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arXiv 2102.05540gr-qchep-th
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一般线性质量引力和一般高曲率引力中的引力波偏振

Gravitational-wave polarizations in generic linear massive gravity and generic higher-curvature gravity

Tomoya Tachinami, Shinpei Tonosaki, Yuuiti Sendouda

摘要:

本文研究了两类推广引力理论中的引力波的偏振。首先,我们通过确定所有服从Klein-Gordon型方程的独立变量,用非Fierz-Pauli型的一般质量项来表示线性质量引力(MG)中的极化。一般MG中的动力学自由度(dofs)由自旋2和自旋0模式组成,前者分解为两个张量(螺旋度2)、两个矢量(螺旋度1)和一个标量(螺旋度0)分量,而后者仅对应于一个标量。我们找到方便的方法分解成不同的横向和纵向极化的系数直接表示的质量参数的线性组合的每个自旋的两个标量模式,从而作为一个有用的工具,在测量的质量GW。然后,我们分析了一般高曲率引力(HCG)的线性扰动,其拉格朗日量是黎曼张量的任意多项式。在平坦的背景下,该理论中的线性动力学自由度被确定为无质量自旋2,有质量自旋2和有质量自旋0模式。由于其巨大的部分包括与通用MG相同的结构,通用HCG中的GW在普通的两个无质量模式之上提供六个巨大的偏振。与MG并行,我们找到了直接与HCG参数相关的标量偏振模式的方便表示。在这个分析中,我们采用两种不同的方法;一个充分利用了通用HCG和MG在线性水平上的部分等价性,而另一个依赖于规范不变的形式主义。我们确认两个结果一致。我们还讨论了通过GW偏振测量确定理论参数的方法。我们的方法不需要测量的传播速度或波形的GW的细节。[删节]

英文摘要:

We study the polarizations of gravitational waves (GWs) in two classes of extended gravity theories. First, we formulate the polarizations in linear massive gravity (MG) with generic mass terms of non-Fierz-Pauli type by identifying all the independent variables that obey Klein-Gordon-type equations. The dynamical degrees of freedom (dofs) in the generic MG consist of spin-2 and spin-0 modes, the former breaking down into two tensor (helicity-2), two vector (helicity-1) and one scalar (helicity-0) components, while the latter just corresponding to a scalar. We find convenient ways of decomposing the two scalar modes of each spin into distinct linear combinations of the transverse and longitudinal polarizations with coefficients directly expressed by the mass parameters, thereby serving as a useful tool in measuring the masses of GWs. Then we analyze the linear perturbations of generic higher-curvature gravity (HCG) whose Lagrangian is an arbitrary polynomial of the Riemann tensor. On a flat background, the linear dynamical dofs in this theory are identified as massless spin-2, massive spin-2, and massive spin-0 modes. As its massive part encompasses the identical structure to the generic MG, GWs in the generic HCG provide six massive polarizations on top of the ordinary two massless modes. In parallel to MG, we find convenient representations for the scalar-polarization modes directly connected to the parameters of HCG. In this analysis, we employ two distinct methods; One takes full advantage of the partial equivalence between the generic HCG and MG at the linear level, whereas the other relies upon a gauge-invariant formalism. We confirm that the two results agree. We also discuss methods to determine the theory parameters by GW-polarization measurements. Our method does not require measuring the propagation speeds or the details of the waveforms of the GWs. [Abridged]

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