The concept of early Universe inflation resolves several problems of hot Big Bang theory and quantitatively explains the origin of the inhomogeneities in the present Universe. However, it is not possible to arrange inflation in a scalar field model with renormalizable potential, such that it would not contradict the recent Planck data. For this reason, inflaton must have also higher derivative couplings suppressed at least by the Planck scale. We show that these couplings may be relevant during reheating and lead to non-negligible production of gravitons. We consider the possibility that the unitarity breaking scale for the model of inflation is lower than the Planck scale and compute production of gravitons during reheating, due to the inflaton decay to two gravitons and graviton bremsstrahlung process. The spectrum of produced gravitons is crucially dependent on reheating temperature and inflaton mass. We find that for low reheating temperature decay to gravitons lead to significant amount of dark radiation. Confronting this result with CMB constraints, we find reheating dependent bounds on the unitarity breaking scale. We also compare the obtained gravitational wave signals with the projected limits of future high frequency gravitational wave experiments.

中文翻译：

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暴胀衰变和轫致辐射产生的引力波


早期宇宙膨胀的概念解决了热门大爆炸理论的几个问题，并定量解释了当前宇宙不均匀性的起源。然而，不可能在具有可重整势的标量场模型中安排通货膨胀，这样它就不会与最近的普朗克数据相矛盾。因此，暴胀子还必须具有至少被普朗克尺度抑制的更高导数耦合。我们证明这些耦合在再加热过程中可能是相关的，并导致产生不可忽略的引力子。我们考虑暴胀模型的幺正性破缺尺度低于普朗克尺度的可能性，并计算再加热期间由于暴胀衰减为两个引力子和引力子轫致辐射过程而产生的引力子。产生的引力子的光谱很大程度上取决于再加热温度和暴胀子质量。我们发现，对于低再加热温度，引力子的衰变会导致大量的暗辐射。面对这个结果与 CMB 约束，我们发现再加热依赖于幺正性破坏尺度的界限。我们还将获得的引力波信号与未来高频引力波实验的预计极限进行了比较。