Symmetric Gravity Research Articles

Deflection of light by wormholes and its shadow due to dark matter within modified symmetric teleparallel gravity formalism

Abstract We explore the possibility of traversable wormhole formation in the dark matter halos in the context of $f(Q)$ gravity. We obtain the exact wormhole solutions with anisotropic matter source based on the Bose-Einstein condensate, Navarro-Frenk-White, and pseudo-isothermal matter density profiles. Notably, we present a novel wormhole solution supported by these dark matters using the expressions for the density profile and rotational velocity along with the modified field equations to calculate the redshift and shape functions of the wormholes. With a particular set of parameters, we demonstrate that our proposed wormhole solutions fulfill the flare-out condition against an asymptotic background. Additionally, we examine the energy conditions, focusing on the null energy conditions at the wormhole's throat, providing a graphical representation of the feasible and negative regions. Our study also examines the wormhole's shadow in the presence of various dark matter models, revealing that higher central densities result in a shadow closer to the throat, whereas lower values have the opposite effect. Moreover, we explore the deflection of light when it encounters these wormholes, particularly noting that light deflection approaches infinity at the throat, where the gravitational field is extremely strong.

Cosmology in energy-momentum squared symmetric teleparallel gravity

In this letter, we explore the f(Q,TμνTμν) gravity theory, building upon the foundations laid by the f(Q) and f(Q,T) gravity theories. Here, Q represents non-metricity and Tμν stands for the energy-momentum tensor. The proposed action encompasses an arbitrary function of both non-metricity Q and the square of the energy-momentum tensor, specifically T2=TμνTμν. We find the analytical solution for the barotropic fluid case p=ωρ for the model f(Q,TμνTμν)=Q+η(TμνTμν). We constrain parameters of the solution H(z) utilizing CC, BAO, and latest Pantheon+SH0ES samples with the help of Monte Carlo Markov Chain sampling technique along with Bayesian statistical analysis. Further, from the Om diagnostic test, we find that the assumed cosmological model favors the quintessence regime.

Seismic fragility assessment of eccentric gravity column-core tube structures subjected to pulse-like ground motions

The effects of pulse-like ground motion and structural eccentricity on the seismic fragility and anti-collapse behavior of the new gravity column-core tube structural system are investigated. Numerical models of the gravity column-core tube structure are first established employing the CANNY program and validated against the shaking table test results. Subsequently, reference symmetric gravity column-core tube structures with 10-, 20- and 30-stories are designed, and then their eccentric structures are established by changing the nodal mass distribution. Ten pulse-like and ten corresponding non-pulse-like ground motion records are selected as the seismic excitations. The seismic fragility and anti-collapse analysis of these eccentric structures are conducted. The results show that the pulse-like ground motion significantly affects the seismic response and fragility of the gravity column-core tube structures, with an apparently higher probability of exceeding the limit states (Pf) for the pulse cases than those for the non-pulse cases. With increasing eccentricity, the Pf shows an increasing trend. Besides, both the pulse-like ground motion and the increase of eccentricity lead to a decline in structural anti-collapse capacity. The results are expected to provide a reference for the seismic design of the new gravity column-core tube structures.

Impact of charge on the stability of pulsar SAX J1748.9-2021 in modified symmetric teleparallel gravity

In this paper, we explore the effect of charge on the stability of pulsar star SAX J1748.9-2021 in f(Q) gravity, where Q represents non-metricity. For this purpose, we apply the Krori-Barua metric ansatz with anisotropic fluid and use a linear f(Q) model f(Q)=ζQ, where ζ is a non-zero constant. We derive exact relativistic solutions of the corresponding field equations. Furthermore, we study its geometric and physical properties through astrophysical observations from the pulsar SAX J1748.9-2021, which is found in X-ray binary systems within globular clusters. We examine features like anisotropic pressure, the mass–radius relationship, redshift, the Zeldovich condition, energy and causality conditions, the adiabatic index, the Tolman–Oppenheimer–Volkoff equation, the equation of state parameter and compactness. Our findings align with the observational data which indicate that the pulsar SAX J1748.9-2021 is viable and stable under this modified theory of gravity.

