Forecastfiso planck

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Overview

We can improve constraints on isocurvature perturbations from Planck with observations from S4.

Here we consider the curvaton model: there is one isocurvature mode: the CDM isocurvature, and the spectral index of the CDM mode is the same as that of the adiabatic scalar perturbations, n_s. In this scenario, the CDM mode is either totally correlated or anti-correlated with the adiabatic perturbations.

The parameter we are constraining is f_iso, the primordial fraction of CDM isocurvature amplitude to the scalar perturbation amplitude. Specifically, the final spectra is

Cl^{tot} = Cl^{ad} + f_iso^2 Cl^{cdm iso} + 2* f_iso * Cl^{correlated}

where Cl^{cdm iso} is generated such that it has the same primordial power A_s as the scalar perturbations, and similarly for Cl^{correlated}.

Planck test

To check that we are getting reasonable results, we run the Fisher matrix with LCDM+Mnu+f_iso with Planck noise levels, beams, and fsky as specified in previous forecast checks.

We tested for two fiducial cosmologies: (1) f_iso=0; (2) f_iso=0.01. The following constraints use TT/EE/TE lensed spectra.

The following are the constraints we get:

LCDM+Mnu+f_iso=0 LCDM+Mnu+f_iso=0.01
och2 0.001523 0.001503
obh2 0.000163 0.000160
onuh2 0.005396 0.005281
10^9 As 0.2589 0.2529
ns 0.00486 0.00483
tau 0.0597 0.0584
hubble 4.84 4.73
f_iso 0.00391 0.00430

We are doing a literature search to find previous forecasts that uses a similar parameterization (as opposed to the alpha or beta parameterization) to compare our results.