A new f(Q)f(Q) cosmological model with H(z)H(z) quadratic expansion

We present a new $f(Q)$ cosmological model capable of reproducing late-time acceleration, i.e. $f\left( Q\right) = \lambda_{0}\left( \lambda +Q\right) ^{n}$ by supporting certain parametrization of the Hubble parameter. By using observational data from Hubble, Pantheon, and Baryonic Acoustic Oscillations (BAO) dataset, we investigate the constraints on the proposed quadratic Hubble parameter $H(z)$. This proposal caused the Universe to transition from its decelerated phase to its accelerated phase. Further, the current constrained value of the deceleration parameter from the combined Hubble+Pantheon+BAO dataset is $q_{0}=-0.285\pm 0.021$, which indicates that the Universe is accelerating. We also analyze the evolution of energy density, pressure, and EoS parameters to infer the Universe's accelerating behavior. Finally, we use a stability analysis with linear perturbations to assure the model's stability.Comment: Physics of the Dark Universe published versio

Quasinormal Modes of Black holes in f(Q)f(Q) gravity

In this work, we have studied the quasinormal modes of a black hole in a model of the type $f(Q)=\underset{n}{\sum}a_{n}\left(Q-Q_{0}\right)^{n}$ in $f(Q)$ gravity by using a recently introduced method known as Bernstein spectral method and confirmed the validity of the method with the help of well known Pad\'e averaged higher order WKB approximation method. Here we have considered scalar perturbation and electromagnetic perturbation in the black hole spacetime and obtained the corresponding quasinormal modes. We see that for a non-vanishing nonmetricity scalar $Q_0$, quasinormal frequencies in scalar perturbation are greater than those in electromagnetic perturbation scenarios. On the other hand, the damping rate of gravitational waves is higher for electromagnetic perturbation. To confirm the quasinormal mode behaviour, we have also investigated the time domain profiles for both types of perturbations.Comment: 15 pages, 6 figures. Published versio

A New Om(z)Om(z) Diagnostic of Dark Energy in General Relativity Theory

In this paper, we propose a new parametrization of dark energy based on the $Om(z)$ diagnostic tool behavior. For this purpose, we investigate a functional form of the $Om(z)$ that predicts the popular dark energy dynamical models, namely phantom and quintessence. We also found the famous cosmological constant for specified values of the model's parameters. We employed the Markov Chain Monte Carlo approach to constrain the cosmological model using Hubble, Pantheon samples, and BAO datasets. Finally, we used observational constraints to investigate the characteristics of dark energy evolution and compare our findings to cosmological predictions.Comment: The European Physical Journal C accepted versio

Quasinormal modes and greybody factors of symmergent black hole

Symmergent gravity is an emergent gravity framework in which gravity emerges guided by gauge invariance, accompanied by new particles, and reconciled with quantum fields. In this paper, we perform a detailed study of the quasinormal modes and greybody factors of the black holes in symmergent gravity. Its relevant parameters are the quadratic curvature term $c_{\rm O}$ and the vacuum energy parameter $\alpha$. In our analyses, effects of the both parameters are investigated. Our findings suggest that, in both positive and negative direction, large $|c_{\rm O}|$ values of the parameter on the quasinormal modes parallel the Schwarzschild black hole. Moreover, the quasinormal model spectrum is found to be sensitive to the symmergent parameter $\alpha$. We contrast the asymptotic iteration and WKB methods in regard to their predictions for the quasinormal frequencies, and find that they differ (agree) slightly at small (large) multipole moments. We analyze time-domain profiles of the perturbations, and determine the greybody factor of the symmergent black hole in the WKB regime. The symmergent parameter $\alpha$ and the quadratic curvature term $c_{\rm O}$ are shown to impact the greybody factors significantly. We provide also rigorous limits on greybody factors for scalar perturbations, and reaffirm the impact of model parameters.Comment: 23 pages, 16 figures. Published versio

Quasinormal Modes and Optical Properties of 4-D black holes in Einstein Power-Yang-Mills Gravity

This paper explores the impact of the Yang-Mills charge parameter and the exponent term on a $4$D black hole solution in the Einstein Power-Yang-Mills theory. Through an investigation of the massless scalar quasinormal mode spectrum, black hole shadow, and emission rate, we have determined that the effects of these two parameters are opposite. Specifically, the Yang-Mills charge parameter causes an increase in the real quasinormal frequencies with a correspondingly smaller damping rate. It also results in a smaller black hole shadow and a lower evaporation rate.Comment: 13 pages, 9 figure

