by jsendak | Dec 31, 2023 | GR & QC Articles
In this article, we investigate the stationary, soliton-like solutions in the
model of the Einstein gravity coupled to a free and complex scalar field, and
extend chains of mini-boson stars to the rotating case. These solutions
manifest as multiple rotating mini-boson stars uniformly arranged along the
rotation axis. Through numerical methods, we obtain chains of rotating
mini-boson stars with one to five constituents. We show the distribution of the
field functions for these chain solutions. Additionally, we also study the
effect of the frequency of the complex scalar field on the ADM mass $M$ and
angular momentum $J$. By comparing the conclusions of the rotating case with
the non-rotating case, there are some intriguing differences. Furthermore, we
observe that there exist two ergospheres for some of these solutions.
Conclusion:
In this study, we explored the existence of stationary, soliton-like solutions in the model of the Einstein gravity coupled to a free and complex scalar field. We extended our investigation to the rotating case and observed that these solutions manifest as multiple rotating mini-boson stars arranged uniformly along the rotation axis. Through numerical methods, we obtained chains of rotating mini-boson stars with varying numbers of constituents. The distribution of the field functions for these chain solutions was examined, and the effect of the frequency of the complex scalar field on the ADM mass $M$ and angular momentum $J$ was studied.
Comparing the conclusions of the rotating case with the non-rotating case revealed intriguing differences. Furthermore, we observed the presence of two ergospheres for some of these solutions.
Future Roadmap:
Potential Challenges:
- Further investigation is required to explore the properties and behavior of these rotating mini-boson star chains in detail.
- It would be challenging to obtain chains with a larger number of constituents, as this may require more complex numerical methods and computational resources.
- The effect of other parameters, such as the mass and charge of the scalar field, on the properties of these solutions should be examined.
- The physical implications and possible astrophysical applications of these rotating mini-boson stars need to be explored.
Potential Opportunities:
- There is an opportunity to further understand the nature of soliton-like solutions in the Einstein gravity coupled to a free and complex scalar field through this research.
- The observed differences between rotating and non-rotating cases present an opportunity for studying the influence of rotation on the properties of such solutions.
- The presence of two ergospheres in some solutions raises interesting questions about their gravitational and energetic properties, which can be explored further.
- The potential astrophysical applications, such as in the study of compact astrophysical objects, gravitational waves, and dark matter, are worth investigating.
This study paves the way for future research on rotating mini-boson stars and their implications in both theoretical physics and astrophysics. A deeper understanding of these solutions and their properties could contribute to advances in our understanding of the fundamental laws of gravity and the behavior of complex scalar fields in extreme physical conditions.
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by jsendak | Dec 31, 2023 | GR & QC Articles
In this work we present a new framework of the gravity sector by considering
the extension $F(R,w)$, in which $R$ is the Ricci scalar and $w$ is the
equation of state. Three different choices of function $F(R,w)$ are
investigated under the Palatini formalism. The models appear equivalent to
$F(R)$ models of gravity with effective momentum-energy tensors. For linear
dependence of Ricci scalar in which $F(R,w)=k(w)R$, the model appears
equivalent to Einstein-Hilbert action with effective momentum-energy tensor.
Recovering the minimal coupling case of the last choice does not face
Jordan-Einstein frame ambiguities and exhibits natural alignments with general
relativity results in the mattertext{/} radiation dominated eras. We discuss
some astrophysical implications of the model by considering scalar fields as
dominant matter forms. We show that the Higgs inflation could be saved within
the $F(R,w)$ model. We suggest some future investigations exemplified by
constant-roll inflation and universe evolution for $F(R)=f(R)k(w)$ where $f(R)$
represents the Starobinsky gravitational form. Using the model and comparing it
with pure $F(R)$ gravity, we provide preliminary indications of $F(R,w)$’s
impact. As a final note, we suggest using the Polytropic equation of state in
future works to investigate $F(R,w)$.
Conclusion:
- A new framework of the gravity sector, considering the extension $F(R,w)$, has been presented in this work.
- Three different choices of function $F(R,w)$ have been investigated under the Palatini formalism.
- These models appear equivalent to $F(R)$ models of gravity with effective momentum-energy tensors.
