The existence and stability of the Einstein static solution have been built in the Einstein-Cartan gravity. We show that this solution in the presence of perfect fluid with spin density satisfying the Weyssenhoff restriction is cyclically stable around a center equilibrium point. Thus, study of this solution is interesting because it supports non-singular emergent cosmological models in which the early universe oscillates indeterminately about an initial Einstein static solution and is thus past eternal.
The rotational dynamics of an $N$-body system at the first post-Newtonian order in Einstein-Cartan theory is derived. This result is achieved by performing the point-particle limit of the equations of motion of the Weyssenhoff fluid, which models the quantum spin effects residing inside the bodies. For the special case of binary systems, we determine the Lagrangian function and the resulting first integrals underlying the translational dynamics and the spin precession.
Darboux coordinates for the Hamiltonian of first order Einstein-Cartan gravity
基于对一阶Einstein-Cartan作用量（arXiv：0902.0856 [gr-qc]和arXiv：0907.1553 [gr-qc]）的哈密顿公式的初步分析，我们导出了达布坐标，它是一个在大于2的所有时空维中保持与原始作用量等价的唯一的、一致的变量变化。相当大的简化的哈密顿公式使用达布坐标，直接分析相比，明确证明。即使是一个不完整的哈密尔顿分析结合已知的对称性的爱因斯坦-嘉当作用和等价的哈密尔顿和拉格朗日公式允许我们明确地得出结论，\textit{unique} \textit{gauge}不变性所产生的第一类约束的爱因斯坦-嘉当作用和相应的哈密尔顿是\textit{translation and rotation in the tangent space}。尽管行为的显式不变性是同构不变性，但它不是由理论的第一类约束产生的。
In this paper we investigate the gravitational-wave generation problem at the first post-Newtonian order in the context of Einstein-Cartan theory by exploiting the Blanchet-Damour formalism. The quantum intrinsic spin carried by slowly moving, weakly stressed, weakly self-gravitating sources is described geometrically by means of the torsion tensor. We obtain the expression of the source multipole moments with the required accuracy. The analysis of the physical meaning of the lowest-order non-radiative moments and of the asymptotic gravitational waveform is also performed. Eventually, we draw …
This paper reviews the Einstein Cartan theory (ECT), the famous extension of general relativity (GR) in presence of spacetime torsion. The vacuum equations are derived step by step. Vielbein formulation is discussed for determining the field equations in presence of matter. This review would be easily comprehensible for any student familiar with general relativity. Further, ECT is used to describe superstrings with intrinsic torsion, assuming a $D_p$-brane in presence of a curved background of the NS-NS Kalb-Ramond field. D-brane worldvolume is a flat spacetime governed by the Dirac-Born-Infel…
Unimodular gravity is an interesting approach to address the cosmological constant problem, since the vacuum energy density of quantum fields does not gravitate in this framework, and the cosmological constant appears as an integration constant. These features arise as a consequence of considering a constrained volume element 4-form that breaks the diffeomorphisms invariance down to volume preserving diffeomorphisms. In this work, the first-order formulation of unimodular gravity is presented by considering the spin density of matter fields as a source of spacetime torsion. Even though the mos…
Translational invariance of the Einstein-Cartan action in any dimension
我们证明，从一阶制定的爱因斯坦-嘉当行动，它是可能的，以获得基本的微分恒等式，导致平移不变性的行动在切空间。场的变换被明确地写为一阶和二阶公式，并研究了变换的群性质。这一点，结合哈密顿公式（arXiv：0907.1553 [gr-qc]）的初步结果，使我们能够得出这样的结论：在没有任何修改的情况下，在大于2的任何维度上的爱因斯坦-嘉当作用量不仅具有旋转不变性，而且具有\textit{translational invariance in the tangent space}的形式。我们认为，\textit{not}只有一个完整的哈密顿分析可以明确地给出一个答案的问题是什么规范对称性，但也纯拉格朗日方法允许我们找到相同的规范对称性从\textit{basic}微分恒等式。
Two of the major open questions in particle physics are: (1) Why are the elementary fermionic particles that are so far observed have such low mass-energy compared to the Planck energy scale? And (2), what mechanical energy may be counterbalancing the divergent electrostatic and strong force energies of point-like charged fermions in the vicinity of the Planck scale? In this paper, using a hitherto unrecognized mechanism derived from the non-linear amelioration of Dirac equation known as the Hehl-Datta equation within Einstein-Cartan-Sciama-Kibble (ECSK) extension of general relativity, we pre…
We derive the Schrödinger-Newton equation as the non-relativistic limit of the Einstein-Dirac equations. Our analysis relaxes the assumption of spherical symmetry, made in earlier work in the literature, while deriving this limit. Since the spin of the Dirac field couples naturally to torsion, we generalize our analysis to the Einstein Cartan-Dirac (ECD) equations, again recovering the Schrödinger-Newton equation.
