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arXiv 0906.0463gr-qc
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时空共形涨落与量子退相

Spacetime Conformal Fluctuations and Quantum Dephasing

Paolo M. Bonifacio

摘要:

任何与复杂环境相互作用的量子系统都会经历退相干。由于物质场处于基态,空的空间充满了真空能量,代表了任何量子粒子都必须应对的潜在环境。特别是量子引力真空涨落应该是退相干的普遍来源。为了研究这个问题,我们采用了一种随机的方法,通过一个经典的,随机波动的度量(随机引力框架)接近普朗克尺度的时空波动模型。我们丰富了经典计划的度量扰动弯曲的背景,也包括物质场和度量共形波动。我们表明,在一般情况下,共形调制度量诱导退相作为一个有效的非线性牛顿势在适当的非相对论极限的最小耦合克莱因-戈登场的结果。真空涨落的特殊情况下被认为是和定量估计的预期效果推导。其次,我们解决的问题,如何共形波动可能产生的物理。通过应用随机引力框架,我们首先表明,标准GR似乎禁止自发共形度量调制。最后,我们认为,一个不同的结果如下标量张量引力理论,如Brans-Dicke理论。在这种情况下,度规的共形调制自然地产生,作为Brans-Dicke场的波动的结果,并且预期会发生测试粒子的量子退相。对于大的负值的耦合参数的共形起伏也可能有助于减轻由于量子物质场的大零点能量的众所周知的问题。

英文摘要:

Any quantum system interacting with a complex environment undergoes decoherence. Empty space is filled with vacuum energy due to matter fields in their ground state and represents an underlying environment that any quantum particle has to cope with. In particular quantum gravity vacuum fluctuations should represent a universal source of decoherence. To study this problem we employ a stochastic approach that models spacetime fluctuations close to the Planck scale by means of a classical, randomly fluctuating metric (random gravity framework). We enrich the classical scheme for metric perturbations over a curved background by also including matter fields and metric conformal fluctuations. We show in general that a conformally modulated metric induces dephasing as a result of an effective nonlinear newtonian potential obtained in the appropriate nonrelativistic limit of a minimally coupled Klein-Gordon field. The special case of vacuum fluctuations is considered and a quantitative estimate of the expected effect deduced. Secondly we address the question of how conformal fluctuations could physically arise. By applying the random gravity framework we first show that standard GR seems to forbid spontaneous conformal metric modulations. Finally we argue that a different result follows within scalar-tensor theories of gravity such as e.g. Brans-Dicke theory. In this case a conformal modulation of the metric arises naturally as a result of the fluctuations in the Brans-Dicke field and quantum dephasing of a test particle is expected to occur. For large negative values of the coupling parameter the conformal fluctuations may also contribute to alleviate the well known problem of the large zero point energy due to quantum matter fields.

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