By the use of homotopy perturbation method-Padé (HPM-Padé) technique, a new analytical approximation of luminosity distance in the flat universe is proposed, which has the advantage of significant improvement for accuracy in approximating luminosity distance over cosmological redshift range within 0≤z≤2.5. Then we confront the analytical expression of luminosity distance that is obtained by our new

I propose a new model of preinflation, where the universe suffers a transition from an initial stable state [such that the universe is initially at the minimum of a ϕ-quartic potential: V(ϕ)∼ϕ4], to an unstable evolving state that drives the initial accelerated expansion. Using Relativistic Quantum Geometry (RQG), I demonstrate that back-reaction produced by the inflaton field fluctuations should be

Using the static, spherically symmetry condition for space time, we have obtained several geometries for wormholes which is supported by a general form of dark energy in the f(T) scenario of gravity ( T is the torsion scalar). It has been shown that some obtained geometries can explain the traversable wormhole, but the NEC or WEC are not violated. These solutions are obtained according to some specific

In this work, we studied the slow-roll approximation of cosmic inflation within the context of f(R,T) gravity, where R is the scalar curvature, and T is the trace of the energy–momentum tensor. By choosing a minimal coupling between matter and gravity, we obtained the modified slow-roll parameters, the scalar spectral index (ns), the tensor spectral index (nT), and the tensor-to-scalar ratio (r). We

A four-dimensional regularization of Lovelock–Lanczos gravity up to an arbitrary curvature order is considered. We show that Lovelock–Lanczos terms can provide a non-trivial contribution to the Einstein field equations in four dimensions, for spherically symmetric and Friedmann–Lemaître–Robertson–Walker spacetimes, as well as at first order in perturbation theory around (anti) de Sitter vacua. We will

In this paper we study the perturbation theory of the recently proposed Regularized Lovelock Gravity (Glavan and Lin, 2020), on the curved Friedmann–Lemaître–Robertson–Walker (FLRW) space–time. We provide the first order perturbation equations both in the scalar and tensor sector in the presence of an additional minimally coupled scalar field. A general expression for the velocity of gravitational

The Hawking–Page (HP) phase transitions of the anti-de Sitter black holes in the extended phase space are studied in a novel four-dimensional Einstein–Gauss–Bonnet (4EGB) gravity, which is proposed by rescaling the Gauss–Bonnet (GB) coupling constant α→α∕(d−4) in d dimensions and redefining the four-dimensional gravity in the limit d→4. The GB term shows nontrivial contributions to both black hole

One problem of the ΛCDM model is the tension between the S8 found in Cosmic Microwave Background (CMB) experiments and the smaller one obtained from large-scale observations in the late Universe. The σ8 quantifies the relatively high level of clustering. Likelihood analyses of the Redshift Space Distortion (RSD) selected data set yields: S8=0.700−0.037+0.038. The fit has 3σ tension with the Planck

The Phenomenologically Emergent Dark Energy model, a dark energy model with the same number of free parameters as the flat ΛCDM, has been proposed as a working example of a minimal model which can avoid the current cosmological tensions. A straightforward question is whether or not the inclusion of massive neutrinos and extra relativistic species may spoil such an appealing phenomenological alternative

The Hubble parameter H(z), as a function of redshift, is modified by the presence of a new term originated from the extrinsic curvature in a four embedded space–time. Assuming an asymptotic expansion factor a∼0 or, equivalently z→∞, it is obtained a nearly resemblance of the present model (β-model) with the wCDM model with H(z)∼HwCDM(z) at background level. We test the models using a pack of recent

Motivated by a wider acceptance of the quantum cosmology and the idea of multiverse, we follow the second and third quantization formalism for the conceptual comprehension of quantum multiverse. The other motivating feature to pursue the present study is that at the different levels of quantization the equation of quantum state is similar to that of harmonic oscillator, which encourages us to give

We have explored the modified Chaplygin gas (MCG) in the background of Brans–Dicke theory in presence of radiation and dark matter. We have assumed that the MCG, radiation and dark matter are conserved separately. To investigate the fitting observational data, we constrain the model using current observations and then compare with ΛCDM model in Einstein’s gravity and in BD theory using the information

