More on the spectrum of perturbations in string gas cosmology
More on the spectrum of perturbations in string gas cosmology
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DOI：
10.1088/1475-7516/2006/11/009
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发表时间：
2006-08
影响因子：
6.4
通讯作者：
R. Brandenberger;S. Kanno;J. Soda;D. Easson;J. Khoury;P. Martineau;A. Nayeri;S. Patil
中科院分区：
文献类型：
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作者：
R. Brandenberger;S. Kanno;J. Soda;D. Easson;J. Khoury;P. Martineau;A. Nayeri;S. Patil
弦气体宇宙学在爱因斯坦框架下被重写。在一个有效的理论中，闭合弦的气体被耦合到没有任何伸缩子的伸缩子引力背景中，从爱因斯坦框架的观点来看，在弦坐标系中准静态的Hagedorn相对应于扩展的非加速相。在这个玩具模型中出现的爱因斯坦标架曲率奇异性与弦标架中的伸缩子的爆炸有关。然而，对于较大的扩张器来说，玩具模型显然不适用。因此，必须有一个新的弦相，它很可能是随着冻结的膨胀而静止的。有了这样一个阶段，弦气体宇宙学中的视界问题就可以成功地得到解决。从弦框架(在弦框架下更容易理解涨落的产生)和爱因斯坦框架(其中演化方程是众所周知的)的角度，重新讨论了由处于热平衡的长弦气体播种的Hagedorn相中宇宙微扰的产生。结果表明，在某些早期阶段固定伸缩子对于获得弦气体宇宙学中宇宙涨落的尺度不变谱是重要的。
String gas cosmology is rewritten in the Einstein frame. In an effective theory in which a gas of closed strings is coupled to a dilaton gravity background without any potential for the dilaton, the Hagedorn phase which is quasi-static in the string frame corresponds to an expanding, non-accelerating phase from the point of view of the Einstein frame. The Einstein frame curvature singularity which appears in this toy model is related to the blowing up of the dilaton in the string frame. However, for large values of the dilaton, the toy model clearly is inapplicable. Thus, there must be a new string phase which is likely to be static with frozen dilaton. With such a phase, the horizon problem can be successfully addressed in string gas cosmology. The generation of cosmological perturbations in the Hagedorn phase seeded by a gas of long strings in thermal equilibrium is reconsidered, from both the point of view of the string frame (in which it is easier to understand the generation of fluctuations) and that of the Einstein frame (in which the evolution equations are well known). It is shown that fixing the dilaton at some early stage is important for obtaining a scale-invariant spectrum of cosmological fluctuations in string gas cosmology.