Physics of the Dark Universe最新文献

Exploring the effect of exotic fields around black holes on particle dynamics may help to understand the nature of dark matter and energy. The quintessential field can be treated as one of such fields. In this work, we investigate the motion of spinning particles in the vicinity of rotating black holes immersed in quintessential dark energy, characterized by the equation of state (EoS) parameter $\omega \in (-1;-1/3)$ governing the equation of state of the dark energy and dimensionless quintessential field parameter $C$. Using the Mathisson–Papapetrou–Dixon (MPD) equations, we derive the effective potential and study superluminal bound values for the particle spin. Also, we investigate the behaviors of the innermost and outermost stable circular orbit (ISCO & OSCO) of spinning test particles and their energy and angular momentum at the orbits. Note that the OSCO exists due to the third cosmological-like horizon caused by the quintessential field and shows that the ISCO and OSCO coincide at critical values of the quintessential field and EoS parameters, which also depend on the particle and black hole spin. Finally, we explore collisions of spinning particles and analyze the center-of-mass energies and critical angular momentum, which allows the collisions of the particles near the black hole.

Unveiling the notion of complexity within the static spherical distribution, this paper extends its exploration in the charged $f\left(R\right)$ framework. For this, we start with the formulation of the modified Einstein–Maxwell field equations, describing the anisotropic interior. By orthogonally splitting the curvature tensor, a collection of specific scalars emerges, with one standout, $Y_{TF}$, titled as the complexity factor in the current fluid distribution. Tackling the field equations with additional degrees of freedom, we introduce the vanishing complexity condition. This condition, combined with three additional constraints, paves the way for the development of different models. The resulting solutions are also illustrated graphically for chosen parametric values. Through this analysis, we draw the compelling conclusion that all three models fulfill the essential criteria necessary for physically relevant structures to exist for specific parametric values.

This paper delves into the thermodynamic properties of RN AdS black hole immersed in perfect fluid dark matter. We vary the Newton’s gravitational constant, cosmological constant and the perfect fluid dark matter parameter in the bulk. When studying the first law of thermodynamics for black holes, the boundary conformal field theory introduces the central charge, leading to modifications in the thermodynamic volume and chemical potential of black hole. Our analysis shows that the black hole’s free energy is affected by changes in both the central charge and the parameter of perfect fluid dark matter. The $F-T$ curve shows a swallowtail behavior when central charge is above a critical value, which means the occurrence of first-order phase transition from a small black hole to a large black hole. Additionally, we analyzed the heat capacity as a function of temperature for different PFDM parameter values to study the stability of the black hole.

JWST’s recent discovery of well-formed galaxies and supermassive black holes only a few hundred Myr after the big bang seriously challenges the timeline predicted by $\Lambda$CDM. Now, the latest identification of polycyclic aromatic hydrocarbons (PAHs) at $z=6.71$, together with these earlier inconsistencies, makes the time compression problem in this model quite overwhelming. We consider the timeline associated with the formation and growth of PAH grains based on current astrophysical models and argue that their appearance at $z=6.71$ favors the structure formation history in $R_h=ct$ rather than that of Planck-$\Lambda$CDM. We estimate the time at which they must have started growing in each case, and then trace their history through various critical events, such as the end of the ‘dark ages’, the beginning of Pop III star formation, and the onset of reionization. Together, these three distinct discoveries by JWST, viz. high-$z$ galaxies, high-$z$ quasars and the surprisingly early appearance of PAHs, all paint a fully consistent picture in which the timeline in $\Lambda$CDM is overly compressed at $z\gtrsim 6$, while strongly supporting the expansion history in the early Universe predicted by $R_h=ct$.

We investigate the dynamics of spinning particles with an electric charge orbiting electrically charged Kerr–Newman black holes. First, we derive the equations of motion for the test particles using the Mathisson-Papapetrou-Dixon (MPD) equations, taking into account electromagnetic interaction and the interaction between the particle spin and the spacetime curvature known as the Lorentz coupling term in the MPD equation. We analyze the related effective potential in various scenarios of particle spin, angular momentum, and black hole spin orientation. In addition, we provide graphical analyses of the radius of innermost stable circular orbits (ISCOs) of the particles, their angular momentum, and energy at ISCOs and superluminal bounds. The ISCOs for positive and negatively charged particles are almost the same. The combined effects of the black hole and particle spins enhance the Coulomb interaction effect on the ISCO radius. The ISCO energy and angular momentum decrease with the increase in particle spin. In the Reissner–Nordström (RN) black hole limit, the decreasing rate is faster at positive values of the particle spin, and the spin limit changes in the Kerr–Newman black hole case. Finally, we study collisions between spinning charged particles near Kerr–Newman black holes. The critical values of the angular momentum of spinning charged particles are explored, and the particles can collide in various cases of particle and black hole spin, as well as the particle angular momentum. We also analyze electromagnetic and spin effects on the center-of-mass energy of the colliding particles.