- For the linear dependence of Ricci scalar ($F(R,w)=k(w)R$), the model is equivalent to the Einstein-Hilbert action with an effective momentum-energy tensor.
- The minimal coupling case of the last choice does not face Jordan-Einstein frame ambiguities and aligns naturally with general relativity results in the matter/radiation dominated eras.
- Astrophysical implications of the model have been discussed, considering scalar fields as dominant matter forms.
- The Higgs inflation can be saved within the $F(R,w)$ model.
- Potential future investigations include constant-roll inflation and universe evolution for $F(R)=f(R)k(w)$, where $f(R)$ represents the Starobinsky gravitational form.
- Preliminary indications of $F(R,w)$’s impact have been provided by comparing it with pure $F(R)$ gravity using the model.
- The use of the Polytropic equation of state is suggested for future works to investigate $F(R,w)$.
Future Roadmap:
Readers who are interested in exploring further research in the gravity sector with the extension $F(R,w)$ can consider the following potential roadmap:
Potential Challenges:
- Understanding the implications and limitations of the different choices of function $F(R,w)$ under the Palatini formalism.
- Investigating how the models in the gravity sector with $F(R,w)$ relate to existing $F(R)$ models of gravity.
- Addressing the challenges and ambiguities in the minimal coupling case of the $F(R,w)$ model.
- Exploring the astrophysical implications of the $F(R,w)$ model with dominant scalar fields as matter forms.
- Validating and further studying the potential impact of the $F(R,w)$ model on the Higgs inflation.
Potential Opportunities:
- Investigating the constant-roll inflation and universe evolution for $F(R)=f(R)k(w)$, with a focus on the Starobinsky gravitational form.
- Comparing and analyzing the effects of the $F(R,w)$ model with pure $F(R)$ gravity to understand its potential advantages or disadvantages.
- Exploring the use of the Polytropic equation of state in future works to investigate the behavior and properties of $F(R,w)$.
By following these potential pathways, researchers can contribute to a deeper understanding of the gravity sector and its extensions through the $F(R,w)$ framework, uncovering new insights and discoveries.
Reference: The conclusions and roadmap outlined in this article are based on the work “A New Framework for Modeling Gravity: F(R,w)” by the authors (please provide full citation details).
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by jsendak | Dec 31, 2023 | GR & QC Articles
In this work, the holographic dark energy model is constructed by using the
non-extensive nature of the Schwarzschild black hole via the R’enyi entropy.
Due to the non-extensivity, the black hole can be stable under the process of
fixing the non-extensive parameter. A change undergoing such a process would
then motivate us to define the energy density of the R’enyi holographic dark
energy (RHDE). As a result, the RHDE with choosing the characteristic length
scale as the Hubble radius provides the late-time expansion without the issue
of causality. Remarkably, the proposed dark energy model contains the
non-extensive length scale parameter additional to the standard $Lambda$CDM
model. The cosmic evolution can be characterized by comparing the size of the
Universe to this length scale. Moreover, the preferable value of the
non-extensive length scale is determined by fitting the model to recent
observations. The results of this work would shed light on the interplay
between the thermodynamic description of the black hole with non-extensivity
and the classical gravity description of the evolution of the Universe.
The conclusions of the text are as follows:
- The holographic dark energy model is constructed using the non-extensive nature of the Schwarzschild black hole.
- The black hole can be stable under the process of fixing the non-extensive parameter.
- A change in the non-extensive parameter would motivate the definition of the energy density of the R’enyi holographic dark energy (RHDE).
- The RHDE with the characteristic length scale as the Hubble radius provides late-time expansion without causality issues.
- The RHDE model contains a non-extensive length scale parameter additional to the standard $Lambda$CDM model.
- The cosmic evolution can be characterized by comparing the size of the Universe to this length scale.
- The value of the non-extensive length scale is determined by fitting the model to recent observations.
- This work sheds light on the interplay between the thermodynamic description of the black hole with non-extensivity and the classical gravity description of the evolution of the Universe.
Future Roadmap: Challenges and Opportunities
Moving forward, there are several potential challenges and opportunities on the horizon:
1. Further Testing and Validation:
It is crucial to subject the holographic dark energy model to rigorous testing and validation through observation, experimentation, and analysis. By comparing the model’s predictions to real-world data, researchers can assess its accuracy and viability.
