and, in conjunction with their typical high peak luminosity ($10^{36}$ W$\sim 4\times 10^9L_\odot$), justifies the effort to improve their use as cosmological *standardizable* candles. After some phenomenological standardization recipes (cf. Section \[sec:light\_curve\_fitting\]), the scatter in $M_B$ decreases to around 0.15 mag, which amounts to a fractional uncertainty in luminosity of $-13\%$ and in luminosity distance of $7\%$.

Already in the landmark papers from the two original surveying groups [@Riess1998; @Perlmutter1999], a legitimate concern was expressed about the presence of not properly accounted for systematic effects. At that time, however, there was only a small number (the order of tens) of observed SNe Ia in any of the available samples, so the uncertainties were statistically limited; the main task was gathering new, larger, uniform datasets. For the recent compilations and surveys [@Wood-Vasey2007; @Kowalski2008; @Hicken2009; @Conley2011; @Kessler2009; @Amanullah2010], and the more so for the future ones [@Pan-STARRS; @DES; @LSST], we are no longer sample-limited; the urgency is again on the physics of the SN Ia phenomenon and all the aspects which impact it: nature of progenitor binary system (single-degenerate versus double degenerate, tardy versus prompt events) [@Dilday2010; @Hayden2010; @Maoz2010], properties of host galaxy [@Sullivan2010; @Lampeitl2010; @Gupta2011], mechanisms of explosion [@Hillebrandt2000], extinction/intrinsic color 