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1.
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In this study, we investigate the possibilities of generating baryon number asymmetry under thermal equilibrium within the frameworks of teleparallel and symmetric teleparallel gravities. Through the derivative couplings of the torsion scalar and the non-metricity scalar to baryons, baryon number asymmetry is produced in the radiation dominated epoch. For gravitational baryogenesis mechanisms in these two frameworks, the produced baryon-to-entropy ratio is too small to be consistent with observations. However, the gravitational leptogenesis models within both frameworks have the potential to explain the observed baryon-antibaryon asymmetry.  相似文献   

2.
Gamal G. L. Nashed 《中国物理 B》2012,21(1):10401-010401
In the context of the covariant teleparallel framework, we use the 2-form translational momentum to compute the total energy of two general spherically symmetric frames. The first one is characterized by an arbitrary function H(r), which preserves the spherical symmetry and reproduces all the previous solutions, while the other one is characterized by a parameter ξ which ensures the vanishing of the axial of trace of the torsion. We calculate the total energy by using two procedures, i.e., when the Weitzenböck connection Γαβ is trivial, and show how H(r) and ξ play the role of an inertia that leads the total energy to be unphysical. Therefore, we take into account Γαβ and show that although the space×we use contain an arbitrary function and one parameter, they have no effect on the form of the total energy and momentum as it should be.  相似文献   

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4.
In this work, in order to compute energy and momentum distributions (due to matter plus fields including gravitation) associated with the Brans–Dicke wormhole solutions we consider Møller’s energy-momentum complexes both in general relativity and the teleparallel gravity, and the Einstein energy-momentum formulation in general relativity. We find exactly the same energy and momentum in three of the formulations. The results obtained in teleparallel gravity is also independent of the teleparallel dimensionless coupling parameter, which means that it is valid not only in the teleparallel equivalent of general relativity, but also in any teleparallel model. Furthermore, our results also sustains (a) the importance of the energy-momentum definitions in the evaluation of the energy distribution of a given spacetime and (b) the viewpoint of Lessner that the Møller energy-momentum complex is a powerful concept of energy and momentum. (c) The results calculated supports the hypothesis by Cooperstock that the energy is confined to the region of non-vanishing energy-momentum tensor of matter and all non-gravitational fields.  相似文献   

5.
    
We calculate energy and momentum of a spherically symmetric dilaton frame using the gravitational energy‐momentum 3‐form within the tetrad formulation of general relativity (GR). The frame we use is characterized by an arbitrary function ? with the help of which all the previously found solutions can be reproduced. We show how the effect of inertia (which is mainly reproduced from ?) makes the total energy and momentum always different from the well known result when we use the Riemannian connection . On the other hand, when use is made of the covariant formulation of teleparallel gravity, which implies to take into account the pure gauge connection, teleparallel gravity always yields the physically relevant result for the energy and momentum.  相似文献   

6.
There is a significant difference between the calculation based on the theory of general relativity and observation of rotation curves of spiral galaxies. To describe this discrepancy, two distinct theories have been proposed so far: existence of dark matter and modification of underlying gravitational theory. In the absence of dark matter, it is assumed that the theory of general relativity on galactic scales needs to be modified. This letter is devoted to explaining this difference in a modified teleparMIeI gravity. We show that modified teleparallel gravity favors flatness of rotation curves of spiral galaxies much in the same way as observation shows.  相似文献   

7.
In the context of the covariant teleparallel framework,we use the 2-form translational momentum to compute the total energy of two general spherically symmetric frames.The first one is characterized by an arbitrary function H(r),which preserves the spherical symmetry and reproduces all the previous solutions,while the other one is characterized by a parameter ξ which ensures the vanishing of the axial of trace of the torsion.We calculate the total energy by using two procedures,i.e.,when the Weitzenbo¨ck connection Γ_α~β is trivial,and show how H(r) and ξ play the role of an inertia that leads the total energy to be unphysical.Therefore,we take into account Γ_α~β and show that although the spacetimes we use contain an arbitrary function and one parameter,they have no effect on the form of the total energy and momentum as it should be.  相似文献   

8.
We use the Møller energy-momentum complex both in general relativity and teleparallel gravity to evaluate energy distribution (due to matter plus fields including gravity) in the dyadosphere region for Reissner-Nordström black hole. We found the same and acceptable energy distribution in these different approaches of the Møller energy-momentum complex. Our teleparallel gravitational result is also independent of the teleparallel dimensionless coupling constant, which means that it is valid in any teleparallel model. This paper sustains (a) the importance of the energy-momentum definitions in the evaluation of the energy distribution of a given space-time and (b) the viewpoint of Lessner that the Møller energy-momentum complex is a powerful concept for energy and momentum.  相似文献   

9.
    
