以宇宙微波背景B模偏振探索迴圈量子宇宙學中的「前世宇宙」

Abstract

我們希望透過觀測宇宙微波背景輻射的 B 模偏振，來探索迴圈量子宇宙學中所預測的「前世宇宙」，特別是驗證由前世宇宙中雙星系統所產生、並且經歷大反彈時期而存活下來的重力波，至今仍可被觀測的可能性。這個研究奠基於使用 ADM 形式描述的動力學，其中考慮了由量子理論所簡化的第零階繞異性修正。本論文提出了一個新的研究架構：利用轉移函數來演化前世宇宙的重力波，藉此得知它們在現今宇宙應有的樣貌。這是個透明且直覺的過程，讓人們能夠精準地討論在不同的迴圈量子宇宙學參數之下，這些來自前世宇宙的重力波將會為宇宙微波背景輻射 B 模偏振帶來什麼影響。我們期待能夠在不久的未來，科學家能夠透過觀測 B 模偏振的頻譜，藉此驗證這些來自前世宇宙的線索。值得一提的是，擁有時間對稱大反彈的宇宙所存在的可能性，已經被卜朗克計劃及 BICEP2 實驗的最新結果所排除。

We aim to use the observations of B-mode polarization in the cosmic microwave background (CMB) to probe the ``parent universe' under the context of loop quantum cosmology (LQC). In particular, we investigate the possibility for the gravitational waves (GWs) such as those from the stellar binary systems in the parent universe to survive the big bounce and thus to be still observable today. Our study is based on the background dynamics with the zeroth-order holonomy correction using the Arnowitt-Deser-Misner (ADM) formalism. We propose a new framework in which transfer functions are invoked to bring the GWs in the parent universe through the big bounce, inflation, and big bang to reach today. This transparent and intuitive formalism allows us to accurately discuss the influence of the GWs from the parent universe on the B-mode polarization in the CMB today under backgrounds of different LQC parameters. These features can soon be tested by the forthcoming CMB observations and we note that the LQC backgrounds with symmetric bouncing scenarios are ruled out by the latest observational results from Planck and BICEP2/Keck experiments.