Static, cylindrically symmetric spacetime in the coincident f(Q) gravity

In this paper we consider a static, cylindrically symmetric spacetime with coincident f(Q) gravity. Since the field equation of this spacetime in symmetric teleparallel gravity is suitable for choosing the function of f(Q) in the form of power series and exponential forms which are in coherent with cosmological observations, anisotropic perfect fluid solutions of these forms are discussed for this spacetime. Energy densities, directional pressures and energy conditions are plotted and analysed for a few different metric potentials. Although corresponding cosmic strings violate all energy conditions in both f(Q) functions, the corresponding Levi-Civita solution violates all energy conditions in the power law function of f(Q), but for exponential f(Q) gravity they are satisfied in small regions.

Greybody factor of uncharged black hole in symmetric teleparallel gravity

In this study, we investigate the greybody factor of a (3+1)-dimensional black hole solution in the context of alternative f(Q) gravity with minimum scalar field coupling. We obtain the radial equation by applying the Klein–Gordon equation and transforming it into a Schrodinger wave equation using the tortoise coordinate. This transformation enables us to determine the effective potential and its graphical behavior for different values of the coupling constant and relevant physical parameters. We obtain two solutions for the radial equation corresponding to the event and cosmological horizons. To determine the greybody factor and its behavior, we combine these two solutions in the intermediate regime. The greybody factor increases with an increase in radius and coupling constant. This indicates that in alternative gravity, the larger black hole will die sooner as compared to cosmic gravity.

Stability and viability of charged anisotropic pulsar SAX J1748.9-2021 in extended symmetric teleparallel gravity

This manuscript aims to study the viability and stability of a pulsar SAX J1748.9-2021, containing a charged anisotropic matter configuration within the framework of f(Q,T) theory (Q and T are the non-metricity scalar and energy–momentum tensor, respectively). We employ a non-singular solution and a specific model of this gravitational theory and use junction conditions to determine the unknown constants in the metric coefficients. We explore different geometric and physical properties using astrophysical observations from the pulsar SAX J1748.9-2021, which is found in X-ray binary systems within globular clusters. This framework establishes relationships between various physical quantities, including fluid parameters, anisotropy, mass–radius relation, redshift, the Zeldovich condition, energy conditions, causality conditions, adiabatic index, Tolman–Oppenheimer–Volkoff equation, equation of state parameter and compactness. Our findings affirm the feasibility and stability of the proposed charged pulsar within this theoretical framework.

Generalized ghost dark energy model in extended modified theory of symmetric teleparallel gravity

Generalized ghost dark energy model in extended modified theory of symmetric teleparallel gravity

Chern-Simons gravity and PT symmetry

This paper considers the possibility that, starting from a relativistic Hermitian quantum field theory in the ultraviolet (UV) regime, and applying a nonperturbative renormalization-group (RG) flow, we arrive at a situation where there are infrared (IR) singularities in the RG flow of couplings. The latter can be resolved by assuming that the theory can have a phase described by a related non-Hermitian PT-symmetric modification in the IR. The UV-to-IR (Hermitian-to-PT-symmetric) transition can occur in a single renormalization-group flow of the pertinent couplings, as demonstrated in concrete examples. When embedded in a gravitational setting such a transition can lead to a repulsive gravity phase. If there is a RG flow to a repulsive PT -symmetric gravity, then this would be an alternative to dark energy. The discussion here is presented in the context of a string-inspired Chern-Simons gravitational effective action, which involves a pseudoscalar (axionlike) field coupled to Abelian gauge fields and gravity; it may also hold more generally in gravity with torsion. The validity of such a scenario in realistic theories might alleviate the need for de Sitter phases in the current epoch of cosmological evolution, thus avoiding their associated conceptual and technical complications. Published by the American Physical Society 2024

Modelling the accelerating universe with f(Q) gravity: observational consistency

In this paper, we present a cosmological model within the framework of symmetric teleparallel gravity, focusing on f(Q) gravity, where Q represents the non-metricity scalar. Utilizing cosmological datasets, we derive an accelerating cosmological model by constraining its free parameters. To achieve this, we determine the parametric form of the Hubble parameter using a well-motivated f(Q) function. Remarkably, all obtained values fall within the range suggested by cosmological observations. By employing the best-fit parameters, we calculate the present geometrical parameters and demonstrate the accelerating behaviour of the Universe. Furthermore, we thoroughly examine the evolutionary behaviours of the Universe, noting that our model converges to the Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda $$\\end{document}CDM model at late times. Finally, we investigate the energy conditions and find a violation of the strong energy condition, which could provide a valuable understanding of the nature of dark energy.

