Dynamics of thin-shell wormholes within the context of f(R)gravity by joining two identical copies of Reissner–Nordstrom–de Sitter manifold using the cut and paste approach is discussed. The stability of wormholes is analyzed through the radial perturbation about the static solution and the modified generalized Chaplygin gas equation of state (EoS). This formalism gives rise two specific different

The neutrino minimal standard model (νMSM) has been tightly constrained in the recent years, either from dark matter (DM) production or from X-ray and small-scale observations. However, current bounds on sterile neutrino DM can be significantly modified when considering a νMSM extension, in which the DM candidates interact via a massive (axial) vector field. In particular, standard production mechanisms

A (3+1)-dimensional Einstein–Gauss–Bonnet effective description of gravity has been recently formulated as the D→4 limit of the higher dimensional field equations after the rescaling of the coupling constant. This approach has been recently extended to the four-dimensional Einstein–Lovelock gravity. Although validity of the regularization procedure has not been shown for the general case, but only

We study a collapsing system attracted by a spherically symmetric gravitational source, with an increasing mass, that generates back-reaction effects that are the source of space–time waves. As an example, we consider an exponential collapse and the space–time waves emitted during this collapse due to the back-reaction effects, originated by geometrical deformation driven by the increment of the gravitational

For any non-rotating effective quantum (uncharged) black hole model to be viable, its asymptotic structure of spacetime should reduce to that of a Schwarzschild black hole. After examining the asymptotic structure of quantum black holes proposed in Ashtekar et al., (2018), we find that the solution is actually not asymptotically flat. Departure from asymptotically flat spacetime is a direct consequence

I use Unified Spinor Fields (USF), to discuss the creation of magnetic monopoles during preinflation, as excitations of the quantum vacuum coming from a condensate of massive charged vector bosons. For a primordial universe with total energy Mp, and for magnetic monopoles created with a total Planck magnetic charge qM=qP=±e∕α and a total mass mM, it is obtained after quantisation of the action that

The knowledge of the universe future is of fundamental importance for any advanced civilization. We study the future of the singular dark universe where thermal effects due to the Hawking radiation on the apparent horizon of the FRW universe are taken in the consideration. It is shown that the dark universe which ends up as finite-time Type I and Type III singularity or the infinite-time Little Rip

The viability of slow-roll approximation is examined by considering the structure of phase spaces in scalar–tensor theories of gravitation and the analysis is exemplified with a nonminimally coupled scalar field to the spacetime curvature. The slow-roll field equations are obtained in the Jordan frame in two ways: first using the direct generalization of the slow-roll conditions in the minimal coupling

Recently Glavan and Lin (2020) formulated a novel Einstein–Gauss–Bonnet gravity in which the Gauss–Bonnet coupling has been rescaled as α∕(D−4) and the 4D theory is defined as the limit D→4, which preserves the number degrees of freedom thereby free from the Ostrogradsky instability. We present exact spherically symmetric nonstatic null dust solutions in the novel 4D Einstein–Gauss–Bonnet gravity that

We present an analysis of Murchison Widefield Array radio telescope data from ω Cen, possibly a stripped dwarf spheroidal galaxy core captured by our Galaxy. Recent interpretations of Fermi-LAT γ-ray data by Brown et al. (2019) and Reynoso-Cordova et al. (2019) suggest that ω Cen may contain significant Dark Matter. We utilize their best-fit Dark Matter annihilation models, and an estimate of the magnetic

We present a detailed study of the collapse of a spherical matter overdensity and the non-linear growth of large scale structures in the Galileon ghost condensate (GGC) model. This model is an extension of the cubic covariant Galileon (G3) which includes a field derivative of type (∇μϕ∇μϕ)2 in the Lagrangian. We find that the cubic term activates the modifications in the main physical quantities whose

The current Universe is composed by a mixture of relativistic species, baryonic matter, dark matter and dark energy which evolve in a non-trivial way at perturbative level. An advanced description of the cosmological dynamics should include non-standard features beyond the simplistic approach idealized by the standard cosmology in which cosmic components do not interact, are adiabatic and dissipationless

