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This paper is devoted to studying the observational signatures modified by Bardeen black hole via shadow and strong lensing observations. Influence of the modified Bardeen black hole parameters q, g, and the parameter $\mu$ on the shadow radius of the black hole have been investigated numerically and graphically. Recently, EHT collaboration observed the image and shadow of supermassive black holes $M87^*$ and $SgrA^*$ where the shadow angular diameter $\theta_d=42\pm3$ for $M87^*$ and $\theta_d=51.8\pm2.3$ for $SgrA^*$. The modified black hole parameters q and $\mu$ for the fixed value of g have been constrained by the EHT collaboration data for the angular shadow diameter of $M87^*$ and $SgrA^*$. It has been observed that the constrain ranges of the parameters $\mu$ and $q$ of modified Bardeen black hole as $-0.89\leq \mu/8M^2 \leq 0.4$ and $0\leq |q|\leq 0.185$ for $M87^*$; and $-1.38\leq \mu/8M^2 \leq 0.1$ and $0\leq |q|\leq 0.058$ for $SgrA^*$, keeping the fixed value $g/2M=0.2$. Modified Bardeen black holes with the additional parameters $\mu$,$g$ and $q$ besides the mass M of the black hole as the supermassive black holes $M87^*$ and $SgrA^*$; and it is observed that to be a viable astrophysical black hole candidate. Furthermore, Gravitational lensing in the strong field limit for modified Bardeen black hole has been investigated numerically as well as graphically and compared to the other ordinary astrophysical black hole such as Schwarzschild ($\mu=\&q=0$) and regular Bardeen ($\mu=0$) black hole., Comment: 20 pages, 30 figures

We consider the propagation of gravitational waves in the late-time Universe in the presence of matter distribution inhomogeneities, and we also consider the cosmic fluid to be viscous. In this work, we investigate the cumulative effect of inhomogeneities and viscosity of the cosmic-fluid on the observables associated with the sources of the gravitational waves. Employing Buchert's averaging procedure in the backreaction framework, we consider a model of spacetime in which matter is distributed in-homogeneously across space. Using the modified redshift versus distance relation, through the averaging process in the context of the model, we study the variation of the redshift-dependent part of the observed gravitational wave amplitude for different combinations of our model parameters while simultaneously considering damping of the gravitational wave amplitude due to viscosity of the cosmic-fluid. Then, we investigate the differences occurring in the variation of the redshift-dependent part of the observed gravitational wave amplitude due to consideration of viscous attenuation. We show that there are significant deviations after the inclusion of viscous attenuation in our analysis, depending on the chosen value of the coefficient of viscosity. Our result signifies the importance of the effect of viscosity, within the model of an inhomogeneous Universe, on precision measurements of parameters of compact-binary sources of gravitational waves., Comment: 15 pages, 5 figures

We consider the accretion of dark energy by constituent black holes in binary formations during the present epoch of the Universe. In the context of an observationally consistent dark energy model, we evaluate the growth of black holes' masses due to accretion. We show that accretion leads to faster circularization of the binary orbits. We compute the average power of the gravitational waves emitted from binaries, which exhibits a considerable enhancement due to the effect of growth of masses as a result of accretion. This in turn, leads to a significant reduction of the coalescence time of the binaries. We present examples pertaining to various choices of the initial masses of the black holes in the stellar mass range and above, in order to clearly establish a possible observational signature of dark energy in the emerging era of gravitational wave astronomy., Comment: 9 pages, 6 figures, 1 Table

We consider the propagation of gravitational waves in the late time Universe with the presence of structure. Before detection, gravitational waves emitted from distant sources have to traverse through regions of spacetime which are far from smooth and homogeneous. We investigate the effect of inhomogeneities on the observables associated with the gravitational wave sources. In particular, we evaluate the impact of inhomogeneities on gravitational wave propagation by employing Buchert's framework of averaging. In context of a toy model within the above framework, it is first shown how the redshift versus distance relation gets affected through the averaging process. We then study the variation of the redshift dependent part of the observed gravitational wave amplitude for different combination of our model parameters. We show that the variation of the gravitational wave amplitude with respect to redshift can deviate significantly compared to that in the $\Lambda$CDM-model. Our result signifies the importance of local inhomogeneities on precision measurements of parameters of gravitational wave sources., Comment: 8 pages, 5 figures

In this paper, we examine neutron star structure in perturbative $f(R)$ gravity models with realistic equation of state. We obtain mass-radius relations in two gravity models of the form $f_{1}(R)=R+ \alpha R(e^{-R/R_0}-1)$ and $f_{2}(R)=R+\alpha R^2$. For this purpose, we consider NS with several nucleonic as well as strange EoSs generated in the framework of relativistic mean field models. The strange particles in the core of NS are in the form of $\Lambda$ hyperons and quarks, in addition to the nucleons and leptons. The M-R relation of the chosen EoSs lies well within the observational limit in the case of GR. We show that these EoSs provide the most stringent constraint on the perturbative parameter $\alpha$ and therefore can be considered as important experimental probe for modified gravity at astrophysical level., Comment: 9 figures

