Composite Higgs Models from Gauge/Gravity Duality

2012年，大型强子对撞机发现了希格斯玻色子，这无疑是几十年来基础物理学研究的顶峰，也是粒子物理学标准模型的一个成功故事。然而，目前尚不清楚为什么这种粒子相对较轻，以及它的潜在形式是否在《自然》中实现。复合希格斯模型提供了希格斯玻色子作为伪南布-戈德斯通玻色子的动力学解释。其基本机制类似于低能QCD中的手性对称破缺。由于潜在的强相互作用，质谱的预测是困难的。近年来，基于规范/重力对偶的全息方法在这个方向上取得了巨大的进展。这既包括自下而上的全息方法，涉及双五维重力作用，也包括自上而下的方法，在十维弦理论中实现。后者包括例如基于D3/ d7膜系统的模型，其中全局U(1)轴对称被自发破坏。在这两种方法中，全息介子质谱与实验数据吻合较好。此外，在复合希格斯模型中，使用这些方法进行质量比预测的初步结果与晶格计算存在的模型很好地吻合。最近，我们建立了新的全息复合希格斯模型——包括自底向上和自顶向下——包括高维算子，提供了“部分复合”概念的全息实现。这些模型允许汤川耦合和顶夸克混合的计算。我们的全息自底向上和自顶向下模型需要进一步扩展，因为它们是基于U(1)全局对称群，而不是QCD和现实复合希格斯模型所需要的非阿贝尔群。这个项目的目标是通过将非阿贝尔全局对称性纳入我们的模型来克服这一限制。通过这种方式，我们期望一方面解释QCD中观测到的f0和a0介子质量之间的质量差。另一方面，我们的目标是改进复合希格斯模型的预测，最终可以用作对撞机研究的输入。为此，我们将使用自上而下和自下而上的全息模型。

The discovery of the Higgs boson at the LHC in 2012 has certainly been the crowning of many decades of research in fundamental physics and a success story for the Standard Model of particle physics. However, it is not known why this particle is relatively light and if the proposed form of its potential is the one realized in Nature. Composite Higgs models offer a dynamical explanation of the Higgs boson as a pseudo Nambu-Goldstone-boson. The basic mechanism is similar to chiral symmetry breaking in low-energy QCD. Predictions for the mass spectrum are difficult due to the underlying strong interactions. In recent years, holographic approaches based on gauge/gravity duality have generated huge progress in this direction. This includes both bottom-up holographic approaches involving dual five-dimensional gravity actions as well as top-down ones realized in ten-dimensional string theory. The latter include for instance models based D3/D7-brane systems in which a glocal U(1) axial symmetry is spontaneously broken. In both approaches, the holographic meson mass spectra show good agreement with experimental data. Moreover within composite Higgs models, first results using these methods for mass ratio predictions give good agreement with the models for which lattice calculations exist. Recently, we have established new holographic Composite Higgs models - both bottom-up and top down - that include higher-dimensional operators, providing a holographic realisation of the concept of `partial compositeness'. These models allow for a calculation of Yukawa couplings and top quark mixing. Our holographic bottom-up and top-down models require further extension though since they are based on a U(1) global symmetry group instead of non-abelian groups needed for both QCD as well as realistic composite Higgs models. It is the aim of this project to overcome this limitation by including non-abelian global symmetries into our models. In this way we expect to explain on the one hand the observed mass difference between the f0 and a0 meson masses in QCD. On the other hand we aim for improved predictions for composite Higgs models which can eventually be used as input for collider studies. For this we will work with both top-down and bottom-up holographic models.