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, Keshab
• 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: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=617921
• 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.

过去几年我在麦吉尔的研究方向一直是强耦合规范理论，一个例子是量子色动力学（QCD）。我特别尝试对这些理论进行一些分析控制。显然，由于强相互作用，标准微扰技术（例如费曼图）对于分析这些理论没有用处。在“颜色”数量N变大的极限下，弦理论领域的新发展表明，这些理论可能存在对偶引力描述，其中所有非微扰物理都可以简单地使用经典超引力技术进行分析！在过去的几年中，我们已经能够纯粹使用超重力技术来开发一个模型，该模型可以在低能和高能下模拟大 N 热 QCD。我们一直在使用这个模型来计算热 QCD 的许多可观测物理现象，即剪切粘度、熵、QGP 相、约束和解约束动力学、夸克元素熔化等。毫无疑问，这些发展是及时的，在接下来的几年里，我想花时间进一步发展这一图景，并将其扩展到彩色超导相。大N热QCD和彩色超导的物理原理有着惊人的相似之处，我们在这里开发的引力描述可能可以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。我认为这是文献中提出的许多其他模型所缺少的一个优点。标准 QCD 的高能行为很简单：它是一个几乎自由的理论。在大颜色极限中，即在大 N 极限中，高能量行为是共形的，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，高能量行为由大半径区域捕获，低能量行为由小半径区域捕获。然而，完整的引力对偶解决方案仍然没有构建出来，我的长期目标之一是完成这幅图画。这项练习在技术上具有挑战性，但我相信，通过我的研究生的努力和帮助，我们应该能够完成对偶描述。一旦对偶描述被提出，分析出 QCD 的各种性质将是非常有趣的，而使用以前的技术是不可能解决这些性质的。我的第二个建议是研究最近引起一些兴趣的宇宙学的某些方面。有一段时间，人们认为只要违反某些禁行条件，弦理论就很容易产生去西特型真空。还提出了一种候选解决方案，该解决方案考虑了各种非微扰效应，这至少为我们提供了一种研究弦理论中的去西特解决方案的方法，尽管没有构建明确的解决方案。然而，最近有人提出了有关这种方法的某些问题。我明年左右的目标之一就是解决这个问题。这是一项技术上具有挑战性的练习，因为弦理论中导致宇宙加速的明确超引力解决方案很难构建。如果成功，这可能是依赖时间的超重力解决方案的第一个重要示例。我的第三个建议是详细阐述最近提出的异质弦理论中的规范/引力对偶性，其中我们给出了规范理论的引力对偶性，其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了解这个理论。最后，我的第四个建议是使用弦理论技术来扩展新发现的共形 Seiberg-Witten 型规范理论。