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arXiv 2007.11915gr-qcastro-ph.COhep-th
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具有线性耦合的Einstein-Gauss-Bonnet暴胀中的近无质量引力子对标量场的恒滚

A Nearly Massless Graviton in Einstein-Gauss-Bonnet Inflation with Linear Coupling Implies Constant-roll for the Scalar Field

V. K. Oikonomou, F. P. Fronimos

摘要:

引人注目的GW 170817事件表明引力子几乎是无质量的,因为从两颗中子星合并发出的伽马射线几乎与引力波同时到达。因此,引力子在暴胀和后暴胀时期也必须是无质量的,因为没有明显的理由相信不是这样。在这封信中,我们将研究引力子无质量的约束对标量场与四维高斯-邦纳不变量线性耦合的爱因斯坦-高斯-邦纳理论的理论意义。正如我们所展示的,原始引力波的引力波速度等于1的约束,严重地限制了标量场的动力学,强加了一个直接的恒滚演化。GW 170817兼容的线性耦合的Einstein-Gauss-Bonnet理论的原始标量扰动的谱指数与非线性耦合的相同理论相比是不同的。线性耦合因此,该模型的现象学预计是不同的,我们简要讨论这个问题。此外,常滚条件总是与非高斯性有关,因此在线性耦合的Einstein-Gauss-Bonnet理论中引入无质量引力子可能导致非高斯性,这是一个有趣的问题,因此我们也简要地讨论了这个问题。

英文摘要:

The striking GW170817 event indicated that the graviton is nearly massless, since the gamma rays emitted from the two neutron stars merging arrived almost simultaneously with the gravitational waves. Thus, the graviton must also be massless during the inflationary and post-inflationary era, since there is no obvious reason to believe otherwise. In this letter we shall investigate the theoretical implications of the constraint that the graviton is massless to an Einstein-Gauss-Bonnet theory with linear coupling of the scalar field to the four dimensional Gauss-Bonnet invariant. As we show, the constraint of having gravitational wave speed of the primordial gravitational waves equal to one, severely restricts the dynamics of the scalar field, imposing a direct constant-roll evolution on it. Also, as we show, the spectral index of the primordial scalar perturbations for the GW170817-compatible Einstein-Gauss-Bonnet theory with linear coupling is different in comparison to the same theory with non-linear coupling. Thus the phenomenology of the model is expected to be different, and we briefly discuss this issue too. In addition, the constant-roll condition is always related to non-Gaussianities, thus it is interesting that the imposition of a massless graviton in an Einstein-Gauss-Bonnet theory with linear coupling may lead to non-Gaussianities, so we briefly discuss this issue too.

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