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）相结合而产生的理论。长期以来，它一直是疯狂猜测的主题，不受硬科学所特有的通常的观察和实验链的约束。观测和理论宇宙学的最新进展已经改变了这一点，提供了有史以来第一个量子引力数据，具有巨大的增长潜力。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，这些波动在空间中延伸得如此之远，以至于它们变得有效地平行，从而能够生存到当前的时代。该项目将研究这些波动如何影响引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伟大转变的一部分，它们揭示的现象可能有助于我们更好地理解当前的宇宙。涉及未分化引力子和/或无质量的最小耦合标量的相互作用可以在原始膨胀期间引起大大增强的量子效应。这是宇宙学扰动的来源，最近的工作已经从这些初级效应转向次级效应，次级效应是由功率谱和其他量的环路修正引起的。PI将在未来三年内通过六个领域的继续工作来解决这些问题：计算和完全重整化引力子环对一般规范中1 PI 2点函数的贡献;基于度规的非局部泛函定义宇宙学可观测量的非线性扩展;计算时空膨胀不变测度的一个和两个环期望值;研究非微扰的长期影响，使用物质量子的膨胀引力子的散射;调查非本地修改后的重力模型的通货膨胀，后期的时间加速和MOND;和探索的现象学意义的通货膨胀扰动建立从过去的演变。

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.