by jsendak | Mar 5, 2025 | GR & QC Articles
arXiv:2503.01934v1 Announce Type: new
Abstract: If two particles collide in the vicinity of a black hole horizon, their center of mass energy is practically unlimited, so another black hole with a large mass and thus entropy can be created. The resulting black hole can then merge with the original one. If the black hole is created very close to the horizon, its energy will be highly redshifted for an asymptotic observer. However, its entropy is not redshifted. We demonstrated that the newly created entropy can be higher than the Bekenstein-Hawking entropy of the final black hole, though we neglect that a certain amount of energy can escape to infinity, carrying away part of the entropy produced in the process. This is a counter-example to the statement that the black hole thermal entropy counts all the states inside the black hole. Unlike similar examples, this colliding process does not involve exotic matter, alternative theories of gravity, nor artificial ad hoc gluing of two different spacetimes.
Conclusions:
- When two particles collide near a black hole horizon, their center of mass energy is practically unlimited, allowing for the creation of another black hole with a large mass and entropy.
- The resulting black hole can merge with the original one.
- If the black hole is created close to the horizon, its energy will be redshifted for an asymptotic observer, but its entropy is not affected.
- The newly created entropy can be higher than the Bekenstein-Hawking entropy of the final black hole, although some energy and entropy may escape to infinity.
- This counters the belief that the black hole thermal entropy accounts for all the states inside it.
- The colliding process described does not involve exotic matter, alternative theories of gravity, or artificial gluing of spacetimes.
Future Roadmap:
The findings of this study pose interesting challenges and opportunities for further exploration in the field of black hole physics:
1. Investigate the behavior of black holes near the horizon:
Further research is needed to understand the dynamics of black holes and the precise mechanisms that contribute to the creation of new black holes near the event horizon. This will involve studying the energy-redshifting phenomenon and its implications for black hole formation and merging.
2. Quantify the escape of energy and entropy:
It is important to accurately calculate the amount of energy and entropy that can escape to infinity during the black hole collision and merging process. Understanding this escaping mechanism will provide deeper insights into the overall entropy balance and the validity of the Bekenstein-Hawking entropy as a measure of all states within a black hole.
3. Explore the limitations and applicability of the findings:
As with any scientific study, it is crucial to investigate the limitations and specific conditions under which the described colliding process occurs. Further analysis is required to determine if the results hold true in various scenarios and if any additional factors or conditions need to be considered for a comprehensive understanding of black hole entropy.
4. Explore related concepts in black hole physics:
The counter-example presented in this study opens up avenues for exploring other related concepts, such as the behavior of exotic matter, alternative theories of gravity, and artificial gluing of spacetimes. Investigating these areas could provide a deeper understanding of the interconnectedness and interplay between different aspects of black hole physics.
Challenges and Opportunities:
The roadmap outlined above faces several challenges and offers significant opportunities:
1. Complexity of black hole dynamics:
Studying black hole dynamics is a complex task that requires advanced mathematical models and computational simulations. Overcoming these challenges will require interdisciplinary collaborations and advancements in computational techniques.
2. Verification and validation:
The findings presented in this study need to be verified and validated through additional experiments, observations, and theoretical studies. This requires collaborations between astrophysicists, theoretical physicists, and experimentalists to gather sufficient evidence and reach a consensus.
3. Accessibility to observation and measurement:
Black holes are inherently challenging to observe and measure due to their extreme gravitational effects and the limitations of current observational technologies. Advances in observational capabilities, such as gravitational wave detectors and future space telescopes, will provide opportunities for collecting empirical data to validate theoretical predictions.
4. Bridging theoretical and observational approaches:
Integrating theoretical predictions with observational data is crucial for a comprehensive understanding of black holes. Bridging the gap between theoretical models and observational constraints requires close collaboration between theorists and observers, as well as innovative approaches to combine data and theoretical simulations.
Note: The roadmap presented here represents potential directions for future research and exploration in the field of black hole physics. It is important to acknowledge that this is just one study and further investigations are necessary to build upon and confirm these findings.
