by jsendak | Sep 27, 2024 | GR & QC Articles
arXiv:2409.17193v1 Announce Type: new
Abstract: We investigate the cosmic evolution of the Universe across different cosmological epochs in exponential Weyl-type $f(Q, T)$ gravity model. The theoretical analysis involves a detailed dynamical system approach, where we define dimensionless variables and derive a system of linear differential equations to identify critical points corresponding to the radiation, matter and de Siter phase. The findings show the transition from deceleration to acceleration phase, with stable and unstable critical points characterizing different phases of the evolution. In the second approach, we validate the theoretical predictions by using observational data from Cosmic Chronometers ($CC$) and $Pantheon^+$ datasets. We constrain the Hubble parameter and subsequently analysed the other cosmological and geometrical parameters. In this approach also, the transition from deceleration to acceleration has been confirmed, with the equation of state (EoS) parameter approaching $Lambda$CDM at late times. The further validate this, we present the behaviour of state finder pair. We obtain the age of the Universe $13.81$ Gyr according to $CC$ data and $13.96$ Gyr with the $Pantheon^+$ dataset. The model behaviour in both the approaches shows strong agreement in the late-time behavior of the Universe. The evolutionary behaviour of Hubble parameter and distance modulus, reinforcing the reliability of the Weyl-type $f(Q, T)$ gravity model in describing the expansion history of Universe.
In this study, the authors investigate the cosmic evolution of the Universe using the exponential Weyl-type $f(Q, T)$ gravity model. They employ a dynamical system approach, deriving a system of linear differential equations and identifying critical points corresponding to different cosmological epochs.
By analyzing the theoretical predictions, the researchers find a transition from a deceleration phase to an acceleration phase, with stable and unstable critical points characterizing different phases of the evolution. To validate their findings, they use observational data from Cosmic Chronometers ($CC$) and $Pantheon^+$ datasets.
Using the observational data, the authors constrain the Hubble parameter and analyze other cosmological and geometrical parameters. These analyses confirm the transition from deceleration to acceleration, with the equation of state (EoS) parameter approaching $Lambda$CDM at late times.
To further validate their results, the authors present the behavior of the state finder pair. They obtain an age of the Universe of .81$ Gyr according to the $CC$ data and .96$ Gyr with the $Pantheon^+$ dataset. The model’s behavior in both approaches shows strong agreement in the late-time behavior of the Universe, reinforcing the reliability of the Weyl-type $f(Q, T)$ gravity model in describing the expansion history of the Universe.
Future Roadmap
Challenges
- One of the potential challenges that researchers may face is obtaining more precise observational data. The accuracy of the model’s predictions heavily relies on the quality and quantity of the data used for validation.
- Further investigation is needed to explore the limitations of the Weyl-type $f(Q, T)$ gravity model and its applicability beyond the current observations. This will require more advanced theoretical analyses and simulations.
- Understanding the physical interpretation of the critical points identified in the dynamical system approach is another challenge that researchers might encounter. Elucidating the implications of these critical points could provide deeper insights into the cosmic evolution.
Opportunities
- As new observational techniques and instruments are developed, researchers will have the opportunity to collect more precise and extensive data sets. This will enable more accurate validation of the Weyl-type $f(Q, T)$ gravity model and potentially uncover new phenomena in the cosmic evolution.
- Exploring alternative gravity models and comparing them with the Weyl-type $f(Q, T)$ model could provide valuable insights into the nature of the Universe’s expansion. This could open up new avenues for understanding fundamental physics and the nature of dark energy.
- Collaboration between theorists and experimentalists will be crucial in advancing our understanding of the cosmic evolution. By combining theoretical analyses with cutting-edge observations, researchers can refine and improve the models, leading to a more comprehensive understanding of the Universe.
Conclusion
This study highlights the cosmic evolution of the Universe using the exponential Weyl-type $f(Q, T)$ gravity model. The theoretical analysis and observational data validation both confirm a transition from a deceleration phase to an acceleration phase. The model’s agreement with the late-time behavior of the Universe, as well as the obtained age estimates, reinforce the reliability of the Weyl-type $f(Q, T)$ gravity model. However, further investigations, improvements in observational data, and collaboration between different branches of physics are necessary to overcome challenges and unlock new opportunities for understanding the cosmic evolution.