We investigate the reliability of standard N-body simulations by modeling of the well-known Hernquist halo with the help of GADGET-2 code (which uses the tree algorithm to calculate the gravitational force) and ph4 code (which uses the direct summation). Comparing the results, we find that the core formation in the halo center (which is conventionally considered as the first sign of numerical effects

A class of modified gravity theories with higher order derivative terms of a function of the matter Lagrangian f(Lm) is considered. We will consider the Newtonian limit of the theory and show that the model predicts the standard Poisson equation for a massive test particle due to the higher order nature of the derivative matter coupling. Generally the energy–momentum tensor is not conserved, leading

We attempt a novel mechanism to understand the underlying cause of late-time cosmic acceleration using a distinguished physical process taking place in the late Universe. In our opinion, the turning of massive neutrinos from relativistic to non-relativistic might cause a phase transition at late times. We implement this idea using massless λϕ4 theory coupled to massive neutrino matter such that the

The recent astonishing realization of the negative absolute temperature (NAT) for motional degrees of freedom (Braun et al., 2013) inspires its possible application to the early universe. The existence of the upper bound on the energy of the system is the sufficient requirement for a NAT and this might correspond to the Planck scale at the Big Bang model. It has been argued that standard inflation

We examine interactions between dark matter and dark energy in light of the latest cosmological observations, focusing on a specific model with coupling proportional to the dark energy density. Our data includes Cosmic Microwave Background (CMB) measurements from the Planck 2018 legacy data release, late-time measurements of the expansion history from Baryon Acoustic Oscillations (BAO) and Supernovae

We study the effects of dark energy (DE) anisotropic stress on features of the matter power spectrum (PS). We employ the Parametrized Post-Friedmannian (PPF) formalism to emulate an effective DE, and model its anisotropic stress properties through a two-parameter equation that governs its overall amplitude (g0) and transition scale (cg). For the background cosmology, we consider different equations

We study the emission of large-scales wavelength space–time waves during the inflationary expansion of the universe, produced by back-reaction effects. As an example, we study an inflationary model with variable time scale, where the scale factor of the universe grows as a power of time. The coarse-grained field to describe space–time waves is defined by using the Levy distribution, on the wavenumber

We study strongly supercooled cosmological phase transitions. We perform numerical lattice simulations of two-bubble collisions and demonstrate that, depending on the scalar potential, in the collision the field can either bounce to a false vacuum or remain oscillating around the true vacuum. We study if these cases can be distinguished from their gravitational wave signals and discuss the possibility

The dark matter explanation of the 3.5 keV line is strongly disfavored by our work in Dessert et al. (2020). Boyarsky et al. (2004) questions that conclusion: modeling additional background lines is claimed to weaken the limit sufficiently to re-allow a dark matter interpretation. We respond as follows. (1) A more conservative limit is obtained by modeling additional lines; this point appeared in its

Lovelock gravitation theory is a natural extension of the General Relativity to higher dimensions with the inclusion of only second-order terms correspond to the Einstein–Gauss–Bonnet gravity. In this paper, we find an exact Hayward black hole solution of D≥5-dimensional spacetime for Einstein–Gauss–Bonnet (EGB) gravity with negative cosmological constant (Λ) minimally coupled to non-linear electrodynamics

Allowing for a nonvanishing spin tensor for cold dark matter (ωDM=0) has the consequence of giving rise to an effective FLRW dynamics with a small negative barotropic constant for an effective dark matter density (−1∕3<ωeff≤0). This turns out to solve the Hubble parameter tension in a straightforward way.

