The long-lived stau as a thermal relic

The results presented in this thesis have in part already been published in Refs. [1, 2, 3, 4, 5] listed overleaf (page v). We consider physics beyond the Standard Model which implies the existence a of long-lived electromagnetically charged massive particle species (CHAMP) which we denote by X ±. We discuss in detail the unique sensitivity the early Universe exhibits on the mere presence and on the decay of such a particle. A CHAMP can be realized in supersymmetric (SUSY) extensions of the Standard Model. We carry out a detailed study of gravitino (G) dark matter scenarios in which the lighter scalar tau (stau, τ 1) is the lightest Standard Model superpartner so that τ 1 = X. We also provide a thorough investigation of the thermal freeze-out process of τ 1. The thesis is divided into three parts: Part I: In this part we consider a generic but weak-scale CHAMP. In Chapter 1 we set the stage for the coming investigations by shortly reviewing the framework of Big Bang Nucleosynthesis (BBN), by working out the typical CHAMP freeze-out abundance, and by reviewing the stringent constraints arising from such a decaying component during/after BBN. We also take a critical look at the BBN constraints arising from the hadronic decay modes of an arbitrary exotic. In particular, we develop on a refined treatment of the Coulomb stopping mechanism of charged hadrons. In Chapter 2 we discuss the physics which emerges when the light elements fused in BBN are captured by X − at the time of primordial nucleosynthesis. Since the associated, most striking effects were only discovered recently, we provide a detailed exposition of the topic. In particular, we explicitly show how to obtain the rates for bound state formation which carry a finite charge radius correction of the nucleus. In the remainder of this chapter, which is based on [4], we focus on the catalytic production of 6 Li and 9 Be. There, we also discuss the issue of a potential late-time catalysis due to proton-CHAMP bound states. Upon solution of the full set of Boltzmann equations we obtain stringent constraints on the primordial presence of long-lived X − from overproduction of 6 Li. Moreover, setting an upper limit on the abundance of primordial 9 Be allows us iii iv to constrain this scenario also from catalytic 9 Be production. Part II: The second part is devoted to scenarios in …