The Early Universe as a Window to Quantum Gravity

最近的观测已经能够探测到在所谓的大爆炸后零点几秒内发生的物理过程的残留物。在理论方面，我们对宇宙演化的理解虽然相当复杂，但仍然不完整。要描述非常早期的宇宙，需要深刻理解如何使爱因斯坦的引力理论和量子力学保持一致，而这样的理论还没有完全发展起来。该项目试图通过将量子引力的思想和技术融入宇宙学来填补这一空白，目标是克服当前模型的局限性。因此，这个项目的目标是双重的：扩大我们对宇宙起源和命运的理解，并用上一代观测来对抗新的量子引力概念。拟议的研究旨在开发将量子重力物理纳入早期宇宙模型的近似方法。研究将集中在量子宇宙学的理论和现象学方面，特别强调来自环圈量子引力的技术。从理论的角度，它将探索物质场如何在引力的量子方面很重要的区域中传播，以及我们熟悉的弯曲时空中的量子场理论是如何从更基本的理论中产生的。从现象学的观点来看，由此产生的理论框架将被应用于扩展宇宙模型，以包括普朗克尺度物理。研究将涉及导致宇宙微波背景和星系分布中温度各向异性的标量扰动、非高斯性、原始磁场，并将特别关注早期宇宙中产生的引力波。

Recent observations have been able to detect remnants of physical processes that occurred a tiny fraction of second after the so-called big bang. On the theoretical side our understanding of the cosmic evolution although quite sophisticated is still incomplete. A deep understanding of how to make Einstein's theory of gravity and quantum mechanics consistent is needed to describe the very early universe, and such a theory is not fully developed yet. This project seeks to contribute to filling this gap by incorporating ideas and techniques of quantum gravity to cosmology with the goal of overcoming limitations of current models. The objective of this project is therefore twofold: to extend our understanding of the origin and fate of the universe, and to confront new quantum-gravity ideas with the last generation of observations.The proposed research aims at developing approximate methods to incorporate quantum gravity physics in models of the early universe. Investigations will focus on theoretical as well as phenomenological aspects of quantum cosmology, with special emphasis on techniques coming from loop quantum gravity. From the theoretical point of view, it will be explored how matter fields propagate on regimes in which the quantum aspects of gravity are important, and the way in which the familiar quantum field theory in curved space-times emerges from the more fundamental theory. From the phenomenological viewpoint, the resulting theoretical framework will be applied to extend cosmological models to include Planck scale physics. Investigations will cover scalar perturbations that are responsible for the temperature anisotropies in the cosmic microwave background and galaxy distribution, non-Gaussianity, primordial magnetic fields, and particular attention will be paid to gravitational waves generated in the early universe.