by jsendak | Jan 11, 2024 | GR & QC Articles
Modified Newtonian Dynamics (MOND), postulating a breakdown of Newtonian
mechanics at low accelerations, has considerable success at explaining galaxy
kinematics. However, the quadrupole of the gravitational field of the Solar
System (SS) provides a strong constraint on the way in which Newtonian gravity
can be modified. In this paper we assess the extent to which modified gravity
formulations of MOND are capable of accounting simultaneously for the Radial
Acceleration Relation (RAR) — encapsulating late-type galaxy dynamics — the
Cassini measurement of the SS quadrupole and the kinematics of wide binaries in
the Solar neighbourhood. We achieve this by extending the method of Desmond
(2023) to infer the location and sharpness of the MOND transition from the
SPARC RAR under broad assumptions for the behaviour of the interpolating
function and external field effect. We constrain the same quantities from the
SS quadrupole, finding that it requires a significantly sharper transition
between the deep-MOND and Newtonian regimes than is allowed by the RAR (an
8.7$sigma$ tension under fiducial model assumptions). This may be relieved by
allowing additional freedom in galaxies’ mass-to-light ratios — which also
provides a better RAR fit — and more significantly by removing galaxies with
bulges. We show that the SS quadrupole constraint implies, to high precision,
no deviation from Newtonian gravity in wide binaries in the Solar
neighbourhood, and speculate on possible resolutions of this incompatibility
between SS and galaxy data within the MOND paradigm.
Examine the conclusions of the following text and outline a future roadmap for readers, indicating potential challenges and opportunities on the horizon.
The Road Ahead: Challenges and Opportunities
The conclusions of the study suggest that modified gravity formulations of Modified Newtonian Dynamics (MOND) may face challenges in simultaneously accounting for the Radial Acceleration Relation (RAR), the Cassini measurement of the Solar System (SS) quadrupole, and the kinematics of wide binaries in the Solar neighbourhood. However, there are also potential opportunities for further investigation within the MOND paradigm. Here is a future roadmap for readers:
1. Exploring MOND’s Ability to Account for RAR
One challenge highlighted by the study is the tension between the MOND formulation and the RAR. Readers can delve deeper into understanding the specific constraints placed on the transition between deep-MOND and Newtonian gravity regimes by the RAR. Further research could focus on refining assumptions about the interpolating function and external field effect to achieve a better fit with the RAR data.
2. Investigating Impact of Mass-to-Light Ratios
The study suggests that allowing additional freedom in galaxies’ mass-to-light ratios could potentially alleviate the tension between the SS quadrupole constraint and the RAR. Readers can explore the implications of varying mass-to-light ratios and how it affects the overall fit with both the RAR and SS quadrupole data. This avenue of research could shed light on the connection between galaxy dynamics and modified gravity formulations.
3. Reconsidering Galaxies with Bulges
An opportunity arises from the finding that removing galaxies with bulges could significantly improve compatibility between the SS quadrupole constraint and the RAR. Readers can engage in further investigation to understand the role of bulges in the context of MOND and its impact on the overall dynamics of galaxies. This exploration may lead to insights into the underlying mechanisms of modified gravity in galaxy kinematics.
4. Addressing Incompatibility in Solar Neighbourhood Binaries
The study highlights that the SS quadrupole constraint implies no deviation from Newtonian gravity in wide binaries in the Solar neighbourhood. Readers can explore potential resolutions for this incompatibility within the MOND paradigm. By investigating alternative explanations or extending MOND’s framework, researchers may uncover new insights into the behavior of gravity at small scales.
Conclusion
While the study presents challenges for modified gravity formulations of MOND, it also offers opportunities for further research and exploration. By delving deeper into the tensions identified and investigating potential solutions, future work can advance our understanding of galaxy dynamics and the role of modified gravity in explaining the universe’s behavior.
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by jsendak | Jan 11, 2024 | GR & QC Articles
The visible universe is filled with different types of plasma media in the
form of stars, nebulas and other forms of excited gases. These matter fields
have a high influence on the gravity and are likely to be present around the
black holes due to the immense gravitational attraction. Since a plasma medium
affects the speed of light, therefore we investigated the null geodesics and
various optical features around the rotating black hole in Kalb-Ramond gravity
immersed in plasma medium. Various plasma distributions are considered to
develop a comparative study for their influence on unstable null circular
orbits, shadows and evaporation rate of the black hole in the presence of a
plasma medium. Moreover, the shadow results are also compared with Event
Horizon Telescope data for M78* and Sgr A* in order to estimate the parametric
bounds for which the rotating black hole in Kalb-Ramond gravity is considered
either M87* or Sgr A* under the different values of plasma parameters. From
this analysis, we also found the distribution of plasma that has a significant
impact on the above mentioned features and is most likely to be present around
M87* and Sgr A*.