In this paper we construct a dissipative quintessential cosmic inflation. For this purpose, we add a multiplicative dissipative term in the standard quintessence field Lagrangian. We consider the specific form of dissipation as the time integral including the Hubble parameter and an arbitrary function that describes the dissipative properties of the quintessential scalar field. Inflation parameters and observables are calculated under slow-roll approximations and a detailed calculation of the cosmological perturbations is performed in this setup. We consider different forms of potentials and calculate the scalar spectral index and tensor-to-scalar ratio for a constant as well as variable dissipation function. To check the reliability of this model, a numerical analysis on the model parameters space is done in confrontation with recent observational data. By comparing the results with observational joint datasets at 68% and 95% confidence levels, we obtain some constraints on the model parameters space, specially the dissipation factor with e-folds numbers $N=55$ and $N=60$. As some specific results, we show that the power-law potential with a constant dissipation factor and $N=60$ is mildly consistent with observational data in some restricted domains of the model parameter space with very small and negative dissipation factor and a negligible tensor-to-scalar ratio. But this case with $N=55$ is consistent with observation considerably. For power-law potential and variable dissipation factor as $Q=\alpha {\varphi }^n$, the consistency with observation is also considerable with a reliable tensor-to-scalar ratio. The quadratic and quartic potentials with variable dissipation function as $Q=\alpha {\varphi }^n$ are consistent with Planck2018 TT, TE, EE+lowE+lensing data at the 68% and 95% levels of confidence for some intervals of the parameter $n$.

We study the dynamics of the field equations in a five-dimensional spatially flat Friedmann–Lemaître–Robertson–Walker metric in the context of a Gauss–Bonnet–Scalar field theory where the quintessence scalar field is coupled to the Gauss–Bonnet scalar. Contrary to the four-dimensional Gauss–Bonnet theory, where the Gauss–Bonnet term does not contribute to the field equations, in this five-dimensional Einstein–Scalar–Gauss–Bonnet model, the Gauss–Bonnet term contributes to the field equations even when the coupling function is a constant. Additionally, we consider a more general coupling described by a power-law function. For the scalar field potential, we consider the exponential function. For each choice of the coupling function, we define a set of dimensionless variables and write the field equations into a system of ordinary differential equations. We perform a detailed analysis of the dynamics for both systems and classify the stability of the equilibrium points. We determine the presence of scaling and super-collapsing solutions using the cosmological deceleration parameter. This means that our models can explain the Universe’s early and late-time acceleration phases. Consequently, this model can be used to study inflation or as a dark energy candidate.

In this work, we investigate the physical behavior and stability of compact stars in $F\left(Q\right)$ gravity. We employ the Buchdahl metric to examine the dynamics of a relativistic, newly charged, isotropic fluid model. The interplay between gravity and electromagnetism is included in the analysis of the system by taking into account the charged state of the fluid, providing insights into how charged fluids behave in gravitational theories. The exterior solution under Schwarzschild–de Sitter (dS) spacetime is linked to the interior solution at the boundary to identify the constants. It is important to note that the Buchdahl ansatz provides a mathematically viable solution for a given transformation in the context of electric charge when pressure and density are maximum in the center and monotonically fall towards the boundary. We have taken into account the compact star Her X-1 with $M=(0.85\pm 0.15)M_{\odot }$; Radius $=13.26_{-1.08}^{+1.08}$ km for graphical analysis. In the context of $F\left(Q\right)$, the physical acceptability of the model has been examined by looking at the required physical attributes, such as energy conditions, causality, hydrostatic equilibrium, pressure–density ratio, etc. that are satisfied throughout the stellar configuration. It is concluded that the present approach allows a suitable modeling of astrophysical compact objects in $F\left(Q\right)$ gravity.

This work explores the phenomenon of plasma lensing in weak plasma fields around Euler–Heisenberg black holes submerged in perfect fluid dark matter. For both uniform and non-uniform plasma environments, the deflection angle is systematically determined, investigating the impact of different parameters on the deflection angle in each plasma field. We also discuss on the gravitational deflection ring using the deflection angle for uniform and non-uniform plasma. We also investigate the energy collision inside the black hole, offering a thorough investigation of the relationship between energy collision, gravitational deflection, and plasma lensing for Euler–Heisenberg black holes encircled by perfect fluid dark matter. we concluded that the deflection angle in uniform plasma is greater than in non-uniform plasma. Similarly, image magnification from the source is higher in higher plasma concentration. Image is also more magnified in the uniform plasma than in the SIS plasma field. Ring deflection angle in Uniform plasma is also more than SIS plasma field.