Fields, Strings and Lattices: From the Inflationary Universe to High-Energy Colliders

场、弦和晶格：从暴胀宇宙到高能对撞机

• 批准号: ST/P00055X/1
• 负责人: Gert Aarts
• 金额: $ 126.78万
• 依托单位: Swansea University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FP00055X%2F1
• 关键词: Fields; Strings; Lattices; Inflationary; Universe

Research in particle physics and cosmology connects the largest scales, those of the Universe as a whole, with the smallest, namely those of fundamental particles and strings. By trying to understand how the Universe evolved after the Big Bang, we may gain insight into which particles are yet to be discovered at e.g. the Large Hadron Collider at CERN, and vice versa, a fascinating prospect!It is commonly assumed that the early Universe went through a period of rapid expansion, dubbed inflation. The mechanisms underlying inflation can be investigated in a number of ways. In the so-called bottom-up approach, one aims to find predictions that are independent of details of models, but only depend on symmetries and the nature of the source of inflation. It is then possible to extract universal features leading to observational predictions and point towards physics beyond our currently known Standard Models of Particle Physics and Cosmology. In the complementary top-down approach, one starts with the given theory, e.g. one that is motivated by string theory, and derives its consequences, which, again might be testable by observations. These approaches can also be used to study the period of cosmic acceleration our Universe is currently going through, i.e. dark energy.String theory is a theory of gravity (and other forces) operating at very high-energy scales. Besides its possible role as a fundamental theory, it has many intricate aspects which require a level of understanding deeply rooted in symmetries and dualities (a transformation that leads to two 'dual' formulations which are superficially very different but yet equivalent). By studying those, one may not only understand string theory better, but also arrive at dual theories which are relevant for e.g. physics beyond the Standard Model (BSM) probed at the LHC, especially if the BSM model is strongly coupled.In order to make predictions for the LHC, it is necessary to perform very precise calculations, in BSM models and in the Standard Model itself. Some of these calculations can be done by expanding in a small parameter. This does not mean that the computation is easy though, since many scattering processes may contribute. However, it might be that by re-organising these contributions a new, more efficient, formulation can be found.When there is no small parameter, a theory has to be solved as it stands. Often this can be attempted numerically, by formulating it on a space-time lattice. Since this involves very many degrees of freedom, typically one has to employ the largest supercomputers in the world. The theory of the strong interaction, Quantum Chromodynamics (QCD), is one of those theories in which a small parameter is absent. Although it is formulated in the terms of quarks (as matter particles) and gluons (as force carriers), these are not the particles that appear in the spectrum, which are instead protons, neutrons, pions etc. However, since QCD is so hard to solve, there may be other particles not yet detected and also not yet understood theoretically: examples are so-called glueballs and hybrid mesons. By studying QCD on the lattice, these ideas can be tested quantitatively.A related question concerns what happens with all these particles when the temperature (as in the early Universe) or the matter density (as in neutron stars) is increased. Also this can be studied numerically and a transition to a new phase of matter at high temperature, the quark-gluon plasma, has been observed. Since this phase is currently being explored at the LHC, by colliding heavy ions, quantitative predictions on the spectrum and on transport properties, such as how viscous the plasma is, are needed here as well. Some BSM models also lack a small parameter and hence are studied using similar lattice computing techniques. By scanning models with distinct features, again hints for the LHC may be found, e.g. with regard to unusual spectral features.

