Symmetric Teleparallel Gravity Research Articles

Thermal analysis with emission energy of perturbed black hole in f(Q) gravity

In the present paper, we investigate the thermodynamics of a new perturbed black hole solution in symmetric teleparallel gravity. Our main focus is on the solution for a nonlinear model like Q+αQ2. We study new features of null geodesics and quasi-normal modes that occur for the current perturbed black hole solution. We inspect the critical behavior of thermal fluctuation and phase transitions in the background of a considered black hole solution and get the Davies points. To complete this study, we also explore the interesting aspects of the emission energy and quantum fluctuations. We highlight that our results are in good agreement with the thermodynamics of the previous black hole solutions and assumptions presented in the literature.

Thermodynamics of Charged Black Hole in Symmetric Teleparallel Gravity

AbstractIn the current study, we examine the thermodynamics of a novel symmetric teleparallel gravity charged black hole solution. Our main focus is on the approximated solution for a nonlinear model like . For this purpose, we calculate the Hawking temperature and discuss the stable configuration of considered black hole using heat capacity. Then, we explore the effects of thermal corrections on thermodynamical quantities as well as energies of the system. We study the phase transitions of the system in the background of thermal fluctuations. It is concluded that the presence of coupling constant enhances the thermodynamical stable configuration of uncharged and charged BH geometries. To complete this study, we also explore the interesting aspects of the emission energy and quantum fluctuations. We highlight that our results are in good agreement with the thermodynamics of the previous black hole solutions and assumptions presented in the literature.

Relativistic wormhole surrounded by dark matter halos in symmetric teleparallel gravity

AbstractIn this article we study the wormhole geometry in the galactic halo region under modified gravity, especially symmetric teleparallel gravity, where the nonmetricity scalar drives the gravitational interaction. The wormhole solutions for the assumed form have been presented, where α and β are the model parameters. The assumption of is based on the fact that its behavior should change with assumed parametric values of α as well as β within specific physical bounds. Two such models are presented based on the physically motivated shape function and energy conditions. We have elaborately shown, via mathematical calculations and graphical plots, the following features in our model: (i) energy conditions, especially NEC, which is very instructive in connection to energy violation in modified gravity theory, (ii) the wormhole solutions in the regime of Navarro‐Frenk‐White (NFW) density profiles for the galactic halo regions, (iii) treatment with particles moving in closed orbits around the wormholes which exhibit epicyclic frequencies, and (iv) the red‐blue shifts of the light coming from the wormhole throat in the vicinity of the dark matter halos. All the results and behaviors are satisfactory as well as interesting.

Cosmic transit behavior of the expanding cosmos in symmetric teleparallel gravity

Cosmic transit behavior of the expanding cosmos in symmetric teleparallel gravity

Yukawa–Casimir Wormholes in f(Q) Gravity

Casimir energy is always suggested as a possible source to create a traversable wormhole. It is also used to demonstrate the existence of negative energy, which can be created in a lab. To generalize this idea, Yukawa modification of a Casimir source has been considered in Remo Garattini (Eur. Phys. J. C 81 no.9, 824, 2021). In this work, we explore the Yukawa–Casimir wormholes in symmetric teleparallel gravity. We have taken four different forms of f(Q) to obtain wormhole solutions powered by the original Casimir energy source and Yukawa modification of the Casimir energy source. In power law form f(Q)=αQ2+β and quadratic form f(Q)=αQ2+βQ+γ, where α,β,γ are constants and Q is non-metricity scalar, we analyze that wormhole throat is filled with non-exotic matter. We find self-sustained traversable wormholes in the Casimir source where null energy conditions are violated in all specific forms of f(Q), while after Yukawa modification, it is observed that violation of null energy conditions is restricted to some regions in the vicinity of the throat.

Cosmic jerk parameter in symmetric teleparallel cosmology

In this paper, we have examined the recently proposed modified symmetric teleparallel gravity, in which gravitational Lagrangian is given by an arbitrary function of non-metricity scalar Q. We have considered a constant jerk parameter to express the Hubble rate. Moreover, we have used 31 points of OHD datasets and 1701 points of Pantheon+ datasets to constraint our model parameters by means of the Markov Chain Monte Carlo analysis. The mean values and the best fit obtained give a consistent Hubble rate and deceleration parameter compared to the observation values. In order to study the current accelerated expansion scenario of the Universe with the presence of the cosmological fluid as a perfect fluid, we have considered two forms of teleparallel gravity. We have studied the obtained field equations with the proposed forms of f(Q) models, specifically, linear $$f\left( Q\right) =\alpha Q+\beta $$ and nonlinear $$f\left( Q\right) =Q+mQ^{n}$$ models. Next, we have discussed the physical behavior of cosmological parameters such as energy density, pressure, EoS parameter, and deceleration parameter for both model. To ensure the validity of our proposed cosmological models, we have checked all energy conditions. The properties of these parameters confirm that our models describe the current acceleration of the expansion of the Universe. This result is also corroborated by the energy conditions criteria. Finally, the EoS parameter for both models indicates that the cosmological fluid behaves like a quintessence dark energy model.

