Pre-inflation from the multiverse: can it solve the quadrupole problem in the cosmic microwave background?
12 pags., 5 figs., 2 apps. ; We analyze a quantized toy model of a universe undergoing eternal inflation using a quantum-field-theoretical formulation of the Wheeler–DeWitt equation. This so-called third quantization method leads to the picture that the eternally inflating universe is converted to a multiverse in which sub-universes are created and exhibit a distinctive phase in their evolution before reaching an asymptotic de Sitter phase. From the perspective of one of these sub-universes, we can thus analyze the pre-inflationary phase that arises naturally. Assuming that our observable universe is represented by one of those sub-universes, we calculate how this pre-inflationary phase influences the power spectrum of the cosmic microwave background (CMB) anisotropies and analyze whether it can explain the observed discrepancy of the power spectrum on large scales, i.e. the quadrupole issue in the CMB. While the answer to this question is negative in the specific model analyzed here, we point out a possible resolution of this issue. ; This article is based upon work from COST Action CA15117 "Cosmology and Astrophysics Network for Theoretical Advances and Training Actions (CANTATA)", supported by COST (European Cooperation in Science and Technology). The research of M. B.-L. is supported by the Basque Foundation of Science Ikerbasque. She and J. M. also would like to acknowledge the partial support from the Basque government Grant No. IT956-16 (Spain) and the project FIS2017-85076-P (MINECO/AEI/FEDER, UE). The research of M. K. was financed by the Polish National Science Center Grant DEC2012/06/A/ST2/00395 as well as by a Grant for the Short Term Scientific Mission (STSM) "Multiverse impact onto the cosmic microwave background and its relation to modified gravity" (COST-STSM-CA15117- 36137) awarded by the above-mentioned COST Action. For their kind hospitality while part of this work was done, M. K. and J. M. would like to thank the Centro de Matemática e Aplicações of the Universidade da Beira Interior in Covilhã, Portugal and M. K. also thanks the Department of Theoretical Physics and History of Science of the University of the Basque Country (UPV/EHU).