tokens: I sincerely thank Pavel Naselsky, Sebastian von Hausegger and James Creswell for valuable discussions and suggestions, as well as the anonymous referee for carefully reading the article and giving very helpful comments. This research has made use of data/product from the WMAP (The WMAP data release 2013) and Planck (The Planck data release 2015) collaborations. Some of the results in this paper are derived using the HEALPix ( Górski et al. 2005 ) package. This work was partially funded by the Danish National Research Foundation (DNRF) through establishment of the Discovery Center and the Villum Fonden through the Deep Space project. Hao Liu is also supported by the Youth Innovation Promotion Association, CAS.
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