摘要
热大爆炸宇宙学取得巨大的成功,它所预言的哈勃定律、宇宙微波背景辐射和轻元素丰度等都得到了观测的广泛证实.但是热大爆炸宇宙理论自身有着无法解释的疑难问题,比如宇宙空间平坦性问题、视界问题等.为了解决热大爆炸宇宙学的诸多疑难问题,一个最简单经济的方案是在宇宙热大爆炸前发生一段由真空能推动的宇宙近指数膨胀的宇宙演化过程,即宇宙暴胀.事实上,发生在宇宙极早期的暴胀过程不仅可以合理地解释所有这些热大爆炸宇宙学中的疑难问题,而且起源于暴胀期间的量子扰动自然地提供了宇宙晚期结构形成所需的原初密度涨落.反过来,探测宇宙微波背景辐射微小的各向异性和宇宙结构成了探索早期宇宙暴胀物理过程的关键手段.尽管现有的大量宇宙学观测强有力地支持暴胀宇宙学,然而当前在宇宙大尺度上似乎依然存在一些偏离标准暴胀宇宙学预言的迹象,这些迹象可能暗示宇宙在极早期暴胀前还经历了一段收缩过程.
The hot big bang cosmology is very successful, and the Hubble law, the cosmic microwave background radiation and the abundance of light elements etc. predicted by the hot big bang model have been confirmed by a plenty of cosmological observations. However, the hot big bang model still suffers from several puzzles, such as the flatness problem, the hori- zon problem, the unwanted relics and so on. The inflation model which was proposed by Alan Guth in the early of 1980s is an elegant paradigm which provides a simple solution to all of the problems in the hot big bang model. Due to the nearly exponential expansion of space during inflation, the initial spatial curvature and inhomogeneities are smoothed away. In this sense, a spatially flat universe can be taken as one of the key predictions of inflationary universe and it has been confirmed by a lot of cosmological observations. On the other hand, during inflation, the Universe is ＂small＂ and the quantum effects become significant. Actually, such quantum fluctuations will finally seed the formation of large-scale structure and the anisotropies in the cosmic microwave background. Because the Hubble parameter is roughly a constant during inflation, the power spectrum of the density perturbation generated by the quantum fluctuations is expected to be nearly scale-invariant. Actually, all of the current cosmological observations really prefer a Gaussian and nearly scale-invariant primordial power spectrum of density perturbations which is nicely consistent with the prediction of the simple inflation models. In addition, inflation also predicts that there should be primordial gravitational waves which generate the B-mode polarization in the cosmic microwave background. In the early of 2014, BICEP2 collaborations reported an excess of B-mode power over the based lensed standard cosmological model expectation at the cosmic scales. Unfortunately, it is finally confirmed to be the foreground contaminations, not originated from the primordial gravita- tional waves. Up to now, ones only set a restricted upper limit on the amplitude of primordial gravitational-wave power spectrum. Such a small upper limit implies that the inflation is driven by an effective cosmological constant at the leading order. In order for naturally ending inflation at a time in the early universe, there should be a dynamical term in the po- tential of inflation field as well. The precise measurement of the spectral index of scalar power spectrum from Planck satellite favors the so-called Starobinsky＇s inflation model which is driven by the R2 term adding to the Einstein-Hilbert action. However, why the higher order corrections should be exponentially suppressed in the Starobinsky＇s inflation model is still an open question. In addition, if a contraction phase happened before the inflation, it may modify the pri- mordial density perturbation power spectrum at very large scales and may help us to explain some hints of the anomalies on such scales.
作者
黄庆国
朴云松
Qing-Guo Huang;Yun-Song Piao(Institute of Theoretical Physics,Chinese Academy of Sciences,Beijing 100190,China;School of Physical Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2018年第24期2509-2517,共9页
Chinese Science Bulletin
关键词
热大爆炸
暴胀
原初引力波
反弹暴胀
hot big bang
inflation
primordial gravitational wave
bouncing inflation