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by jsendak | Feb 27, 2025 | GR & QC Articles
arXiv:2502.18560v1 Announce Type: new
Abstract: The quantum nature of gravity remains an open question in fundamental physics, lacking experimental verification. Gravitational waves (GWs) provide a potential avenue for detecting gravitons, the hypothetical quantum carriers of gravity. However, by analogy with quantum optics, distinguishing gravitons from classical GWs requires the preservation of quantum coherence, which may be lost due to interactions with the cosmic environment causing decoherence. We investigate whether GWs retain their quantum state by deriving the reduced density matrix and evaluating decoherence, using an environmental model where a scalar field is conformally coupled to gravity. Our results show that quantum decoherence of GWs is stronger at lower frequencies and higher reheating temperatures. We identify a model-independent amplitude threshold below which decoherence is negligible, providing a fundamental limit for directly probing the quantum nature of gravity. In the standard cosmological scenario, the low energy density of the universe at the end of inflation leads to complete decoherence at the classical amplitude level of inflationary GWs. However, for higher energy densities, decoherence is negligible within a frequency window in the range $100 {rm Hz} text{-} 10^8 {rm Hz}$, which depends on the reheating temperature. In a kinetic-dominated scenario, the dependence on reheating temperature weakens, allowing GWs to maintain quantum coherence above $10^7 {rm Hz}$.
The Quantum Nature of Gravity and the Detectability of Gravitons
Gravity, one of the fundamental forces of nature, is still not fully understood in the framework of quantum physics. While we have theories like general relativity to describe gravity, there is no experimental evidence for the existence of gravitons, the hypothetical quantum particles carrying gravity. In this study, we explore the potential of gravitational waves (GWs) to provide a way to detect gravitons. However, distinguishing gravitons from classical GWs is a challenging task due to the loss of quantum coherence caused by interactions with the cosmic environment.
Investigating Quantum Decoherence in Gravitational Waves
To evaluate the preservation of quantum coherence in GWs, we analyze the decoherence effect using an environmental model where a scalar field is conformally coupled to gravity. By deriving the reduced density matrix, we are able to quantify the level of decoherence in GWs. Our findings reveal that the degree of quantum decoherence in GWs is dependent on both the frequency of the waves and the reheating temperature of the universe.
Frequency and Reheating Temperature Dependencies
We establish a key observation that quantum decoherence of GWs is stronger at lower frequencies and higher reheating temperatures. At these conditions, the interaction with the cosmic environment causes stronger decoherence effects and makes it more difficult to maintain the quantum state of the GWs.
Fundamental Limit for Probing the Quantum Nature of Gravity
Our research leads to an important conclusion: there exists an amplitude threshold below which the decoherence of GWs becomes negligible. This threshold serves as a fundamental limit for directly investigating the quantum nature of gravity.
Implications in Cosmological Scenarios
In the standard cosmological scenario, where the energy density of the universe is low at the end of inflation, the decoherence effects in GWs reach a complete level at the classical amplitude of inflationary GWs. However, for higher energy densities, the decoherence becomes negligible within a specific frequency range of 0 {rm Hz} text{-} 10^8 {rm Hz}$, which is dependent on the reheating temperature.
In the context of a kinetic-dominated scenario, the dependence on the reheating temperature weakens, allowing GWs to maintain quantum coherence even at frequencies above ^7 {rm Hz}$. This opens up opportunities to study the quantum nature of gravity in different cosmological scenarios.
Future Roadmap: Challenges and Opportunities
Challenges
- The preservation of quantum coherence in GWs is a challenging task due to the strong interactions with the cosmic environment.
- Differentiating gravitons from classical GWs requires addressing the issue of decoherence.
- Understanding the impact of lower frequencies and higher reheating temperatures on quantum decoherence in GWs.
Opportunities
- The identification of an amplitude threshold for negligible decoherence provides a fundamental limit for directly probing the quantum nature of gravity.
- Exploring the specific frequency range and reheating temperature dependencies allows for the investigation of quantum coherence in different cosmological scenarios.
- Advancing our understanding of the quantum nature of gravity through experimental verification of gravitons using GW detection methods.
Note: This study contributes to the ongoing quest to unify quantum mechanics and gravity, shedding light on the quantum nature of gravity and its potential experimental detection through GWs.
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by jsendak | Feb 24, 2025 | GR & QC Articles
arXiv:2502.14927v1 Announce Type: new
Abstract: Our present contribution sets out to investigate how combined effects of Lorentz-symmetry violation (LSV) and Loop-Quantum-Gravity(LQG)-modified photon dispersion relations affect the threshold anomaly of cosmic photons. The point of departure is the post-Maxwellian version of Electromagnetism induced by LQG effects. We then consider the problem of gamma-ray attenuation by the Extragalactic Background Light (EBL) and the Cosmic Microwave Background Radiation (CMB) dominated by the Breit-Wheeler Effect. By following this path, we aim at the establishment of a new bridge between LSV and astrophysical phenomena in the framework of LQG.