There is a significant difference between the calculation based on the theory of general relativity and observation of rotation curves of spiral galaxies. To describe this discrepancy, two distinct theories have been proposed so far: existence of dark matter and modification of underlying gravitational theory. In the absence of dark matter, it is assumed that the theory of general relativity on galactic scales needs to be modified. This letter is devoted to explaining this difference in a modified teleparallel gravity. We show that modified teleparallel gravity favors flatness of rotation curves of spiral galaxies much in the same way as observation shows.  相似文献   

10.
    
In this study of the modified f ( Q ) $f(Q)$ theory of gravity in the spatially flat Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime, all the affine connections compatible with the symmetric teleparallel structure are explored; three classes of such connections exist, each involving an unknown time-varying parameter γ ( t ) $gamma (t)$ . Assuming ordinary barotropic fluid as the matter source, the Friedmann-like pressure and energy equations are derived. Next constraints on the parameters of two separate f ( Q ) $f(Q)$ models, f ( Q ) = Q + β Q 2 $f(Q)=Q+beta Q^2$ and f ( Q ) = Q + β Q $f(Q)=Q+beta sqrt {-Q}$ from the traditional energy conditions are imposed. Observational values of some prominent cosmological parameters are used for this purpose, yielding an effective equation of state ω e f f = 0.82 $omega ^{eff}=-0.82$ .  相似文献   

11.
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We analyze the four common types of finite-time singularity using a generic framework of the phase portrait geometric approach. This technique requires the Friedmann system to be written as a one-dimensional autonomous system. We employ a scale factor that has been used widely in the literature to realize the four finitetime singularity types, then we give a detailed discussion for each case showing possible novel models. Moreover,we show how different singularity types can play essential roles in different cosmological scenarios. Among several modified gravity theories, we show that the f(T) cosmology is compatible with the phase portrait analysis, since the field equations include Hubble derivatives only up to first order. Therefore, we reconstruct the f(T) theory which generates these phase portraits. We also perform a complementary analysis using the effective equation of state.Furthermore, we investigate the role of the torsion fluid in realizing the cosmic singularities.  相似文献   

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This study explores the Gaussian and the Lorentzian distributed spherically symmetric wormhole solutions in the gravity. The basic idea of the Gaussian and Lorentzian noncommutative geometries emerges as the physically acceptable and substantial notion in quantum physics. This idea of the noncommutative geometries with both the Gaussian and Lorentzian distributions becomes more striking when wormhole geometries in the modified theories of gravity are discussed. Here we consider a linear model within gravity to investigate traversable wormholes. In particular, we discuss the possible cases for the wormhole geometries using the Gaussian and the Lorentzian noncommutative distributions to obtain the exact shape function for them. By incorporating the particular values of the unknown parameters involved, we discuss different properties of the new wormhole geometries explored here. It is noted that the involved matter violates the weak energy condition for both the cases of the noncommutative geometries, whereas there is a possibility for a physically viable wormhole solution. By analyzing the equilibrium condition, it is found that the acquired solutions are stable. Furthermore, we provide the embedded diagrams for wormhole structures under Gaussian and Lorentzian noncommutative frameworks. Moreover, we present the critical analysis on an anisotropic pressure under the Gaussian and the Lorentzian distributions.  相似文献   

14.
    
