Title: On the importance of heavy fields during inflation Show Chinese title

Title: 在膨胀期间重场的重要性

Abstract: We study the dynamics of two-field models of inflation characterized by a hierarchy of masses between curvature and isocurvature modes. When the hierarchy is large, a low energy effective field theory (EFT) exists in which only curvature modes participate in the dynamics of perturbations. In this EFT heavy fields continue to have a significant role in the low energy dynamics, as their interaction with curvature modes reduces their speed of sound whenever the multi-field trajectory is subject to a sharp turn in target space. Here we analyze under which general conditions this EFT remains a reliable description for the linear evolution of curvature modes. We find that the main condition consists on demanding that the rate of change of the turn's angular velocity stays suppressed with respect to the masses of heavy modes. This adiabaticity condition allows the EFT to accurately describe a large variety of situations in which the multi-field trajectory is subject to sharp turns. To test this, we analyze several models with turns and show that, indeed, the power spectra obtained for both the original two-field theory and its single-field EFT are identical when the adiabaticity condition is satisfied. In particular, when turns are sharp and sudden, they are found to generate large features in the power spectrum, accurately reproduced by the EFT. Show Chinese abstract

Abstract: 我们研究了由曲率和等曲率模式之间质量层次结构所表征的双场暴胀模型的动力学。当层次结构较大时，存在一个低能有效场理论（EFT），其中只有曲率模式参与扰动的动力学。在这个EFT中，重场在低能动力学中继续发挥重要作用，因为当多场轨迹在目标空间中受到急剧转弯时，它们与曲率模式的相互作用会降低其声速。在这里，我们分析了在哪些一般条件下，该EFT仍然是曲率模式线性演化的可靠描述。我们发现主要条件是要求转弯的角速度变化率相对于重模的质量保持抑制。这个绝热条件使得EFT能够准确描述多场轨迹受到急剧转弯的各种情况。为了验证这一点，我们分析了几种具有转弯的模型，并表明当满足绝热条件时，原始双场理论及其单场EFT得到的谱功率是相同的。特别是，当转弯是急剧且突然的时候，它们被发现会在谱功率中产生大的特征，这些特征被EFT准确地再现。