Read the original article
by jsendak | Aug 9, 2024 | GR & QC Articles
arXiv:2408.03961v1 Announce Type: new
Abstract: In the present analysis, we explore a new version of dark energy called Barrow holographic dark energy within the framework modified gravity called $f(Q,T)$ gravity by adopting the simple homogeneous, isotropic, and spatially flat Friedmann-Robertson-Walker (FRW) model of the universe. Our goal is to understand how the universe evolved over time. To do this, we use parameterizetion of Hubble’s parameter method. We then use a powerful tool called Monte Carlo Markov Chain to find the best values for the constants in our formula. We do this by comparing our formula to actual data from observations of the universe. Once we have the best values for the constants, we calculate other important parameters that describe the universe’s evolution. These include: Deceleration parameter which measures how quickly the expansion is slowing down. We found $q_0 = -0.601^{+0.0131}_{-0.0131}$. Equation of state parameter to measures the properties of dark energy. We find $omega_0 = -0.7018^{+0.0101}_{-0.0101}$. We also study the stability and energy conditions along with the state-finder and $O_m(z)$-parameter of our model to ensure it’s consistent with our understanding of the universe.
In this analysis, we have explored a new version of dark energy known as Barrow holographic dark energy within the framework of modified gravity called $f(Q,T)$ gravity. By utilizing the simple homogeneous, isotropic, and spatially flat Friedmann-Robertson-Walker (FRW) model of the universe, our goal was to gain a better understanding of how the universe has evolved over time.
To achieve this, we employed the parameterization of Hubble’s parameter method and used the Monte Carlo Markov Chain technique as a powerful tool to determine the optimal values for the constants in our formula. By comparing our formula to actual data obtained from observations of the universe, we were able to find the best values for these constants. With these values, we calculated other significant parameters that describe the evolution of the universe.
One such parameter is the deceleration parameter, which measures the rate at which the expansion of the universe is slowing down. Our findings indicate a value of $q_0 = -0.601^{+0.0131}_{-0.0131}$. Additionally, we examined the equation of state parameter, which characterizes the properties of dark energy. Our results suggest $omega_0 = -0.7018^{+0.0101}_{-0.0101}$ for this parameter.
In our study, we also assessed the stability and energy conditions, as well as the state-finder and $O_m(z)$-parameter of our model, to ensure its consistency with our existing understanding of the universe.
Future Roadmap: Challenges and Opportunities
The exploration of Barrow holographic dark energy within the framework of modified gravity through the $f(Q,T)$ gravity model presents several challenges and opportunities for future research and discoveries.
1. Improved Data and Observations
While our analysis utilized current data from observational studies, future advancements in data collection and observation techniques could provide more accurate and precise information about the universe. This would enable us to refine our model further and provide more accurate predictions.
2. Testing Alternative Models
As we continue to explore dark energy and modified gravity, it would be beneficial to investigate alternative models to compare their predictions with those of the Barrow holographic dark energy model. By testing and comparing different models, we can gain a deeper understanding of the underlying physics and potentially identify the most accurate representation.
3. Theoretical Frameworks
Further analysis and research are needed to develop and refine the theoretical frameworks that underpin the Barrow holographic dark energy and $f(Q,T)$ gravity models. This includes investigating the mathematical foundations, exploring the limitations of the models, and seeking to integrate them with other existing theories to form a more comprehensive understanding of the universe.
4. Experimental Validation
Experimental validation is crucial to ensure the consistency between the theoretical models and the physical reality. Conducting experiments and making observations that directly test the predictions of the Barrow holographic dark energy and $f(Q,T)$ gravity models would provide valuable insights into the accuracy and reliability of these theories.
5. Cosmological Implications
Exploring the cosmological implications of the Barrow holographic dark energy model and the modified gravity framework can lead to significant discoveries and a deeper understanding of the nature of the universe. Investigating their effects on phenomena such as cosmic microwave background radiation, large-scale structure formation, and the distribution of galaxies can provide crucial insights into the fundamental properties of our universe.
Overall, the exploration of Barrow holographic dark energy within the framework of modified gravity presents exciting opportunities to enhance our understanding of the universe’s evolution. By addressing the challenges mentioned above and building upon the current research, we can continue to unravel the mysteries of dark energy, gravity, and the cosmos.