We consider the equation of motion of a charged particle or a charged compact object in curved space-time, under the reaction of electromagnetic radiation and also consider a physical situation such that the charged particle or compact object emits gravitational radiation, thereby gravitational radiation reaction also acts on it. We investigate the effect of this metric perturbation i.e. the gravitational radiation on the electromagnetic self-force. We show that, besides the interaction terms derived by P. Zimmerman and E. Poisson (Phys. Rev. D 90, 084030, 2014), additional perturbative terms are generated, which are linear in metric perturbation and are generated due to perturbation of the electromagnetic self-force by the metric perturbation. We discuss the conditions of significance of these perturbative terms and also the interaction terms with respect to the gravitational self-force in various astrophysical and cosmological cases ; such as the motion of charged particles around black holes, some extreme mass-ratio inspirals (EMRIs) involving sufficiently accelerated motion of charged stars (specially neutron stars) or charged stellar mass black holes around supermassive black holes, and motion of charged particles around charged primordial black holes formed in the early Universe etc.. We find that in some astrophysical and cosmological cases these perturbative terms can have significant effect in comparison with the gravitational radiation-reaction term., Comment: 15 pages

In this paper we employ Tolman VII solution with exotic matter that may be present in the extremely dense core of compact objects. The Tolman VII solution, an exact analytic solution to the spherically symmetric, static Einstein field equations with a perfect fluid source, has many characteristics that make it interesting for modeling high density stellar astronomical objects. For our purpose we use generalized non-linear equation of state which may incorporate exotic matter along with dust, radiation and dark energy. The equation of state (EoS) has a linear contribution comprising quark/radiation matters and a nonlinear contribution comprising dark energy/exotic matters. The amount of exotic matter contain can be modify by a parameter $n$ which can be linked to adiabatic index. As $n$ increases the exotic contribution increases which stiffens the EoS. The physical properties of the model such as pressure, density, mass function, surface redshift, gravitational redshift are examined and the stability of the stellar configuration is discussed in details. The model has promising features as it satisfies all energy conditions and is free from central singularities. The $M-R$ relation is constructed analytically and the maximum mass and its corresponding radius is determined using the exact solutions and is shown to satisfy various observational stellar compact stars., Comment: 9 Pages, 14 Figs. Accepted in Physics of Dark Universe

In the present letter we examine the possibility of constraining dyon black holes based on the available observational data at the scale of the Solar system. For this we consider the classical tests of general relativity, viz., the perihelion precession of the planet Mercury and the deflection of light by the Sun. In connection to mathematical analysis we are considering static and spherically symmetric dyon black hole which carries both the electric and magnetic charge simultaneously, which are encoded it by the parameters $\lambda_0$ and $\beta_0$. We constrain these two parameters using the Solar system tests and obtain the permissible range from the observations., Comment: 10 pages, major changes in the text, Accepted in European Physical Journal C

We present a novel architectural enhancement of Channel Boosting in a deep convolutional neural network (CNN). This idea of Channel Boosting exploits both the channel dimension of CNN (learning from multiple input channels) and Transfer learning (TL). TL is utilized at two different stages; channel generation and channel exploitation. In the proposed methodology, a deep CNN is boosted by various channels available through TL from already trained Deep Neural Networks, in addition to its original channel. The deep architecture of CNN then exploits the original and boosted channels down the stream for learning discriminative patterns. Churn prediction in telecom is a challenging task due to the high dimensionality and imbalanced nature of the data. Therefore, churn prediction data is used to evaluate the performance of the proposed Channel Boosted CNN (CB CNN). In the first phase, informative discriminative features are being extracted using a stacked autoencoder, and then in the second phase, these features are combined with the original features to form Channel Boosted images. Finally, the knowledge gained by a pretrained CNN is exploited by employing TL. The results are promising and show the ability of the Channel Boosting concept in learning complex classification problems by discerning even minute differences in churners and nonchurners. The proposed work validates the concept observed from the evolution of recent CNN architectures that the innovative restructuring of a CNN architecture may increase the networks representative capacity., Comment: 24 Pages, 5 Figures, 1 Table

In this paper, we examine the cosmological dynamics of a slotheon field in a linear potential. The slotheon correction term $\frac{G^{\mu\nu}}{2M^2}\pi_{;\mu}\pi_{;\nu}$ respects the galileon symmetry in curved space time. We demonstrate the future evolution of universe in this model. We show that in this scenario, the universe ends with the Big Crunch singularity like the standard case. The difference being that the time at which the singularity occurs is delayed in the slotheon gravity. The delay crucially depends upon the strength of slotheon correction., Comment: 7 pages, 6figures

We investigate the future evolution of the universe using the Buchert framework for averaged backreaction in the context of a two-domain partition of the universe. We show that this approach allows for the possibility of the global acceleration vanishing at a finite future time, provided that none of the subdomains accelerate individually. The model at large scales is analogously described in terms of a homogeneous scalar field emerging with a potential that is fixed and free from phenomenological parametrization. The dynamics of this scalar field is explored in the analogous FLRW cosmology. We use observational data from Type Ia Supernovae, Baryon Acoustic Oscillations, and Cosmic Microwave Background to constrain the parameters of the model for a viable cosmology, providing the corresponding likelihood contours., Comment: 12 pages, 8 figures