报告人：蔡一夫  教授（中国科学技术大学天文学系）

时间：2015年9月15日下午4：00

地点：东区理化大楼18层天文台报告厅

报告摘要：We explore a plausible mechanism that the hemispherical power asymmetry in the CMB is produced by the spatial variation of the primordial sound speed parameter. We suggest that in a generalized approach of the δN formalism the local e-folding number may depend on some other primordial parameters besides the initial values of inflaton. Here the δNformalism is extended by considering the effects of a spatially varying sound speed parameter caused by a super-Hubble perturbation of a light field. Using this generalized δN formalism, we systematically calculate the asymmetric primordial spectrum in the model of multi-speed inflation by taking into account the constraints of primordial non-Gaussianities. We further discuss specific model constraints, and the corresponding asymmetry amplitudes are found to be scale-dependent, which can accommodate current observations of the power asymmetry at different length scales.