Cosmological Experiments in He3 - He4 Mixtures

He3 - He4 混合物的宇宙学实验

• 批准号: 9800748
• 负责人: Norbert Mulders
• 金额: $ 38.85万
• 依托单位: University of Delaware
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-03-01 至 2003-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9800748&HistoricalAwards=false
• 关键词: Cosmological; Experiments; He3; He4; Mixtures

Cosmological phase transitions can be a copious source of topological defects. The same happens in condensed matter systems, and experiments on these systems can help in determining the mechanism for defect formation. The similarities between the superfluid transitions in liquid helium and cosmological models containing topological defects is especially strong. As a result, in recent years there has been considerable activity to simulate phase transitions of the early universe using liquid He-3 and He-4.Previous experiments in both He-3 and He-4 have shown that defects, in this case vortices, are indeed created, and that the vortex line density is consistent with estimates based on the mechanism proposed by Zurek, now known as the Kibble-Zurek (K-Z) mechanism. This mechanism makes specific predictions about the scaling of the vortex line density with a) the rate at which the transition takes place and b) the amplitude of the correlation length of the order parameter. In earlier experiments there was little control over the former, while the latter, determined solely by the fluid, could not be changed appreciably either. Prof. Mulder's group will carry out a new experiment, operating close to the tricritical point in He-3 and He-4 mixtures, will have the ability to change both over a wide range. This should result in a definitive test of the K-Z mechanism.This project is jointly supported by the Division of Physics, the Division of Materials Research and the MPS Office of Multidisciplinary Activities.

宇宙学相变可能是拓扑缺陷的丰富来源。同样的情况也发生在凝聚态系统中，对这些系统进行实验可以帮助确定缺陷形成的机制。液氦中的超流体跃迁与包含拓扑缺陷的宇宙学模型之间的相似性特别强。因此，近年来，利用液态氦-3和氦-4模拟早期宇宙相变的活动相当活跃。先前在He-3和He-4上进行的实验表明，缺陷（在这种情况下是漩涡）确实产生了，而且漩涡线密度与基于Zurek提出的机制（现在被称为Kibble-Zurek （K-Z）机制）的估计一致。该机制对旋涡线密度的标度进行了具体的预测：a)跃迁发生的速率和b)阶参数相关长度的振幅。在早期的实验中，前者几乎无法控制，而后者完全由流体决定，也无法明显改变。Mulder教授的团队将进行一项新的实验，在He-3和He-4混合物的三临界点附近操作，将有能力在很大范围内改变两者。这将导致对K-Z机制的明确测试。该项目由物理部、材料研究部和MPS多学科活动办公室共同支持。