Farrars current work focuses mainly on problems at the intersection of astrophysics, cosmology and particle physics, including ultrahigh energy cosmic rays, the nature of dark matter and dark energy, and the origin of the asymmetry between matter and antimatter. UHECRs: Farrar and collaborators use existing UHECR data to deduce properties of their sources and cosmic magnetic fields. Another thrust of NYU research is to improve simulation and reconstruction of cosmic ray air showers. H. Drescher, a postdoc in Farrars group, developed the shower simulation code SENECA; it gives a more realistic description of individual events and is 40 times faster than previous codes. Farrar and Drescher have used it to check the reliability and model independence of UHECR energy calibrations; with Courant grad student D. Krasnov, more powerful methods to identify and reconstruct a primary cosmic rays energy are being developed. Dark Matter and Cosmological Dynamics: Farrar and Peebles showed the mass of dark matter could arise from a Higgs-type interaction with the dark energy field, producing interesting variants to the standard LCDM cosmological model. Farrar is now engaged in several related projects, simulating the impact of such interactions on the formation of structure and using observations of large-scale structure and galactic dynamics to constrain the possibility that dark matter experiences non-gravitational forces. Novel models of Dark Matter: Farrar and Spergel are studying models in which DM is normal matter on a different brane. Farrar and grad student G. Zaharijas have shown that the baryon asymmetry of the universe may be only an asymmetry in "packaging", with the baryon number in nucleons balanced by anti-baryonic dark matter. Observational constraints on such DM have been obtained and are found to be consistent with the expected DM properties. In one such scenario the DM consists of H and anti-H dibaryons, impelling a renewed study of a long-lived H dibaryon.