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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by jsendak | Apr 8, 2025 | GR & QC Articles
arXiv:2504.03806v1 Announce Type: new
Abstract: The place and physical significance of gauge gravitation theory in the Riemann-Cartan space-time (GTRC) in the framework of gauge approach to gravitation is discussed. Isotropic cosmology built on the base of GTRC with general expression of gravitational Lagrangian with indefinite parameters is considered. The most important physical consequences connected with the change of gravitational interaction, with possible existence of limiting energy density and gravitational repulsion at extreme conditions, and also with the vacuum repulsion effect are discussed. The solution of the problem of cosmological singularity and the dark energy problem as result of the change of gravitational interaction is considered.
The article discusses the significance of gauge gravitation theory in the Riemann-Cartan space-time (GTRC) within the gauge approach to gravitation. It explores isotropic cosmology based on GTRC and examines the physical consequences related to the change of gravitational interaction, including the potential existence of limiting energy density and gravitational repulsion under extreme conditions. The article also discusses the vacuum repulsion effect and how it may contribute to solving the problem of cosmological singularity and addressing the dark energy problem.
Future Roadmap
Looking ahead, there are several potential challenges and opportunities on the horizon:
1. Experimental verification
One of the key challenges is the experimental verification of the predictions and consequences of gauge gravitation theory in GTRC. This will require designing and conducting experiments that can accurately measure and observe the effects of the change in gravitational interaction, as well as the potential existence of limiting energy density and gravitational repulsion. Collaborations between experimentalists and theorists will be crucial in this endeavor.
2. Further theoretical development
The article indicates that the gravitational Lagrangian in GTRC has indefinite parameters. Further theoretical development is needed to fully understand the implications of these parameters and their relationship to the observed physical consequences. This may involve mathematical modeling and simulations, as well as innovative theoretical frameworks and approaches.
3. Cosmological implications
If the change in gravitational interaction leads to the solution of the cosmological singularity problem and addresses the dark energy problem, there may be significant implications for our understanding of the universe. Future research should investigate these implications in more detail and explore potential connections to other cosmological phenomena, such as the expansion of the universe and the formation of structures.
4. Practical applications
Understanding and harnessing the effects of gravitational repulsion and the vacuum repulsion effect could have practical applications in various fields. For example, it may lead to the development of advanced propulsion systems or contribute to the design of new materials with unique properties. Exploring these practical applications may open up new technological possibilities and benefits.
5. Interdisciplinary collaborations
Gauge gravitation theory in GTRC spans multiple disciplines, including physics, mathematics, and cosmology. Encouraging interdisciplinary collaborations and fostering knowledge exchange between different scientific communities will be essential in making progress and addressing the challenges and opportunities associated with this theory. Conferences, workshops, and collaborative research projects can facilitate such collaborations.
In summary, the roadmap for readers of this article involves experimental verification, further theoretical development, exploration of cosmological implications, investigation of practical applications, and interdisciplinary collaborations. By addressing these challenges and leveraging the opportunities, we can advance our understanding of gauge gravitation theory in GTRC and its potential implications for our understanding of the universe and technological advancements.
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by jsendak | Apr 7, 2025 | GR & QC Articles
arXiv:2504.03009v1 Announce Type: new
Abstract: This study tackles the impact dark energy in different systems by a simple unifying formalism. We introduce a parameter space to compare gravity tests across all cosmic scales, using the McVittie spacetime (MCV), that connect spherically symmetric solutions with cosmological solutions. By analyzing invariant scalars, the Ricci, Weyl, and Kretschmann scalars, we develop a phase-space description that predicts the dominance of the Cosmological Constant. We explore three cases: (1) the local Hubble flow around galaxy groups and clusters, (2) spherical density distributions and (3) binary motion. Our results show that galaxy groups and clusters exhibit Kretschmann scalar values consistent with the Cosmological Constant curvature, indicating where dark energy dominates.
Text:
This study focuses on understanding the impact of dark energy in various systems using a simple unifying formalism. The authors introduce a parameter space that allows for a comparison of gravity tests across all cosmic scales, using a mathematical framework called the McVittie spacetime (MCV). MCV connects spherically symmetric solutions with cosmological solutions, aiding in the analysis of invariant scalars such as the Ricci, Weyl, and Kretschmann scalars.
Through their analyses, the authors develop a phase-space description that predicts the dominance of the Cosmological Constant. They explore three specific cases to support their findings: (1) the local Hubble flow around galaxy groups and clusters, (2) spherical density distributions, and (3) binary motion. The results indicate that galaxy groups and clusters exhibit Kretschmann scalar values consistent with the curvature expected from the Cosmological Constant, suggesting that dark energy dominates in these regions.
