by jsendak | Jun 6, 2025 | GR & QC Articles
arXiv:2506.04304v1 Announce Type: new
Abstract: Astrophysical observations provide compelling evidence for the existence of dark matter, a non-luminous component dominating the universe’s mass-energy budget. Its gravitational influence is well-established on galactic scales; however, dark matter’s precise nature and effect on spacetime geometry remain open questions. This study investigates modifications to the Schwarzschild metric due to the presence of dark matter, modeled as a perfect fluid with a specific equation of state. We derive an “exponential” metric incorporating this dark matter contribution and calculate its key characteristics: the event horizon, innermost stable circular orbit (ISCO), and photon sphere. Comparing these with Schwarzschild predictions reveals distinct deviations dependent on the dark matter distribution. Furthermore, we analyze the orbital velocity profiles derived from the exponential metric, demonstrating its potential to explain the observed flat rotation curves of galaxies. Our results underscore the importance of considering modified metrics in accurately describing spacetime near massive objects and provide a theoretical framework for further investigations into dark matter’s role in galactic dynamics.
Conclusions:
The study investigates modifications to the Schwarzschild metric due to the presence of dark matter, modeled as a perfect fluid with a specific equation of state. An “exponential” metric that incorporates this dark matter contribution is derived, and key characteristics such as the event horizon, innermost stable circular orbit (ISCO), and photon sphere are calculated. Comparisons with Schwarzschild predictions reveal distinct deviations dependent on the dark matter distribution. The orbital velocity profiles derived from the exponential metric show potential to explain the observed flat rotation curves of galaxies. The results highlight the importance of considering modified metrics in accurately describing spacetime near massive objects and provide a theoretical framework for further investigations into dark matter’s role in galactic dynamics.
Future Roadmap:
- Exploring Dark Matter Properties: Future research can focus on refining the equation of state for dark matter and studying its distribution in more detail to better understand its impact on spacetime geometry.
- Testing Predictions with Observations: Observational data can be utilized to test the predictions of the exponential metric and validate its ability to explain phenomena such as flat rotation curves.
- Developing Advanced Models: Advanced mathematical and computational models can be developed to further investigate the implications of dark matter on galactic dynamics and explore new avenues for theoretical frameworks.
Potential Challenges:
- Obtaining Accurate Data: Gathering precise observational data on dark matter distributions and galactic dynamics can be challenging and may require sophisticated instruments and techniques.
- Complex Mathematical Formulations: Developing and solving complex mathematical equations to describe the interactions between dark matter and spacetime geometry can be difficult and require expertise in theoretical physics.
- Interpreting Observational Results: Interpreting observational results in the context of theoretical predictions may involve uncertainties and require careful analysis to draw meaningful conclusions.
Opportunities on the Horizon:
- Advancements in Cosmology: Further studies on dark matter can lead to significant advancements in our understanding of the universe’s structure and evolution.
- New Insights into Galactic Dynamics: Discoveries related to dark matter can provide new insights into the behavior of galaxies and the mechanisms driving their rotation curves.
- Potential for Breakthrough Discoveries: Theoretical frameworks developed to study dark matter may pave the way for groundbreaking discoveries in astrophysics and cosmology.
Read the original article
by jsendak | May 28, 2025 | GR & QC Articles
arXiv:2505.18192v1 Announce Type: new
Abstract: Gravitational waves offer a key insight into the viability of classes of gravitational theories beyond general relativity. The observational constraints on their speed of propagation can provide strong constraints on generalized classes of broader gravitational frameworks. In this work, we reconsider the general class of Gauss-Bonnet theories in the context of teleparallel gravity, where the background geometry is expressed through torsion. We perform tensor perturbations on a flat FLRW background, and derive the gravitational wave propagation equation. We find that gravitational waves propagate at the speed of light in these classes of theories. We also derive the distance-duality relationship for radiation propagating in the gravitational wave and electromagnetic domains.
Conclusions:
The study of gravitational waves has provided valuable insights into alternative gravitational theories beyond general relativity. Specifically, the speed of propagation of gravitational waves can constrain and inform broader frameworks of gravitational theories.
In this work, the class of Gauss-Bonnet theories in the context of teleparallel gravity was reconsidered. It was found that gravitational waves within these theories propagate at the speed of light. Additionally, the distance-duality relationship for radiation in the gravitational wave and electromagnetic domains was derived.