We carry out a test of the radial acceleration relation (RAR) for galaxy clusters from two different catalogs compiled in literature, as an independent cross-check of two recent analyses, which reached opposite conclusions. The datasets we considered include a Chandra sample of 12 clusters and the X-COP sample of 12 clusters. For both the samples, we find that the residual scatter is small (0.11-0

It turns out that repulsive effect due to rotation of a rotating black hole dominates over attraction due to mass for large r in dimensions >5. This gives rise to a remarkable result that black hole in these higher dimensions in contrast to lower dimensional ones cannot be overspun even under linear test particle accretion. Further if a black hole in dimension >4 has one of its rotation parameters

We study a new class of vector dark energy models where multi-Proca fields Aμa are coupled to cold dark matter by the term f(X)L̃m where f(X) is a general function of X≡−12AaμAμa and L̃m is the cold dark matter Lagrangian. From here, we derive the general covariant form of the novel interaction term sourcing the field equations. This result is quite general in the sense that encompasses Abelian and

We present a comparative analysis of observational low-redshift background constraints on three candidate models for explaining the low-redshift acceleration of the universe. The generalized coupling model by Feng and Carloni and the scale invariant model by Maeder (both of which can be interpreted as bimetric theories) are compared to the traditional parametrization of Chevallier, Polarski and Linder

We present a simple and effective new methodology to build up self-gravitating structures driven by an imperfect fluid distributions. This approach is developed within the framework of f(R,T) gravity theory by combining two geometrical schemes, the gravitational decoupling by means of minimal geometric deformation and the embedding technique, specifically the class I grasp. The former, allows to introduce

A universal mechanism may be responsible for several unresolved cosmic conundra. The sudden drop in the pressure of relativistic matter at W±∕Z0 decoupling, the quark–hadron transition and e+e− annihilation enhances the probability of primordial black hole (PBH) formation in the early Universe. Assuming the amplitude of the primordial curvature fluctuations is approximately scale-invariant, this implies

A model of traversable wormhole in an extended gravity theory has been proposed. The Casimir effect and Generalized Uncertainty Principle (GUP) arising out of the concept of minimal length have been considered to obtain the shape function, radial and tangential pressure of the wormhole. The effects of the GUP parameter and the parameter of the extended gravity theory on the wormhole properties have

The inclusion of the quantum fluctuations of the metric in the geometric action is a promising avenue for the understanding of the quantum properties of gravity. In this approach the metric is decomposed in the sum of a classical and of a fluctuating part, of quantum origin, which can be generally expressed in terms of an arbitrary second order tensor, constructed from the metric, and from the thermodynamic

It is found that, when the coupling constants αp in the theory of regularized Lovelock gravity are properly chosen and the number of Lovelock tensors p→∞, there exist a fairly large number of nonsingular (singularity free) black holes and nonsingular universes. Some nonsingular black holes have numerous horizons and numerous energy levels (a bit like atom) inside the outer event horizon. On the other

We show that the extended cosmological equation-of-state developed starting from a Chaplygin equation-of-state, recently applied to stellar modelling, is a viable dark energy model consistent with standard scalar potentials. Moreover we find a Lagrangian formulation based on a canonical scalar field with the appropriate self-interaction potential. Finally, we fit the scalar potential obtained numerically

Inflation drives quantum fluctuations beyond the Hubble horizon, freezing them out before the small-scale modes re-enter during the radiation dominated epoch, and subsequently decay, while large-scale modes re-enter later during the matter dominated epoch and grow. This distinction shapes the matter power spectrum and provides observational evidence in support of the standard model. In this paper,

The manifesto of the current article is to investigate the compact anisotropic matter profiles in the context of one of the modified gravitational theories, known as f(R,T) gravity, where R is a Ricci Scalar and T is the trace of the energy–momentum tensor. To achieve the desired goal, we capitalized on the spherical symmetric space–time and utilized the embedding class-1 solution via Karmarkar’s condition

