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arXiv 1207.6348gr-qchep-th
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环-重力跃迁振幅的双态结构

The twistorial structure of loop-gravity transition amplitudes

Simone Speziale, Wolfgang M. Wieland

摘要:

自旋泡沫形式提供了圈量子引力的跃迁振幅。动力学的重要方面是了解,但许多悬而未决的问题是pressingon. In本文中,我们解决其中一些使用twistorial描述,这带来了新的光在经典和量子方面的理论。在经典的水平上,我们澄清了所涉及的离散几何的协变性质,以及在导致SU(2)Ashtekar-Barbero变量的简单性约束的作用。我们确定的领域和洛伦兹二面角扭量空间,并表明,他们形成一个典型的对。主要的简单性约束是由简单的扭曲,参数化的SU(2)旋量和二面角。我们构造了一个SU(2)holonomy,并证明它对应于Ashtekar-Barbero连接的(格版本)。我们认为,次要的限制的作用是提供一个非平凡的嵌入的余切丛SU(2)的简单扭空间。在量子层面上,薛定谔表象导致了简单投射自旋网络的旋量版本,其中波函数的辐角是旋量而不是群元素。我们将SL(2,C)余切丛上的Liouville测度改写为扭量空间中的积分.使用这些工具,我们表明,恩格尔-佩雷拉-Rovelli-Livine过渡振幅可以从扭曲空间中的路径积分。我们构造了一个曲率张量,证明了它具有离壳挠率,并且它的黎曼部分是Petrov-D型的。最后,我们联系的半经典渐近行为的模型和我们的建设,澄清关系的Regge几何与原来的相空间。

英文摘要:

The spin foam formalism provides transition amplitudes for loop quantum gravity. Important aspects of the dynamics are understood, but many open questions are pressing on. In this paper we address some of them using a twistorial description, which brings new light on both classical and quantum aspects of the theory. At the classical level, we clarify the covariant properties of the discrete geometries involved, and the role of the simplicity constraints in leading to SU(2) Ashtekar-Barbero variables. We identify areas and Lorentzian dihedral angles in twistor space, and show that they form a canonical pair. The primary simplicity constraints are solved by simple twistors, parametrized by SU(2) spinors and the dihedral angles. We construct an SU(2) holonomy and prove it to correspond to the (lattice version of the) Ashtekar-Barbero connection. We argue that the role of secondary constraints is to provide a non trivial embedding of the cotangent bundle of SU(2) in the space of simple twistors. At the quantum level, a Schroedinger representation leads to a spinorial version of simple projected spin networks, where the argument of the wave functions is a spinor instead of a group element. We rewrite the Liouville measure on the cotangent bundle of SL(2,C) as an integral in twistor space. Using these tools, we show that the Engle-Pereira-Rovelli-Livine transition amplitudes can be derived from a path integral in twistor space. We construct a curvature tensor, show that it carries torsion off-shell, and that its Riemann part is of Petrov type D. Finally, we make contact between the semiclassical asymptotic behaviour of the model and our construction, clarifying the relation of the Regge geometries with the original phase space.

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