Solving thermal QCD using string theory techniques

使用弦理论技术求解热 QCD

• 批准号: SAPIN-2014-00025
• 负责人: Dasgupta, Keshav
• 金额: $ 3.57万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=648685
• 关键词: Solving; thermal; QCD; using; string

My research directions at McGill in the last few years have been along strongly coupled gauge theories, an example being Quantum Chromodynamics (QCD). In particular I have attempted to have some analytical control over these theories. Clearly standard perturbative techniques, like Feynman diagrams, are not useful to analyze these theories because of strong interactions. In the limit where the number of "colors" N is made large, a new development in the field of string theory has shown that there could be a dual gravitational description of these theories wherein all the non-perturbative physics can be analyzed simply using classical supergravity techniques! In the past few years we have been able to develop a model purely using supergravity techniques that mimic large N thermal QCD both at low and high energies. We have been using this model to compute many observable physics of thermal QCD, namely shear viscosity, entropy, QGP phase, confinement and deconfinement dynamics, quarkonium melting etc. These developments are timely no doubt and for the next few years I want to devote my time to develop the picture further and extend this to the color superconductivity phase. The physics of large N thermal QCD and color superconductivity have amazing similarities, and the gravitational description that we have developed here could probably be used to study this further. Additionally, the model that we have developed behave well at high energies too. This is one advantage that I believe is missing in many of the other models proposed in the literature. The high energy behavior of standard QCD is simple: it is an almost free theory. In the large color limit i.e in the large N limit, the high energy behavior is conformal or alternatively, scale-invariant. This is exactly how our model behaves at high energies. In the gravitational dual, the high energy behavior is captured by the regions at large radius and the low energy behavior is captured by the regions at small radius. However the full gravitational dual solution is still not been constructed, and one of my long term aim would be to complete this picture. The exercise is technically challenging, but I believe that with efforts and with the help of my graduate students, we should be able to complete the dual description. Once the dual description is laid out, it will be very interesting to work out analytically the various properties of QCD which were impossible to solve using previous techniques. My second proposal is to work on certain aspects of cosmology that has recently generated some interest. For sometime it was thought that string theory would easily generate de-Sitter type vacua provided certain no-go conditions were violated. A candidate solution was also proposed that took into account various non-perturbative effects that gave us a way at least to study de-Sitter solutions in string theory, although no explicit solutions were constructed. However, recently, certain issues were raised regarding this approach. One of my aim for next year or so would be to resolve this issue. This is a technically challenging exercise as explicit supergravity solutions in string theory that give rise to accelerating universe is very hard to construct. If successful, this would probably be the first non-trivial example of a time-dependent supergravity solution. My third proposal would be to elaborate on the recently proposed gauge/gravity duality in heterotic string theory wherein we gave the gravity dual for a gauge theory whose field theory description was completely mysterious. My aim would be to learn about this theory using our proposed dual. Finally, my fourth proposal would be to extend the newly found conformal Seiberg-Witten type gauge theories using techniques of string theory.

我的研究方向在麦吉尔在过去几年一直沿着强耦合规范理论，一个例子是量子色动力学（QCD）。特别是，我试图对这些理论进行一些分析控制。显然，标准的微扰技术，如费曼图，对分析这些理论是没有用的，因为强相互作用。在“色”数N变大的极限中，弦论领域的一个新发展表明，这些理论可能有一个对偶引力描述，其中所有的非微扰物理都可以简单地用经典超引力技术来分析！在过去的几年里，我们已经能够开发一个模型，纯粹使用超引力技术，模拟大N热QCD在低能量和高能量。我们一直在使用这个模型来计算许多可观察到的物理热QCD，即剪切粘度，熵，QGP阶段，禁闭和解除禁闭动力学，夸克偶素熔化等这些发展是及时的，毫无疑问，在未来几年里，我想把我的时间来进一步发展的图片，并将其扩展到颜色超导相。大N热QCD和色超导的物理学具有惊人的相似性，我们在这里开发的引力描述可能会被用来进一步研究这一点。此外，我们开发的模型在高能量下也表现良好。这是我认为在文献中提出的许多其他模型中所缺少的一个优点。标准QCD的高能行为很简单：它是一个几乎自由的理论。在大色限即大N极限中，高能行为是共形的，或者是尺度不变的。这正是我们的模型在高能量下的表现。在引力对偶中，高能行为被大半径区域捕获，低能行为被小半径区域捕获。然而，完整的引力对偶解还没有构造出来，我的长期目标之一就是完成这幅图。这项工作在技术上是具有挑战性的，但我相信，通过努力和我的研究生的帮助下，我们应该能够完成双重描述。一旦对偶描述被安排好，用分析方法计算出QCD的各种性质将是非常有趣的，这些性质是用以前的技术无法解决的。我的第二个建议是研究宇宙学的某些方面，这些方面最近引起了一些兴趣。有一段时间，人们认为只要违反了某些不允许的条件，弦理论就能轻易地产生德西特型真空。一个候选的解决方案也被提出，考虑到各种非微扰效应，至少给了我们一种方法来研究弦理论中的de-Sitter解决方案，虽然没有明确的解决方案被构造。然而，最近有人就这一办法提出了一些问题。我明年左右的目标之一是解决这个问题。这是一个技术上具有挑战性的练习，因为在弦理论中，产生加速宇宙的显式超引力解是很难构造的。如果成功的话，这可能是第一个非平凡的与时间相关的超引力解的例子。我的第三个建议是详细阐述最近提出的杂化弦理论中的规范/引力对偶，其中我们给出了一个规范理论的引力对偶，而这个规范理论的场论描述是完全神秘的。我的目标是使用我们提出的对偶来学习这个理论。最后，我的第四个建议是用弦理论的技巧来扩展新发现的共形塞伯格-威滕型规范理论。