Cosmological Parameters Degeneracies and Non-Gaussian Halo Bias

We study the impact of the cosmological parameters uncertainties on the measurements of primordial non-Gaussianity through the large-scale non-Gaussian halo bias effect. While this is not expected to be an issue for the standard LCDM model, it may not be the case for more general models that modify the large-scale shape of the power spectrum. We consider the so-called local non-Gaussianity model and forecasts from planned surveys, alone and combined with a Planck CMB prior. In particular, we consider EUCLID- and LSST-like surveys and forecast the correlations among

f_{\rm NL}

and the running of the spectral index

\alpha_s

, the dark energy equation of state

w

, the effective sound speed of dark energy perturbations

c^2_s

, the total mass of massive neutrinos

M_\nu=\sum m_\nu

, and the number of extra relativistic degrees of freedom

N_\nu^{rel}

. Neglecting CMB information on

f_{\rm NL}

and scales

k > 0.03 h

/Mpc, we find that, if

N_\nu^{\rm rel}

is assumed to be known, the uncertainty on cosmological parameters increases the error on

f_{\rm NL}

by 10 to 30% depending on the survey. Thus the

f_{\rm NL}

constraint is remarkable robust to cosmological model uncertainties. On the other hand, if

N_\nu^{\rm rel}

is simultaneously constrained from the data, the

f_{\rm NL}

error increases by

\sim 80%

. Finally, future surveys which provide a large sample of galaxies or galaxy clusters over a volume comparable to the Hubble volume can measure primordial non-Gaussianity of the local form with a marginalized 1--

\sigma

error of the order

\Delta f_{\rm NL} \sim 2-5

, after combination with CMB priors for the remaining cosmological parameters. These results are competitive with CMB bispectrum constraints achievable with an ideal CMB experiment.

Note:

17 pages, 1 figure added, typos corrected, comments added, matches the published version

cosmology: theory
large-scale structure of universe
galaxies: clusters
generalgalaxies: halos
dark energy: equation of state
dark energy: perturbation
neutrino: mass
galaxy: cluster
velocity: acoustic
cosmic background radiation

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Figures(17)

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