Physics of the Dark Universe最新文献

In this manuscript, we investigate the possibility of constructing anisotropic dark matter compact stars motivated by the Einasto density profile. This work develops analytical solutions for an anisotropic fluid sphere within the framework of the well-known Adler–Finch–Skea metric. This toy model incorporates an anisotropic fluid distribution that includes a dark matter component. We use the minimal geometric deformation scheme within the framework of gravitational decoupling to incorporate anisotropy into the pressure profile of the stellar system. In this context, we model the temporal constituent of the $\Theta$-field sector to characterize the contribution of dark matter within the gravitational matter source. We present an alternative approach to studying anisotropic self-gravitating structures. This approach incorporates additional field sources arising from gravitational decoupling, which act as the dark component. We explicitly verify whether the proposed model satisfies all the requirements for describing realistic compact structures in detail. We conclude that the modeling of the Einasto density model with the Adler–Finch–Skea metric gives rise to the formation of well-behaved and viable astrophysical results that can be employed to model the dark matter stellar configurations.

We study scalar cosmological perturbations in $f(R,T)$ modified gravity theories, where $T$ represents the trace of the energy–momentum tensor. We provide detailed equations for the matter energy density contrast. We solve them numerically to facilitate a comparison with available large-scale structure (LSS) formation observational data on $f{\sigma }_8$, while also addressing the $S_8$ tension. We identify $f(R,T)$ models that either lead to growth enhancement or suppression. Since recent results in the literature indicate a preference for the latter feature, this type of analysis is quite useful for selecting viable modifications of gravity. The studied class of such $f(R,T)$ models are either ruled out or severely restricted. After selecting the surviving $f(R,T)$ models we show how they deal with the $S_8$ tension.

In rotating black hole background surrounded by dark matter, we investigated the super-radiant phenomenon of massive scalar field and its associated instability. Using the method of asymptotic matching, we computed the amplification factor of scalar wave scattering to assess the strength of super-radiance. We discussed the influence of dark matter density on amplification factor in this black hole background. Our result indicates that the presence of dark matter has suppressive influence on black hole super-radiance. We also computed the net extracted energy to further support this result. Finally, we analyzed the super-radiant instability caused by massive scalar field using the black hole bomb mechanism and found that the presence of dark matter has no influence on the super-radiant instability condition.

We investigated the quasinormal modes (QNMs) for scalar, Dirac and electromagnetic fields of a Schwarzschild black hole with geometric corrections. In addition to the inherent modes of the Schwarzschild black hole, we discovered the existence of purely imaginary modes induced by the geometric corrections, which dominated the behavior of the perturbation when geometric corrections were pretty small. Notably, we found that these purely imaginary modes are prominent, and their imaginary parts are proportional to the correction parameter $ϵ$. We also explored the large-$l$ limit using the WKB approximation for scalar field. This opens up the possibility of observed geometric corrections in the future.

The goal of this research is to better understand how two identical black hole copies, bounded by a cold dark matter halo, produce and stabilize thin-shell wormholes. The occurrence of a cold dark matter halo is discovered to increase the black hole’s horizon radius. Investigating the stable geometry of these wormholes by linearized radial perturbation analysis is the main objective of the work. It is noteworthy that the development of thin-shell wormholes with reduced energy limitations is associated with the presence of a cold dark matter halo. We study how the stability of the wormholes is affected by variable equations of state, including phantom-like, variable Chaplygin, and barotropic equations of state. The question emphasizes how crucial the existence of a cold dark matter halo is to preserving stable thin-shell wormhole configurations. The findings shed light on the interactions between a cold dark matter halo and wormholes, which improved our knowledge of both phenomena and their possible consequences for extraterrestrial travel.