Investigating the Combined Effects of Lorentz-Symmetry Violation and Loop-Quantum-Gravity on Cosmic Photon Threshold Anomaly
In this article, we explore the potential implications of Lorentz-symmetry violation (LSV) and Loop-Quantum-Gravity (LQG) modified photon dispersion relations on the threshold anomaly of cosmic photons. Our research starts with the post-Maxwellian version of Electromagnetism induced by LQG effects. We then delve into the problem of gamma-ray attenuation by the Extragalactic Background Light (EBL) and the Cosmic Microwave Background Radiation (CMB), focusing on the Breit-Wheeler Effect domination. Through this investigation, we aim to create a connection between LSV and astrophysical phenomena within the framework of LQG.
Future Roadmap: Challenges and Opportunities
1. Further Investigation of LSV and LQG Effects
One of the key challenges for future research is to gain a deeper understanding of the combined effects of Lorentz-symmetry violation and Loop-Quantum-Gravity on various physical phenomena. This requires rigorous theoretical studies and numerical simulations to explore the implications and constraints on LSV and LQG parameters. Collaborative efforts between physicists specializing in LSV and LQG can lead to significant advancements in this field.
2. Experimental Verification
In order to validate the theoretical predictions, experimental verification is required. Designing and conducting experiments that can probe the effects of LSV and LQG on photon dispersion relations and the Breit-Wheeler Effect is a promising avenue for future research. This would involve collaborations between astrophysicists and experimental physicists to design innovative experiments and analyze the resulting data.
3. Implications for Astrophysical Phenomena
The research presented in this article suggests a potential connection between LSV and astrophysical phenomena. Exploring the implications of LSV and LQG on various astrophysical processes, such as gamma-ray attenuation by the EBL and CMB, opens up new avenues for understanding the fundamental laws of physics in extreme cosmic environments. This can lead to novel insights into the behavior of high-energy photons and their interactions.
4. Theoretical and Practical Applications
The findings from this research can have broader implications beyond just theoretical physics. Understanding the fundamental aspects of LSV and LQG could potentially lead to the development of advanced technologies. For example, insights gained from studying the modification of photon dispersion relations could contribute to the improvement of high-energy photon detectors and communication systems.
5. Exploring New Frontiers
The investigation of LSV and LQG effects on cosmic photons is still a relatively unexplored territory. As more research is conducted and new theories and experiments emerge, there is an opportunity to push the boundaries of our understanding further. This field presents exciting prospects for both theoretical and experimental physicists to contribute to the development of a more comprehensive and accurate description of the fundamental nature of the universe.
Conclusion
By investigating the combined effects of Lorentz-symmetry violation and Loop-Quantum-Gravity on the threshold anomaly of cosmic photons, we aim to establish a new bridge between LSV and astrophysical phenomena within the framework of LQG. This roadmap highlights the challenges and opportunities that lie ahead in terms of further theoretical investigations, experimental verification, implications for astrophysics, technological applications, and pushing the boundaries of current knowledge. The exploration of LSV and LQG effects offers an exciting frontier for researchers to unravel the mysteries of the universe.
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by jsendak | Feb 21, 2025 | GR & QC Articles
arXiv:2502.14025v1 Announce Type: new
Abstract: The Simulating eXtreme Spacetimes Collaboration’s code SpEC can now routinely simulate binary black hole mergers undergoing $sim25$ orbits, with the longest simulations undergoing nearly $sim180$ orbits. While this sounds impressive, the mismatch between the highest resolutions for this long simulation is $mathcal{O}(10^{-1})$. Meanwhile, the mismatch between resolutions for the more typical simulations tends to be $mathcal{O}(10^{-4})$, despite the resolutions being similar to the long simulations’. In this note, we explain why mismatch alone gives an incomplete picture of code — and waveform — quality, especially in the context of providing waveform templates for LISA and 3G detectors, which require templates with $mathcal{O}(10^{3}) – mathcal{O}(10^{5})$ orbits. We argue that to ready the GW community for the sensitivity of future detectors, numerical relativity groups must be aware of this caveat, and also run future simulations with at least three resolutions to properly assess waveform accuracy.
Future Roadmap for Readers: Challenges and Opportunities
Introduction
This article discusses the limitations of current simulations in accurately predicting gravitational wave (GW) waveforms, specifically in the context of providing waveform templates for future GW detectors like LISA and 3G detectors. It explains the importance of running simulations with higher resolutions and proposes a future roadmap for numerical relativity groups to enhance waveform accuracy.
Limitations of Current Simulations
The article highlights that while the current simulations using the code SpEC can simulate binary black hole mergers for a significant number of orbits (up to nearly 180 orbits), the resolution used in these simulations results in a significant mismatch compared to higher resolution simulations. The mismatch is on the order of $mathcal{O}(10^{-4})$ for typical simulations and $mathcal{O}(10^{-1})$ for longer simulations. This indicates that the quality of the code and waveform is not accurately represented by mismatch alone.