The field equations of Einstein-massive gravity theory has been solved in a three-dimensional spherically symmetric spacetime, and in the presence of three alternative theories of nonlinear electrodynamics, separately. As the result, three novel classes of nonlinearly charged black holes have been obtained in massive gravity theory, which are asymptotically massive-BTZ black holes. The solutions of

Strong deflection gravitational lensing is investigated for photon coupled to Weyl tensor in a charged Kiselev black hole, and its observables have been found. We get the asymptotically flat solutions, for the appropriate range of the equation of state parameter ω̃. Constructing the action corresponding to the electromagnetic field coupled to Weyl tensor, the equation of motion for the photon coupled

Recently a consistent well-defined 4-dimensional Einstein–Gauss–Bonnet theory of gravity was suggested in [K. Aoki, M. Gorji and S. Mukohyama, Phys. Lett. B 810, 135843 (2020)]. While quasinormal modes of bosonic fields for this theory have been recently studied, there is no such study for fermionic fields. Here we calculate quasinormal modes of the Dirac field for spherically symmetric asymptotically

In this paper we advocate for the idea that two seemingly unrelated mysteries with almost 90 year history – the nature of dark matter and the million-degree solar corona – may be but two sides of the same coin – the axions of dark matter born in the core of the Sun and photons of axion origin in the million-degree solar corona, whose modulations are controlled by the anticorrelated modulation of the

The orbital dynamics in the strong gravitational field might present unique features of quantum gravity and high-dimensional theory. In this paper, a timelike particle’s periodic orbits around the 4-dimensional Einstein–Lovelock (4D−EL) black holes are investigated by employing a classification of the zoom–whirl structure with a rational number q. It is found that these rational (periodic) orbits around

In this paper we investigate a Bianchi type I transitioning Universe in Brans–Dicke theory. To get an explicit solution of the field equations, we assume scalar field as ϕ=ϕ0tαexp(βt)δ with ϕ0, α, β and δ as constants. The values of α and β are obtained by probing the proposed model with recent observational Hubble data (OHD) points. The interacting and non-interacting scenarios between dark matter

Black holes with hair represented by generic fields surrounding the central source of the vacuum Schwarzschild metric are examined under the minimal set of requirements consisting of (i) the existence of a well defined event horizon, namely, we require the Killing horizon coincides with the causal horizon and (ii) the strong or dominant energy condition for the hair outside the horizon. We develop

We propose a simple radiative neutrino mass scenario with a Dirac dark matter candidate, which is minimally realized by a Z3 symmetry. We introduce two Dirac neutrinos and two inert doublets. We demonstrate that the model has a large allowed region that satisfies the constraints from neutrino oscillation data, lepton flavor violations, direct/indirect detection of dark matter and dark matter relic

We compute the quasinormal spectra for scalar, Dirac and electromagnetic perturbations of the Schwarzschild–de Sitter geometry in the framework of scale-dependent gravity, which is one of the current approaches to quantum gravity. Adopting the widely used WKB semi-classical approximation, we investigate the impact on the spectrum of the angular degree, the overtone number as well as the scale-dependent

The baryogenesis presents the theoretical mechanism that describes the matter–antimatter asymmetry in the history of early universe. In this work, we investigate the gravitational baryogenesis phenomena in the frameworks of f(T,TG) (where T and TG are the torsion scalar and teleparallel equivalent to the Gauss–Bonnet term respectively) and f(T,B) (where B denotes the boundary term between torsion and

The non-singular model of the Universe i.e. emergent scenario is now very well known in cosmology. In Einstein gravity such type of singularity free solution is possible in the context of non-equilibrium thermodynamical prescription (both in first and 2nd order theory) with particle creation mechanism. Also there are various models of emergent scenario in different gravity theories. The present work

In this paper, the tachyon scalar field model is compared with the ΛCDM standard model using a set of observational data consisting of BBN, H(z), CMB, BAO, SNIa and f(z)σ8. The comparison is carried out at background and perturbation levels. Since the mass of the tachyon scalar field is very small and its effective sound speed is in the order of the speed of light (ceff≈1), the dark energy component