Read the original article
by jsendak | Aug 2, 2024 | GR & QC Articles
arXiv:2408.00022v1 Announce Type: new
Abstract: The dynamics of perfect fluid as a source in the context of modified gravity, specifically $f(Q,T)$ gravity, are examined within the Friedmann-Lema^itre-Robertson-Walker (FLRW) cosmological model. This gravity is a generic function of the non-metricity scalar $Q$ and its trace $T$. We investigate the characteristics of the derived cosmological model using a parameterized form of Hubble’s parameter, $H(z) = H_0left[Omega_{0m}(1+z)^3 + (1-Omega_{0m})right]^{frac{1}{2}}$ (Mahmood et al. Int. J. Geom. Methods Mod. Phys., https://doi.org/10.1142/S0219887824502049). Our examination reveals how physical parameters such as energy density, pressure, and the equation of state parameter, among others, in our model accurately describe the physical behavior of the cosmos. Furthermore, we explore the kinematic parameters in our model, which provide valuable insights into the cosmos’s expansion history, including its acceleration, deceleration, and the evolution of its large-scale structure. By exploring these aspects, we gain a deeper understanding of the cosmos’s dynamics and evolution within the context of modified gravity.
The article examines the dynamics of a perfect fluid as a source in the context of modified gravity, specifically $f(Q,T)$ gravity, within the Friedmann-Lema^itre-Robertson-Walker (FLRW) cosmological model. The gravity in question is a generic function of the non-metricity scalar $Q$ and its trace $T$. It utilizes a parameterized form of Hubble’s parameter, $H(z) = H_0left[Omega_{0m}(1+z)^3 + (1-Omega_{0m})right]^{frac{1}{2}}$ to investigate the characteristics of the derived cosmological model (Mahmood et al., 2024). The physical parameters such as energy density, pressure, and the equation of state parameter are shown to accurately describe the physical behavior of the cosmos within this model. Additionally, kinematic parameters are explored, providing insights into the expansion history, acceleration, deceleration, and evolution of the large-scale structure of the cosmos. This examination allows for a deeper understanding of the dynamics and evolution of the cosmos within the framework of modified gravity.
Future Roadmap
Challenges
- Further investigation is required to validate the compatibility of the derived cosmological model with observational data. This would involve comparing the model predictions with existing data from cosmological observations and experiments.
- The complex nature of modified gravity theories, such as $f(Q,T)$ gravity, poses challenges in fully understanding and interpreting the physical implications. More theoretical development and experimental verification are needed to establish the validity and applicability of these theories.
- Exploring the implications of the derived cosmological model on other astrophysical phenomena, such as the formation and evolution of galaxies, the distribution of dark matter, and the behavior of black holes, would be crucial to comprehensively understand the impact of modified gravity.
Opportunities
- The study of modified gravity theories opens up new avenues for exploring fundamental questions in cosmology, such as the nature of dark energy and the explanation for the accelerated expansion of the universe. It allows for alternative explanations to the cosmological constant and opens up possibilities for a deeper understanding of the fundamental forces of nature.
- Advancements in observational techniques and data collection, such as those provided by upcoming missions and experiments, offer opportunities to test and validate the predictions of the derived cosmological model. These include missions like the James Webb Space Telescope and experiments like the Square Kilometre Array.
- Collaboration between theoretical physicists, observational astronomers, and experimental scientists would be essential to tackle the interdisciplinary challenges posed by modified gravity theories. Pooling together expertise and resources can lead to significant breakthroughs in understanding the dynamics and evolution of the cosmos.
In conclusion, the examination of the dynamics of a perfect fluid as a source in the context of modified gravity, specifically $f(Q,T)$ gravity, within the FLRW cosmological model provides valuable insights into the behavior and evolution of the cosmos. Future research should address the challenges of validating the model with observational data, understanding the physical implications of modified gravity theories, and exploring the broader implications on other astrophysical phenomena. However, these challenges also present opportunities for further investigation and a deeper understanding of fundamental questions in cosmology.
