Constraining the primordial power spectrum from SNIa lensing dispersion

The (absence of detecting) lensing dispersion of supernovae type Ia (SNIa) can be used as a novel and extremely efficient probe of cosmology. In this preliminary example we analyze its consequences for the primordial power spectrum. The main setback is the knowledge of the power spectrum in the nonlinear regime, 1Mpc-1≲k≲102-103Mpc-1 up to redshift of about unity. By using the lensing dispersion and conservative estimates in this regime of wave numbers, we show how the current upper bound σμ(z≤1)<0.12 on existing data gives strong indirect constraints on the primordial power spectrum. The probe extends our handle on the spectrum to a total of 12-15 inflation e-folds. These constraints are so strong that they are already ruling out a large portion of the parameter space allowed by PLANCK for running α≡dns/dlnk and running of running β≡d2ns/dlnk2. The bounds follow a linear relation to a very good accuracy. A conservative bound disfavors any enhancement above the line β(k0)=0.036-0.42α(k0) and a realistic estimate disfavors any enhancement above the line β(k0)=0.022-0.44α(k0).