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arXiv 1312.3147gr-qchep-th
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量子宇宙学中Wheeler-DeWitt方程的选择定则

Selection rules for the Wheeler-DeWitt equation in quantum cosmology

A. O. Barvinsky, A. Yu. Kamenshchik

摘要:

选择量子宇宙学中波函数的惠勒-德威特方程的物理上有意义的解,可以通过将理论还原到真正的物理自由度和它们的正则量子化的扇区来实现。由此产生的物理波函数酉演变的时间变量内引入这种减少,然后可以提高到宇宙波函数的水平在超空间的3度规。我们应用这种技术在几个简单的minissuperspace模型和讨论在经典和量子水平的物理减少{ \em外在}时间-外在曲率方面确定的时间变量。只有这种外在的时间测量可以始终使用在附近的转折点和反弹的比例因子达到极值。由于3度规尺度因子与外部时间变量正则对偶,从物理波函数到超空间波函数的过渡表示一种广义傅里叶变换。这个变换选择惠勒-德威特方程的平方可积解,这保证了狄拉克量子化方案的正则算子的厄米性。半经典地,这意味着波函数在经典允许的超空间区域中由振荡波表示,而在经典禁止的(势垒下)区域中以指数方式下降。这在具有恒定负电势的标量场的平坦FRW模型和具有正电势的体模标量场的情况下被明确地证明。势为零的标量场的FRW模型并不导致惠勒-德威特方程解的选择规则,但这并不违反厄米性性质,因为所有这些解都是平面波型的,并且描述了没有转折点和反弹的宇宙动力学。

英文摘要:

Selection of physically meaningful solutions of the Wheeler-DeWitt equation for the wavefunction in quantum cosmology, can be attained by a reduction of the theory to the sector of true physical degrees of freedom and their canonical quantization. The resulting physical wavefunction unitarily evolving in the time variable introduced within this reduction can then be raised to the level of the cosmological wavefunction in superspace of 3-metrics. We apply this technique in several simple minisuperspace models and discuss both at classical and quantum level physical reduction in {\em extrinsic} time -- the time variable determined in terms of extrinsic curvature. Only this extrinsic time gauge can be consistently used in vicinity of turning points and bounces where the scale factor reaches extremum. Since the 3-metric scale factor is canonically dual to extrinsic time variable, the transition from the physical wavefunction to the wavefunction in superspace represents a kind of the generalized Fourier transform. This transformation selects square integrable solutions of the Wheeler-DeWitt equation, which guarantee Hermiticity of canonical operators of the Dirac quantization scheme. Semiclassically this means that wavefunctions are represented by oscillating waves in classically allowed domains of superspace and exponentially fall off in classically forbidden (underbarrier) regions. This is explicitly demonstrated in flat FRW model with a scalar field having a constant negative potential and for the case of phantom scalar field with a positive potential. The FRW model of a scalar field with a vanishing potential does not lead to selection rules for solutions of the Wheeler-DeWitt equation, but this does not violate Hermiticity properties, because all these solutions are anyway of plane wave type and describe cosmological dynamics without turning points and bounces.

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