The Influence of Plasma Medium on the Rotating Black Hole in Kalb-Ramond Gravity
The visible universe is filled with various types of plasma media, such as stars, nebulas, and excited gases. These matter fields have a strong gravitational attraction, which is likely to be present around black holes. The presence of a plasma medium affects the speed of light, leading us to investigate the null geodesics and optical features near rotating black holes in Kalb-Ramond gravity immersed in a plasma medium.
Our study involves considering different plasma distributions in order to compare their influence on unstable null circular orbits, shadows, and the evaporation rate of the black hole. To determine the parametric bounds for which the rotating black hole in Kalb-Ramond gravity is considered either M87* or Sgr A*, we compare our shadow results with data from the Event Horizon Telescope for M78* and Sgr A*.
From our analysis, we conclude that the distribution of plasma has a significant impact on the above-mentioned features and is most likely to be present around M87* and Sgr A*. These findings suggest that the plasma medium plays a crucial role in understanding the behavior of black holes in Kalb-Ramond gravity.
Roadmap for Future Research
Continuing research in this field holds many challenges and opportunities. Here is a roadmap for future studies:
- Study Different Plasma Distributions: Further investigate the influence of various plasma distributions on unstable null circular orbits, shadows, and the evaporation rate of rotating black holes. Comparisons with observational data will help refine our understanding.
- Explore Effects on Gravity: Investigate in more detail how plasma media affects the gravitational field around black holes. This will provide insights into the behavior of these cosmic phenomena.
- Extending Analysis to Other Black Holes: Apply the findings to other known black holes apart from M87* and Sgr A*. This will help determine if the observed effects are unique to these specific black holes.
- Consider Additional Gravitational Theories: Extend the study to explore the influence of plasma on rotating black holes in other gravitational theories apart from Kalb-Ramond gravity. Comparisons with different theories could provide further insights.
- Explore Plasma Generation Mechanisms: Investigate the mechanisms responsible for the generation and distribution of plasma around black holes. This will aid in understanding the origin and nature of plasma media in the universe.
- Utilize Advanced Observational Techniques: Make use of advanced observational techniques, such as improved telescopes and data analysis methods, to gather more precise data on shadows and other optical features around black holes.
By addressing these challenges and opportunities, future research will contribute to a deeper understanding of the influence of plasma medium on rotating black holes and further our knowledge of these enigmatic cosmic entities.
Reference: [Insert Reference Here]
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by jsendak | Jan 11, 2024 | GR & QC Articles
The construction of high-resolution shock-capturing schemes is vital in
producing highly accurate gravitational waveforms from neutron star binaries.
The entropy based flux limiting (EFL) scheme is able to perform fast converging
binary neutron star merger simulations reaching up to fourth-order convergence
in the gravitational waveform phase. Here, we extend the applicability of the
EFL method beyond special/general relativistic hydrodynamics to scalar
conservation laws and show how to treat systems without a thermodynamic
entropy. This is an indication that the method has universal applicability to
any system of partial differential equations that can be written in
conservation form. We also present some further very challenging
special/general relativistic hydrodynamics applications of the EFL method and
use it to construct eccentricity reduced initial data for a specific neutron
star binary and show up to optimal fifth-order convergence in the gravitational
waveform phase for this simulation.
Future Roadmap: Challenges and Opportunities
1. Expanding Applicability
The EFL method has shown promising results in producing highly accurate gravitational waveforms from neutron star binaries. Moving forward, one of the key challenges is to further extend the applicability of the EFL method to other systems beyond special/general relativistic hydrodynamics. This would involve exploring its potential in treating scalar conservation laws and systems without a thermodynamic entropy.
2. Universal Applicability
The author suggests that the EFL method may have universal applicability to any system of partial differential equations that can be written in conservation form. This opens up exciting possibilities for applying the method in various scientific fields beyond astrophysics. The challenge here would be to identify and explore potential areas where the EFL method can be utilized effectively.
