges and Opportunities
Potential Challenges
- Theoretical Challenges: Despite the strong evidence in favor of f (R) models, their theoretical foundations may require further refinement. Researchers will need to continue exploring and developing the theoretical aspects of these models to ensure their consistency with other areas of physics and cosmology.
- Data Availability: Obtaining accurate and high-quality data is crucial for further validating and refining the f (R) models. Collaboration among observational astronomers, cosmologists, and theorists will be essential in collecting and analyzing data from various sources to ensure robust conclusions.
- Model Complexity: While f (R) models provide a promising alternative, their increased complexity may pose challenges in terms of computational resources and practical implementation. Efficient algorithms and computational techniques will need to be developed to fully explore and understand the implications of these models.
Potential Opportunities
- Enhanced Understanding of Dark Energy: The acceptance of f (R) models as viable alternatives to the standard {Lambda}CDM model could lead to a deeper understanding of dark energy. This may provide insights into the fundamental nature of the universe and its evolution.
- Exploration of New Observational Probes: Supporting f (R) models presents opportunities for observational astronomers to explore new probes and techniques that can provide further evidence and test the predictions of these models. This could lead to exciting advancements in observational cosmology.
- Implications for Fundamental Physics: If f (R) models are indeed preferred over the standard {Lambda}CDM model, it could have profound implications for our understanding of gravitational physics and the nature of space-time. Exploring these implications could open up new avenues for research and potentially revolutionize our understanding of fundamental physics.
Conclusion
The MCMC fit conducted in this study provides strong evidence in favor of f (R) models as a compelling alternative to the standard {Lambda}CDM model. While there are challenges to overcome, the support from the DESI DR2 Collaboration and other recent studies suggest a promising future for f (R) models in advancing our understanding of dark energy and cosmology. Continued research, collaboration, and refinement of these models will be crucial in shaping the future of cosmology and fundamental physics.
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