Theory and Phenomenology of Classical Scale Invariance, Dark Matter and Ultralight Axions

Abstract

The Standard Model of particle physics does not provide a complete description of nature, there are many questions that remain unsolved. In this work, we study the theory and phenomenology of different models beyond the Standard Model that address some of its shortcomings. Motivated by naturalness arguments, we discuss the idea of classical scale invariance where all the fundamental scales are generated dynamically via quantum effects. We apply this approach to an extension of the inert doublet model and present a model that addresses the dark matter, neutrino masses and the baryon asymmetry of the Universe simultaneously.

We then study a set of simplified models of dark matter to address the effects of three-point interactions between the dark matter particle, its dark coannihilation partner, and the Standard Model degree of freedom, which we take to be the tau lepton. In these models, the contributions from dark matter coannihilation channels are highly relevant for a determination of the correct relic abundance. Firstly, we investigate these effects as well as the discovery potential for dark matter coannihilation partners at the LHC by searches for long-lived electrically charged particles. Secondly, we study the sensitivity that future linear electron-positron colliders will have to these models for the region in the parameter space where the coannihilation partner decays promptly.

Lastly, we discuss an observable for the detection of ultralight axions. In the presence of an ultralight axion, a cloud of these particles will form surrounding a rotating black hole through the mechanism of superradiance. This inhomogeneous pseudo-scalar field configuration behaves like an optically active medium. Consequently, as light passes through the axion cloud it experiences polarisation-dependent bending, we argue that for some regions in the parameter space of axion-like particles this effect can be observed by current radio telescope arrays.