Wormhole geometries supported by strange quark matter and phantom-like generalized Chaplygin gas within [formula omitted] gravity

A crucial aspect of wormhole (WH) physics is the inclusion of exotic matter, which requires violating the null energy condition. Here, we explore the potential for WHs to be sustained by quark matter under conditions of extreme density along with the phantom-like generalized cosmic Chaplygin gas (GCCG) in symmetric teleparallel gravity. Theoretical and experimental studies on baryon structures indicate that strange quark matter, composed of u (up), d (down), and s (strange) quarks, represents the most energy-efficient form of baryonic matter. Drawing from these theoretical insights, we use the Massachusetts Institute of Technology (MIT) bag model equation of state to characterize ordinary quark matter. By formulating specific configurations for the bag parameter, we develop several WH models corresponding to different shape functions for the isotropic and anisotropic cases. Our analysis strongly suggests that an isotropic WH is not theoretically possible. Furthermore, we investigate traversable WH solutions utilizing a phantom-like GCCG, examining their feasibility. This equation of state, capable of violating the null energy condition, can elucidate late-time cosmic acceleration through various beneficial parameters. In this framework, we derive WH solutions for both constant and variable redshift functions. We have employed the volume integral quantifier (VIQ) method for both studies to assess the quantity of exotic matter. Furthermore, we have done the equilibrium analysis through the Tolman–Oppenheimer–Volkoff (TOV) equation, which supports the viability of our constructed WH model.

The non-minimally coupled symmetric teleparallel gravity with electromagnetic field

We construct a symmetric teleparallel gravity model which is non-minimally coupled with electromagnetic field in four dimensions inspired by its Riemannian equivalent. We derive the field equations by taking the variation of this model, which is written here for the first time. Then, we find some classes of spherically symmetric static solutions by the coincident gauge of symmetric teleparallel spacetime.

Cosmological constraints in symmetric teleparallel gravity with bulk viscosity

Cosmological constraints in symmetric teleparallel gravity with bulk viscosity

Probing symmetric teleparallel gravity in the early universe

Probing symmetric teleparallel gravity in the early universe

Traversable wormholes satisfying energy conditions in f(Q) gravity

In this article, a new family of asymptotically flat wormhole solutions in the context of symmetric teleparallel gravity, i.e., f(Q) theory of gravity, are presented. Considering a power-law shape function and some different forms of the f(Q) function, we show that a wide variety of wormhole solutions for which the matter fields satisfy some energy conditions, are accessible. We realize that the presence of f(Q) gravity will be enough to sustain a traversable wormhole without exotic matter. The influence of the free parameters of the shape function and the f(Q) models on the energy conditions is investigated. The equation of state and the boundary conditions are analyzed.

Study of pressure parametric dark energy model in the framework of f(Q) gravity

In this work, we have proposed a simple parametrization for the pressure component [Formula: see text] of the dark energy model and have studied the cosmological implications of this model in the framework of [Formula: see text] modified gravity theory, aka, the symmetric teleparallel gravity theory, where Q is known as the nonmetricity scalar. By considering a particular parametric form of [Formula: see text], we obtained the Hubble solution for the [Formula: see text] modified gravity model. In order to see whether this model is consistent with or challenges the [Formula: see text]CDM limits, we tried to put constraints on the model parameters using the recent observational datasets like Hubble data, Cosmic Chronometer data, Type Ia Supernovae (SNIa) data, baryonic acoustic oscillations (BAO) data. We have employed the [Formula: see text] minimization technique and have carried out the Markov Chain Monte Carlo (MCMC) analysis using emcee package. We have found that the deceleration parameter shows a smooth transition from positive to negative value in recent past which is essential for the structure formation of the Universe. It has been found that the parametric form of the dark energy pressure parameter is consistent with current cosmological scenario.

