标题： 大量弦模式与非奇异的预大爆炸宇宙学 显示英文标题

标题： Massive string modes and non-singular pre-big-bang cosmology

摘要： 微扰性$\alpha '$修正对低能弦有效作用量最近被发现可能对最低阶预大爆炸解的奇点具有正则化效应。 然而，由于方案依赖性的模糊性，在弦常数$\alpha '$的幂级数展开的任何有限阶次上都无法确定它们是否真的实现了正则化。 在物理上，这些修正主要由前几个高能弦态的积分主导。 而非常高的弦态始终具有非微扰的正则化效应，这种效应与$\alpha '$相关，其基本原因是在具有哈勃常数$H$的引力场中，它们以有效的霍金温度$T=H/(2\pi)$被产生，如果该温度超过哈吉多恩温度，将导致无限的产生率。 取决于哪种正则化机制先发生，在模型的弦相中可能出现不同的宇宙学情景，其中哈勃参数要么渐近地趋近于一个常数值，要么接近最大值后反弹。 显示英文摘要

摘要： Perturbative $\alpha '$ corrections to the low energy string effective action have been recently found to have a potentially regularizing effect on the singularity of the lowest order pre-big-bang solutions. Whether they actually regularize it, however, cannot be determined working at any finite order in a perturbative expansion in powers of the string constant $\alpha '$, because of scheme dependence ambiguities. Physically, these corrections are dominated by the integration over the first few massive string states. Very massive string modes, instead, always have a regularizing effect which is non-perturbative in $\alpha '$ and which basically comes from the fact that in a gravitational field with Hubble constant $H$ they are produced with an effective Hawking temperature $T=H/(2\pi)$, and an infinite production rate would occur if this temperature exceeded the Hagedorn temperature. Depending on which regularizing mechanism takes place first, different cosmological scenarios are possible in the string phase of the model, in which the Hubble parameter either approaches asymptotically a constant value or gets close to a maximum value and then bounces back.