Physics of the Dark Universe最新文献

In this paper, we study the characteristics of wormhole models in a particular gravity theory, namely $f\left(Q,T\right)=\sigma Q+\lambda T$. Here, we derived the wormhole models by using dark matter profiles that are Einasto spike and Pseudo isothermal that is ${\rho }_{ES}={\rho }_{0}exp\left(\frac{-2}{\zeta }\left({\left(\frac{r}{r_s}\right)}^{\zeta }-1\right)\right)$ and ${\rho }_{PI}=\frac{\omega }{1+\mu r^2}$ respectively. The obtained solutions for the wormhole’s shape function satisfy the necessary metric requirements. This study focuses on how the parameters $\sigma$ and $\lambda$ affect the equilibrium state of the wormhole solution and violations of energy conditions. We found that every model deviates from the null energy threshold, suggesting the existence of exotic matter that is required for the wormholes to be stable. Furthermore, we deciphered the geometry of wormhole models using embedding diagrams. Additionally, we investigated the repulsive effect of gravity. When the geodesic motion around the wormholes is examined, it is discovered that the photon deflection angle is negative, suggesting the existence of gravity’s repulsive effect for both models.

In the paper only Static Spherically Symmetric space–times in four dimension are considered within modified gravity models. The non-singular static metrics, including black holes not admitting a de Sitter core in the center and traversable wormholes, are reconsidered within a class of higher-order $F\left(R\right)$, satisfying the constraints $F\left(0\right)=\frac{dF}{dR}\left(0\right)=0$. Furthermore, making use of the so called effective field theory formulation of gravity, the quantum corrections to Einstein–Hilbert action due to higher-derivative terms related to curvature invariants are investigated. In particular, in the case of Einstein–Hilbert action plus cubic curvature Goroff–Sagnotti contribution, the second order correction in the Goroff–Sagnotti coupling constant is computed. In general, it is shown that the effective metrics, namely Schwarzschild expression plus small quantum corrections are related to black holes, and not to traversable wormholes. In this framework, within the approximation considered, the resolution of singularity for $r=0$ is not accomplished. The related properties of these solutions are investigated.

New data from ongoing galaxy surveys, such as the Euclid satellite and the Dark Energy Spectroscopic Instrument (DESI), are expected to unveil physics on the largest scales of our universe. Dramatically affected by cosmic variance, these scales are of interest to large-scale structure studies as they exhibit relevant corrections due to general relativity (GR) in the $n$-point statistics of cosmological random fields. We focus on the relativistic, sample-dependent Doppler contribution to the observed clustering of galaxies, whose detection will further confirm the validity of GR in cosmological regimes. Sample- and scale-dependent, the Doppler term is more likely to be detected via cross-correlation measurements, where it acts as an imaginary correction to the power spectrum of fluctuations in galaxy number counts. We present a method allowing us to exploit multi-tracer benefits from a single data set, by subdividing a galaxy population into two sub-samples, according to galaxies’ luminosity/magnitude. To overcome cosmic variance we rely on a multi-tracer approach, and to maximise the detectability of the relativistic Doppler contribution in the data, we optimise sample selection. As a result, we find the optimal split and forecast the relativistic Doppler detection significance for both a DESI-like Bright Galaxy Sample and a Euclid-like H$\alpha$ galaxy population.

Using suitable Renormalization Group (RG) based re-summation of quantum corrections to $R^2$ term, a re-summed version of the effective Lagrangian can be obtained (Demmel et al., 2015). In the context of gravity as an Asymptotically Safe (AS) theory, authors of Refs. Liu et al. (2018), Koshelev et al. (2023) proposed a refined Starobinsky model, $L_{\mathrm{AS}}=M_p^{2}R/2+(\alpha /2)R^2/[1+\beta ln(R/{\mu }^2)]$, where $R$ is the Ricci scalar, $\alpha$ and $\beta$ are constants and $\mu$ is an energy scale. In the present work, we embed this underlying effective Lagrangian within the framework of gravity’s rainbow. By implementing the COBE normalization and the Planck constraint on the scalar spectrum, we demonstrate that the power spectrum of curvature perturbation relies on $\alpha$ and $\beta$, as well as on a rainbow parameter. Similarly, the scalar spectral index $n_s$ is influenced by $\beta$ and the rainbow parameter, yet remains unaffected by $\alpha$. Additionally, the tensor-to-scalar ratio $r$ solely depends on the rainbow parameter. Remarkably, when requiring $n_s$ to be consistent with the Planck collaboration at $1\sigma$ confidence level, the upper limit on the tensor-to-scalar ratio $r<0.036$ can be naturally satisfied. This value potentially holds promise for potential measurement by Stage IV CMB ground experiments and is certainly within reach of future dedicated space missions.

