Particle Physics

The relic neutrino background contains a gapless, spin-2 sound mode, as well as a spin-1 mode if there is a neutrino-antineutrino asymmetry. The self-coupling of the spin-2 mode is given by Z boson exchange in the Standard Model and is parametrically similar to Newton's constant given the expected density of relic neutrinos. I will describe this emergent gravity theory and also describe how emergent theories avoid the Weinberg-Witten theorem, when the constituent degrees of freedom live in a flat Lorentz invariant space.

How do we weigh the Universe? Where is the Dark Matter? I will discuss these questions and show that several independent methods, including the observed present-day abundance of rich clusters , the evolution of cluster abundance with redshift, the baryon-fraction in clusters, the observed Mass-to-Light function from galaxies to superclusters, and other large-scale structure observations, all reveal a universe with a low mass density parameter of ~20% of the critical density. The data suggest that the mass in the Universe, including the dark-matter, approximately follows light on large scales and that most of the mass resides in huge dark halos around galaxies. I will review the combined observational evidence for dark-matter and for dark-energy in the universe and their cosmological implications.