Matter bounce scenario in extended symmetric teleparallel gravity

In this paper, we have shown the matter bounce scenario of the Universe in an extended symmetric teleparallel gravity, the f(Q) gravity. Motivated from the bouncing scenario and loop quantum cosmology (LQC), the form of the function f(Q) has been obtained at the backdrop of Friedmann–Lema{hat{i}}tre–Robertson Walker (FLRW) space time. Considering the background cosmology dominated by dust fluid, the e-folding parameter has been expressed, which contains the nonmetricity term. Since the slow roll criterion in the bouncing context is not valid, we used a conformal equivalence between f(Q) and scalar-tensor model to apply the bottom-up reconstruction technique in the bouncing model. The dynamics of the model has been studied through the phase space analysis, where both the stable and unstable nodes are obtained. Also, the stability analysis has been performed with the first order scalar perturbation of the Hubble parameter and matter energy density to verify the stability of the model.

Integrable teleparallel gravity in the presence of boundaries

Symmetric teleparallel gravity is shown to be integrable in the presence of boundaries, given the consistent implementation of constraints in the covariant phase space formalism.Received 14 October 2022Accepted 3 January 2023DOI:https://doi.org/10.1103/PhysRevD.107.024019© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlternative gravity theoriesGeneral relativityRelativistic aspects of cosmologyGravitation, Cosmology & Astrophysics

Weyl covariance, second clock effect and proper time in theories of symmetric teleparallel gravity

Just after Weyl’s paper (Weyl in Gravitation und Elektrizität, Sitzungsber. Preuss. Akad., Berlin, 1918) Einstein claimed that a gravity model written in a spacetime geometry with non-metricity suffers from a phenomenon, the so-called second clock effect. We give a new prescription of parallel transport of a vector tangent to a curve which is invariant under both of local general coordinate and Weyl transformations in order to remove that effect. Thus since the length of tangent vector does not change during parallel transport along a closed curve in spacetimes with non-metricity, a second clock effect does not appear in general, not only for the integrable Weyl spacetime. We have specially motivated the problem from the point of view of symmetric teleparallel (or Minkowski–Weyl) geometry. We also conclude that if nature respects Lorentz symmetry and Weyl symmetry, then the simplest geometry in which one can develop consistently alternative gravity models is the symmetric teleparallel geometry; Q_{mu nu }ne 0, ; T^mu =0, ; R^mu {}_nu =0. Accordingly we discuss the proper time, the orbit equation of a spinless test body and the Lagrangian for symmetric teleparallel gravity.

Self-similar cosmological solutions in symmetric teleparallel theory: Friedmann-Lemaître-Robertson-Walker spacetimes

The existence of self-similar solutions is discussed in symmetric teleparallel $f(Q)$ theory for a Friedmann-Lema\^{\i}tre-Robertson-Walker background geometry with zero and nonzero spatial curvature. For the four distinct families of connections that describe the specific cosmology in symmetric teleparallel gravity, the functional form of $f(Q)$ is reconstructed. Finally, to see if the analogy with GR holds, we discuss the relation of the self-similar solutions with the asymptotic behavior of more general $f(Q)$ functions.

Parametrization of Deceleration Parameter in f(Q) Gravity

In this paper, we investigate the modified symmetric teleparallel gravity or f(Q) gravity, where Q is the nonmetricity, to study the evolutionary history of the universe by considering the functional form of f(Q)=αQn, where α and n are constants. Here, we consider the parametrization form of the deceleration parameter as q=q0+q1z/(1+z)2 (with the parameters q0(q at z=0), q1, and the redshift, z), which provides the desired property for a sign flip from a decelerating to an accelerating phase. We obtain the solution of the Hubble parameter by examining the mentioned parametric form of q, and then we impose the solution in Friedmann equations. Employing the Bayesian analysis for the Observational Hubble data (OHD), we estimated the constraints on the associated free parameters (H0,q0,q1) with H0 the current Hubble parameter to determine if this model may challenge the ΛCDM (Λ cold dark matter with the cosmological constant, Λ) limitations. Furthermore, the constrained current value of the deceleration parameter q0=−0.832−0.091+0.091 shows that the present universe is accelerating. We also investigate the evolutionary trajectory of the energy density, pressure, and EoS (equation-of-state) parameters to conclude the accelerating behavior of the universe. Finally, we try to demonstrate that the considered parametric form of the deceleration parameter is compatible with f(Q) gravity.