In this article, the viscous fluid cosmological model is analyzed in the framework of recently proposed f ( Q ) $f(Q)$ gravity by assuming three different forms of bulk viscosity coefficients, specifically, ( i ) ζ = ζ 0 + ζ 1 ( a ̇ a ) + ζ 2 ( a ̈ a ̇ ) $(i)zeta =zeta _{0}+zeta _{1}(frac{dot{a}}{a}) +zeta _{2}(frac{{ddot{a}}}{dot{a}})$ , ( i i ) ζ = ζ 0 + ζ 1 ( a ̇ a ) $(ii)zeta =zeta _{0}+zeta _{1}(frac{dot{a}}{a})$ , and ( i i i ) ζ = ζ 0 $(iii)zeta =zeta _{0}$ and a linear f ( Q ) $f(Q)$ model, particularly, f ( Q ) = α Q $f(Q)=alpha Q$ where α 0 $alpha ne 0$ is free model parameter. The bulk viscosity coefficients and the model parameter values using the combined H(z)+Pantheon+BAO data set are estimated. The asymptotic behavior of our cosmological bulk viscous model is studied by utilizing the phase space method. It is found that corresponding to all three cases, our model depicts the evolution of the universe from matter dominated decelerated epoch (a past attractor) to a stable de-sitter accelerated epoch (a future attractor). Furthermore, the physical behavior of effective pressure, effective equation of state (EoS), and the statefinder parameters are studied. It is also found that the pressure component in the presence of bulk viscosity shows negative behavior and the effective EoS parameter predicts the accelerated expansion phase of the universe for all three cases. Moreover, the trajectories of the model lie in the quintessence region and it converges to the ΛCDM fixed point in the far future. It is found that the accelerated de-Sitter like phase comes purely from the ζ ¯ 0 $bar{zeta }_0$ case without any geometrical modification to GR. Moreover, the late-time behavior of all three cases of viscosity coefficients are identical. Furthermore, a non-linear f ( Q ) $f(Q)$ model is considered, specifically, f ( Q ) = Q + β Q 2 $f(Q)=-Q+beta Q^2$ , and then analyzed the behavior of model using dynamical approach. It is also found that the late-time behavior of the considered non-linear model f ( Q ) = Q + β Q 2 $f(Q)=-Q+beta Q^2$ with β 0 $beta le 0$ is similar to the linear case, whereas for the case β > 0 $beta > 0$ results are quite different.  相似文献   

15.
Gamal G.L. Nashed 《中国物理 B》2011,20(11):110401-110401
We compute the total energy and the spatial momentum of four charged rotating (Kerr-Newman) frames by using the gravitational energy-momentum 3-form within the framework of the tetrad formulation of the general relativity theory. We show how the effect of the inertial always makes the total energy divergent. We use a natural regularization method, which yields the physical value for the total energy of the system. We show how the regularization method works on a number of different rotating frames that are related to each other by the local Lorentz transformation. We also show that the inertial has no effect on the spatial momentum components.  相似文献   

16.
17.
In this paper, we consider both Einstein's theory of general relativity and the teleparallel gravity (the tetrad theory of gravitation) analogs of the energy-momentum definition of Møller in order to explicitly evaluate the energy distribution (due to matter and fields including gravity) associated with a general black hole model which includes several well-known black holes. To calculate the special cases of energy distribution, here we consider eight different types of black hole models such as anti-de Sitter Cmetric with spherical topology, charged regular black hole, conformal scalar dyon black hole, dyadosphere of a charged black hole, regular black hole, charged topological black hole, charged massless black hole with a scalar field, and the Schwarzschild-de Sitter space-time. Our teleparallel gravitational result is also independent of the teleparallel dimensionless coupling constant, which means that it is valid not only in teleparallel equivalent of general relativity but also in any teleparallel model. This paper also sustains (a) the importance of the energy-momentum definitions in the evaluation of the energy distribution of a given spacetime and (b) the viewpoint of Lessner that the Møller energy-momentum complex is the powerful concept to calculate energy distribution in a given space-time.  相似文献   

18.
Gamal G L Nashed 《中国物理 B》2011,20(10):100402-100402
Within the framework of the tetrad formulation of general relativity theory, we compute the total energy and momentum of four rotating frames using the gravitational energy-momentum 3-form. We show how the effect of inertia always makes the total energy divergent. We use a natural regularization method to obtain physical values for the total energy of the system and show how it works on a number of explicit examples. We also show by calculation that inertia has no effect on the momentum components.  相似文献   

19.
20.
Gamal  G.L.  Nashed 《中国物理 B》2010,19(11):110505-110505
A theory of (1+1)-dimensional gravity is constructed on the basis of the teleparallel equivalent of general relativity.The fundamental field variables are the tetrad fields e i μ and the gravity is attributed to the torsion.A dilatonic spherically symmetric exact solution of the gravitational field equations characterized by two parameters M and Q is derived.The energy associated with this solution is calculated using the two-dimensional gravitational energy-momentum formula.  相似文献   

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