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arXiv 1709.07087gr-qc
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共形关联标量张量理论中宇宙学观测量的等价性

Equivalence of cosmological observables in conformally related scalar tensor theories

François Rondeau, Baojiu Li

摘要:

标量张量理论可以用不同的坐标系表示,如常用的爱因斯坦坐标系和约旦坐标系,一般认为在这些坐标系中宇宙学观测量是相同的。我们重新审视这一点,使一个详细的并排比较的数量和方程在两个共形相关的框架,从行动和完全协变场方程的线性方程在实空间和傅立叶空间。这证实了场方程和守恒方程在两个框架中是等价的,在这个意义上,我们总是可以在一个框架中重新表达方程,使用相关的变量变换来导出另一个框架中的相应方程。通过解析推导和数值算例表明,只要在爱因斯坦坐标系($1+z\neq1/a$)中使用正确的红移,用视线积分法计算CMB温度各向异性可以用Einstein坐标系或Jordan坐标系中的量来完成,并且结果是相同的。

英文摘要:

Scalar tensor theories can be expressed in different frames, such as the commonly-used Einstein and Jordan frames, and it is generally accepted that cosmological observables are the same in these frames. We revisit this by making a detailed side-by-side comparison of the quantities and equations in two conformally related frames, from the actions and fully covariant field equations to the linearised equations in both real and Fourier spaces. This confirms that the field and conservation equations are equivalent in the two frames, in the sense that we can always re-express equations in one frame using relevant transformations of variables to derive the corresponding equations in the other. We show, with both analytical derivation and a numerical example, that the line-of-sight integration to calculate CMB temperature anisotropies can be done using either Einstein frame or Jordan frame quantities, and the results are identical, provided the correct redshift is used in the Einstein frame ($1+z\neq1/a$).

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