The production of a stochastic background of gravitational waves is a fundamental prediction of any cosmological inflationary model. The features of such a signal encode unique information about the physics of the Early Universe and beyond, thus representing an exciting, powerful window on the origin and evolution of the Universe. We review the main mechanisms of gravitational-wave production, ranging from quantum fluctuations of the gravitational field to other mechanisms that can take place during or after inflation. These include e.g. gravitational waves generated as a consequence of extra particle production during inflation, or during the (p)reheating phase. Gravitational waves produced in inflation scenarios based on modified gravity theories and second-order gravitational waves are also considered. For each analyzed case, the expected power spectrum is given. We discuss the discriminating power among different models, associated with the validity/violation of the standard consistency relation between tensor-to-scalar ratio r and tensor spectral index n_T In light of the prospects for (directly/indirectly) detecting primordial gravitational waves, we give the expected present-day gravitational radiation spectral energy-density, highlighting the main characteristics imprinted by the cosmic thermal history, and we outline the signatures left by gravitational waves on the Cosmic Microwave Background and some imprints in the Large-Scale Structure of the Universe. Finally, current bounds and prospects of detection for inflationary gravitational waves are summarized.

中文翻译：

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通货膨胀引力波

随机产生的引力波是任何宇宙膨胀模型的基本预测。这种信号的特征编码了有关早期宇宙及以后物理学的独特信息，因此代表了关于宇宙起源和进化的令人兴奋的，有力的窗口。我们回顾了引力波产生的主要机制，从引力场的量子涨落到充气期间或之后可能发生的其他机制。这些包括例如由于在充气过程中或（p）加热阶段产生额外的颗粒而产生的重力波。还考虑了基于修正的重力理论和二阶重力波在通货膨胀场景中产生的重力波。对于每种分析情况，都给出了预期的功率谱。我们讨论了不同模型之间的判别力，以及张量与标量比r和张量谱指数n _T之间的标准一致性关系的有效性/违反性鉴于（直接/间接）检测原始引力波的前景，我们给出了预期的当今引力辐射光谱能量密度，突出显示了宇宙热历史印记的主要特征，并概述了引力波留下的特征在宇宙微波的背景下，以及在宇宙的大规模结构中的某些烙印。最后，总结了膨胀引力波检测的现状和发展前景。