Aspects of the standard model landscape and post vacuum transition dynamics

The Standard Model (SM) of particle physics coupled to gravity is a phenomenologically successful effective field theory (EFT) with a number of input parameters which are arbitrary - if not severely tuned from an IR perspective - but are presumably fixed by an underlying UV theory. Several open problems guide the pursuit of new physics just beyond its borders which might or might not exist. On the other hand, the SM along with any additions, is expected to be eventually embedded within a framework that includes quantum gravity. How vast is the landscape of effective field theories - the SM one of them - which can be consistently derived therefrom and what conditions establish its boundary is currently unknown and a topic of intense research. The Standard Model landscape is defined as the space of EFTs obtained from the structure of the SM while allowing its input parameters to scan all possible values, and should correspond to exploring our neighbourhood of a supposed UV landscape. In this thesis I review in detail the structure of the SM, and the successful standard cosmological history based on it. I then explore the SM landscape by varying Yukawa couplings, the QCD theta parameter and the Higgs mass squared parameter, focusing on whether the ensuing vacuum potentials admit long-lived meta-stable states with positive vacuum energy, a property which is conjectured to be incompatible with quantum gravity, and thus partially explain the puzzling hierarchies observed. The only known setting to probe the existence of de Sitter meta-stable states is the possibility that during its cosmological history, the universe as a whole was once in a meta-stable state and proceeded to decay through the nucleation of bubbles of true vacuum in a first order phase transition. This can lead to observable signals such as a stochastic gravitational wave background, with a number many dedicated detectors planned to come online over the next decades. Making contact between theoretical predictions and potential signals however requires a better understanding of friction forces acting on the expanding bubbles. In this thesis I highlight the singularly peculiar reflective properties of longitudinally polarised vector particles and discuss their significant source of friction

Black Hole Genesis of Dark Matter

We present a purely gravitational infra-red-calculable production mechanism for dark matter (DM). The source of both the DM relic abundance and the hot Standard Model (SM) plasma is a primordial density of micro black holes (BHs), which evaporate via Hawking emission into both the dark and SM sectors. The mechanism has four qualitatively different regimes depending upon whether the BH evaporation is `fast' or `slow' relative to the initial Hubble rate, and whether the mass of the DM particle is `light' or `heavy' compared to the initial BH temperature. For each of these regimes we calculate the DM yield, $Y$, as a function of the initial state and DM mass and spin. In the `slow' regime $Y$ depends on only the initial BH mass over a wide range of initial conditions, including scenarios where the BHs are a small fraction of the initial energy density. The DM is produced with a highly non-thermal energy spectrum, leading in the `light' DM mass regime ($\sim260\,\mathrm{eV}$ and above depending on DM spin) to a strong constraint from free-streaming, but also possible observational signatures in structure formation in the spin 3/2 and 2 cases. The `heavy' regime ($\sim1.2\times 10^8\,\mathrm{GeV}$ to $M_{\mathrm{Pl}}$ depending on spin) is free of these constraints and provides new possibilities for DM detection. In all cases there is a dark radiation component predicted.Comment: 16 pages, 8 figures. Fixed typos and added reference

Implementation of K-matrix formalism in the D0 -> K_s pi+ pi- amplitude model

This report presents the work of a summer student project aimed at the implementation of a model for the decay amplitude of $D^0 \rightarrow K_S \pi^+ \pi^-$ in the context of investigating mixing and CP violation in the charm sector. The analysis of this decay gives direct axis to the mixing parameters $x$ and $y$ which can be measured by fitting the model constructed to data. Decay dynamics are understood in terms of resonances, which can as a first aproximation be parametrised by Breit-Wigner curves, failing however to always respect unitarity. To avoid this problem the so-called K-matrix formalism with Production vector is implemented by the student as part of an alternative model making use of techniques from scattering theory. The implementation is done in the framework of a fitter written in CUDA designed to run on a GPU

Reflections on bubble walls

Abstract We discuss the dynamics of expanding bubble walls in the presence of massive dark photons whose mass changes as they cross the wall. For sufficiently thin walls, we show that there exists a transient kinematic regime characterized by a constant reflection probability of longitudinal — but not transverse — modes. This effect can have important implications for the dynamics of expanding vacuum bubbles in the early Universe. Most notably, it leads to a new source of pressure on the expanding interface, featuring a non-monotonic dependence on the γ-factor of the bubble walls and reaching a peak at intermediate γ-factors that we dub Maximum Dynamic Pressure. When this pressure is large enough to halt the acceleration of the bubble walls, the difference in vacuum energy densities goes into making a fraction of the dark photons relativistic, turning them into dark radiation. If the dark radiation remains relativistic until late times, an observable contribution to ∆N eff is possible for phase transitions with strength α ∼ 10 −2 − 10 −1