


Preinflationary universe in loop quantum cosmology 
Institute of Theoretical Physics  Chinese Academy of Sciences  Key Laboratory of Theoretical Physics  Seminar  Title 题目  Preinflationary universe in loop quantum cosmology  Speaker 报告人  Anzhong Wang  Affiliation 所在单位  Zhejiang University of Technology & Baylor University  Date 日期  20170726 (Wednesday) 2：00 p.m.  Venue 地点  ITP New Building 6420  Abstract 摘要  Loop quantum cosmology (LQC) provides an elegant resolution of the big bang singularity by a quantum bounce in the deep Planck era. To study perturbations in such a framework two main approaches have been proposed, the deformed algebra and dressed metric approaches. With some reasonable assumptions, the deformed algebra approach is already ruled out by current observations. In this talk, I shall first give a brief review on LQC and explain the reasons why the deformed algebra approach is inconsistent with observations. Then, I shall present our recent results on the investigations of the dressed metric approach. In particular, I shall show that, when the kinetic energy of the inflaton dominates at the quantum bounce, the evolutions of the flat FLRW background and its linear (scalar and tensor) perturbations are always universally divided into three different phases before reheating: bouncing, transition and slowroll inflation. The evolutions are universal and independent of the inflationary potentials during the bouncing and transition phases and can be given analytically. We calculate the corresponding Bogoliubov coefficients at the onset of the slowroll inflation, which are valid for any inflationary models with a single scalar field, and show that particles are generically created during the preinflationary period. Matching them to those in the slowroll inflationary phase, we investigate the effects of the quantum bounce on the power spectra and find features that can be tested by current and forthcoming observations. In particular, to be consistent with the Planck 2015 data, the universe must have expanded at least 132 efolds since the bounce.  Contact person 所内联系人  RongGen Cai  