In this paper, we study the classical limit and unitary evolution of quantum cosmology by applying the Weyl–Wigner–Groenewold–Moyal formalism of deformation quantization to quantum cosmology of a homogeneous and isotropic universe with positive spatial curvature and conformally coupled scalar field. The corresponding quantum cosmology (similar to the Schrödinger interpretation in canonical quantization

Inflation is the main paradigm for explaining the homogeneity and isotropy of the observed universe. In view of its agreement with the Planck CMB data, we studied in this work Starobinsky inflation in models of induced gravity. Induced gravity theories are attractive because they arise from matter loops and have the potential to qualify as natural.

It is well known that d=2N+1 dimensional pure Lovelock metrics do not describe bounded distributions neither do they admit nontrivial vacuum solutions. On this basis it has been variously claimed that matter fields should be nondynamical. However, from earlier work it has long been demonstrated fairly generally that 2N+1 pure Lovelock solutions are not kinematic. In this work we find perfect fluid

This paper is devoted to studying anisotropic compact stellar structures by adopting embedding class-1 technique in the background of modified Gauss–Bonnet gravity. The unknown constants are evaluated by the matching of interior spacetime with the Schwarzschild exterior geometry corresponding to f(G)=χGn model, where χ and n are positive constants. The observed masses of compact star candidates (SAX

We propose a new algorithm for computing the luminosity distance in the flat universe with a cosmological constant based on Shchigolev’s homotopy perturbation method, where the optimization idea is applied to prevent the arbitrariness of initial value choice in Shchigolev’s homotopy. Compared with the some existing numerical methods, the result of numerical simulation shows that our algorithm is a

Can all binary star systems merge in infinite time by emitting gravitational waves? The answer is no. The orbital radius shrinks from the gravitational wave emission; simultaneously, the universe is expanding if the Hubble–Lemaître law is universal on all distance scales. Inside the gravitational bound state, the cosmic expansion becomes visible near the critical radius given by the equilibrium between

Recently there has been significant interest in regularizing, a D→4 limit, of EGB gravity, and the resulting regularized 4D EGB gravities have nontrivial gravitational dynamics — namely the 4D EGB gravity. We present an exact charged black hole solution to the 4D EGB gravity surrounded by clouds of string (CS) and also analyse their thermodynamic properties. Owing to the corrected black hole due to

We do not solve tensions with concordance cosmology; we do obtain H0≈74km/s/Mpc from CMB+BAO+SN data in our model, but that is not the point. Discrepancies in Hubble constant values obtained by various astrophysical probes should not be viewed in isolation. While one can resolve at least some of the differences through either an early time transition or late time transition in the expansion rate, these

We propose the Kaluza–Klein inspired Brans–Dicke gravity model containing possible existence of dark matter and dark energy. The massive scalar field coupled with gravity in 5 dimensional space–time can be reduced to 4 dimensional gravity along with the dilaton ϕ, gauge fields Aμ, and the tower of scalar fields ηn. Two additional gauge fields are introduced to form “Cosmic Triad” vector field scenario

We study the possibility that in the model introduced in Glavan and Lin (2020), the Gauss–Bonnet term alone gives rise to the cosmic acceleration and super-acceleration in four-dimensional FLRW space–time at the late time. We also discuss transitions from deceleration to acceleration and acceleration to super-acceleration. We show that the Gauss–Bonnet invariant can drive the acceleration in the low

We propose a new coupled three-form dark energy model to relieve the Hubble tension in this paper. Firstly, by performing a dynamical analysis with the coupled three-form dark energy model, we obtain four fixed points, including a saddle point representing a radiation dominated Universe, a saddle point representing a matter dominated Universe, and two attractors representing two saturated de Sitter

We study slowly rotating four-dimensional black holes with flat horizon structure in scale-dependent gravity. First, we obtain the solution, and then we study thermodynamic properties as well as the invariants of the theory. The impact of the scale-dependent parameter is investigated in detail. We find that the scale-dependent solution exhibit a new singularity not present in the classical solution

