Recent studies of inflation with multiple scalar fields have highlighted the importance of non-canonical kinetic terms in novel types of inflationary solutions. This motivates a thorough analysis of non-Gaussianities in this context, which we revisit here by studying the primordial bispectrum in a general two-field model. Our main result is the complete cubic action for inflationary fluctuations written in comoving gauge, i.e. in terms of the curvature perturbation and the entropic mode. Although full expressions for the cubic action have already been derived in terms of fields fluctuations in the flat gauge, their applicability is mostly restricted to numerical evaluations. Our form of the action is instead amenable to several analytical approximations, as our calculation in terms of the directly observable quantity makes manifest the scaling of every operator in terms of the slow-roll parameters, what is essentially a generalization of Maldacena’s single-field result to non-canonical two-field models. As an important application we derive the single-field effective field theory that is valid when the entropic mode is heavy and may be integrated out, underlining the observable effects that derive from a curved field space.

中文翻译：

---

用弯曲场空间重新审视多场膨胀中的非高斯性

最近对多标量场膨胀的研究强调了非规范动力学项在新型膨胀解决方案中的重要性。这激发了在这种情况下对非高斯性的彻底分析，我们在这里通过研究一般两场模型中的原始双谱来重新审视。我们的主要结果是用联动规范编写的暴胀涨落的完整三次动作，即在曲率扰动和熵模式方面。尽管已经根据平面规中的场波动导出了三次作用的完整表达式，但它们的适用性主要限于数值评估。相反，我们的动作形式适用于几种分析近似，由于我们根据直接可观察量的计算表明每个算子在慢滚参数方面的缩放，这本质上是将 Maldacena 的单场结果推广到非规范的双场模型。作为一个重要的应用，我们推导出了单场有效场理论，该理论在熵模很重并且可以被积分时有效，强调了从弯曲场空间得出的可观察效应。