Abstract
We analyse the interplay of the constraints imposed on flavour-symmetric Composite Higgs models by Naturalness considerations and the constraints derived from Flavour Physics and Electroweak Precision Tests. Our analysis is based on the Effective Field Theory which describes the Higgs as a pseudo-Nambu-Goldstone boson and also includes the composite fermionic resonances. Within this approach one is able to identify the directions in the parameter space where the $U(3)$-symmetric flavour models can pass the current experimental constraints, without conflicting with the light Higgs mass. We also derive the general features of the $U(2)$-symmetric models required by the experimental bounds, in case of elementary and totally composite $t_R$. An effect in the $Z \bar b b$ coupling, which can potentially allow for sizable deviations in $Z \to \bar b b$ decay parameters without modifying flavour physics observables, is identified. We also present an analysis of the mixed scenario, where the top quark mass is generated due to Partial Compositeness while the light quark masses are Technicolor-like.
Highlights
SM-neutral states [18,19,20,21], one can expect a large number of new physics signatures related to the direct production at the LHC [22, 23], as well as to the indirect new physics probes, such as flavour and electroweak precision tests (EWPT) observables
We analyse the interplay of the constraints imposed on flavour-symmetric Composite Higgs models by Naturalness considerations and the constraints derived from Flavour Physics and Electroweak Precision Tests
The main goal of this work is to consider the constraints imposed on Composite Higgs models with light composite colored fermions by flavour and electroweak precision tests (EWPT), and in particular to test the viability of different flavour patterns
Summary
The CH models under consideration can be seen as consisting of two sectors. The first one is the composite sector, containing the composite Higgs boson and other composite resonances. The second sector of the model contains the elementary copies of all SM states except for the Higgs (and optionally for the right-handed top quark) transforming under the SM gauge symmetry group GSM ⊂ G This elementary sector does not respect the full global symmetry G, so once the two sectors are coupled, the one-loop effective potential generated by the elementary-composite interactions allows the Higgs to have a mass and fixes its vacuum expectation value (VEV) in a GSM-breaking direction. The most appealing way to break the Goldstone symmetry, generate the Higgs mass and the top quark mass without introducing too large flavour-violating effects is provided by the mechanism of partial compositeness This mechanism postulates that the UV Lagrangian above the G symmetry breaking scale contains linear couplings between elementary fermions q and strong sector operators. We will first discuss the PNGB Higgs alone, add a detailed description of the top quark sector, and eventually extend our framework to the first two families of quarks
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