Gravitational waves from compact objects - a tool for testing strong gravity and nuclear matter at extreme densities

重力在天体物理学、宇宙学和基础物理学的几乎每一项拨款挑战中都扮演着核心角色，这使得它成为一个强大的跨学科的主题。最近，在检验广义相对论预言的努力中有了一项重大突破，即直接探测引力波。在接下来的几年里，通过对宇宙中已知的最致密物体--中子星和黑洞--的合并进行引力波观测，将打开一种前所未有的视角，了解宇宙中以前不可见的部分。另一方面，宇宙的加速膨胀，这是当今物理学中最重要的悬而未决的问题之一，可以归因于我们在天体物理和宇宙尺度上缺乏对引力的理解，在这些尺度上，纯粹的广义相对论被打破，产生了更完整的引力理论。从试图统一强引力区中所有相互作用或量子修正的理论中，也预测了爱因斯坦理论的修改。此外，广义相对论确实以惊人的精度得到了检验，但只在弱场区域进行了检验，而强场区域则没有得到很好的探索和限制。目前项目的目的是在广义引力理论中系统地探索中子星和黑洞合并产生的引力波发射，涵盖合并的几乎所有阶段：初始阶段、合并后阶段，在某些情况下--引力波余辉。我们将涵盖广泛的另类引力理论，这些理论在理论上是有良好动机的，并与观测结果一致。这将是第一次进行这种规模的研究，因为到目前为止，一些替代的引力理论或某些引力波发射机制的结果主要是孤立的。以上述结果为基础，第二个极其重要的目标将是打破合并中子星引力波观测中状态方程不确定性和潜在引力理论不确定性之间的简并。然而，状态方程上的大多数观测约束都隐含地假设纯广义相对论是引力的基本理论。这给检验其他引力理论带来了严重困难。由于未来对合并中子星的引力波观测的主要目标之一是对极端密度下物质的行为施加限制，因此开发一种独立于基本引力理论的方法非常重要。

Gravity plays a central role in almost every grant challenge in astrophysics, cosmology and fundamental physics making it a subject to a strong interdisciplinarity. Recently there was a major breakthrough in the efforts to test the predictions of general relativity, namely the direct detection of gravitational waves. In the following years, an unprecedented view of previously invisible parts of the Universe will be opened through gravitational wave observations of mergers of the most compact objects known to exist in the universe - the neutron stars and the black holes. On another front, the accelerated expansion of the Universe, that is one of the most important open problems in physics nowadays, can be attributed to our lack of understanding of gravity on astrophysical and cosmological scales where the pure general relativity breaks down giving rise to a more complete theory of gravity. Modifications of Einstein's theory are predicted as well from the theories trying to unify all the interaction or the quantum corrections in the strong gravity regime. Moreover, general relativity is indeed tested with remarkable accuracy but only in the weak field regime, while the strong field regime is poorly explored and constrained. The aim of the current project is to perform a systematic effort in exploring the gravitational wave emission from merging neutron stars and black holes in generalized theories of gravity covering almost all stages of the merger: the inspiral, the post-merger phase and in some cases - the gravitational wave afterglow. We will cover a wide class of alternative theories of gravity that are theoretically well motivated and in agreement with the observations. This would be the first study of this magnitude since up to now mainly isolated results of some alternative theories of gravity or of certain mechanisms of gravitational wave emission were obtained. Using the above results as a basis, the second extremely important goal would be to break the degeneracy between equation of state uncertainties and uncertainties in the underlying gravitational theory for the gravitational wave observations of merging neutron stars. Most of the observational constraints on the equation of state, though, implicitly assume pure general relativity as the underlying theory of gravity. This poses serious difficulties in testing the alternative theories of gravity. Since one of the main goals of the future gravitational wave observations of merging neutron stars is to impose constraints on the behavior of matter at extreme densities, developing a methodology that is independent of the underlying theory of gravity is of great importance.