High Energy Physics

I will discuss cosmological, astrophysical and collider constraints on thermal dark matter with mass in the range 1 MeV to 10 GeV. CMB observations can be evaded if the DM relic density is sufficiently asymmetric, while collider constraints generally require sufficiently light mediators. These light mediators can give rise to significant DM self-interactions, and I will describe bounds on such interactions from dark matter halo shapes. Finally, I will describe how these constraints map onto the parameter space of DM-electron and DM-nucleon scattering cross sections for direct detection.

We propose that the fermionic superpartner of a weak-scale Goldstone boson can be a nat- ural WIMP candidate. The p-wave annihilation of this `Goldstone fermion' into pairs of Gold- stone bosons automatically generates the correct relic abundance, whereas the XENON100 direct detection bounds are evaded due to suppressed couplings to the Standard Model. Further, it is able to avoid indirect detection constraints because the relevant s-wave annihi- lations are small. The interactions of the Goldstone supermultiplet can induce non-standard Higgs decays and novel collider phenomenology.

We show that a baryon asymmetry can be generated by dissipative effects during warm inflation via a supersymmetric two-stage mechanism, where the inflaton is coupled to heavy mediator fields that then decay into light species through B- and CP-violating interactions. In contrast with thermal GUT baryogenesis models, the temperature during inflation is always below the heavy mass threshold, simultaneously suppressing thermal and quantum corrections to the inflaton potential and the production of dangerous GUT relics. This naturally gives a small baryon asymmetry close to the observed value, although parametrically larger values may be diluted after inflation along with any gravitino overabundance. Furthermore, this process yields baryon isocurvature perturbations within the range of future experiments, making this an attractive and testable model of GUT baryogenesis.

What is everything in the universe made of? What was the universe like billions of years ago? These are eternal questions that humans have pondered throughout the ages. Today, we are on the verge of potentially making revolutionary breakthroughs in answering them. The Large Hadron Collider (LHC) at CERN is a 27-kilometre long underground experiment located on the Swiss-French border near Geneva. It smashes subatomic particles together at vast speeds in an effort to learn more about the fundamental building blocks that make up everything around you. It is the biggest, most ambitious scientific experiment in human history. On December 13, the LHC announced the latest findings in its search for the last undiscovered particle in our current model of subatomic particles. This particle is the near-mythical 'Higgs Boson' — the particle thought to be involved in giving other particles their mass. This educational event, geared towards high school students, teachers and the general public, followed CERN's announcement and discussed its findings and implications in clear, accessible language. Host Damian Pope and PI Researchers Natalia Toro, Philip Schuster, and experimental particle physicist Andy Haas of New York University participate in an informative and interactive discussion.

Both Tevatron experiments have recently reported an anomalous forward-backward asymmetry in top-antitop production. Their inclusive results are roughly 3 standard deviations larger than the standard model prediction and may be evidence of new physics that couples to the top quark. In this talk, I will present a weakly-coupled light axigluon model (< Mtop) with flavor universal couplings as a possible explanation. Surprisingly,a particle with these properties can generate a large ttbar asymmetry with model-parameters safe from dijet resonance searches, flavor changing neutral currents, and constraints from the Z pole.