粒子物理学和宇宙学的研究将最大尺度（整个宇宙）与最小尺度（即基本粒子和弦）联系起来。通过尝试了解大爆炸后宇宙如何演化，我们可以深入了解哪些粒子尚未被发现，例如在宇宙中。欧洲核子研究中心的大型强子对撞机，反之亦然，这是一个令人着迷的前景！人们普遍认为早期宇宙经历了一个快速膨胀的时期，称为通货膨胀。通货膨胀的潜在机制可以通过多种方式进行研究。在所谓的自下而上的方法中，人们的目标是找到独立于模型细节的预测，但仅取决于对称性和通货膨胀来源的性质。然后就可以提取导致观测预测的通用特征，并指向超出我们当前已知的粒子物理和宇宙学标准模型的物理。在互补的自上而下的方法中，人们从给定的理论开始，例如一种由弦理论激发的理论，并得出其结果，这又可以通过观察来检验。这些方法还可以用于研究宇宙目前正在经历的宇宙加速时期，即暗能量。弦理论是一种在非常高能量尺度上运行的重力（和其他力）理论。除了作为基础理论的可能作用之外，它还有许多复杂的方面，需要对对称性和对偶性有深刻的理解（这种转变导致两种表面上非常不同但实际上等效的“对偶”公式）。通过研究这些，人们不仅可以更好地理解弦理论，而且还可以得出与例如弦理论相关的对偶理论。 LHC 探测到的标准模型 (BSM) 之外的物理学，特别是当 BSM 模型强耦合时。为了对 LHC 进行预测，有必要在 BSM 模型和标准模型本身中执行非常精确的计算。其中一些计算可以通过扩展一个小参数来完成。但这并不意味着计算很容易，因为许多散射过程可能有所贡献。然而，通过重新组织这些贡献，可能会找到一个新的、更有效的公式。当没有小参数时，必须按原样解决理论。通常这可以通过在时空晶格上表达来进行数值尝试。由于这涉及很多自由度，因此通常必须使用世界上最大的超级计算机。强相互作用理论，量子色动力学（QCD），是不存在小参数的理论之一。虽然它是用夸克（作为物质粒子）和胶子（作为力载体）来表述的，但这些并不是出现在光谱中的粒子，而是质子、中子、介子等。然而，由于 QCD 太难了为了解决这个问题，可能还有其他粒子尚未被检测到，理论上也尚未被理解：例如所谓的胶球和混合介子。通过研究晶格上的 QCD，可以定量地检验这些想法。一个相关的问题涉及当温度（如早期宇宙）或物质密度（如中子星）增加时所有这些粒子会发生什么。这也可以进行数值研究，并且已经观察到在高温下物质向新相（夸克-胶子等离子体）的转变。由于大型强子对撞机目前正在通过碰撞重离子来探索这一阶段，因此这里也需要对光谱和传输特性（例如等离子体的粘度）进行定量预测。一些 BSM 模型也缺少小参数，因此使用类似的格计算技术进行研究。通过扫描具有独特特征的模型，可以再次找到大型强子对撞机的线索，例如关于不寻常的光谱特征。

项目成果

Medium effects and parity doubling of hyperons across the deconfinement phase transition

超子在解禁相变过程中的中等效应和宇称倍增

• DOI: 10.1051/epjconf/201817507016
• 发表时间: 2018
• 期刊: EPJ Web of Conferences
• 作者: Aarts G

Mesonic correlators at non-zero baryon chemical potential

非零重子化学势的介子相关器

• DOI: 10.48550/arxiv.2001.04415
• 发表时间: 2020
• 作者: Aarts G

Heavy-flavor production and medium properties in high-energy nuclear collisions --What next?

• DOI: 10.1140/epja/i2017-12282-9
• 发表时间: 2016-12
• 期刊: The European Physical Journal A
• 作者: G. Aarts;J. Aichelin;C. Allton;R. Arnaldi;S. Bass;C. Bedda;N. Brambilla;E. Bratkovskaya

Lattice QCD at nonzero temperature and density

• DOI: 10.1088/1742-6596/2207/1/012055
• 发表时间: 2021-11
• 期刊: Journal of Physics: Conference Series
• 作者: G. Aarts;C. Allton;S. Hands;B. Jäger;S. Kim;M. Lombardo;A. Nikolaev;S. Ryan;J. Skullerud

Parity doubling of nucléons, Delta and Omega baryons across the deconfinement phase transition

核子、Delta 和 Omega 重子在解禁闭相变过程中宇称倍增

• DOI: 10.1051/epjconf/201713707004
• 发表时间: 2017
• 期刊: EPJ Web of Conferences
• 作者: Aarts G