Composite Higgs Models from Gauge/Gravity Duality

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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.