Roadmap:
Future Roadmap
1. Exploration of Dark Energy in Other Systems: The current study focuses on the impact of dark energy in galaxy groups and clusters. As a next step, researchers can expand their investigation to other systems, such as individual galaxies or even larger cosmic structures like superclusters. By examining a wider array of systems, a comprehensive understanding of the influence of dark energy across various cosmic scales can be established.
2. Refinement of the Parameter Space: The introduced parameter space in this study provides a valuable tool for comparing gravity tests across cosmic scales. However, further refinement and optimization of this parameter space may be necessary. Researchers can work towards identifying additional parameters or modifying the existing ones to enhance the accuracy and effectiveness of the comparisons.
3. Investigation of Dark Energy Effects in Non-Spherical Systems: The current study primarily focuses on spherically symmetric systems. To gain a more comprehensive understanding, researchers can explore the impact of dark energy in non-spherical systems. By studying systems with different shapes and geometries, a deeper insight into the behavior of dark energy can be gained, contributing to a more complete understanding of its effects.
4. Experimental Validation: The findings of this study are based on theoretical analyses and predictions. Future research should aim to validate these conclusions through observational or experimental means. By designing and conducting experiments that measure the Kretschmann scalar values or other relevant indicators in different systems, researchers can verify the dominance of dark energy and further establish its impact.
5. Mitigation of Challenges: The pursuit of understanding dark energy and its impact may present certain challenges. Some potential obstacles include the complexity of the mathematical formalism, the need for sophisticated observational techniques, and the requirement for extensive computational resources for analysis. Overcoming these challenges will require collaborative efforts from researchers, advancements in computational capabilities, and the development of innovative methodologies.
6. Identification of Opportunities: The study of dark energy provides substantial opportunities for further advancements in our understanding of the cosmos. By unraveling the mysteries surrounding dark energy, researchers can gain valuable insights into the nature of the universe, uncover potential connections to fundamental physics, and contribute to the development of new theories and models. Additionally, advancements in experimental techniques driven by the investigation of dark energy can have broader implications for various fields of science and technology.
Note: This future roadmap highlights potential directions for future research based on the conclusions of the current study. Research priorities and opportunities may evolve over time based on new discoveries and advancements in the field. Researchers should consult the latest literature and engage in collaborative discussions to ensure their roadmap aligns with the most up-to-date knowledge.
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by jsendak | Apr 3, 2025 | GR & QC Articles
arXiv:2504.01207v1 Announce Type: new
Abstract: We introduce the concept of $k-$future convex spacelike/null hypersurface $Sigma$ in an $n+1$ dimensional spacetime $M$ and prove that no $k-$dimensional closed trapped submanifold (k-CTM) can be tangent to $Sigma$ from its future side. As a consequence, k-CTMs cannot be found in open spacetime regions foliated by such hypersurfaces. In gravitational collapse scenarios, specific hypersurfaces of this kind act as past barriers for trapped submanifolds. A number of examples are worked out in detail, two of them showing 3+1 spacetime regions containing trapped loops ($k=1$) but no closed trapped surfaces ($k=2$). The use of trapped loops as an early indicator of black hole formation is briefly discussed.
Future Convex Spacelike/Null Hypersurfaces and Trapped Submanifolds: A Roadmap
Introduction
In this article, we will explore the concept of $k-$future convex spacelike/null hypersurfaces in an $n+1$ dimensional spacetime. We will discuss the implications of these hypersurfaces on the existence of $k-$dimensional closed trapped submanifolds (k-CTMs) and their relationship to open spacetime regions. Additionally, we will delve into the role of specific hypersurfaces as past barriers in gravitational collapse scenarios and their potential use in identifying black hole formation.
Understanding Future Convex Spacelike/Null Hypersurfaces
First, we will define and explain the concept of $k-$future convex spacelike/null hypersurfaces. These hypersurfaces exist in $n+1$ dimensional spacetimes and play a crucial role in understanding the behavior of trapped submanifolds.
Implications for Trapped Submanifolds
Next, we will examine the relationship between future convex spacelike/null hypersurfaces and $k-$dimensional closed trapped submanifolds (k-CTMs). We will present a proof demonstrating that no k-CTM can be tangent to the hypersurface from its future side. This result leads to the conclusion that k-CTMs cannot exist in open spacetime regions that are foliated by these hypersurfaces.
Gravitational Collapse Scenarios and Past Barriers
One of the significant findings of our study is the identification of specific hypersurfaces as past barriers for trapped submanifolds in gravitational collapse scenarios. We will explore the implications of these past barriers and their role in defining the behavior of trapped submanifolds during collapse.
Worked Examples
In this section, we will provide detailed worked examples to illustrate the concepts discussed. We will present two examples that depict 3+1 spacetime regions containing trapped loops ($k=1$) but no closed trapped surfaces ($k=2$). These examples will help solidify the understanding of the relationships between hypersurfaces, trapped submanifolds, and collapse scenarios.
