Primordial Non-Gaussianities (PNG) and zero bias tracers of the Large Scale Structure

Apr 09, 2018 - 11:00 am to 12:00 pm

Campus, Varian 355

Emanuele Castorina (Berkeley Center for Cosmological Physics)

The statistical properties of the primordial curvature perturbations are a key ingredient of the success of the LCDM model in explaining the Universe as we observe it today.


In simplest model of inflation initial fluctuations are Gaussian for all practical purposes, and measurements of the CMB bispectrum by the Planck satellite constrain any deviation from the Gaussian regime in a part in ten thousands.

On the other hand the theoretical target for the amplitude of PNG in the initial perturbations is roughly an order of mangnitude smaller than what Planck has measured.

Unfortunately we have mostly saturated the information content in the CMB, and any further improvement will come from the late time distribution of galaxies or any other tracers of the Large Scale Structure (LSS) of the Universe.

In this talk, I will present a new method to constrain PNG of the local kind using unclustered tracers of the LSS. In the limit of low noise in the data, zero bias tracers yield large improvement over standard methods, mostly due to vanishing sampling variance. We propose a simple technique to construct such a tracer, using environmental information obtained from the original sample, and validate our method with N-body simulations.

Our approach is very close to optimal, and opens the possibility to reach the theoretical target on PNG using measurements of power spectrum alone.

Time allowing, the relation of environmental bias to other sources of assembly (secondary) bias will also be discussed using simple analytical models.