Importance of High-Resolution Simulations
The article emphasizes the need for waveform templates that accurately represent the behavior of GW signals for future detectors, which require templates with $mathcal{O}(10^{3}) – mathcal{O}(10^{5})$ orbits. To achieve this, numerical relativity groups must be aware of the limitations caused by mismatch and run simulations with at least three resolutions to properly assess waveform accuracy.
Roadmap for Enhancing Waveform Accuracy
- Awareness: Numerical relativity groups must be aware of the limitations of mismatch in assessing waveform accuracy. This requires understanding the incomplete picture provided by mismatch alone.
- Higher Resolutions: To improve waveform accuracy, future simulations should be conducted with higher resolutions. This will help reduce the mismatch between simulations and provide more reliable waveform templates for future detectors.
- Multi-Resolution Simulations: Simulations should be run with at least three resolutions to properly assess waveform accuracy. This will allow for a more comprehensive understanding of the code quality and waveform behavior.
Conclusion
The challenges and opportunities on the horizon involve improving the accuracy of GW waveform templates for future detectors. By addressing the limitations of mismatch and conducting simulations with higher resolutions, numerical relativity groups can provide more reliable waveform predictions. This roadmap will help prepare the GW community for the sensitivity of future detectors and enhance our understanding of extreme spacetimes.
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by jsendak | Feb 20, 2025 | GR & QC Articles
arXiv:2502.13152v1 Announce Type: new
Abstract: The Lagrangian formulation of Gravitoelectromagnetism (GEM) theory is considered. GEM is a gravitational theory constructed based on the similarities between gravity and electromagnetism. In this framework, we investigate gravitational Compton scattering by calculating its cross section at both zero and finite temperatures. Thermal effects are introduced via the Thermo Field Dynamics formalism. Some comparisons between GEM theory and QED have been developed. The limits of high temperature have been analyzed.
GEM Theory and Gravitational Compton Scattering
In this article, we explore the Lagrangian formulation of Gravitoelectromagnetism (GEM) theory and its application to gravitational Compton scattering. GEM is a gravitational theory that draws upon similarities between gravity and electromagnetism, providing a new perspective on gravitational interactions.
The Lagrangian Formulation of GEM Theory
GEM theory is formulated using a Lagrangian approach, which allows us to study the dynamics of gravitational fields and their interactions. This provides a powerful framework for investigating gravitational phenomena and comparing them to their electromagnetic counterparts.
Gravitational Compton Scattering
By applying GEM theory, we can study gravitational Compton scattering, a process where a gravitational wave interacts with a particle and changes its momentum. We calculate the cross section for this scattering process at both zero and finite temperatures.
Thermal Effects and Thermo Field Dynamics
Incorporating thermal effects into the study of gravitational Compton scattering, we utilize the Thermo Field Dynamics formalism. This allows us to account for the influence of temperature on the scattering process and explore its implications.
Comparisons with QED
We also compare GEM theory to Quantum Electrodynamics (QED), the theory of electromagnetic interactions. This analysis helps us understand the similarities and differences between gravitational and electromagnetic interactions, shedding light on the nature of gravity itself.
Limits of High Temperature
We analyze the limits of high temperature within the context of GEM theory. This investigation provides insights into the behavior of gravitational Compton scattering at extreme thermal conditions and contributes to our understanding of gravitational interactions in various environments.
Roadmap for Readers
This article begins by introducing the Lagrangian formulation of GEM theory and its application to gravitational Compton scattering. We delve into the theoretical framework, discussing the similarities and differences between gravity and electromagnetism. Through the calculations of cross sections, we explore the effects of temperature on gravitational Compton scattering using the Thermo Field Dynamics formalism. Additionally, we compare GEM theory to QED to gain a comprehensive understanding of gravitational interactions. Finally, we analyze the limits of high temperature and their implications for gravitational Compton scattering.
Challenges and Opportunities
- Challenge: The study of GEM theory and gravitational Compton scattering requires a deep understanding of advanced theoretical concepts. Readers may need to familiarize themselves with Lagrangian formalism and the basics of GEM theory before proceeding.
- Opportunity: Exploring the similarities between GEM theory and QED provides an exciting avenue for interdisciplinary research, potentially leading to insights into quantum gravity.
- Challenge: Incorporating thermal effects into the study of gravitational Compton scattering introduces additional complexities, requiring readers to grasp the Thermo Field Dynamics formalism.