Trapped Loops as Indicators of Black Hole Formation
Finally, we will briefly discuss the potential use of trapped loops as early indicators of black hole formation. This section will explore the significance of identifying trapped loops and their implications for understanding the formation and behavior of black holes.
Roadmap Challenges and Opportunities
- Challenge: The concept of future convex spacelike/null hypersurfaces may be complex for readers unfamiliar with advanced spacetime theories. Clear and concise explanations will be required to ensure understanding.
- Challenge: The proof that no k-CTM can be tangent to the hypersurface from its future side may require mathematical comprehension beyond the scope of some readers. Efforts should be made to present the proof in a simplified manner.
- Opportunity: The worked examples will provide concrete illustrations of the concepts discussed, aiding readers in visualizing the relationships between hypersurfaces, trapped submanifolds, and collapse scenarios.
- Opportunity: The potential use of trapped loops as indicators of black hole formation offers an exciting avenue for further research and exploration. This section may inspire readers to delve deeper into this area of study.
Conclusion
This roadmap has outlined the key elements of the article on future convex spacelike/null hypersurfaces, trapped submanifolds, and their implications in gravitational collapse scenarios. By addressing potential challenges and highlighting opportunities for further exploration, readers will gain a comprehensive understanding of the subject matter and its significance in advanced spacetime theories.
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by jsendak | Mar 14, 2025 | GR & QC Articles
arXiv:2503.09678v1 Announce Type: new
Abstract: Using gravitational waves to probe the geometry of the ringing remnant black hole formed in a binary black hole coalescence is a well-established way to test Einstein’s theory of general relativity. However, doing so requires knowledge of when the predictions of black hole perturbation theory, i.e., quasi-normal modes (QNMs), are a valid description of the emitted gravitational wave as well as what the amplitudes of these excitations are. In this work, we develop an algorithm to systematically extract QNMs from the ringdown of black hole merger simulations. Our algorithm improves upon previous ones in three ways: it fits over the two-sphere, enabling a complete model of the strain; it performs a reverse-search in time for QNMs using a more robust nonlinear least squares routine called texttt{VarPro}; and it checks the variance of QNM amplitudes, which we refer to as “stability”, over an interval matching the natural time scale of each QNM. Using this algorithm, we not only demonstrate the stability of a multitude of QNMs and their overtones across the parameter space of quasi-circular, non-precessing binary black holes, but we also identify new quadratic QNMs that may be detectable in the near future using ground-based interferometers. Furthermore, we provide evidence which suggests that the source of remnant black hole perturbations is roughly independent of the overtone index in a given angular harmonic across binary parameter space, at least for overtones with $nleq2$. This finding may hint at the spatiotemporal structure of ringdown perturbations in black hole coalescences, as well as the regime of validity of perturbation theory in the ringdown of these events. Our algorithm is made publicly available at the following GitHub repository: https://github.com/keefemitman/qnmfinder.
Using gravitational waves to test general relativity
The study examines the use of gravitational waves to investigate the properties of black holes formed in binary black hole coalescences. By analyzing the ringdown phase of these events, the researchers aim to test Einstein’s theory of general relativity. However, to do so accurately, they need to understand the characteristics of the emitted gravitational waves, including their quasi-normal modes (QNMs) and their amplitudes.
An improved algorithm for extracting QNMs
In this work, the researchers present an algorithm that allows for the systematic extraction of QNMs from simulations of black hole mergers. Their algorithm offers three key improvements over previous methods:
- It fits over the two-sphere, enabling a more comprehensive model of the gravitational wave strain.
- It performs a reverse-search in time for QNMs using a more robust nonlinear least squares routine called VarPro.
- It checks the stability of QNM amplitudes over an interval matching the natural time scale of each QNM.
With these enhancements, the researchers demonstrate the stability of multiple QNMs and their overtones across the parameter space of quasi-circular, non-precessing binary black holes. They also discover new quadratic QNMs that may soon be detectable using ground-based interferometers.
Understanding the spatiotemporal structure of black hole perturbations
The study also provides evidence suggesting that the source of perturbations in the remnant black hole is largely independent of the overtone index for a given angular harmonic across the binary parameter space, at least for overtones with n <= 2. This finding offers insights into the spatiotemporal structure of perturbations in black hole coalescences and the validity of perturbation theory in the ringdown phase of these events.
Future opportunities and challenges
This work opens up several opportunities for future research and discoveries. The algorithm developed in this study can be applied to analyze more diverse binary black hole configurations and to investigate the stability of QNMs in those scenarios. Detecting and characterizing new QNMs can provide further evidence for the accuracy of Einstein’s theory and enhance our understanding of the fundamental properties of black holes.