Casimir wormholes in modified symmetric teleparallel gravity

In recent years there has been a growing interest in the field of Casimir wormhole. In classical general relativity (GR), it is known that the null energy condition (NEC) has to be violated to have a wormhole to be stable. The Casimir effect is an experimentally verified effect that is caused due to the vacuum field fluctuations in quantum field theory. Since the Casimir effect provides the negative energy density, thus this act as an ideal candidate for the exotic matter needed for the stability of the wormhole. In this paper, we study the Casimir effect on the wormhole geometry in modified symmetric teleparallel gravity or f(Q) gravity, where the non-metricity scalar Q drives the gravitation interaction. We consider three systems of the Casimir effect such as (i) two parallel plates, (ii) two parallel cylindrical plates, and (iii) two-sphere separated by a large distance to make it more experimentally feasible. Further, we studied the obtained wormhole solutions for each case with energy conditions at the wormhole throat with radius r_0 and found that some arbitrary quantity violates the classical energy conditions at the wormhole throat. Furthermore, the behavior of the equation of state (EoS) is also analyzed for each case. Finally, we investigate the stability of the obtained Casimir effect wormhole solutions with the generalized Tolman–Oppenheimer–Volkoff (TOV) equation.

Thermodynamical aspects of Bianchi type-I Universe in quadratic form of [formula omitted] gravity and observational constraints

In this paper, we discuss the Bianchi type-I cosmological model in the framework of symmetric teleparallel gravity say f(Q) gravity in which the non-metricity term Q is responsible for the gravitational interaction. We consider a special form of the f(Q) function which can be cast as f(Q)=λQn, where λ and n both are the dynamical model parameters. Such a choice can be viewed as a hybrid scale factor that leads to a relation between cosmic time and redshift as t=(αt0β)W[βαeβ−ln⁡(1+z)α] which describes a ΛCDM model of the Universe with the expansion evolving from decelerating to an acceleration phase. The best values for the model parameters i.e. α and β that would accord with the most current observational datasets are then estimated. We make use of 57 points from the Hubble dataset, 1048 points from the supernovae of type Ia dataset and 6 points from the BAO dataset. We use the Markov Chain Monte Carlo (MCMC) technique in conjunction with Bayesian analysis and the likelihood function. Further, we study the validity of our model with the investigation of the thermodynamical quantities, energy conditions along with some physical variables such as the EoS, and jerk parameters. Next, our results are discussed in light of current observational data and trends.

Anisotropic electrically charged stars in f(Q) symmetric teleparallel gravity

Anisotropic electrically charged stars in f(Q) symmetric teleparallel gravity

Bulk viscous fluid in extended symmetric teleparallel gravity

In this paper, we investigate the existence of bulk viscous FLRW cosmological models in a recently proposed extended symmetric teleparallel gravity or fQ,T gravity in which Q is the non-metricity and T is the trace of the energy–momentum tensor. We consider a simple coupling between matter and non-metricity, specifically, fQ,T=αQm+1+λT and fQ,T=αQ+λT where α, λ and m are free model parameters. The exact cosmological solutions are found by assuming the scale factor in the form of the hybrid expansion law. This type of relation generates a time-varying deceleration parameter with the transition of the Universe from the early decelerating phase to the present accelerating phase. In the presence of viscous fluid, we analyze some cosmological parameters of our cosmological model such as the energy density, bulk viscous pressure, bulk viscous coefficient, equation of state parameter, and energy conditions. Finally, we conclude our fQ,T cosmological models agree with the recent astronomical observations.