The paper presents late time cosmology in f(Q,T) gravity where the dark energy is purely geometric in nature. We start by employing a well motivated f(Q,T) gravity model, f(Q,T)=mQn+bT where m,n and b are model parameters. Additionally we also assume the universe to be dominated by pressure-less matter which yields a power law type scale factor of the form a(t)=c2(At+c1)1A, where A=3(8π+b)n(16π+3b)

We study the bound on the compactness of a stellar object in pure Lovelock theories of arbitrary order in arbitrary spacetime dimensions, involving electromagnetic field. The bound we derive for a generic pure Lovelock theory, reproduces the known results in four dimensional Einstein gravity. Both the case of a charged shell and that of a charge sphere demonstrates that for a given spacetime dimension

This current study is focussed to discuss the existence of a new family of compact star solutions by adopting the Karmarkar condition in the background of Bardeen black hole geometry. For this purpose, we consider static spherically symmetric spacetime with anisotropic fluid distribution in the presence of electric charge. We consider a specific model of grr metric function, to describe a new family

The primordial black hole (PBH) abundance evaluated by the conventional Press–Schechter (PS) probability distribution is shown to be equivalent to the high-peak limit of a special point-like peak statistics via unphysical dimensionality reduction of the Bardeen–Bond–Kaiser–Szalay (BBKS) theory. The fact that PBHs are formed at high peak values νc≫1 leads to a systematic bias proportional to νc3 between

We investigate particle motion in the vicinity of a 4D Einstein–Gauss–Bonnet (EGB) black hole immersed in external asymptotically uniform magnetic field. It is well known that magnetic fields can strongly affect charged particle motion in the black hole vicinity due to the Lorenz force. We find that the presence of the Gauss–Bonnet (GB) coupling gives rise to a similar effect, reducing the radius of

In this work we study the scalar power spectrum and the spectral index for the Starobinsky inflationary model using the phase integral method up-to third-order of approximation. We show that the semiclassical methods reproduce the scalar power spectrum for the Starobinsky model with a good accuracy, and the value of the spectral index compares favourably with observations. Also, we compare the results

A general formalism recently proposed to study Newtonian polytropes for anisotropic fluids (Abellán et al., 2020) is here extended to the relativistic regime. Thus, it is assumed that a polytropic equation of state is satisfied by, both, the radial and the trangential pressures of the fluid. Doing so the generalized Lane–Emden equations are obtained and solved. Some specific models are obtained, and

The present paper is devoted to investigating the possibility of getting stellar interiors for ultra-dense compact spherical systems portraying an anisotropic matter distribution, employing the gravitational decoupling by means of Minimal Geometric Deformation (MGD) procedure within the modified theory of gravity: f(R,T). In this regard, we have considered the algebraic function as f(R,T)=R+2χT. The

As we know the thermodynamic quantities such as entropy and extremal bounds of black holes play an important role in general relativity. On the other hand, such quantities are changed by the perturbative corrections. In this paper we take advantage from such corrections and obtain the universal relations between the entropy and extremal bound of black hole. In this way perturbative corrections for

We investigate the possibility of dark matter being a pure geometrical effect, rather than a particle or a compact object, by exploring a specific modified gravity model: mimetic dark matter. We present an alternative formulation of the theory, closer to the standard cosmological perturbation theory framework. We make manifest the presence of arbitrary parameters and extra functions, both at background

A novel function for modified gravity is proposed, f(R,T)=R+λR2+2βln(T), with constants λ and β, scalar curvature R, and the trace of stress energy tensor T, satisfying T=ρ−3p>0. Subsequently, two equations of state (EoS) parameters, namely ω and a parametric form of the Hubble parameter H, are employed in order to study the accelerated expansion and initial cosmological bounce of the corresponding

An ultralight scalar boson with mass m1≃10−22eV is gaining credence as a Dark Matter (DM) candidate that explains the dark cores of dwarf galaxies as soliton waves. Such a boson is naturally interpreted as an axion generic in String Theory, with multiple light axions predicted in this context. We examine the possibility of soliton structures over a wide range of scales, accounting for galaxy core masses

We have explored exact solutions free from any physical and geometrical singularities, as well as the existence of compact stellar systems throughout linear and Starobinsky-f(R,T)−gravity theory. As we generally well-known, the general exact solutions of the altered Einstein Field Equations (EFEs) in the background of this gravity theory are one of the most complex tasks. To acquire simpler solution

