Liu, ZG (reprint author), Univ Chinese Acad Sci, Sch Phys, Beijing 100049, Peoples R China.
; Piao, Yun-Song] Univ Chinese Acad Sci, Sch Phys, Beijing 100049, Peoples R China
; [Guo, Zong-Kuan] Chinese Acad Sci, Inst Theoret Phys, State Key Lab Theoret Phys, Beijing 100190, Peoples R China
Recent Planck measurements show some CMB anomalies on large angular scales, which confirms the early observations by WMAP. We show that an inflationary model, in which before the slow-roll inflation the Universe is in a superinflationary phase, can generate a large-scale cutoff in the primordial power spectrum, which may account for not only the power suppression on large angular scales, but also a large dipole power asymmetry in the CMB. We discuss an implementation of our model in string theory.