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/P000479/1
• 负责人: Antonio Rago
• 金额: $ 35.97万
• 依托单位: Plymouth 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%2FP000479%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的尺度，即整个宇宙的尺度，与最小的尺度，即基本粒子和弦的尺度联系起来。通过试图了解宇宙在大爆炸后是如何演化的，我们可能会深入了解哪些粒子还没有在欧洲核子研究中心的大型强子对撞机上被发现，反之亦然，这是一个迷人的前景！人们通常认为早期的宇宙经历了一段快速膨胀的时期，也就是所谓的膨胀。通胀背后的机制可以通过多种方式进行研究。在所谓的自下而上方法中，人们的目标是找到与模型细节无关的预测，但只取决于对称性和通胀来源的性质。然后，就有可能提取导致观测预测的普遍特征，并指向我们目前已知的粒子物理和宇宙学标准模型之外的物理学。在互补的自上而下的方法中，一个人从给定的理论开始，例如一个由弦理论驱动的理论，并推导出它的结果，这也可能是可以通过观察来检验的。这些方法还可以用来研究我们的宇宙目前正在经历的宇宙加速周期，即暗能量。弦理论是一种在非常高能量尺度上运行的引力(和其他力)的理论。除了作为基础理论的可能作用外，它还有许多错综复杂的方面，这需要深深植根于对称性和对偶性的理解水平(这种转换导致了两个表面上非常不同但又是等价的“对偶”公式)。通过研究这些，人们不仅可以更好地理解弦理论，而且还可以得出与在大型强子对撞机上探索的超越标准模型(BSM)的物理相关的对偶理论，特别是如果BSM模型是强耦合的。为了对LHC进行预测，有必要在BSM模型和标准模型本身中进行非常精确的计算。其中一些计算可以通过在一个小参数中展开来完成。然而，这并不意味着计算很容易，因为许多散射过程可能起作用。然而，通过重新组织这些贡献，可能会找到一种新的、更有效的公式。当存在不小的参数时，一个理论必须按现状解决。这通常可以通过在时空格子上表述来进行数值尝试。由于这涉及非常多的自由度，通常情况下，人们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)是一种缺少小参数的理论。虽然它是用夸克(作为物质粒子)和胶子(作为力载流子)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很难求解，可能还有其他粒子还没有被探测到，也还没有从理论上理解：例如所谓的胶球和混合介子。通过在晶格上研究QCD，这些想法可以得到定量的检验。一个相关的问题是，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。这也可以用数值方法研究，并观察到在高温下物质的一个新相--夸克-胶子等离子体的转变。由于大型强子对撞机目前正在探索这一阶段，因此也需要对光谱和输运性质(如等离子体的粘性有多大)进行定量预测。一些BSM模型也缺少一个小参数，因此使用类似的格子计算技术进行研究。通过扫描具有不同特征的模型，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

Numerical experiments using deflation with the HISQ action

使用 HISQ 动作进行紧缩的数值实验

• DOI: 10.1051/epjconf/201817514016
• 发表时间: 2018
• 期刊: EPJ Web of Conferences
• 作者: Davies C

Determination of the quark condensate from heavy-light current-current correlators in full lattice QCD

• DOI: 10.1103/physrevd.100.034506
• 发表时间: 2018-11
• 期刊: Physical Review D
• 影响因子: 5
• 作者: C. Davies;K. Hornbostel;J. Komijani;J. Koponen;G. Lepage;A. Lytle;C. McNeile

Approaching the master-field: Hadronic observables in large volumes

• DOI: 10.22323/1.396.0383
• 发表时间: 2021-10
• 期刊: Proceedings of The 38th International Symposium on Lattice Field Theory — PoS(LATTICE2021)
• 作者: M. Cè;M. Bruno;J. Bulava;A. Francis;P. Fritzsch;J. Green;M. Hansen;A. Rago

Ergodicity of the LLR method for the Density of States

状态密度 LLR 方法的遍历性

• DOI: 10.1051/epjconf/201817502005
• 发表时间: 2018
• 期刊: EPJ Web of Conferences
• 作者: Cossu G

Strong-Isospin-Breaking Correction to the Muon Anomalous Magnetic Moment from Lattice QCD at the Physical Point.

物理点晶格 QCD 对 μ 子反常磁矩的强同位旋破缺修正。

• DOI: 10.1103/physrevlett.120.152001
• 发表时间: 2018
• 期刊: Physical review letters
• 影响因子: 8.6
• 作者: Chakraborty B