String theory, hight emperature QCD and inflationary cosmology

在我最后的拨款申请中，我总结了我在两个基本研究领域的工作：弦宇宙学和通量紧化。我继续研究这两个主题，并且也开始使用弦理论的工具研究热场理论，如高温量子光盘等。由于弦理论的一些有趣的输入，高温QCD领域最近变得非常活跃。弦理论预测，某些规范理论可以在双重力背景下研究，这些规范理论的所有计算在重力理论中都有一对一的对应关系。这将特别意味着，规范理论的某些非平凡计算（这些计算被认为是不可能用传统技术完成的）现在可以很容易地使用这种新的对偶性来完成。利用这些技术，一年前人们发现，任何热流体的粘度与其熵的比值都不可能小于某一数值。这是一个非常令人惊讶的结论，直接从弦理论方法中得出（使用常规规范理论技术很难预测这一点）。然而问题是这个“边界”是否稳健。我们最近发现，可以通过结合弦理论修正来降低预测界限。然而，分析是高度复杂的，需要时间和少数研究生的努力才能完全解决这个问题。如果我们能在这里找到一个新的界限，那将是非常有趣的，因为这将是弦理论在现实世界中的第一个具体预测。

In my last grant proposal I summarised my works on two basic areas of research: string cosmology and flux compactifications. I have continued on these two topics, and have also started working on thermal field theories like high temperature QCD etc using tools of string theory. The field of high temperature QCD has recently become very active due to some interesting inputs from string theory. String theory predicts that certain gauge theories could be studied from dual gravity backgrounds where all calculations of these gauge theories have one-to-one correspondences in the gravity theories. This would mean, in particular, that certain non-trivial calculations of gauge theories (that were thought to be rather impossible to do using conventional techniques) could now be easily performed using this new duality. Using these techniques, a year ago it was found that the ratio of the viscosity of any thermal fluid to its entropy cannot be smaller than a certain number. This was a very surprising conclusion that came out directly from applying string theory methods (its difficult to predict this using conventional gauge theory techniques). Question however is whether this "bound" is robust. We have recently found that the predicted bound could be lowered by incorporating string theory corrections. However the analysis is highly involved and would require time and the efforts of few graduate students to work this out completely. It will be really fascinating if we could find a new bound here, as this would be the first concrete prediction of string theory for the real world.