Spherically symmetric anisotropic charged neutron stars in f(Q, T) gravity

In this work, we have investigated a new solution for charged anisotropic compact stellar system in the framework of an extended theory of symmetric teleparallel gravity known as f(Q, T) gravity with the non-metricity term Q and the trace T for energy–momentum tensor. We have constructed a complete set of the gravitational field equations for a non-linear function f(Q,T)=αQ+β(1+Q2)+λT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(Q,T)=\\alpha Q + \\beta (1+Q^{2}) + \\lambda T$$\\end{document} with α,β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha , \\beta $$\\end{document} and λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda $$\\end{document} are dimensionless constant parameters in case of static spherically symmetric space-time. To evaluate the expression of relevant unknown constants interior space-time has been matched with exterior Reissner–Nordstro¨\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ddot{\ extrm{o}}$$\\end{document}m metric. We have performed a graphical discussion in detail to test the behavior of physical parameters in the interior region of a stellar system like energy density, radial and tangential pressure, anisotropies of matter portion, electric field intensity etc. Also, to check the physical validity of our solutions, we have performed various tests viz., energy conditions, stability, mass–radius relation, surface redshift etc. The hydrostatic equilibrium position of our stellar system has been analysed through the TOV equation. Finally, we have determined that our stellar structure solutions satisfy all required physical conditions for viability and acceptability in the context of some pulsar like neutron stars. So our model can be used to characterise the neutron stars in f(Q, T) modified gravity.

Constraints on bulk viscosity in [formula omitted] gravity from H(z)/Pantheon+ data

In this study, we investigate the role of bulk viscosity in f(Q,T) gravity in explaining late-time cosmic acceleration. This model, an extension of symmetric teleparallel gravity, introduces viscosity into cosmic matter dynamics for a more realistic representation. Specifically, we consider the linear form of f(Q,T)=αQ+βT, where α and β are free model parameters. To assess the model, we derive its exact solution and use Hubble parameter H(z) data and Pantheon + SNe Ia data for parameter estimation. We employ the χ2 minimization technique alongside the MCMC random sampling method to determine the best-fit parameters. Then, we analyze the behavior of key cosmological parameters, including the deceleration parameter, bulk viscous matter-dominated universe density, effective pressure, and the effective EoS parameter, accounting for the viscous type fluid. We observe a transition in the deceleration parameter from a positive (decelerating) to a negative (accelerating) phase at transition redshift zt. The matter density shows the expected positive behavior, while the pressure, influenced by viscosity, exhibits negative behavior, indicative of accelerating expansion. Furthermore, we investigate the energy conditions and find that while the NEC and DEC meet positivity criteria, the SEC is violated in the present and future epochs. The Om(z) diagnostic suggests that our model aligns with quintessence behavior. Finally, our f(Q,T) cosmological model, incorporating bulk viscosity effects, provides a compelling explanation for late-time cosmic behavior, consistent with observational data.

Dynamics and Stability via Thin‐Shell of Approximated Black Holes in f(Q)$f(\mathbb {Q})$ Gravity

AbstractThe current study is devoted to exploring the geometrical configuration of a thin‐shell in the background of symmetric teleparallel gravity. For this purpose, the well‐known cut‐and‐paste approach by matching the inner flat and outer newly calculated class of approximated black hole (BH) solutions in symmetric teleparallel gravity are considered, i.e., uncharged, charged, and anti‐de‐Sitter BHs. The dynamical analysis of thin‐shell configuration by adopting the massive and massless scalar field via Klein‐Gordon's equation of motion is discussed. The effective potential and proper time derivative of shell radius for both massive and massless scalar shells are used to discuss the collapse, expansion, and oscillatory behavior. The stable configuration of thin‐shell is observed through the linearized radial perturbation approach with a phantomlike equation of state, i.e., quintessence, dark energy, and phantom energy. It is noted that stable/unstable behavior of thin‐shell is found after the expected position of the event horizon of an exterior manifold. It is concluded that the stability of a thin‐shell is greater for BH with cosmological constant as compared to the uncharged and charged BHs.

Some aspects of Morris-Thorne wormhole in gravity

The aim of this manuscript is to study traversable wormhole geometries in the non-metricity and matter coupling gravity. We investigate the Morris-Thorne wormhole metric within the framework of extended symmetric teleparallel gravity. With an anisotropic matter distribution, we explore two distinct wormhole models under two different scenarios. First, we consider the equations of state, and then we assume specific shape functions for each scenario. In both cases, the shape function satisfies all fundamental criteria for a traversable wormhole. We present our results through graphical representations and analyze the energy conditions. Furthermore, we examine the behavior of the wormhole through the anisotropic parameter. Finally, we present our conclusions based on the obtained results.