The advent of new deep＋ wide photometric lensing surveys will open up the possibility of direct measurements of the dark matter halos of dwarf galaxies. The HSC wide survey will be the first with the statistical capability of measuring the lensing signal with high signal-to-noise at log(M∗)∼8. At this same mass scale, The Rubin Observatory LSST will have the most overall constraining power with a predicted

In this work, we investigate the recently introduced phenomenological emergent dark energy (PEDE) model and the anisotropic extension of PEDE (APEDE) via Bianchi type-I spacetime metric with the latest observational data involving both low and high redshift datasets as, Hubble, Cosmic Microwave Background (CMB), Baryon Acoustic Oscillations (BAO) and Pantheon. We perform Bayesian inference analysis

Some dark energy cosmological models are constructed in the framework of a generalised Brans–Dicke theory which contains a self interacting potential and a dynamical coupling parameter. The models are constructed in the background of an anisotropic metric. The dark sector of the universe is considered through a unified linear equation of state. The parameters of the unified dark fluid have been constrained

We show that in the inhomogeneous Lemaître–Tolman–Bondi space–time there are specific regions in which repulsive gravity exists. To find these regions, we use an invariant definition of repulsive gravity based upon the behavior of the curvature eigenvalues. In addition, we analyze the effects of repulsive gravity on the dynamics of the gravitational collapse. In particular, we investigate the collapse

Dark matter (DM) which constitutes five-sixths of all matter is hypothesized to be a weakly interacting non-baryonic particle, created in the early stages of cosmic evolution. It can affect various cosmic structures in the Universe via gravitational interactions. The effect of DM in main sequence stars and stellar remnants like neutron stars and white dwarfs has already been studied. Red giant phase

In this paper, we shall consider f(R) gravity and its cosmological implications, when an extra matter term generated by thermal effects is added by hand in the Lagrangian. We formulate the equations of motion of the theory as a dynamical system, that can be treated as an autonomous one only for specific solutions for the Hubble rate, which are of cosmological interest. Particularly, we focus our analysis

This paper is devoted to analyzing the critical phenomenon and phase transition of quintessential Kerr–Newman-anti-de Sitter black hole in the framework of Maxwell equal-area law. For this purpose, we first derive thermodynamic quantities such as Hawking temperature, entropy and angular momentum in the context of extended phase space. These quantities satisfy Smarr–Gibbs–Dehum relation in the presence

Recently, a novel Einstein–Gauss–Bonnet gravity in four dimensions has been introduced (Glavan and Lin, 2020). We will investigate cosmological consequences of this model in details. We will consider linear matter density perturbations and also estimate relevant modified gravity parameters. Specially we will concentrate on the growth rate of non-relativistic matter perturbations on top of FRW geometry

In this paper we investigate the inflationary phenomenology of an Einstein–Gauss–Bonnet theory compatible with the GW170817 event, by imposing the constant-roll evolution on the scalar field. We develop the constant-roll GW170817-compatible Einstein–Gauss–Bonnet formalism, and we calculate the slow-roll indices and the observational indices of inflation, for several models of interest. As we demonstrate

Recently, spontaneous scalarization of charged black holes has attracted a great deal of attention and motivated several studies of Einstein–Maxwell-scalar models. These studies have, however, only considered a massless and non-self-interacting scalar field. In this work a more realistic treatment of the problem is considered by studying the effects of scalar field mass and self-interacting terms on

In this paper, we have investigated the dynamics of magnetized particles around 4-D Einstein Gauss–Bonnet black hole immersed in an external asymptotically uniform magnetic field. We have shown that the magnetic interaction parameter responsible for circular orbits decreases for negative values of the Gauss–Bonnet parameter α and the range where magnetized particle’s stable circular orbits are allowed

In this paper, we explore the dynamics of neutral and charged particles in presence/absence of magnetic field around the quantum corrected-Schwarzschild black hole as well as the time conformal quantum corrected-Schwarzschild black hole. We investigate the conditions under which the particles move towards or away from the vicinity of black hole when they collide with other particles. We study the effective