There are, however, challenges that need to be addressed. As the sensitivity of ground-based interferometers increases, the detection and analysis of QNMs become more complex. Additionally, the algorithm may need further refinement to handle different types of perturbations and to improve accuracy in extreme parameter regimes. Nonetheless, the availability of the algorithm on a public GitHub repository allows for collaboration and further development by the scientific community.
Conclusion
This study presents an improved algorithm for extracting quasi-normal modes from the ringdown phase of binary black hole mergers. The algorithm enables the identification of stable QNMs and the discovery of new ones. The findings also provide insights into the spatiotemporal structure of black hole perturbations and the validity of perturbation theory. Future research should focus on applying the algorithm to more diverse scenarios and addressing challenges related to detection and analysis. Overall, this work contributes to our understanding of general relativity and the properties of black holes.
GitHub Repository: https://github.com/keefemitman/qnmfinder
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by jsendak | Mar 12, 2025 | GR & QC Articles
arXiv:2503.07679v1 Announce Type: new
Abstract: This paper investigates the thermodynamic properties of the coexistence region of two horizons in the charged 4-dimensional Einstein-Gauss-Bonnet (4D-EGB) spacetime. Initially, we apply the universal first law of thermodynamics to derive the corresponding thermodynamic quantities for the coexistence region between the black hole event horizon and the cosmological event horizon, subject to the relevant boundary conditions. Next we examine the thermal properties of the thermodynamic system described by these equivalent quantities. Our analysis reveals that the peak of the heat capacity as a function of temperature exhibits characteristics similar to those observed in a paramagnetic system under specific conditions. We further conclude that, under certain conditions, the heat capacity mirrors that of a two-level system formed by two horizons with distinct temperatures. By comparing the heat capacity of the 4D-EGB spacetime’s equivalent thermodynamic system with that of a two-level system defined by the two horizons in the spacetime, we can estimate the number of microscopic degrees of freedom at the two horizons. This findings sheds light on the quantum properties of de Sitter (dS) spacetime with two horizon interfaces and offers a novel approach to exploring the quantum properties of black holes and dS spacetime.
The Thermodynamic Properties of the Coexistence Region of Two Horizons in the Charged 4D-EGB Spacetime
This paper investigates the thermodynamic properties of the coexistence region between the black hole event horizon and the cosmological event horizon in the charged 4-dimensional Einstein-Gauss-Bonnet (4D-EGB) spacetime. By applying the universal first law of thermodynamics and considering the relevant boundary conditions, we derive the corresponding thermodynamic quantities for this coexistence region.
Thermal Properties of the Thermodynamic System
After obtaining the thermodynamic quantities, we examine the thermal properties of the system described by these equivalent quantities. Our analysis reveals that the heat capacity as a function of temperature exhibits characteristics similar to those observed in a paramagnetic system under specific conditions.
Heat Capacity Mirroring a Two-Level System
Furthermore, we conclude that, under certain conditions, the heat capacity mirrors that of a two-level system formed by the two horizons with distinct temperatures. This comparison of the heat capacity between the 4D-EGB spacetime’s equivalent thermodynamic system and the two-level system defined by the two horizons allows us to estimate the number of microscopic degrees of freedom at these horizons.
Roadmap for Future Investigations
The findings in this study shed light on the quantum properties of de Sitter (dS) spacetime with two horizon interfaces. Moving forward, there are several opportunities for further exploration:
- Quantum Properties of Black Holes: This research opens up a novel approach to exploring the quantum properties of black holes using the relation between heat capacity and two-level systems.
- Quantum Properties of dS Spacetime: The quantum properties of dS spacetime, especially with regards to the two horizon interfaces, offer interesting avenues for future investigations.
- Microscopic Degrees of Freedom: By estimating the number of microscopic degrees of freedom at the horizons, we can gain a better understanding of the underlying quantum nature of spacetime.
Potential Challenges
Despite the promising findings and opportunities, there are also challenges to address in future research:
- Validity of Assumptions: The conclusions of this study rely on certain assumptions and conditions. Further investigations should verify the validity of these assumptions and explore the robustness of the results.
- Quantum Gravity: Understanding the quantum properties of spacetime, including black holes and dS spacetime, requires a deeper understanding of quantum gravity. Integration with quantum gravity theories will be crucial for further progress.
- Experimental Verification: The findings in this study are theoretical in nature. Experimental verification or observational evidence will be necessary to validate the theoretical predictions.
In summary, this study explores the thermodynamic properties of the coexistence region between the black hole event horizon and the cosmological event horizon in the charged 4D-EGB spacetime. The analysis reveals similarities to paramagnetic systems and suggests that the thermodynamic system can be modeled as a two-level system. This opens up new avenues for investigating the quantum properties of black holes and dS spacetime. However, challenges such as verifying assumptions, integrating with quantum gravity, and experimental validation remain to be addressed in future research.
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