Dynamical electroweak symmetry breaking by quasiconformal technicolour theories

Abstract

In technicolour (TC) theories, the electroweak (EW) symmetry is broken by chiral symmetry breaking (χSB) in an additional strongly interacting sector, added to the standard model (SM) without elementary Higgs sector. Quasiconformal, that is, walking technicolour (WTC) models with matter in higher representations of the technicolour gauge group are viable candidates for breaking the electroweak symmetry dynamically. They are not at odds with available electroweak precision data. Here, we start with a brief introduction into dynamical electroweak symmetry breaking by technicolour theories. Subsequently, we discuss the phase diagram of strongly interacting theories in the Nc-N f -plane or, equivalently, the dR-N f -plane, where Nc stands for the number of colours, N f for the number of flavours, and dR for the dimension of the representation; and how to relate said phase diagram to the task of finding candidates for quasiconformal technicolour models. Continuing from there, we select the prime candidates [among them Minimal Walking Technicolour (MWT)] by using constraints from available electroweak precision data like, for example, bounds on flavour changing neutral currents (FCNCs), oblique parameters and the masses mπ of extra Nambu–Goldstone modes. The latter issue is also linked to the stability of the vacuum. We discuss the features of selected candidates in more detail. Their signals can be detected at the LHC, they feature dark matter (DM) candidates, and they are being studied actively with lattice computations, nonperturbative β -function techniques as well as AdS/CFT methods.