Primordial Non-Gaussianity and the NRAO VLA Sky Survey
  The NRAO VLA Sky Survey (NVSS) is the only dataset that allows an accurate
determination of the auto-correlation function (ACF) on angular scales of
several degrees for Active Galactic Nuclei (AGNs) at typical redshifts $z
\simeq 1$. Surprisingly, the ACF is found to be positive on such large scales
while, in the framework of the standard hierarchical clustering scenario with
Gaussian primordial perturbations it should be negative for a
redshift-independent effective halo mass of order of that found for
optically-selected quasars. We show that a small primordial non-Gaussianity can
add sufficient power on very large scales to account for the observed NVSS ACF.
The best-fit value of the parameter $f_{\rm NL}$, quantifying the amplitude of
primordial non-Gaussianity of local type is $f_{\rm NL}=62 \pm 27$ ($1\,\sigma$
error bar) and $25<f_{\rm NL}<117$ ($2\,\sigma$ confidence level),
corresponding to a detection of non-Gaussianity significant at the $\sim
3\,\sigma$ confidence level. The minimal halo mass of NVSS sources is found to
be $M_{\rm min}=10^{12.47\pm0.26}h^{-1}M_{\odot}$ ($1\,\sigma$) strikingly
close to that found for optically selected quasars. We discuss caveats and
possible physical and systematic effects that can impact on the results.