We compute the quasinormal frequencies for scalar and electromagnetic perturbations of an improved Schwarzschild geometry in the framework of asymptotically safe gravity, which is one of the 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 black hole mass. We

We discuss propagation of the axial gravitational waves (AGWs) in the spatially flat conformal Friedmann–Lemaitre–Robertson–Walker (FLRW) spacetime, which is dominated by a perfect fluid, in the generalized Rastall theory of gravity (gRT). On this purpose, we perturb the spatially flat metric, background material content and the four-velocity components with the help of Regge–Wheeler perturbations

Cosmological neutrinos and anti-neutrinos are thought to have been created in the Big Bang in almost unlimited numbers. Being Fermions, they may condense into stable objects called Condensed Neutrino Objects (CNO). CNOs could be the Dark Matter everyone is looking for. Weak lensing data indicates that the degenerate neutrino mass (called the neutrino mass scale) ∼0.8 eV/c2. Being condensed degenerate

We study the nonsingular black hole in Anti de-Sitter background taking the negative cosmological constant as the pressure of the system. We investigate the horizon structure, and find the critical values m0 and k̃0, such that m>m0 (or k̃k̃0), no black hole solution exists. In turn, we calculate the thermodynamical properties and by observing the behaviour of Gibb’s free energy and specific heat, we

The existence of quintessential dark energy around a black hole has considerable consequences on its spacetime geometry. Hence, in this article, we explore its effect on horizons and the silhouette generated by a Kerr–Newman black hole in quintessential dark energy. Moreover, to analyse the deflection angle of light, we utilize the Gauss–Bonnet theorem. The obtained result demonstrates that, due to

Due to the inverse Primakoff effect, it has been shown that when axions mix with a DC B→-field, the resulting electrical action will produce an AC electromotive force, which oscillates at the Compton frequency of the axion. As in standard electrodynamics, this electromotive force may be modelled as an oscillating effective impressed magnetic current boundary source. We use this result to calculate

The orbital dynamics in a black hole spacetime can give us a chance to get deep insight into quantum gravity and fundamental physics. In this paper, we mainly focus on a massive particle’s motion around a quantum-corrected Schwarzschild black hole. In order to reveal some signatures of the adiabatic inspiral stage for probing the gravitational wave, the geodesics and periodic orbits around the black

In this paper, we studied the “hyperon puzzle”, a problem that nevertheless the large number of studies is still an open problem. The solution of this issue requires one or more mechanisms that could eventually provide the additional repulsion needed to make the EoS stiffer and, therefore, the value of Mmax,T compatible with the current observational limits. In this paper we proposed that including

A Bayesian statistical analysis using redshift space distortions data is performed to test a model of Symmetric Teleparallel Gravity where gravity is non-metrical. The cosmological background mimics a ΛCDM evolution but differences arise in the perturbations. The linear matter fluctuations are numerically evolved and the study of the growth rate of structures is analysed in this cosmological setting

In this work we explore the connections between Newman-Penrose scalars, including the Penrose-Rindler K-curvature, with the equation of state of asymptotically Anti-de Sitter Reissner-Nordström black holes. After briefly reviewing the equation of state for these black holes from the point of view of both the Extended Phase Space and the Horizon Thermodynamics approaches, a geometric splitting is given

The article communicates gravitational baryogenesis in non-minimal f(T) gravity and f(T,B) teleparallel gravity where T denote the torsion scalar and B a boundary term. These extended teleparallel theories of gravity differ from the usual f(T) gravity and therefore could provide key insights in expounding the baryon asymmetry of the universe. Furthermore, such a study also put constraints on the model

We present an efficient numerical code and conduct, for the first time, a null and model-independent CMB test of statistical isotropy using Multipole Vectors (MVs) at all scales. Because MVs are insensitive to the angular power spectrum Cℓ, our results are independent from the assumed cosmological model. We avoid a posteriori choices and use a pre-defined range of scales ℓ∈[2,30], ℓ∈[2,600] and ℓ∈[2

