Christian Fidler

The intrinsic bispectrum of the Cosmic Microwave Background

We develop a new, efficient code for solving the second-order Einstein-Boltzmann equations, and use it to estimate the intrinsic CMB non-Gaussianity arising from the non-linear evolution of density perturbations. The full calculation involves contributions from recombination and less tractable contributions from terms integrated along the line of sight. We investigate the bias that this intrinsic bispectrum implies for searches of primordial non-Gaussianity. We find that the inclusion or omission of certain line of sight terms can make a large impact. When including all physical effects but lensing and time-delay, we find that the local-type f_nl would be biased by f_nl ~ 0.5, below the expected sensitivity of the Planck satellite. The speed of our code allows us to confirm the robustness of our results with respect to a number of numerical parameters.

Impact of polarization on the intrinsic cosmic microwave background bispectrum

We compute the bispectrum induced in the cosmic microwave background (CMB) temperature and polarisation by the evolution of the primordial density perturbations using the second-order Boltzmann code SONG. We show that adding polarisation increases the signal-to-noise ratio by a factor four with respect to temperature alone and we estimate the observability of this intrinsic bispectrum and the bias it induces on measurements of primordial non-Gaussianity. When including all physical effects except the late-time non-linear evolution, we find for the intrinsic bispectrum a signal-to-noise of S/N = 3.8, 2.9, 1.6 and 0.5 for, respectively, an ideal experiment with an angular resolution of `max = 3000, the proposed CMB surveys PRISM and COrE, and Planck’s polarised data; the bulk of this signal comes from the E-polarisation and from squeezed configurations. We discuss how CMB lensing is expected to reduce these estimates as it suppresses the bispectrum for squeezed configurations and contributes to the noise in the estimator. We find that the presence of the intrinsic bispectrum will bias a measurement of primordial non-Gaussianity of local type by f intr NL = 0.66 for an ideal experiment with `max = 3000. Finally, we verify the robustness of our results by reproducing the analytical approximation for the squeezed-limit bispectrum in the general polarised case.

Relativistic interpretation of Newtonian simulations for cosmic structure formation

The standard numerical tools for studying non-linear collapse of matter are Newtonian

Cosmological

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N

-body simulations. Previous work has shown that these simulations are in accordance with General Relativity (GR) up to first order in perturbation theory, provided that the effects from radiation can be neglected. In this paper we show that the present day matter density receives more than 1

-body simulations including radiation perturbations

\%

The Intrinsic Matter Bispectrum in

corrections from radiation on large scales if Newtonian simulations are initialised before

\Lambda

z=50

CDM

. We provide a relativistic framework in which \emph{unmodified} Newtonian simulations are compatible with linear GR even in the presence of radiation. Our idea is to use GR perturbation theory to keep track of the evolution of relativistic species and the relativistic space-time consistent with the Newtonian trajectories computed in

The effect of early radiation in N-body simulations of cosmic structure formation

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