Coincident gauge for static spherical field configurations in symmetric teleparallel gravity

In symmetric teleparallel gravities, where the independent connection is characterized by nonmetricity while curvature and torsion are zero, it is possible to find a coordinate system whereby the connection vanishes globally and covariant derivatives reduce to partial derivatives – the coincident gauge. In this paper we derive general transformation rules into the coincident gauge for spacetime configurations where the both the metric and connection are static and spherically symmetric, and write out the respective form of the coincident gauge metrics. Taking different options in fixing the freedom in the connection allowed by the symmetry and the field equations, the Schwarzschild metric in the coincident gauge can take for instance the Cartesian, Kerr–Schild, and diagonal (isotropic-like) forms, while the BBMB black hole metric in symmetric teleparallel scalar–tensor theory a certain diagonal form fits the coincident gauge requirements but the Cartesian and Kerr–Schild forms do not. Different connections imply different value for the boundary term which could in principle be physically relevant, but simple arguments about the coincident gauge do not seem to be sufficient to fix the connection uniquely. As a byproduct of the investigation we also point out that only a particular subset of static spherically symmetric connections has vanishing nonmetricity in the Minkowski limit.

Interaction of divergence-free deceleration parameter in Weyl-type f(Q,T) gravity

We study an extension of symmetric teleparallel gravity i.e. Weyl-type f(Q,T) gravity and the divergence-free parametrization of the deceleration parameter q(z)=q0+q1z(1+z)1+z2 (q0 and q1 are free constants) to explore the evolution of the universe. By considering the above parametric form of q, we derive the Hubble solution and further impose it in the Friedmann equations of Weyl-type f(Q,T) gravity. To see whether this model can challenge the ΛCDM limits, we computed the constraints on the model parameters using the Bayesian analysis for the Observational Hubble data (OHD) and the Pantheon sample (SNeIa). Furthermore, the deceleration parameter depicts the accelerating behavior of the universe with the present value q0 and the transition redshift zt (at which the expansion transits from deceleration to acceleration) with 1−σ and 2−σ confidence level. We also examine the evolution of the energy density, pressure, and effective equation of state parameters. Finally, we demonstrate that the divergence-free parametric form of the deceleration parameter is consistent with the Weyl-type f(Q,T) gravity.

Barrow holographic dark energy models in f(Q) symmetric teleparallel gravity with Lambert function distribution

The paper presents Barrow holographic dark energy (infrared cut-off is the Hubble horizon) suggested by Barrow [The area of a rough black hole, Phys. Lett. B 808 (2020) 135643] recently in an anisotropic Bianchi type-I Universe within the framework of [Formula: see text] symmetric teleparallel gravity, where the non-metricity scalar [Formula: see text] is responsible for the gravitational interaction. We consider two cases: Interacting and non-interacting models of pressureless dark matter and Barrow holographic dark energy by solving [Formula: see text] symmetric teleparallel field equations. To find the exact solutions of the field equations, we assume that the time-redshift relation follows a Lambert function distribution as [Formula: see text], where [Formula: see text], [Formula: see text] and [Formula: see text] are non-negative constants and [Formula: see text] represents the age of the Universe. Moreover, we discuss several cosmological parameters such as energy density, equation of state (EoS) and skewness parameters, squared sound speed, and [Formula: see text] plane. Finally, we found the values of the deceleration parameter (DP) for the Lambert function distribution as [Formula: see text] and [Formula: see text] which are consistent with recent observational data, i.e. DP evolves with cosmic time from initial deceleration to late-time acceleration.

Wormhole in f(Q) gravity

In this paper, exact asymptotically flat wormhole solutions in the context of symmetric teleparallel gravity, i.e., $f(Q)$ theory of gravity, are investigated. Since modified theories of gravity provide new field equations, we have analyzed some possible wormhole solutions by using modified field equations. Four different forms of the $f(Q)$ function are considered then the shape function is calculated with some different equations of state. Also we have used a power-law shape function with these models, which lead to an asymptotically barotropic equation of state. Some physical and mathematical properties of the solutions, like energy conditions and boundary conditions, are addressed .

Flat FLRW Universe in logarithmic symmetric teleparallel gravity with observational constraints

In this paper, we investigate the homogeneous and isotropic flat Friedmann–Lemaître–Robertson–Walker Universe in the logarithmic form of gravity, where Q is the non-metricity scalar, specifically, , where α and β are free model parameters. In this study, we consider a parametrization of the Hubble parameter as , where γ and η are model/free parameters which are constrained by an R 2-test from 57 points of the Hubble datasets in the redshift range 0.07 < z < 2.36. Further, we investigate the physical properties of the model. We analyze the energy conditions to check the compatibility of the model. We found the strong energy condition is violated for the logarithmic form of gravity due to the reality that the Universe in an accelerating phase. Finally, we discuss some important cosmological parameters in this context to compare our model with dark energy models such as jerk parameter and statefinder parameters.