Turning noise into signal: learning from the scatter in the Hubble diagram

Type Ia supernovae (SNe) are still the only established high-redshift standard candles, with an intrinsic dispersion of less than 0.15 in magnitude after standardization. In the late 90s, using a sample of about 50 of these objects the discovery of the accelerated expansion was established by Riess et al. (1998); Perlmutter et al. (1999). The confidence in that result was enhanced soon after in Bahcall et al. (1999) by combining the SNe with galaxy surveys early Cosmic Microwave Background (CMB) data on large-scales. It is nowadays a well-established result, with strong evidence coming from observations of the Baryonic Acoustic Oscillations and of the anisotropies of the CMB. In this talk, I will show that the SNe Ia Hubble diagram residual also contains valuable information and how this information can be retrieved with precision. I will also discuss the complementarity of this information with respect to the ones obtained from other data sets and how they will improve substantially with more SNe.