Quantum Field Theory and Cosmology

量子引力是将引力与相对论（观察者如何比较时间和距离）和量子力学（其关键原理是每个自由度都有微小的运动）结合起来形成的理论。长期以来，它一直是人们疯狂猜测的对象，没有经过通常作为硬科学特征的一连串观察和实验的检验。观测和理论宇宙学的最新进展通过提供有史以来第一个量子引力数据改变了这一点，并且具有巨大的增长潜力。非常早期的宇宙膨胀得如此之快，加速度如此之高，以至于真空中通常微小的引力场波动被放大到一个仍然很小但可测量的量。同样重要的是，这些波动在太空中延伸得如此之远，以至于它们实际上变成了化石，因此能够存活到现在。这个项目将研究这些波动如何影响重力本身，以及其他力和粒子。这些研究是量子引力从科幻小说到科学事实的巨大转变的一部分，它们揭示的现象可能有助于我们更好地理解当前的宇宙。在原始暴胀期间，涉及未分化引力子和/或无质量、最小耦合标量的相互作用可以大大增强量子效应。这是宇宙学扰动的来源，最近的工作已经从这些主要影响转向由功率谱和其他量的环路修正引起的次要影响。PI将在未来三年内通过继续在六个领域开展工作来解决这些问题：计算和完全重整引力子环对一般量规中1PI 2点函数的贡献；基于度规的非定域泛函定义宇宙学观测的非线性扩展计算时空膨胀不变测度的一环和二环期望值；利用暴胀引力子对物质量子的散射研究非摄动长期效应研究膨胀、晚时间加速和MOND的非局部修正引力模型；并探索从过去的进化中建立起来的暴胀扰动的现象学含义。

Quantum gravity is the theory that arises from combining gravity with relativity (how observers compare time and distance) and quantum mechanics (the key principle of which is that every degree of freedom has a tiny amount of motion). It has long been the subject of wild speculation, unchecked by the usual chain of observation and experiment which characterizes hard science. Recent advances in observational and theoretical cosmology have changed this by providing the first quantum gravitational data ever taken, with a vast potential for increase. The very early universe was expanding so rapidly and with such a high degree of acceleration that the usually tiny fluctuations of gravitational fields in empty space were amplified to a still-small but measurable amount. Equally important, these fluctuations were stretched out in space so far that they became effectively fossilized, and were thereby able to survive down to the current epoch. This project will study how these fluctuations affect gravity itself, and also the other forces and particles. Such studies are part of the great transformation of quantum gravity from science fiction to science fact, and the phenomenon they reveal may help us to better understand the current universe.Interactions which involve undifferentiated gravitons and/or massless, minimally coupled scalars can give rise to greatly enhanced quantum effects during primordial inflation. This is the source of cosmological perturbations and recent work has turned from these primary effects to secondary effects arising from loop corrections to the power spectra and other quantities. The PI will address these problems over the next three years by continuing work in six areas: Computing and fully renormalizing graviton loop contributions to 1PI 2-point functions in general gauges; defining nonlinear extensions of cosmological observables based on nonlocal functionals of the metric; computing the one and two loop expectation value of an invariant measure of spacetime expansion; studying nonperturbative secular effects using the scattering of matter quanta by inflationary gravitons; investigating nonlocal modified gravity models of inflation, of late time acceleration and of MOND; and exploring phenomenological implications of inflationary perturbations build up from past evolution.