A general geometric construction of a generic null hypersurface in presence of torsion in the spacetime (Riemann-Cartan background), generated by a null vector $l^a$, is being developed here. We then explicitly define and structure various corresponding kinematical quantities. The dynamics of the null surface, particularly given by $\hat{G}_{ab}k^al^b$, is also discussed. The later one is constructed under the {\it geodesic constraint} condition. This yields a relation among the rate of change of expansion scalar corresponding to auxiliary null vector $k^a$ and various kinematical entities on …
Cosmologies based on General Relativity encompassing an anti-symmetric connection (torsion) can display nice desirable features as the absence of the initial singularity and the possibility of inflation in the early stage of the universe. After briefly reviewing the standard approach to the cosmology with torsion, we generalize it to demonstrate that several theories of torsion gravity are possible using different choices of the diffeomorphic invariants in the Lagrangians. As a result, distinct cosmologies emerge. In all of them it is possible that the universe avoids the initial singularity a…
The Hamiltonian formulation of N-bein, Einstein-Cartan, gravity in any dimension: the Progress Report (Extended version of a talk given on CAIMS-2009, June 11-14, London, Canada)
本文分析了N-bein、Einstein-Cartan、引力的哈密顿形式，在任何大于2的维数上，都采用一阶形式。这个哈密顿公式允许明确地显示三维情况下的特殊性（\textit{A.M.Frolov et al, 0902.0856 [gr-qc]}）发生并根据本报告中的结果推测，存在一个一般的N-bein重力公式的\textit{all}维度特征：在消除第二类约束之后，剩余的第一类次级约束中的Poisson括号的代数是Poincare代数，并且在所有维度N中，bein，Cartan-Einstein，重力\textit{is the Poincare gauge theory}。对应于第一类约束代数的规范对称性有两个参数--旋转（洛伦兹）和平移。平移不变性对所有维度都是共同的，但在N-beins和连接的规范变换的一般表达式中，某些项在特定的三维情况下为零。我们的猜想的证明是详细概述。一些简单但繁琐的计算仍有待完成，以调用我们的猜想-定理，并将报告后。
We study scalar, fermionic and gauge fields coupled nonminimally to gravity in the Einstein-Cartan formulation. We construct a wide class of models with nondynamical torsion whose gravitational spectra comprise only the massless graviton. Eliminating non-propagating degrees of freedom, we derive an equivalent theory in the metric formulation of gravity. It features contact interactions of a certain form between and among the matter and gauge currents. We also discuss briefly the inclusion of curvature-squared terms.
The dynamical evolution of the Hajicek $1$-form is derived in Einstein-Cartan (EC) theory. We find that like Einstein theory of gravity, the evolution equation is related to a projected part of the Einstein tensor $(\hat{G}_{ab})$ on a generic null surface $\mathcal{H}$, particularly $\hat{G}_{ab}l^a q^b_{~c}$, where $l^a$ and $q^a_{~c}$ are the outgoing null generators of $\mathcal{H}$ and the induced metric to a transverse spatial cross-section of $\mathcal{H}$ respectively. Under the {\it geodesic constraint} a possible fluid interpretation of this evolution equation is then proposed. We fi…
In this paper, we use a new asymptotically flat and spherically symmetric solution in the generalized Einstein-Cartan-Kibble-Sciama (ECKS) theory of gravity to study the weak gravitational lensing and its shadow cast. To this end, we first compute the weak deflection angle of generalized ECKS black hole using the Gauss-Bonnet theorem in plasma medium and in vacuum. Next by using the Newman-Janis algorithm without complexification, we derive the rotating generalized ECKS black hole and in the sequel study its shadow. Then, we discuss the effects of the ECKS parameter on the weak deflection angl…
In the standard Einstein-Cartan theory(EC), matter fields couple to gravitation field through the Minimal Coupling Procedure(MCP), yet leaving the theory an ambiguity: applying MCP to the action or to the equation of motion would lead to different gravitational couplings. We propose a new covariant derivative to remove the ambiguity, then discuss the relation between our proposal and previous treatments on this subject.
We formulate the Einstein-Cartan-Dirac equations in the Newman-Penrose (NP) formalism, thereby presenting a more accurate and explicit analysis of previous such studies. The equations show in a transparent way how the Einstein-Dirac equations are modified by the inclusion of torsion. In particular, the Hehl-Datta equation is presented in NP notation. We then describe a few solutions of the Hehl-Datta equation on Minkowski space-time, and in particular report a solitonic solution which removes the unphysical behavioiur of the corresponding Dirac solution. The present work serves as a prelude to…
