David E. Morrissey

Baryon destruction by asymmetric dark matter

We investigate new and unusual signals that arise in theories where dark matter is asymmetric and carries a net antibaryon number, as may occur when the dark matter abundance is linked to the baryon abundance. Antibaryonic dark matter can cause induced nucleon decay by annihilating visible baryons through inelastic scattering. These processes lead to an effective nucleon lifetime of 10 29 − 10 32 years in terrestrial nucleon decay experiments, if baryon number transfer between visible and dark sectors arises through new physics at the weak scale. The possibility of induced nucleon decay motivates a novel approach for direct detection of cosmic dark matter in nucleon decay experiments. Monojet searches (and related signatures) at hadron colliders also provide a complementary probe of weak-scale dark-matter–induced baryon number violation. Finally, we discuss the effects of baryon-destroying dark matter on stellar systems and show that it can be consistent with existing observations.

Very Light Scalar Top Quarks at the LHC

A very light scalar top (stop) superpartner is motivated by naturalness and electroweak baryogenesis. When the mass of the stop is less than the sum of the masses of the top quark and the lightest neutralino superpartner, as well as the of the masses of the lightest chargino and the bottom quark, the dominant decay channels of the stop will be three-body, four-body, or flavour violating. In this work, we investigate the direct and indirect constraints on a light stop, we compute the relative decay branching fractions to these channels, and we study the sensitivity of existing LHC searches to each of them.

Electroweak Baryogenesis from Exotic Electroweak Symmetry Breaking

We investigate scenarios in which electroweak baryogenesis can occur during an exotic stage of electroweak symmetry breaking in the early Universe. This transition is driven by the expectation value of a new electroweak scalar instead of the standard Higgs field. A later, second transition then takes the system to the usual electroweak minimum, dominated by the Higgs, while preserving the baryon asymmetry created in the first transition. We discuss the general requirements for such a two-stage electroweak transition to be suitable for electroweak baryogenesis and present a toy model that illustrates the necessary ingredients. We then apply these results to construct an explicit realization of this scenario within the inert two Higgs doublet model. Despite decoupling the Higgs from the symmetry-breaking transition required for electroweak baryogenesis, we find that this picture generically predicts new light states that are accessible experimentally.

Modified Higgs boson phenomenology from gauge or gaugino mediation in the next-to-minimal supersymmetric standard model

In the Next-to-Minimal Supersymmetric Standard Model (NMSSM), the presence of light pseudoscalars can have a dramatic effect on the decays of the Standard Modellike Higgs boson. These pseudoscalars are naturally light if supersymmetry breaking preserves an approximate U(1)R symmetry, spontaneously broken when the Higgs bosons take on their expectation values. We investigate two classes of theories that possess such an approximate U(1)R at the mediation scale: deformations of gauge and gaugino mediation. In the models we consider, we find two disjoint classes of phenomenologically allowed parameter regions. One of these regions corresponds to a limit where the singlet of the NMSSM largely decouples. The other can give rise to a Standard Model-like Higgs boson with a dominant branching into light pseudoscalars.

Tension between gauge coupling unification, the Higgs boson mass, and a gauge-breaking origin of the supersymmetric μ-term

We investigate the possibility of generating the

Changes in dark matter properties after freeze-out

\ensuremath{\mu}

Connecting (supersymmetry) CERN LHC measurements with high scale theories

-term in the minimal supersymmetric standard model (MSSM) by the condensation of a field that is a singlet under the standard model (SM) gauge group but charged under an additional family-independent

Confronting the moduli-induced lightest-superpartner problem

U(1{)}_{X}

Compressing the Inert Doublet Model

gauge symmetry. We attempt to do so while preserving the gauge coupling unification of the MSSM. For this, we find that SM nonsinglet exotics must be present in the spectrum. We also prove that the pure

Light axial vector bosons, nuclear transitions, and the

U(1{)}_{X}