The present article investigates the effect of $f\left(Q\right)$ parameters on two classes of exact spherically symmetric self-bound isotropic solutions for compact objects. The field equation in $f\left(Q\right)$ gravity is solved using Korkina–Orlyanskii and Buchdahl models. The physical validity of both models has been verified using regularity, stability, and hydrostatic equilibrium tests. We have also shown the effect of $f\left(Q\right)$ gravity parameter $\alpha$ on the stability and mass–radius relation. We predicted the radii of observable compact objects GW 190814, PSR J0740+6620 PSR J1614, 2230, Cen X-3, and LMC X-4. In the absence of $\beta$, the massive neutron star GW 190814 is detected at greater values of $\alpha =1.5$ and 1.2 for models I and II respectively. The corresponding estimated radii for both models are $15.30_{-0.29}^{+0.18}\mathrm{km}$ and $15.03_{-0.25}^{+0.17}\mathrm{km}$. Additionally, as the non-metricity scalar $\alpha$ increases, the mass–radius decreases, and when $\beta$ increases with fix $\alpha$, the reverse scenario arises. Our finding indicates that a lower $mass-gap$ can be achieved in $f\left(Q\right)$ gravity theory as compared to the standard theory of gravity.

This manuscript investigates sources that are spherically symmetric when subjected to an electromagnetic field (EMF), specifically concentrating the fluid distribution in non-static spacetime. We analyzed the source in $f\left(R\right)$ gravity, where $R$ is the Ricci scalar. We investigate the fluid’s collapse by using the strategy that the metric satisfies the conformal killing vector (CKV) equation. To make our system solvable, we imposed some limitations on it, i.e., the homologous collapse and the diminishing of complexity factor. It is analyzed that the electric field intensity has an effect on physical variables like energy density and stress components. It is also concluded that temperature distribution implicitly depends on electric field intensity.

The nonminimal coupling of the nonzero vacuum expectation value of the self-interacting antisymmetric Kalb–Ramond field with gravity leads to a power-law hairy BH having a parameter $s$, which encompasses the Reissner-Nordström black hole ($s=1$). It is obtained the axially symmetric counterpart of this hairy solution, namely, the rotating Kalb–Ramond black hole, which encompasses, as special cases, Kerr ($s=0$) and Kerr–Newman ($s=1$) black holes. With rotating Kalb–Ramond black hole metric, we study its horizon structure and motion of the test particles in the near of the equatorial plane and we determine radial motion equations which governing $t$ and $\varphi$. We also explore thatthe black hole mass increasing when falling many of mass-less particles are relative to the black hole mass. We consider how the Kalb–Ramond parameters depend on increasing its mass. Furthermore, we analyze the Keplerian frequency, as well as the vertical and horizontal oscillations of basic frequencies, using a graph-based approach. The frequency charts are contingent upon the Kalb–Ramond parameters $s$ and $\Gamma$. By consulting certain sources, ones can investigate the distinctions between KR gravity and other models.

A crucial aspect of wormhole (WH) physics is the inclusion of exotic matter, which requires violating the null energy condition. Here, we explore the potential for WHs to be sustained by quark matter under conditions of extreme density along with the phantom-like generalized cosmic Chaplygin gas (GCCG) in symmetric teleparallel gravity. Theoretical and experimental studies on baryon structures indicate that strange quark matter, composed of u (up), d (down), and s (strange) quarks, represents the most energy-efficient form of baryonic matter. Drawing from these theoretical insights, we use the Massachusetts Institute of Technology (MIT) bag model equation of state to characterize ordinary quark matter. By formulating specific configurations for the bag parameter, we develop several WH models corresponding to different shape functions for the isotropic and anisotropic cases. Our analysis strongly suggests that an isotropic WH is not theoretically possible. Furthermore, we investigate traversable WH solutions utilizing a phantom-like GCCG, examining their feasibility. This equation of state, capable of violating the null energy condition, can elucidate late-time cosmic acceleration through various beneficial parameters. In this framework, we derive WH solutions for both constant and variable redshift functions. We have employed the volume integral quantifier (VIQ) method for both studies to assess the quantity of exotic matter. Furthermore, we have done the equilibrium analysis through the Tolman–Oppenheimer–Volkoff (TOV) equation, which supports the viability of our constructed WH model.