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arXiv 2402.17844hep-thgr-qc
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后量子经典引力的重整化

Renormalisation of postquantum-classical gravity

Andrzej Grudka, Tim R. Morris, Jonathan Oppenheim, Andrea Russo, Muhammad Sajjad

AI总结:

针对微扰量子引力不可重整化的问题,研究提出时空几何为经典、耦合量子物质的后量子经典引力理论,证明其形式可重整化且无快子与负模鬼场,给出完全正动力学证据并计算加速度功率谱,对相关研究与实验有重要意义。

摘要:

协调量子理论与广义相对论的障碍之一,是构建一种既与观测结果一致,又能在高能下给出有限结果的理论,从而使该理论在任意短距离下都成立。量子场论通过重整化过程实现这一点,但众所周知,微扰量子引力即使不与物质耦合,也不具备可重整化性。近期,有人提出了一种量子引力的替代方案,其中时空几何被视为经典而非量子的,但仍与量子物质场耦合[1,2]。只要动力学从根本上是随机的,就能自洽地实现这一点。本文中,我们发现纯引力理论在形式上是可重整化的。我们通过路径积分表述,将经典-量子作用量与可重整化的二次引力的作用量关联起来,从而得出这一结论。由于该作用量引发的是时空的随机动力学,而非量子场的确定性演化,因此这种经典-量子理论不存在快子和负模鬼场。剩下的关键问题是,重整化方案是否能保持完全正(CP)动力学。这一考量似乎指向了标度不变且渐近自由的理论。我们通过证明标量模的两点函数为正,为该理论具备完全正性提供了进一步证据。为支持使用精密加速度计测试时空的量子特性,我们还计算了加速度的功率谱密度。本文呈现的结果对暴胀、宇宙微波背景(CMB)数据以及测试时空量子特性的实验具有诸多启示。它们还可能为在时空可被视为有效经典的量子引力区域计算概率提供一种方法。

英文摘要:

One of the obstacles to reconciling quantum theory with general relativity, is constructing a theory which is both consistent with observation, and and gives finite answers at high energy, so that the theory holds at arbitrarily short distances. Quantum field theory achieves this through the process of renormalisation, but famously, perturbative quantum gravity fails to be renormalisable, even without coupling to matter. Recently, an alternative to quantum gravity has been proposed, in which the geometry of spacetime is taken to be classical rather than quantum, while still being coupled to quantum matter fields [1, 2]. This can be done consistently, provided the dynamics is fundamentally stochastic. Here, we find that the pure gravity theory is formally renormalisable. We do so via the path integral formulation by relating the classical-quantum action to that of quadratic gravity which is renormalisable. Because the action induces stochastic dynamics of space-time, rather than deterministic evolution of a quantum field, the classical-quantum theory is free of tachyons and negative norm ghosts. The key remaining question is whether the renormalisation prescription retains completely positive (CP) dynamics. This consideration appears to single out the scale invariant and asymptotically free theory. We give further evidence that the theory is CP, by showing that the two-point function of the scalar mode is positive. To support the use of precision accelerometers in testing the quantum nature of spacetime, we also compute the power spectral density of the acceleration. The results presented here have a number of implications for inflation, CMB data, and experiments to test the quantum nature of spacetime. They may also provide a way to compute probabilities in the regime of quantum gravity where spacetime can be treated as effectively classical.

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