Constraining the initial conditions of the Universe using large scale
  structure
  Primordial non-Gaussianity induces a scale-dependent bias in large scale
structure (LSS) data, proportional to $f_{\rm NL}/k^2$ for the exact local
ansatz. Recent work has shown that models of inflation that predict a large
squeezed limit bispectrum, such as multi-field models and single field
inflation with a modified initial state, typically give rise to a generalized
local ansatz, with the scale-dependent bias now proportional to ${\cal A}_{\rm
NL}/k^\alpha$. We use photometric measurements of the angular power spectrum of
luminous red galaxies and quasars in the Sloan Digital Sky Survey Data Release
Eight (SDSS DR8) with the above parameterization to constrain the amplitude
${\cal A}_{\rm NL}$ and scale-dependence $\alpha$. We find that the
marginalized upper limit on $\alpha$ is 2.0 at the $95\%$ confidence level,
consistent with the local ansatz. We also present Fisher forecasts for a survey
of the same size as DR8 to assess the role of systematics in current
photometric LSS data. Moreover, we present analytic results on the expected
mass dependence of ${\cal A}_{\rm NL}$ for different inflationary models, which
can be an important observable for future surveys, if primordial
non-Gaussianity is non-zero.