Read the original article
by jsendak | Jun 5, 2024 | GR & QC Articles
arXiv:2406.01632v1 Announce Type: new
Abstract: In this paper, we investigate the anisotropic interior spherically symmetric solutions by utilizing the extended gravitational decoupling method in the background of $f(G,T)$ gravity, where $G$ and $T$ signify the Gauss-Bonnet term and trace of the stress-energy tensor, respectively. The anisotropy in the interior geometry arises with the inclusion of an additional source in the isotropic configuration. In this technique, the temporal and radial potentials are decoupled which split the field equations into two independent sets. Both sets individually represent the isotropic and anisotropic configurations, respectively. The solution corresponding to the first set is determined by using the Krori-Barua metric potentials whereas the second set contains unknown which are solved with the help of some constraints. The ultimate anisotropic results are evaluated by combining the solutions of both distributions. The influence of decoupling parameter is examined on the matter variables as well as anisotropic factor. We illustrate the viable and stable features of the constructed solutions by using energy constraints and three stability criteria, respectively. Finally, we conclude that the obtained solutions are viable as well as stable for the whole domain of the coupling parameter.
Article Title: Investigating Anisotropic Interior Spherically Symmetric Solutions in $f(G,T)$ Gravity
Introduction
In this paper, the authors explore anisotropic interior spherically symmetric solutions in the framework of $f(G,T)$ gravity. By utilizing the extended gravitational decoupling method, the authors aim to understand the influence of a decoupling parameter on the matter variables and anisotropic factor. This investigation provides insights into the viability and stability of the constructed solutions.
Methodology
The extended gravitational decoupling method is employed to study the anisotropic interior geometry in $f(G,T)$ gravity. By decoupling the temporal and radial potentials, the field equations are split into two independent sets. The first set represents the isotropic configuration and is determined using the Krori-Barua metric potentials. The second set, which corresponds to the anisotropic configuration, contains unknowns that are solved with the help of constraints.
Results
The authors obtain anisotropic results by combining the solutions of both distributions. They evaluate the influence of the decoupling parameter on the matter variables and anisotropic factor. The viability of the solutions is illustrated using energy constraints, while three stability criteria are employed to assess their stability.
Conclusion
The authors conclude that the obtained solutions in $f(G,T)$ gravity are both viable and stable across the entire domain of the coupling parameter. These findings contribute to the understanding of anisotropic interior spherically symmetric solutions and have potential implications for future studies in this field.
Roadmap for Readers:
- Introduction to anisotropic interior spherically symmetric solutions in $f(G,T)$ gravity
- Overview of the extended gravitational decoupling method
- Explanation of the field equations and their decoupling into two independent sets
- Solution determination for the isotropic configuration using Krori-Barua metric potentials
- Solution determination for the anisotropic configuration with the help of constraints
- Combining the solutions to obtain anisotropic results
- Analysis of the influence of the decoupling parameter on matter variables and anisotropic factor
- Evaluation of viability using energy constraints
- Assessment of stability using three stability criteria
- Conclusion on the viability and stability of the solutions in the whole domain of the coupling parameter
Potential Challenges:
- Complex mathematical equations and concepts may require a strong understanding of theoretical physics.
- The extended gravitational decoupling method may be unfamiliar to readers, necessitating additional background research.
- The constraints used to solve for the unknowns in the anisotropic configuration may present computational challenges.
- The evaluation of viability and stability criteria may involve intricate calculations.
Potential Opportunities:
- This paper contributes to the field of anisotropic interior spherically symmetric solutions in $f(G,T)$ gravity, providing a potential avenue for further research and exploration.
- Readers can gain insights into the decoupling method and its application in gravitational physics.
- The obtained solutions’ viability and stability can inspire future investigations in related areas.
- The influence of the decoupling parameter on matter variables and anisotropic factor opens avenues for expanding the understanding of these variables.
Note: The text above is just a sample outline and does not contain the entire content of the article.
