Particle Physics

No known astrophysical mechanisms are expected to generate a significant high-energy flux of cosmic-ray electrons and positrons (CREs) from the Sun. However, some recently considered classes of dark matter models predict such a signal. We analyzed the CRE events collected by the Fermi-LAT during its first year of operation to search for a flux excess correlated with the Sun's direction, and found no evidence of a significant signal. I will discuss the constraints these results place on secluded dark matter models and inelastic dark matter models.

One of the most exciting, albeit slightly speculative, components of the Fermi mission is to search for evidence of energetic events related to dark matter decay or annihilation. The best targets for this search a regions where we suspect there is dark matter, but see few conventional gamma-ray sources such as molecular clouds, cosmic ray sources, or compact objects. Much emphasis has been placed on local dwarf satellites in particular, since many of these systems show evidence for relatively deep potential wells, but have few stars and no recent star formation. In this talk I will propose another possible target for indirect dark matter searches, among our nearby galactic neighbours.

The existence of dark matter is hardly in doubt, yet astrophysicists continue to search in vain for any non-gravitational signals of it. In the case of weakly interacting massive particle (WIMP) models, ongoing annihilation or decay of WIMPs to Standard Model particles could provide observable signals, e.g. as excess gamma rays in the center of the Milky Way or as excess ionization at high redshift. I will present our latest results on the most rigorous constraint from astrophysics: the effect of WIMP annihilation on the ionization history of the Universe, as recorded in the CMB.

A wide range of results have led to a confusing situation in the area of direct WIMP detection. I'll review the status of these results. The features of the results imply that almost any explanation will require a departure from standard assumptions (Maxwellian halo, elastic WIMP scattering or otherwise) so I'll review the techniques to compare experiments without appealing to these assumptions. In particular, I'll comment on the status of light WIMPs and the iodine interpretations of DAMA (such as inelastic dark matter) in light of the most recent results.

The world's most ambitious scientific experiment is buried 100 meters underground, straddling Switzerland and France. A billion times every minute, the Large Hadron Collider (LHC) slams together protons, while four giant detectors watch closely. - So how does the Large Hadron Collider work? - Why can slamming tiny particles into each other provide clues about the nature of all space and time? - What mysteries are physicists trying to solve with data from the LHC? - How does the cutting edge of particle physics relate to the world around us, from the patterns of stars in the sky to the fact that they shine at all? Natalia Toro, PI Faculty, works at the intersection of theories and hard data. She will explain how complex collision data from the LHC is being digested and examined right now, and how it may set the course for the science of the future.

The hierarchy of the Yukawa couplings is an outstanding problem of the standard model. We present a class of models in which the first and second generation fermions are SUSY partners of pseudo-Nambu-Goldstone bosons that parameterize an E_7/SO(10) Kahler manifold, explaining the small values of these fermion masses relative to those of the third generation. We consider experimental constraints on this scenario, and find that the simplest model with universal gaugino masses is already ruled out by the LHC. However, models with non-universal gaugino masses will likely be excluded only by direct dark matter searches.

The observed conservation of Baryon and Lepton number may arise because they are gauge symmetries. Models are discussed where Baryon and lepton number are the charges for a spontaneously broken U(1) gauge symmetries. The best of these models is: (1) free of Landau poles that are near the weak scale, (2) has no flavor changing neutral currents at tree level and (3) contains a dark matter candidate.