fNL向绝热极限的演化
Evolution of fNL to the adiabatic limit
摘要：
我们研究多场模型中的暴胀扰动，zeta通常会演化到所有等曲率模式衰减--“绝热极限”。我们使用数值方法来探索的非线性参数fNL的敏感性的过程中，实现这一限制，发现一个明显的依赖模型特定的数据，如在慢辊故障或再加热的时间尺度的时间。在模型的总和可分离的潜在的isocurvature模式衰减之前的慢滚阶段结束时，我们给出了一个分析标准的渐近值fNL是大的。其他例子可以使用瀑布场来终止暴胀，而fNL是瞬时大的，由从山脊下降或收敛到山谷引起。我们表明，这两种类型的演变区分的符号的双谱，并给出近似表达式的峰值fNL。
英文摘要：
We study inflationary perturbations in multiple-field models, for which zeta typically evolves until all isocurvature modes decay--the "adiabatic limit". We use numerical methods to explore the sensitivity of the nonlinear parameter fNL to the process by which this limit is achieved, finding an appreciable dependence on model-specific data such as the time at which slow-roll breaks down or the timescale of reheating. In models with a sum-separable potential where the isocurvature modes decay before the end of the slow-roll phase we give an analytic criterion for the asymptotic value of fNL to be large. Other examples can be constructed using a waterfall field to terminate inflation while fNL is transiently large, caused by descent from a ridge or convergence into a valley. We show that these two types of evolution are distinguished by the sign of the bispectrum, and give approximate expressions for the peak fNL.
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