Read the original article
by jsendak | Feb 23, 2024 | GR & QC Articles
arXiv:2402.13360v1 Announce Type: new
Abstract: This study explores the behavior of compact stars within the framework of $f(R,L_m,T)$ gravity, focusing on the functional form $f(R,L_m,T) = R + alpha TL_m$. The modified Tolman-Oppenheimer-Volkoff (TOV) equations are derived and numerically solved for several values of the free parameter $alpha$ by considering both quark and hadronic matter — described by realistic equations of state (EoSs). Furthermore, the stellar structure equations are adapted for two different choices of the matter Lagrangian density (namely, $L_m= p$ and $L_m= -rho$), laying the groundwork for our numerical analysis. As expected, we recover the traditional TOV equations in General Relativity (GR) when $alpha rightarrow 0$. Remarkably, we found that the two choices for $L_m$ have appreciably different effects on the mass-radius diagrams. Results showcase the impact of $alpha$ on compact star properties, while final remarks summarize key findings and discuss implications, including compatibility with observational data from NGC 6397’s neutron star. Overall, this research enhances comprehension of $f(R,L_m,T)$ gravity’s effects on compact star internal structures, offering insights for future investigations.
This study examines the behavior of compact stars within the framework of $f(R,L_m,T)$ gravity, focusing specifically on the functional form $f(R,L_m,T) = R + alpha TL_m$. The modified Tolman-Oppenheimer-Volkoff (TOV) equations are derived and numerically solved for different values of the parameter $alpha$, considering both quark and hadronic matter with realistic equations of state. The stellar structure equations are adapted for two choices of the matter Lagrangian density, laying the foundation for the numerical analysis.
When $alpha$ approaches zero, the traditional TOV equations in General Relativity (GR) are recovered. However, it was discovered that the two choices for $L_m$ have significantly different effects on the mass-radius diagrams. This highlights the impact of $alpha$ on the properties of compact stars. The study concludes by summarizing the key findings and discussing their implications, including their compatibility with observational data from NGC 6397’s neutron star.
Overall, this research enhances our understanding of the effects of $f(R,L_m,T)$ gravity on the internal structures of compact stars. It provides insights that can contribute to future investigations in this field.
Roadmap for Future Investigations
To further explore the implications and potential applications of $f(R,L_m,T)$ gravity on compact stars, several avenues of research can be pursued:
1. Expansion to Other Functional Forms
While this study focuses on the specific functional form $f(R,L_m,T) = R + alpha TL_m$, there is potential for investigation into other functional forms. Different choices for $f(R,L_m,T)$ may yield interesting and diverse results, expanding our understanding of compact star behavior.
2. Exploration of Different Equations of State
Currently, the study considers realistic equations of state for both quark and hadronic matter. However, there is room for exploration of other equations of state. By incorporating different equations of state, we can gain a more comprehensive understanding of the behavior of compact stars under $f(R,L_m,T)$ gravity.
3. Inclusion of Additional Parameters
Expanding the analysis to include additional parameters beyond $alpha$ can provide a more nuanced understanding of the effects of $f(R,L_m,T)$ gravity on compact stars. By investigating how different parameters interact with each other and impact the properties of compact stars, we can uncover new insights into the behavior of these celestial objects.
4. Comparison with Observational Data
While this study discusses the compatibility of the findings with observational data from NGC 6397’s neutron star, it is important to expand this comparison to a wider range of observational data. By comparing the theoretical predictions with a larger dataset, we can validate the conclusions drawn and identify any discrepancies or areas for further investigation.
Challenges and Opportunities
Potential Challenges:
- Obtaining accurate and comprehensive observational data on compact stars for comparison with theoretical predictions can be challenging due to their extreme conditions and limited visibility.
- Numerically solving the modified TOV equations for various parameter values and choices of matter Lagrangian density may require significant computational resources and optimization.
- Exploring different functional forms and equations of state can lead to complex analyses, requiring careful interpretation and validation of results.
Potential Opportunities:
- The advancements in observational techniques and instruments provide opportunities for obtaining more precise data on compact stars, enabling more accurate validation of theoretical models.
- Ongoing advancements in computational power and numerical techniques allow for more efficient and faster solution of the modified TOV equations, facilitating the exploration of a broader parameter space.
- The diverse range of functional forms and equations of state available for investigation provides ample opportunities for uncovering novel insights into the behavior and properties of compact stars.
By addressing these challenges and capitalizing on the opportunities, future investigations into the effects of $f(R,L_m,T)$ gravity on compact star internal structures can continue to push the boundaries of our understanding and pave the way for further advancements in the field.
Read the original article