Future Roadmap:
Potential Challenges:
- Verifying the speed of gravitational wave propagation in other gravitational theories
- Exploring the implications of the distance-duality relationship for observational astronomy
- Testing the predictions of Gauss-Bonnet theories in teleparallel gravity through experimental or observational data
Opportunities on the Horizon:
- Developing a deeper understanding of alternative gravitational theories
- Advancing our knowledge of the fundamental properties of gravitational waves
- Applying insights from gravitational wave studies to improve our understanding of the Universe’s structure and evolution
Read the original article
by jsendak | May 27, 2025 | GR & QC Articles
arXiv:2505.17158v1 Announce Type: new
Abstract: We study spinors in the framework of general relativity, starting from the Dirac field Lagrangian in the approximation of weak gravity. We focus on how fermions couple to gravity through the spin connection, and we analyze these couplings by analogy with the Ginzburg-Landau model and the Yukawa interaction known from the Higgs mechanism. By solving the field equations, we explore how these couplings affect the spacetime metric. In particular, torsion generated by fermionic spin currents naturally emerges and leads to the breaking of Lorentz symmetry. As a consequence, gravity acquires a mass and fermions gain additional mass contributions through their interaction with this gravitational field. These effects are localized and diminish quickly with distance. Our model offers an alternative explanation to phenomena usually attributed to dark matter and dark energy. We link these cosmological effects to chirality-flip processes of Majorana neutrinos interacting with a massive graviton. Right-handed Majorana neutrinos, which are sterile under Standard Model interactions, generate repulsive gravitational curvature and act as a source of dark energy, while left-handed neutrinos contribute to attractive gravitational effects akin to dark matter. The spin-gravity coupling modifies the curvature of spacetime, influencing galaxy rotation, the accelerated expansion of the universe, and the bending of light. In short, the intrinsic spin of fermions, when coupled to gravity via torsion, changes gravity from a long-range, massless force to a short-range, massive one. This new framework provides fresh insights into fundamental physics and cosmology, potentially explaining dark matter and dark energy phenomena through spin-related gravitational effects.
Future Roadmap: Challenges and Opportunities
After examining the conclusions of the study on spinors in the framework of general relativity, it is clear that there are many exciting avenues for further exploration in the realm of fundamental physics and cosmology. Below is a roadmap outlining potential challenges and opportunities on the horizon:
Challenges:
- Experimental Verification: One of the key challenges moving forward will be to experimentally verify the predictions made by this new framework. Developing experimental setups to test the effects of spin-gravity coupling on spacetime curvature and gravitational interactions will be crucial.
- Theoretical Extensions: Further theoretical work will be needed to expand on the implications of torsion generated by fermionic spin currents and its effects on gravitational mass. Developing a more comprehensive understanding of these phenomena will be essential for building a complete picture.
- Cosmological Consequences: Exploring the cosmological consequences of this new framework, particularly in relation to dark matter and dark energy, will present challenges in observational astronomy and theoretical cosmology. Understanding how these spin-related gravitational effects manifest on a cosmic scale will be a key area of focus.
Opportunities:
- Alternative Explanations: This new framework offers an alternative explanation for phenomena typically attributed to dark matter and dark energy. Exploring the implications of spin-gravity coupling could lead to a paradigm shift in our understanding of the universe.
- Technological Applications: The insights gained from this study could have potential technological applications in areas such as gravitational wave detection, precision cosmology, and quantum gravity research. These applications may open up new possibilities for innovation and discovery.
- Interdisciplinary Collaboration: Collaboration across multiple disciplines, including particle physics, general relativity, and cosmology, will be essential for advancing research in this field. Bringing together experts from diverse backgrounds could lead to new breakthroughs and insights.
In conclusion, the study of spinors in the framework of general relativity has opened up a wealth of possibilities for further exploration and discovery. By addressing the challenges and seizing the opportunities presented by this new framework, researchers have the potential to make significant strides in our understanding of fundamental physics and cosmology.
Read the original article
by jsendak | May 24, 2025 | GR & QC Articles
arXiv:2505.15853v1 Announce Type: new
Abstract: The main aim of this study is to examine the behaviour of physical parameters of an anisotropic compact star model demonstrating spherical symmetry in F(Q) modified gravity. To evaluate the behaviour and the stability of an anisotropic compact star model, we utilise the measured mass and radius of an anisotropic compact star model. This study obtained an anisotropic compact star model by solving Einstein field equations. The field equations have been simplified by an appropriate selection of the metric elements and the Karmarkar condition. By solving the field equation to develop a differential equation that establishes a relationship between two essential components of spacetime. A physical analysis of this model reveals that the resulting stellar structure for anisotropic matter distribution is a physically plausible representation of a compact star with an energy density of order $10^14 g/cm^3$. Using the Tolman-Oppenheimer-Volkoff equation, causality condition and Harrison-Zeldovich-Novikov Condition, we investigate the hydrostatic equilibrium and stability of the compact star Cen X-3. We further determined the mass-radius relation of this compact star for different values of delta}1.
Conclusions
The study successfully examined the behaviour of physical parameters in an anisotropic compact star model under F(Q) modified gravity. By solving Einstein field equations and conducting a physical analysis, it was determined that the resulting stellar structure is a plausible representation of a compact star with high energy density.
Further investigations into the hydrostatic equilibrium and stability of the compact star Cen X-3 were carried out using established equations and conditions, leading to the determination of the mass-radius relation for different values of delta1.
Future Roadmap
Challenges
- Continued validation: Further validation of the model with observational data and experimental results is essential to confirm its accuracy and applicability.
