Particle Physics

The continued lack of definitive signals at direct detection experiments places many models of weakly interacting dark matter into tension. Direct detection is naturally suppressed in models where the dark matter co-annihilates with another particle in the early universe.  The cosmology, direct detection, and LHC signals of such models can often be well understood by considering only the most relevant low-energy degrees of freedom.  We draw lessons for the Minimal Supersymmetric Standard Model.

A new analysis of electron-proton scattering data (those published in 2010 by the Mainz A1 collaboration and previous world compilations) to determine the proton electric and magnetic radii is presented. The analysis enforces model-independent constraints of form factor analyticity and investigates a wide range of possible systematic effects. Employing standard models for radiative corrections, our improved analysis yields proton electric radii for the Mainz and world data sets that are consistent, although a simple combination yields a value r_E = 0.904(15) fm that is 4-sigma larger than the CREMA muonic hydrogen determination. Remaining possible deficiencies are discussed that, if addressed, could reconcile the values from muonic hydrogen spectroscopy and ep-scattering.

Extensions of the Standard Model (SM) Higgs sector often predict the existence of new vacua and can feature novel patterns of symmetry breaking in the early universe. In this talk, I will discuss the implications of such scenarios for electroweak scale cosmology, baryogenesis, and Higgs phenomenology. I will focus on two classes of models, one involving a gauge singlet scalar field and the other an inert SU(2) doublet scalar. The former can give rise to a strong first-order electroweak phase transition, but also to rapidly expanding bubbles which can pose a problem for viable electroweak baryogenesis. In the latter, electroweak symmetry can be spontaneously broken by a first-order phase transition to an exotic vacuum, allowing for successful electroweak baryogenesis decoupled from the Standard Model-like Higgs field. Nevertheless, this class of scenarios generically predicts modifications of the SM-like Higgs couplings within reach of present-day collider experiments.