3. Challenging Applications
Furthermore, the article mentions the presentation of more challenging applications of the EFL method in special/general relativistic hydrodynamics. These applications could involve complex scenarios or unique conditions that require advanced numerical techniques. Overcoming these challenges would provide valuable insights and enhance the understanding of relativistic hydrodynamics.
4. Optimizing Convergence
The EFL method has demonstrated up to fourth-order convergence in the gravitational waveform phase for binary neutron star merger simulations. However, the article presents an opportunity to achieve even higher convergence by constructing eccentricity reduced initial data for a specific neutron star binary and reaching up to optimal fifth-order convergence in the gravitational waveform phase. This optimization would require careful analysis and adjustment of the simulation parameters.
Conclusion
The future roadmap for readers interested in the EFL method includes expanding its applicability to other systems, exploring its universal applicability, tackling challenging applications in special/general relativistic hydrodynamics, and optimizing convergence in gravitational waveform simulations. By addressing these challenges and seizing the opportunities on the horizon, researchers can further enhance the accuracy and understanding of gravitational waveform predictions for neutron star binaries and potentially extend the method’s applicability to other domains as well.
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by jsendak | Jan 10, 2024 | GR & QC Articles
We investigate the amplification of the genuine tripartite nonlocality (GTN)
and the genuine tripartite entanglement (GTE) of Dirac particles in the
background of a Schwarzschild black hole by a local filtering operation under
decoherence. It is shown that both the physically accessible GTN and the
physically accessible GTE are decreased by the Hawking effect and decoherence.
The “sudden” death of the physically accessible GTN occurs at some critical
Hawking temperature, and the critical Hawking temperature degrades as the
decoherence strength increases. In particular, it is found that the critical
Hawking temperature of “sudden death” can be prolonged by applying the local
filtering operation, which means that the physically accessible GTN can exist
for a longer time. Furthermore, we also find that the physically accessible GTE
approaches to the nonzero stable value in the limit of infinite Hawking
temperature for most cases, but if the decoherence parameter p is less than 1,
the “sudden death” of GTE will take place when the decoherence strength is
large enough. It is worth noting that the nonzero stable value of GTE can be
increased by performing the local filtering operation, even in the presence of
decoherence. Finally, we explore the generation of physically inaccessible GTN
and GTE of other tripartite subsystems under decoherence, it is shown that the
physically inaccessible GTN cannot be produced, but the physically inaccessible
GTE can be produced, namely, GTE can pass through the event horizon of black
hole, but the GTN cannot do it. In addition, we can see that the generated
physically inaccessible GTE can be increased by applying the local filtering
operation, even if the system suffers decoherence.
Conclusions:
- The genuine tripartite nonlocality (GTN) and genuine tripartite entanglement (GTE) of Dirac particles in the background of a Schwarzschild black hole are decreased by the Hawking effect and decoherence.
- The “sudden” death of the physically accessible GTN occurs at a critical Hawking temperature, degraded by increasing decoherence strength.
- The critical Hawking temperature of “sudden death” can be prolonged by applying a local filtering operation, allowing the physically accessible GTN to exist for a longer time.
- The physically accessible GTE approaches a nonzero stable value in the limit of infinite Hawking temperature, but “sudden death” of GTE occurs when the decoherence strength is large enough for certain cases.
- The nonzero stable value of GTE can be increased by performing the local filtering operation, even in the presence of decoherence.
- The generation of physically inaccessible GTN is not possible under decoherence, but physically inaccessible GTE can be produced, passing through the event horizon of a black hole.
- The generated physically inaccessible GTE can be increased by applying the local filtering operation, even in the presence of decoherence.
Future Roadmap
The findings from this study provide insights into the behavior of genuine tripartite nonlocality and entanglement of Dirac particles near a Schwarzschild black hole under the influence of decoherence. Moving forward, there are several potential challenges and opportunities on the horizon:
- Exploration of other black hole backgrounds: It would be valuable to investigate how genuine tripartite nonlocality and entanglement behave in the presence of different types of black holes, such as Kerr black holes or charged black holes. This could offer a more comprehensive understanding of the effects of different black hole properties.
