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.