Title: Non-Gaussianity in two-field inflation beyond the slow-roll approximation Show Chinese title

Title: 双场暴胀非高斯性超出慢滚近似

Abstract: We use the long-wavelength formalism to investigate the level of bispectral non-Gaussianity produced in two-field inflation models with standard kinetic terms. Even though the Planck satellite has so far not detected any primordial non-Gaussianity, it has tightened the constraints significantly, and it is important to better understand what regions of inflation model space have been ruled out, as well as prepare for the next generation of experiments that might reach the important milestone of Delta f_NL(local) = 1. We derive an alternative formulation of the previously derived integral expression for f_NL, which makes it easier to physically interpret the result and see which types of potentials can produce large non-Gaussianity. We apply this to the case of a sum potential and show that it is very difficult to satisfy simultaneously the conditions for a large f_NL and the observational constraints on the spectral index n_s. In the case of the sum of two monomial potentials and a constant we explicitly show in which small region of parameter space this is possible, and we show how to construct such a model. Finally, the new general expression for f_NL also allows us to prove that for the sum potential the explicit expressions derived within the slow-roll approximation remain valid even when the slow-roll approximation is broken during the turn of the field trajectory (as long as only the epsilon slow-roll parameter remains small). Show Chinese abstract

Abstract: 我们使用长波长形式主义来研究在具有标准动能项的双场膨胀模型中产生的双谱非高斯性水平。 尽管普朗克卫星迄今为止尚未探测到任何原始非高斯性，但它已经显著收紧了约束条件，因此理解哪些膨胀模型空间区域已被排除非常重要，同时为下一代实验做好准备，这些实验可能会达到重要的里程碑 Δf_NL(local) = 1。 我们推导出一种先前推导出的 f_NL 积分表达式的替代公式，这使得更容易从物理上解释结果并看到哪些类型的势能可以产生大的非高斯性。 我们将此应用于和势的情况，并表明同时满足大的 f_NL 条件和观测对光谱指数 n_s 的限制非常困难。 在两个单项式势能与常数之和的情况下，我们明确指出了参数空间中的小区域，在此区域内这是可能的，并展示了如何构建这样的模型。 最后，新的 f_NL 通用表达式还使我们能够证明，对于和势，即使在慢滚近似被打破时（只要 ε 慢滚参数仍然很小），在场轨迹转弯期间，通过慢滚近似得出的显式表达式仍然有效。