Impact of energy-momentum conservation violation on the configuration of compact stars and their GW echoes

This work investigates the impacts of energy-momentum conservation violation on the configuration of strange stars constraint with gravitational wave (GW) event GW190814 as well as eight recent observations of compact objects. The gravitational wave echoes from these interesting classes of compact objects are also calculated. To describe the matter of strange stars, we have used two different equations of state (EoSs): first an ad-hoc exotic EoS, the stiffer MIT Bag model and next realistic CFL phase of quark matter EoS. We choose Rastall gravity as a simple model with energy-momentum conservation violation with a set of model parameter values. Our results show that this gravity theory permits stable solutions of strange stars and the resulting structures can foster GW echoes. We illustrate the implication of the gravity theory and found that the negative values of the Rastall parameter result in more compact stellar configurations and lower GW echo frequency. With an increase in the Rastall parameter, both the compactness of the stellar configurations and echo time decrease. It is worth mentioning here that with the chosen set of some probable strange star candidates from observational data and also in light of GW 190814, we have evaluated the radii of stellar models. Also, the GW echo frequencies associated with strange stars are found to be in the range of $\approx 41-58$ kHz for both cases.Comment: 8 figures and 4 table

Deflection angle and quasinormal modes of a de Sitter black hole in f(T,B)f(\mathcal{T}, \mathcal{B}) gravity

This work is intended to investigate the influence of the boundary term on the bending angle of light for a static spherically symmetric black hole in $f(\mathcal{T}, \mathcal{B})$ modified gravity. To this end, we use the Ishihara et al. method which allows us to derive the deflection angle of light for an observer and source at finite distances from a lens object in a non-asymptotically flat spacetime. This method interprets the viewpoint of the receiver. The obtained deflection angle becomes divergent at far distances from the lens object, which is due to the non-asymptotically flat spacetime. However, the divergence of the deflection angle can be controlled with the boundary term parameter $c_0$. For small values of the parameter $c_0$ this divergence can be minimized within the finite range of the source and observer. We also calculate the quasinormal modes of axial gravitational perturbations in the background of the black hole using the Pad\'e averaged sixth order WKB approximation method. We observed that the boundary term of the model has notable influence on the quasinormal modes of the black hole. It is seen that for the physically perceptible quasinormal mode frequencies from the black hole, the value of the boundary term parameter $c_0$ should be less than $0.08$. This result in fact supports the outcome of our deflection angle analysis.Comment: 12 pages, 4 figure

A new

In this paper, we have introduced a new f(R) gravity model as an attempt to have a model with more parametric control, so that the model can be used to explain the existing problems as well as to explore new directions in physics of gravity, by properly constraining it with recent observational data. Here basic aim is to study the properties of Gravitational Waves (GWs) in this new model. In f(R) gravity metric formalism, the model shows the existence of scalar degree of freedom as like other f(R) gravity models. Due to this reason, there is a scalar mode of polarization of GWs present in the theory. This polarization mode exists in a mixed state, of which one is transverse massless breathing mode with non-vanishing trace and the other is massive longitudinal mode. The longitudinal mode being massive, travels at speed less than the usual tensor modes found in General Relativity (GR). Moreover, for a better understanding of the model, we have studied the potential and mass of scalar graviton in both Jordan frame and Einstein frame. This model can pass the solar system tests and can explain primordial and present dark energy. Also, we have put constraints on the model. It is found that the correlation function for the third mode of polarization under certain mass scale predicted by the model agrees well with the recent data of Pulsar Timing Arrays. It seems that this new model would be useful in dealing with different existing issues in the areas of astrophysics and cosmology

Weak gravitational lensing and shadow cast by rotating black holes in axionic Chern-Simons theory

We investigate the impact of the axionic coupling parameter on the bending angle of light and the shadow cast by slowly rotating black holes in Chern-Simons modified gravity. We utilize the Ishihara \etal method to derive the deflection angle of light for an observer and source located at finite distances from a lens object in an asymptotically flat spacetime, using the Gauss-Bonnet theorem. The deflection angle exhibits an increasing trend up to a certain point, followed by a decrease as a function of the impact parameter, with the presence of the axion matter field causing the observed increase. Additionally, we calculate the Einstein ring radius as a direct application of the weak deflection angle. We also investigate the effect of the axion matter field on the time delay of light and analyze its impact on the shadow cast by slowly rotating black holes. Our findings reveal a significant effect of the axionic coupling parameter on the black hole's shadow.Comment: 18 pages and 9 figures. arXiv admin note: text overlap with arXiv:2211.0241