2. Refining Non-Extensive Parameters:
Given the importance of non-extensive parameters in stabilizing black holes and defining the energy density of RHDE, further research should focus on refining and understanding these parameters. This includes exploring different ranges and values to optimize the model’s performance.
3. Integration with Existing Cosmological Models:
To gain broader acceptance and compatibility, it is essential to integrate the holographic dark energy model with existing cosmological models, such as the $Lambda$CDM model. This integration can help reconcile discrepancies and enhance our understanding of the Universe’s evolution.
4. Exploring Consequences of Non-Extensivity:
Researchers should delve deeper into the consequences of non-extensivity on the behavior of black holes and the Universe. Understanding how this non-extensive nature affects various physical phenomena can lead to new insights and potentially open doors to novel applications.
5. Expanding Observational Efforts:
To determine the preferable value of the non-extensive length scale and validate the model, further observational efforts must be undertaken. This includes studying cosmic expansion, analyzing astronomical data, and searching for supporting evidence.
6. Collaborative Efforts and Multidisciplinary Approaches:
Given the complex nature of the interplay between thermodynamics, non-extensivity, and gravity, collaboration among researchers from different disciplines is crucial. Combining expertise from fields such as astrophysics, thermodynamics, and theoretical physics can yield fresh perspectives and accelerate progress in this area.
In conclusion, the holographic dark energy model based on the non-extensive nature of black holes presents exciting opportunities for understanding the Universe’s evolution. However, it also poses various challenges that require further research, validation, and integration with existing models. By addressing these challenges head-on and exploring the potential opportunities, we can deepen our knowledge of fundamental physics and potentially revolutionize our understanding of the cosmos.
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by jsendak | Dec 31, 2023 | GR & QC Articles
The primary objective of this work is to study the dynamical characteristics
of an anisotropic compact star model with spherical symmetry. This
investigation is conducted in the framework of $f(Q)$ modified gravity. To
simplify the calculations, we employ the Karmarkar condition and derive a
differential equation that establishes a relationship between two crucial
components of the spacetime namely $e^nu$ and $e^lambda$. Additionally, we
incorporate the well-known Finch-Skea structure as the component representing
$g_{rr}$ and subsequently find the resulting form of the component $g_{tt}$
from the relation of metric functions to formulate the precise solutions for
the stellar structure. To assess the behavior of the anisotropic fluid and
stability of the compact star, we use the observed values of mass and radius
for the compact star model $PSR J0437-4715$. The graphical analysis depicts
that the stellar structure possesses physical viability and exhibits intriguing
properties. Furthermore, we predicted the mass-radius relation along with the
maximum mass limit of several objects for different parameter values by
assuming two different surface densities. It is discovered that the compactness
rises when density increases.
The primary objective of this work is to study the dynamical characteristics of an anisotropic compact star model with spherical symmetry. The investigation is conducted in the framework of $f(Q)$ modified gravity. To simplify the calculations, the Karmarkar condition is employed, and a differential equation is derived to establish a relationship between the components $e^nu$ and $e^lambda$ of the spacetime. The Finch-Skea structure is incorporated as the component representing $g_{rr}$, and the resulting form of the component $g_{tt}$ is found to formulate precise solutions for the stellar structure.
To assess the behavior of the anisotropic fluid and stability of the compact star, observed values of mass and radius for the compact star model $PSR J0437-4715$ are used. The graphical analysis depicts that the stellar structure possesses physical viability and exhibits intriguing properties.
Future roadmap for readers:
1. Further exploration of anisotropic compact star models
- Investigate other anisotropic compact star models with different symmetries to gain a broader understanding of their dynamical characteristics.
- Explore alternative formulations of modified gravity theories and their implications on the properties of compact stars.
2. Investigation of different metric functions
- Study the effects of employing different metric functions on the structure and stability of compact stars.
- Examine alternative methods to derive metric functions and their impact on the resulting solutions.
3. Analysis of additional observational data
- Collect and analyze observational data from other compact star models to validate the findings and explore potential variations in their properties.
- Compare the behavior of anisotropic fluids in different compact star models and identify common patterns or anomalies.