- Opportunity: Investigating the limits of high temperature in GEM theory opens possibilities for understanding gravitational interactions in extreme environments, such as the early universe or black hole surroundings.
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by jsendak | Feb 11, 2025 | GR & QC Articles
arXiv:2502.05217v1 Announce Type: new
Abstract: In this paper, we consider the spherically symmetric gravitational collapse of isotropic matter undergoing dissipation in the form of heat flux, with a generalized Vaidya exterior, in the context of $f(R, T)$ gravity. Choosing $f(R, T)=R+2lambda T$, and applying the $f(R, T)$ junction conditions on the field equations for the interior and exterior regions, we have obtained matching conditions of the matter-Lagrangian and its derivatives across the boundary. The time of formation of singularity and the time of formation of apparent horizon have been determined and constraints on the integration constants are examined for which the final singularity is hidden behind the horizon.
In this paper, the authors study the gravitational collapse of isotropic matter with dissipation in the form of heat flux, using the framework of $f(R, T)$ gravity. They focus on the spherically symmetric case, with a generalized Vaidya exterior. The specific choice for the $f(R, T)$ function is $f(R, T)=R+2lambda T$, and the authors apply the $f(R, T)$ junction conditions to the field equations for the interior and exterior regions.
One of the main results of the study is the matching conditions of the matter-Lagrangian and its derivatives across the boundary. These matching conditions are important for a consistent description of the gravitational collapse process.
The authors then determine the time of formation of the singularity and the time of formation of the apparent horizon. They examine the constraints on the integration constants that lead to the singularity being hidden behind the horizon.
Roadmap for Readers
To further explore the topic of spherically symmetric gravitational collapse and its relation to $f(R, T)$ gravity, readers can follow the suggested roadmap:
1. Understand the basics of gravitational collapse
Before diving into the specific case of spherically symmetric collapse, it is important to have a solid understanding of the basics of gravitational collapse. Readers should familiarize themselves with concepts such as singularities, event horizons, and the different types of collapse scenarios.
2. Study the Vaidya metric and its application to gravitational collapse
The Vaidya metric is a useful tool for describing the gravitational collapse process. Readers should study the properties of the Vaidya metric and its application to modeling collapse scenarios. This will provide the necessary background for understanding the specific case considered in the paper.
3. Learn about $f(R, T)$ gravity
$f(R, T)$ gravity is a modified theory of gravity that includes additional terms in the gravitational action. Readers should familiarize themselves with the basic concepts of $f(R, T)$ gravity and its motivations. Understanding the field equations and the junction conditions will be crucial for comprehending the results presented in the paper.
4. Analyze the matching conditions derived in the paper
The matching conditions of the matter-Lagrangian and its derivatives across the boundary are an essential result of the study. Readers should carefully analyze these matching conditions and understand their implications for the physical description of the collapse process.
5. Explore the constraints on integration constants
The constraints on the integration constants, which determine whether the singularity is hidden behind the horizon, are an important aspect of the study. Readers should investigate the different constraints and their implications. This will provide insights into the behavior of collapsing systems in $f(R, T)$ gravity.
6. Consider other applications and extensions
Finally, readers can consider other applications and extensions of the results presented in the paper. This could include studying different matter models, exploring alternative $f(R, T)$ functions, or investigating the implications for black hole formation.
Challenges and Opportunities
While studying the spherically symmetric collapse in the context of $f(R, T)$ gravity opens up new avenues of research, several challenges and opportunities lie ahead:
- Theoretical Challenges: The theoretical analysis of gravitational collapse in modified gravity theories is a challenging task. Readers should be prepared to delve into advanced mathematical techniques and field equations.
- Experimental Verification: The predictions of $f(R, T)$ gravity for gravitational collapse need to be tested against observational data or laboratory experiments. The opportunities for experimental verification can lead to a deeper understanding of the theory.
- Extensions and Generalizations: The results obtained in this paper are specific to spherically symmetric collapse with a particular $f(R, T)$ function. Readers can explore extensions of the study to other geometries, matter models, or different choices of $f(R, T)$ functions.
- Connections to Other Fields: Gravitational collapse has connections to various fields, such as astrophysics and cosmology. Readers can explore the interdisciplinary aspects and implications of the results in this paper.
In summary, readers interested in the spherically symmetric gravitational collapse and its relation to $f(R, T)$ gravity should follow a roadmap that includes understanding the basics, studying the specific case presented in the paper, analyzing the derived matching conditions and constraints, and exploring further applications and extensions. Along the way, they will encounter theoretical challenges, opportunities for experimental verification, possibilities for generalizations, and connections to other fields.
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