## Unveiling Composite Dynamics

Who: Kasper Langæble (CP3-Origins)
When: Monday, August 15, 2016

In this thesis we investigate the phenomenological viability of a recently proposed class of composite Dark Matter (DM) models where the relic density is determined by $$3\to2$$ number-changing processes in the dark sector. Here the dark pions of the strongly interacting field theory constitute the DM particles.
In order to do so, we first briefly review the current description of Nature and how composite states of the known fundamental forces are essential to our understanding of Nature. In particular, this leads us to the theory of quantum chromodynamics (QCD), which at low energy describes the proton and the neutron in terms of the elementary particles, the quarks and the gluons. A successful method for describing low energy QCD is Chiral Perturbation Theory ($\chi$PT), which is derived from the spontaneously broken symmetries of QCD. Therefore we present the global symmetries of QCD in the chiral limit, and the concept of spontaneous symmetry breaking, before introducing the approach of $$\chi$$PT in a general setting that describes any pattern of chiral symmetry breaking.
In the published paper, we perform a consistent next-to-leading and next-to-next-to-leading order investigation using $$\chi$$PT of The SIMPlest Miracle. Our work demonstrates that a leading order analysis cannot be used to draw conclusions about the feasibility of the model. We further show that higher order corrections substantially increase the tension with phenomenological constraints challenging the viability of the simplest realization of the SIMP paradigm.