The Physics of the $\theta$-angle for Composite Extensions of the Standard Model

Understand

We analyse the $\theta$-angle physics associated to extensions of the standard model of particle interactions featuring new strongly coupled sectors.

• We start by providing a pedagogical review of the $\theta$-angle physics for Quantum Chromodynamics (QCD) including also the axion properties.
• We then move to analyse composite extensions of the standard model elucidating the interplay between the new $\theta$-angle with the QCD one.
• We consider first QCD-like dynamics and then generalise it to consider several kinds of new strongly coupled gauge theories with fermions transforming according to different matter representations.