- Quantifying the impact of other decoherence models: The current study focused on decoherence caused by local filtering operations. It would be interesting to explore the effects of other types of decoherence models, such as environmental noise or interaction with additional particles. Understanding how different decoherence mechanisms affect the physical accessibility of GTN and GTE could shed light on their robustness in practical scenarios.
- Experimental verification: Conducting experimental tests to validate the theoretical predictions made in this study would be a crucial next step. This would involve designing and implementing experiments that can simulate the behavior of Dirac particles near a black hole under controlled conditions of decoherence. Such experiments could provide evidence for the observed phenomena and contribute to the development of quantum technologies.
- Applications in quantum information processing: The study highlights the importance of GTN and GTE in the context of quantum information processing. Further research could explore how the manipulation and control of GTN and GTE near black holes could be harnessed for quantum communication, cryptography, and computation. Understanding the potential applications of these phenomena could enable advancements in quantum technologies.
Overall, the study sets a foundation for future investigations and opens up new avenues for exploration in the field of quantum physics and black hole dynamics. By addressing the challenges and opportunities outlined above, researchers can continue to deepen our understanding of these fascinating phenomena and potentially unlock groundbreaking applications in the field of quantum mechanics.
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by jsendak | Jan 10, 2024 | GR & QC Articles
Gravitational waves are a unique probe of the early Universe, as the Universe
is transparent to gravitational radiation right back to the beginning. In this
article, we summarise detection prospects and the wide scope of primordial
events that could lead to a detectable stochastic gravitational wave
background. Any such background would shed light on what (if anything) lies
beyond the Standard Model, sometimes at remarkably high scales. We overview the
range of strategies for detecting a stochastic gravitational wave background
before delving deep into three major primordial events that can source such a
background. Finally, we summarize the landscape of other sources of primordial
backgrounds.
Gravitational waves provide a unique opportunity to probe the early Universe, as they can travel through space without being affected by any obstacles. This article explores the potential for detecting a stochastic gravitational wave background, which could provide valuable insights into the physics beyond the Standard Model at high scales.
Detection Prospects
Understanding the detection prospects of a stochastic gravitational wave background is crucial in studying the early Universe. With advancements in technology and techniques, detecting these gravitational waves is becoming more feasible. Scientists are continuously improving the sensitivity of gravitational wave detectors, such as LIGO and VIRGO, to increase the chances of detecting this cosmic signal.
Primordial Events
The article delves into three major primordial events that could be responsible for generating a detectable stochastic gravitational wave background. These events are:
- Inflation: The rapid expansion of the Universe in its early stages can produce gravitational waves. Detecting these waves would provide evidence for inflation and shed light on the physics behind this phenomenon.
- Phase Transitions: Transitions between different phases of matter in the early Universe can also generate gravitational waves. Studying this background can give insights into the fundamental forces and particles at play during these phase transitions.
- Cosmic Strings: Cosmic strings are hypothetical one-dimensional objects that could have formed in the early Universe. Their motion can create gravitational waves that leave a distinct signature in the background.
Other Sources of Primordial Backgrounds
In addition to these major primordial events, there are other potential sources of primordial backgrounds that are briefly summarized in the article. These include early universe relics, such as primordial black holes and topological defects, which can contribute to the gravitational wave background.
Roadmap for Future Research
As we move forward, the roadmap for researchers in this field involves:
- Improving Detector Sensitivity: Efforts should be made to enhance the sensitivity of current gravitational wave detectors, as well as developing new technologies to detect even fainter signals.
- Refining Analysis Techniques: Developing more advanced and accurate data analysis techniques will help extract crucial information from the detected gravitational wave signals.
- Expanding Observational Reach: Collaborations between gravitational wave observatories worldwide should be encouraged to cover a wider region of the sky and improve the chances of detecting a stochastic gravitational wave background.
- Exploring New Physics: A detected stochastic gravitational wave background would provide valuable insights into physics beyond the Standard Model. Researchers should explore new theories and models that can explain the observed signals and help unravel the mysteries of the early Universe.
Challenges and Opportunities
While there are immense opportunities in detecting a stochastic gravitational wave background, there are also several challenges to overcome:
- Sensitivity: Increasing the sensitivity of detectors to detect faint gravitational wave signals from the early Universe is a technological challenge that requires continuous advancements.
- Noise Reduction: Filtering out various sources of noise, such as seismic activities and instrumental uncertainties, is crucial to ensure accurate detection and analysis of gravitational wave signals.
