The Kodama state is unique in being an exact solution to all the constraints of quantum gravity that also has a well defined semi-classical interpretation as the quantum version of a classical spacetime, namely de Sitter or anti-de sitter space. Despite this, the state fails to pass some of the key tests of a physically realistic quantum state. In an attempt to resolve this problem, we track down the root of the problem to a choice for a particular parameter: the Immirzi parameter. The Kodama state takes this parameter to be complex, whereas modern formulations of canonical quantum gravity require that the parameter is real. We generalize the Kodama state to real values of the Immirzi parameter, and find that the generalization opens up a large Hilbert space of states, one of which can be directly interpreted as particular slicing of de Sitter space. We then show that these states resolve, or are expected to resolve many of the problems associated with the original version of the Kodama state. In order to resolve the interpretation of the multitude of states, we develop a new model of covariant classical and quantum gravity where the full Lorentz group is retained as a local symmetry group, and the canonical evolution generated by the constraints has a close relation to a larger group: the de Sitter group. This formalism gives strong evidence that the multitude of generalized Kodama states can be unified into a single quantum state that is quantum de Sitter space.
A Quantum Gravitational Mechanism for Isotropization of de Sitter Cosmologies
Brown University（布朗大学）；Imperial College London（帝国理工学院）；Massachusetts Institute of Technology（麻省理工学院）；Harvard University（哈佛大学）；Flatiron Institute（平顿研究所）
Unruh-DeWitt detector and the interpretation of the horizon temperature in spherically symmetric dynamical space-times
本文从点状探测器的角度研究了动态球对称黑洞或宇宙视界的温度。首先，我们简要回顾了一般动力学球对称时空的Hamilton-Jacobi隧穿方法，并给出了隧穿方法的两个应用。然后，我们应用一个著名的相对论量子理论技术，即Unruh-DeWitt检测器形式主义的共形耦合标量场在一个通用的FRW时空。作为应用，对于一般静态黑洞和FRW de Sitter黑洞，利用特殊的Kodama观测者轨道，完全恢复了隧道半经典结果，并通过Tolman因子自动校正.本文对FRW宇宙的温度作了一些讨论。对于用爱因斯坦-德西特宇宙内插德西特空间的更一般的空间，存在第二组极点，其确切作用仍有待澄清，加上一个额外的波动项描述达到平衡的方式，类似于德西特空间。在德西特空间中发现的简单的热解释丢失了，同时迫使宇宙学FRW模型对视界表面引力有不同的量子解释。
Quantum de Sitter and Analytically Continued Chern Simons Theory
Brown Center for Theoretical Physics and Innovation, Department of Physics, Brown University（布朗大学理论物理与创新中心物理系）；Department of Mathematics, MIT（麻省理工学院数学系）
An algebra for covariant observers in de Sitter space
School of Physical Science and Technology, Ningbo University（宁波大学物理科学与技术学院）；School of Physics, Peking University（北京大学物理学院）；Center for High Energy Physics, Peking University（北京大学高能物理中心）