- Complexity of calculations: The complex nature of the calculations involved in solving the field equations and establishing relationships between spacetime components may pose challenges in practical applications.
- Exploration of alternative scenarios: Exploring additional scenarios and variations in the model could provide a more comprehensive understanding of the physical parameters and behaviours involved.
Opportunities
- Advancements in gravitational theories: The study opens up opportunities for advancements in gravitational theories, particularly in the context of modified gravity and anisotropic compact star models.
- Technological applications: The insights gained from this research could lead to advancements in technologies related to space exploration, astrophysics, and gravitational studies.
- Collaborative research: Collaboration with other researchers and institutions in related fields could facilitate the development and enhancement of the model, as well as the exploration of new avenues of research.
Read the original article
by jsendak | May 23, 2025 | GR & QC Articles
arXiv:2505.14734v1 Announce Type: new
Abstract: In this paper, based on the action of a complex scalar field minimally coupled to a gravitational field, we numerically obtain a series of massive boson star solutions in a spherically symmetric background with a quartic-order self-interaction potential. Then, considering a thin accretion flow with a certain four-velocity, we further investigate the observable appearance of the boson star using the ray-tracing method and stereographic projection technique. As a horizonless compact object, the boson star’s thin disk images clearly exhibit multiple light rings and a dark central region, with up to five bright rings. As the observer’s position changes, the light rings of some boson stars deform into a symmetrical “horseshoe” or “crescent” shape. When the emitted profile varies, the images may display distinct observational signatures of a “Central Emission Region”. Meanwhile, it shows that the corresponding polarized images not only reveal the spacetime features of boson stars but also reflect the properties of the accretion disk and its magnetic field structure. By comparing with black hole, we find that both the polarized signatures and thin disk images can effectively provide a possible basis for distinguishing boson stars from black holes. However, within the current resolution limits of the Event Horizon Telescope (EHT), boson stars may still closely mimic the appearance of black holes, making them challenging to distinguish at this stage.
Conclusions:
- Numerical solutions for massive boson star in a spherically symmetric background obtained
- Thin accretion flow with four-velocity used to investigate observable appearance of boson star
- Thin disk images of boson star show multiple light rings, dark central region, and symmetrical shapes
- Polarized images of boson star reveal spacetime features, accretion disk properties, and magnetic field structure
- Comparing with black holes, polarized signatures and thin disk images can help distinguish boson stars
- Current resolution limits of Event Horizon Telescope may make it challenging to distinguish boson stars from black holes
Future Roadmap:
- Improving resolution of telescopes like the Event Horizon Telescope to better distinguish boson stars from black holes
- Developing advanced image processing techniques to enhance the observable features of boson stars
- Conducting further simulations and experiments to refine the understanding of boson stars and their unique characteristics
- Exploring additional observational methods beyond ray-tracing and stereographic projection to study boson stars
- Collaborating with interdisciplinary teams to combine theoretical predictions with observational data for comprehensive analysis
Potential Challenges:
- Technical limitations in improving telescope resolution may hinder the distinction between boson stars and black holes
- Complexity of boson star properties and interactions may require sophisticated modeling and simulation techniques
- Limited funding and resources for conducting extensive research on boson stars and their observational signatures
Potential Opportunities:
- Advancements in technology and image processing algorithms could facilitate clearer differentiation of boson stars from black holes
- Growing interest in astrophysical objects beyond black holes could attract more research interest and funding in the field of boson stars
- Collaboration with international teams and institutions could provide access to a wider range of observational data and expertise
Read the original article
by jsendak | May 22, 2025 | GR & QC Articles
arXiv:2505.13513v1 Announce Type: new
Abstract: The gauge-theoretical method introduced in our previous paper is applied to solving the axisymmetric and static Einstein-Maxwell equations. We obtain the solutions of non-Weyl class, where the gravitational and electric or magnetic potentials are not functionally related. In the electrostatic case, we show that the obtained solution coincides with the solution given by Bonnor in 1979. In the magnetostatic case, we present a solution describing the gravitational field created by two magnetically charged masses. In this solution, we show a case where the Dirac string does not stretch to spatial infinity but lies between the magnetically charged masses.
Future Roadmap
Potential Challenges:
- Integration of gauge-theoretical methods into broader physics frameworks
- Verification and validation of solutions in practical scenarios
- Applicability of solutions to real-world problems
- Understanding the implications of non-Weyl class solutions
Opportunities on the Horizon:
- Further exploration of non-functionally related potentials in gravitational and electromagnetic fields
- Development of new mathematical tools for solving complex field equations
- Integration of gauge-theoretical methods into advanced technology applications
- Potential discovery of new physical phenomena through unconventional solutions
With the advancements in gauge-theoretical methods for solving complex field equations, the future holds promise for exploring new frontiers in gravitational and electromagnetic field interactions. By addressing challenges and seizing opportunities on the horizon, researchers can pave the way for groundbreaking discoveries in theoretical and applied physics.
Read the original article