- Data Analysis: Developing sophisticated analysis techniques to extract meaningful information from the detected signals is an ongoing research area.
- Probability of Detection: The stochastic nature of gravitational waves means that a detection is not guaranteed. Researchers need to optimize observational strategies to maximize the chances of detecting this cosmic signal.
Despite these challenges, the potential rewards of detecting a stochastic gravitational wave background, including understanding the physics beyond the Standard Model and uncovering the mysteries of the early Universe, make this field of research highly exciting and promising.
“Detecting a stochastic gravitational wave background would provide valuable insights into the physics beyond the Standard Model and unravel the mysteries of the early Universe.”
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by jsendak | Jan 10, 2024 | GR & QC Articles
With about a hundred binary black hole (BBH) mergers detected by
LIGO-Virgo-KAGRA, and with several hundreds expected in the current O4 run, GWs
are revolutionizing our understanding of the universe. Some BBH sources are too
faint to be individually detected, but collectively they may give rise to a
stochastic GW background (SGWB). In this paper, we calculate the SGWB
associated with BBH mergers dynamically assembled in dense star clusters, using
state-of-the-art numerical models. We discuss the role of modeling the
evolution of the mass distribution of BBH mergers, which has significant
implications for model selection and parameter estimation, and could be used to
distinguish between different channels of BBH formation. We demonstrate how the
birth properties of star clusters affect the amplitude and frequency spectrum
of the SGWB, and show that upcoming observation runs of ground-based GW
detectors may be sensitive enough to detect it. Even in the case of a
non-detection, we find that GW data can be used to constrain the highly
uncertain cluster birth properties, which can complement direct observations of
young massive clusters and proto-star clusters in the early universe by JWST.
With the increasing number of binary black hole (BBH) mergers detected by LIGO-Virgo-KAGRA, and even more expected in the current O4 run, gravitational waves (GWs) are revolutionizing our understanding of the universe. However, some BBH sources are too faint to be individually detected, leading to the concept of a stochastic GW background (SGWB) formed by the collective merger of these sources. In this paper, we have used advanced numerical models to calculate the SGWB associated with BBH mergers dynamically assembled in dense star clusters.
Importance of Modeling the Mass Distribution
One of the key aspects that we have focused on is modeling the evolution of the mass distribution of BBH mergers. This is crucial for model selection and parameter estimation, as it allows us to distinguish between different channels of BBH formation. By studying the birth properties of star clusters, we have been able to determine how they affect the amplitude and frequency spectrum of the SGWB.
Potential Detection of SGWB
We find that upcoming observation runs of ground-based GW detectors may have enough sensitivity to detect the SGWB. This would be a significant milestone in our understanding of the universe, as it would provide further evidence for the existence of faint BBH sources that cannot be individually detected. The detection of the SGWB would confirm the importance of stochastic processes in the formation and evolution of black holes.
Using GW Data to Constrain Cluster Birth Properties
Even in the case of a non-detection, our study shows that GW data can still be valuable in constraining the highly uncertain cluster birth properties. This information can complement direct observations of young massive clusters and proto-star clusters in the early universe, such as those provided by the James Webb Space Telescope (JWST). Therefore, even without a detection, our research has implications for a wide range of astrophysical studies.
Roadmap for the Future
Looking ahead, there are several challenges and opportunities on the horizon. Here is a roadmap for future research:
- Refine Numerical Models: Continuously improve numerical models used to calculate the SGWB associated with dynamically assembled BBH mergers in star clusters.
- Increase Sensitivity of GW Detectors: Work towards enhancing the sensitivity of ground-based GW detectors, allowing for more accurate detection of the SGWB.
- Explore Other Sources: Investigate the possibility of stochastic backgrounds from other gravitational wave sources, such as neutron star mergers or cosmic string networks.
- Combine Multiple Observational Approaches: Further integrate GW data with direct observations from telescopes like JWST to better understand the formation and evolution of star clusters and black holes.
- Interpret Non-Detections: Analyze non-detection scenarios to extract valuable information about cluster birth properties and improve our understanding of BBH formation channels.
In conclusion, our research on the SGWB associated with BBH mergers in star clusters has shed light on the importance of modeling their mass distribution and has shown promise for future detections using ground-based GW detectors. The valuable insights gained from this study, whether through a detection or non-detection, can contribute to advancing our understanding of the universe and its astrophysical processes.
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