In this paper, we construct anisotropic spherical solutions from known isotropic solutions through extended gravitational decoupling method in the background of self-interacting Brans–Dicke theory. The field equations are decoupled into two sets by applying geometric deformations on radial as well as temporal metric components. The first array corresponds to isotropic fluid while influence of the anisotropic

This paper is devoted to develop compact stellar configuration and to evaluate exact interior solutions in the background of f(T,T) gravity, where T be the torsion scalar and T be the trace of energy momentum tensor. We develop a new set up for embedding class I model under well-known Karmarkar condition for LMC X-4 and Vela X-1 compact stars using specific linear function f(T,T)=αT(r)+βT(r)+Φ, where

We study neutrino oscillations in a medium of dark matter which generalizes the standard matter effect. A formula is derived to describe the effect of medium and its mediator to neutrinos. Neutrinos and anti-neutrinos receive opposite contributions from asymmetric distribution of (dark) matter and anti-matter, and thus it could appear in precision measurements of neutrino or anti-neutrino oscillations

In this work we shall present models of F(R) gravity which realize in a unified way the inflationary era along with a post-inflationary early dark energy era, with the late-time dark energy era. We shall use two approach methods in order to realize the unified cosmological eras, firstly we specify a Hubble rate which may describe the three distinct acceleration eras, and then by using well known F(R)

Global cosmic strings are generically predicted in particle physics beyond the Standard Model, e.g., a post-inflationary global U(1) symmetry breaking which may associate with axion-like dark matter. We demonstrate that although subdominant to Goldstone emission, gravitational waves (GWs) radiated from global strings can be observable with current/future GW detectors. The frequency spectrum of such

We consider gravitational collapse in the recently proposed 4D limit of Einstein–Gauss–Bonnet gravity. We show that for collapse of a sphere made of homogeneous dust the process is qualitatively similar to the case of pure Einstein’s gravity. The singularity forms as the endstate of collapse and it is trapped behind the horizon at all times. However, and differently from Einstein’s theory, as a consequence

This paper encompasses a set of stellar equations that administer the formation and evolution of self-gravitating, dissipative spherically symmetric fluid distributions having anisotropic stresses in the presence of electromagnetic field. The Riemann tensor is split orthogonally to procure five scalar functions named as structure scalars which are then utilized in the stellar equations. It is shown

In this paper, we study the thermodynamics and statistics of the galaxies clustering affected by the dynamical dark energy. We consider two important dark energy models based on time dependent equation of state to evaluate the gravitational partition function. In the first model, we consider barotropic dark energy with time dependent equation of state. However, in the second model, we consider various

An effective Lagrangian approach, partly inspired by Quantum Loop Cosmology (QLC), is presented and formulated in a non flat FLRW space–times, making use of modified gravitational models. The models considered are non generic, and their choice is dictated by the necessity to have at least second order differential equations of motion in a non flat FLRW space–time. This is accomplished by a class of

In this paper, we study thermodynamics, quasi-normal modes and thermal fluctuations of a charged black hole with Weyl corrections. We first obtain thermodynamic quantities such as Hawking temperature, entropy, and heat capacity for non-rotating as well as rotating versions of this black hole. We also evaluate temperature through quantum tunneling mechanism which is exactly the same as found through

In this paper, we introduce static black hole with accounting of f(R) gravity. First, we study thermal properties and phase transition of corresponding black hole. Also, here we do correction to the entropy and temperature at same time in above mentioned black hole. Second step, we obtain such corrected thermodynamical properties and study the P−V critically and phase transition. We also investigate

In this paper, we estimate the cross-correlation power spectra between the Planck 2018 cosmic microwave background (CMB) temperature anisotropy map and the unresolved γ-ray background (UGRB) from the 9-years Fermi-Large Area Telescope (LAT) data. In this analysis, we use up to nine energy bins over a wide energy range of [0.631, 1000] GeV from the Fermi-LAT UGRB data. Firstly, we find that the Fermi