EW Precision Tests

The composite Higgs dynamics gives rise to a rich set of new-physics effects that can be used to probe this scenario through a comparison with the experimental data. One of the most distinctive phenomena is the presence of composite resonances around the TeV scale, which can be straightforwardly tested in collider experiments. A second important signature is the peculiar pattern of distortions of the Higgs couplings, which constitutes a direct manifestation of the non-linear Nambu–Goldstone structure. In addition to these features, the composite dynamics gives also rise to many indirect effects. These noticeably include a set of corrections to the Electro-Weak (EW) observables that describe the physics of the light Standard Model (SM) fermions and of the gauge fields. The importance of these observables comes from the fact that they can be measured in high-precision experiments and thus can be used to test even tiny corrections coming from a new-physics dynamics. Obvious examples are the Z-pole observables measured at the LEP experiment and the properties of the bottom quark easily accessible at b-factories. All these measurements agree with the SM and have been extensively used to set stringent constraints on beyond the Standard Model (BSM) scenarios. They constitute the so-called EW Precision Tests (EWPT) of the SM.