Research Interests

Outreach - Talks




Dark Energy and the CC problem

Particle physics theories typically predict the presence of a vacuum energy, at worst of the order of the Planck mass MPl ~ 1072GeV4, which would cause the Universe to accelerate with a Hubble parameter H ~ 1061km/s Mpc, or at best of the order of the supersymmetry breaking scale Msusy ~ TeV4. Since this is clearly incompatible with observations, physicists have for a long time assumed that some symmetry sets this vacuum energy to zero. However, in 1998, observations of type Ia supernovae measured for the first time the acceleration of the Universe with precision, corresponding to a Hubble parameter of order H ~ 70km/s Mpc, i.e. consistent with a cosmological constant of order 1048GeV4, that is 120 orders of magnitude smaller than predicted from particle physics. This measurement was soon confirmed by many other sources, such as the CMB, matter density and gravitational lensing and is to date arguably the most embarrassing puzzle of modern cosmology.