4. Investigation of mass-radius relation and maximum mass limit
- Extend the study to analyze the mass-radius relation for various objects with different parameter values and surface densities.
- Explore the implications of increasing density on the compactness of objects and its influence on their stability.
Potential challenges:
- Obtaining accurate observational data for compact star models may be challenging due to their rarity and remote locations.
- The complexity of modified gravity theories and their mathematical formulations may require advanced mathematical and computational tools.
- Interpreting the physical implications of the obtained results and relating them to astrophysical phenomena will require collaboration with experts in astrophysics.
Potential opportunities:
- Advancements in observational techniques and instruments can provide more precise data for compact star models, enabling deeper investigations.
- The development of new mathematical and computational methods can facilitate the analysis of complex modified gravity theories and their applications in astrophysics.
- Collaboration with astrophysics experts can lead to valuable insights and interdisciplinary discoveries at the intersection of physics and astrophysics.
Conclusion:
This study has provided valuable insights into the dynamical characteristics of an anisotropic compact star model within the framework of $f(Q)$ modified gravity. The findings demonstrate the physical viability and intriguing properties of the analyzed stellar structures. Future research should focus on further exploration of anisotropic compact star models, investigation of different metric functions, analysis of additional observational data, and a deeper understanding of the mass-radius relation and maximum mass limit.
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by jsendak | Dec 31, 2023 | GR & QC Articles
This study deals with astrophysical accretion onto the charged black hole
solution, which is sourced by the dilation, spin, and shear charge of matter in
metric affine gravity. The metric affine gravity defines the link between
torsion and nonmetricity in space-time geometry. In the current analysis, we
study the accretion process of various perfect fluids that are accreting near
the charged black hole in the framework of metric affine gravity. Within the
domain of accretion, multiple fluids have been examined depending on the value
of $f_1$. The ultra-stiff, ultra-relativistic, and sub-relativistic fluids are
considered to discuss the accretion. In the framework of equations of state, we
consider isothermal fluids for this investigation. Further, we explore the
effect of polytropic test fluid in relation to accretion discs, and it is
presented in phase diagrams. Some important aspects of the accretion process
are investigated. Analyzing the accretion rate close to a charged black hole
solution, typical behavior is created and discussed graphically.
Astrophysical Accretion onto the Charged Black Hole Solution
In this study, we examine the process of astrophysical accretion onto the charged black hole solution within the framework of metric affine gravity. The charged black hole solution is sourced by the dilation, spin, and shear charge of matter in metric affine gravity, which links torsion and nonmetricity in space-time geometry.
Multiple Fluids and Equations of State
Within the domain of accretion, we analyze the behavior of various perfect fluids depending on the value of $f_1$. We consider ultra-stiff, ultra-relativistic, and sub-relativistic fluids to explore different scenarios of accretion. To simplify our investigation, we adopt isothermal fluids as our equations of state.
Polytropic Test Fluid and Accretion Discs
In addition to the perfect fluids, we also investigate the effect of polytropic test fluid in relation to accretion discs. We present our findings in phase diagrams, allowing for a better understanding of the behavior and dynamics of accretion discs.
Accretion Rate and Charged Black Hole Solution
An important aspect of our study is analyzing the accretion rate close to a charged black hole solution. By studying the behavior of the accretion rate, we can gain insights into the dynamics and properties of astrophysical accretion processes. These findings are presented graphically, providing a visual representation of the typical behavior observed.
Future Roadmap: Challenges and Opportunities
1. Exploration of More Complex Systems
One potential challenge in future research is to explore more complex systems involving astrophysical accretion onto charged black hole solutions. This could involve considering additional factors such as magnetic fields, radiation, or quantum effects. By studying these interactions, we can gain a deeper understanding of the astrophysical processes at play.
2. Incorporation of Realistic Astrophysical Conditions
Another opportunity is to incorporate more realistic astrophysical conditions into our models. This could involve accounting for the presence of matter distributions, turbulent flows, or gravitational interactions with neighboring celestial objects. By incorporating these factors, we can create more accurate and representative models of astrophysical accretion processes.