In this paper, we thoroughly explore two crucial aspects of a quantum Schwarzschild black solution within four-dimensional space–time: (i) the weak deflection angle, (ii) the rigorous greybody factor and, (iii) the Dirac quasinormal modes. Our investigation involves employing the Gauss–Bonnet theorem to precisely compute the deflection angle and establishing its correlation with the Einstein ring. Additionally, we derive the rigorous bounds for greybody factors through the utilization of general bounds for reflection and transmission coefficients in the context of Schrodinger-like one-dimensional potential scattering. We also compute the corresponding Dirac quasinormal modes using the WKB approximation. We reduce the Dirac equation to a Schrodinger-like differential equation and solve it with appropriate boundary conditions to obtain the quasinormal frequencies. To visually underscore the quantum effect, we present figures that illustrate the impact of varying the parameter $r_0$, or more specifically, in terms of the parameter $\alpha$. This comprehensive examination enhances our understanding of the quantum characteristics inherent in the Schwarzschild black solution, shedding light on both the deflection angle and greybody factors in a four-dimensional space–time framework.

In this study, we investigate the signatures of a non-commutative black hole solution. Initially, we calculate the thermodynamic properties of the system, including entropy, heat capacity, and Hawking radiation. For the latter quantity, we employ two distinct methods: surface gravity and the topological approach. Additionally, we examine the emission rate and remnant mass within this context. Remarkably, the lifetime of the black hole, after reaching its final state due to the evaporation process, is expressed analytically up to a grey-body factor. We estimate the lifetime for specific initial and final mass configurations. Also, we analyze the tensorial quasinormal modes using the 6th-order WKB method. Finally, we study the deflection angle, i.e., gravitational lensing, in both the weak and strong deflection limits.

There are no known exact isotropic or anisotropic stellar models with an equation of state in energy–momentum trace-coupling (EMTC) modifications of general relativity — the simplest linear case of $f(R,T)$ gravity. The difficulty lies in the intricate entanglement of the density and pressure functions that generate intractable governing equations when an equation of state is introduced. For example there is no interior Schwarzschild incompressible star analogue in the well studied $f(R,T)$ theory. In Einstein’s theory it is straightforward to find anisotropic stellar models with a linear equation of state since the system is under-determined and there remains one more choice to nominate any of the variables. This is also true in EMTC theories however, the master field equation is more formidable. If interpreted as a linear second order equation, no viable solutions emerge by prescribing one of the gravitational potentials or by suppressing some terms in the spirit of Tolman (1939). Rewriting as a nonlinear first order equation and speculating on a power-law form of the temporally directed gravitational potential results in success in finding a physically viable compact star distribution. Specifically the model has monotonic decrease of both pressure and density and a surface of vanishing pressure exists. Several stability tests are imposed and the model performs according to expectations. The singularity at the stellar center may be cured by insertion of a regular core enveloped by our fluid model in a multi-layered star.

We investigate the rotating 4D Gauss–Bonnet (GB) black holes surrounded by Perfect Fluid Dark Matter (PFDM) using the Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*). This rotating black hole, influenced by an additional GB parameter $\alpha$ and a DM parameter $\beta$, deviates from the Kerr black hole geometry, offering a more complex horizon structure. Our findings reveal that the shadow size decreases and oblateness increases with higher values of $\alpha$, $\beta$, and the spin parameter $a$. By plotting the shadow area $A$ and oblateness $D$ as functions of $\alpha$ and $\beta$ for various $a$ values, we determine the unique black hole parameters through the intersection points of the $A$ and $D$ curves. We constrain the GB and DM parameters with the EHT shadow observational results of Sgr A* for an inclination angle of 90° and 50°. The results, which align with EHT observations of Sgr A*, suggest that dark matter may exist in significant quantities around the galactic centre, challenging the traditional Kerr black hole model and offering new avenues for understanding complex interactions. Thus, It is essential to consider that rotating 4D GB black holes surrounded by PFDM could be strong candidates for astrophysical black holes.

In this paper, we derive observational constraints on an anisotropic $w$CDM model from datasets including Baryonic Acoustic Oscillations (BAOs), Cosmic Chronometer (CC), Big Bang Nucleosynthesis (BBN), Pantheon Plus (PP) compilation of Type Ia supernovae, and SH0ES Cepheid host distance anchors. We find that anisotropy is of the order $10^{-13}$, and its presence in the $w$CDM model reduces the $H_0$ tension by $\sim 2\sigma$ and $\sim 1\sigma$ in the analyses with BAO+CC+BBN+PP and BAO+CC+BBN+PPSH0ES data combinations, respectively. In both analyses, the quintessence form of dark energy is favored at 95% CL.

In this paper, we study the geodesics, periodic orbits, and plasma effects on gravitational weak lensing around the self-dual black hole in loop quantum gravity characterized by the parameter $ϵ$. We determine the marginal bound orbits (MBO) and innermost stable circular orbits (ISCO) around the self-dual black hole and show that these orbits decrease with an increase in the parameter $ϵ$. Interestingly, we also observe that the energy increase but the angular momentum of the ISCO decrease with an increasing $ϵ$. We further examine periodic orbits of massive particles that involve a rational number represented by a triplet of integers and show that, for a constant rational number, the energy becomes lower as a consequence of the presence of the parameter $ϵ$. Finally, we delve into the impact of the quantum correction parameter $ϵ$ and the plasma effects on the deflection angle and the total magnification of lensed images. We show that the deflection angle decreases under the influences of both the parameter $ϵ$ and the non-uniform plasma frequency, but it increases due to the impact of uniform plasma.