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
non-linear regime, 1 Mpc^{-1} < k < 10^2-10^3 Mpc^{-1} up to redshift of about
unity. By using the lensing dispersion and conservative estimates in this
regime of wavenumbers, we show how the current upper bound sigma_mu(z=1) <
0.12on 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 alpha
= d n_s / d ln k and running of running beta = d^2 n_s / d ln k^2. The bounds
follow a linear relation to a very good accuracy. A conservative bound
disfavors any enhancement above the line beta(k_0)=0.036-0.42 alpha(k_0) and a
realistic estimate disfavors any enhancement above the line
beta(k_0)=0.022-0.44 alpha(k_0).