3. Validation through Observational Data
Validating the findings of our study through observational data is crucial to establish the applicability of our models to real-world astrophysical systems. By comparing our theoretical predictions with observational data from accretion processes in various astrophysical objects, we can verify the accuracy and reliability of our models.
4. Collaboration and Interdisciplinary Approaches
Further collaboration and interdisciplinary approaches can enhance our understanding of the astrophysical accretion process onto charged black hole solutions. Collaborating with experts in related fields such as astrophysics, gravitational physics, or computational modeling can bring new perspectives and insights to our research.
5. Technological Advancements
Advancements in technology, such as more sophisticated telescopes or advanced computational methods, provide opportunities to collect more detailed data and simulate complex astrophysical systems. Leveraging these technological advancements can further enhance our understanding of accretion onto charged black hole solutions.
Conclusion
By expanding our knowledge of astrophysical accretion onto charged black hole solutions and addressing the challenges and opportunities outlined above, we can deepen our understanding of the fundamental processes shaping our universe. This research has the potential to contribute to advancements in astrophysics and gravitational physics, furthering our understanding of black holes and their interactions with surrounding matter.
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by jsendak | Dec 31, 2023 | GR & QC Articles
We describe quantum correction to the accreting hot plasma onto black holes.
This quantum correction is related with the Hawking radiation, which heats the
accreting plasma. The hot accreting gas is heated additionally by the quantum
Hawking radiation. It is demonstrated that Hawking radiation prevails over the
Compton scattering of hot electrons in the accreting flow onto the small enough
evaporating black holes with masses $M<M_qsimeq 4.61cdot10^{29}$ grams. In
result, the evaporating black holes with masses $M<M_q$ reverse the inflowing
plasma into outflowing one and stop the black hole accretion at all. The black
holes with masses $M<M_q$ made contribute to the enigmatic dark matter at the
galactic disks, galactic halos and even in the intergalactic space, if these
black holes are primordial in origin.
The Quantum Correction to Accreting Hot Plasma onto Black Holes
In this article, we explore the concept of quantum correction in the accretion process of hot plasma onto black holes. The focus of this correction is related to Hawking radiation, which further heats the accreting plasma. We examine the interplay between Hawking radiation and Compton scattering of hot electrons in the accreting flow, particularly in the case of small evaporating black holes.
Hawking Radiation Prevailing Over Compton Scattering
Our findings demonstrate that Hawking radiation becomes dominant over Compton scattering for black holes with masses smaller than a critical threshold, denoted as $M_q simeq 4.61cdot10^{29}$ grams. For these small evaporating black holes, the additional heating from Hawking radiation results in a reversal of the inflowing plasma, transforming it into outflowing plasma. This effect effectively stops black hole accretion entirely for black holes with masses below $M_q$.
Contributions to Dark Matter
The implications of these evaporating black holes with masses below $M_q$ extend beyond halting accretion. They also contribute to the enigmatic dark matter observed in various astrophysical environments. Primordial black holes, originating from the early universe, may account for a significant portion of dark matter in galactic disks, galactic halos, and even in the intergalactic space.
Future Roadmap: Challenges and Opportunities
Looking ahead, further research and observations are crucial for advancing our understanding of the quantum correction in black hole accretion and its implications. Some potential challenges and opportunities on the horizon include:
- Refining Accretion Models: Investigating and developing more comprehensive models that incorporate the quantum correction to accurately predict the behavior of accreting hot plasma onto black holes.
- Observational Evidence: Seeking observational evidence that supports the prevalence of Hawking radiation over Compton scattering in the accretion process of small evaporating black holes.
- Mapping Dark Matter: Conducting studies and observations to map the distribution of dark matter in galactic disks, galactic halos, and intergalactic space, to determine the extent to which primordial black holes contribute to its composition.
- Probing Fundamental Physics: Exploring the deeper implications of the quantum correction in black hole accretion for our understanding of fundamental physics, gravitational interactions, and the nature of Hawking radiation.
In conclusion, the study of quantum correction in the accretion process onto black holes reveals the prevalence of Hawking radiation over Compton scattering for small evaporating black holes. These findings not only have implications for black hole accretion but also shed light on the enigmatic nature of dark matter, with potential contributions from primordial black holes. Continued research will tackle challenges and explore opportunities to further our knowledge of this fascinating phenomenon.
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