Speaker
Description
Primordial non-Gaussianity represents one of the most powerful observational probes of the physics of the early Universe. Standard bispectrum-based estimators, used to constrain primordial non-Gaussianity from CMB observations, are typically derived under the assumption of statistical isotropy, which implies a diagonal harmonic covariance matrix. However, this assumption may break down in cosmological scenarios with non-trivial spatial topology, where anisotropic harmonic correlations and off-diagonal mode couplings can arise.
In this work, we investigate the robustness of standard isotropic estimators of primordial non-Gaussianity when applied to CMB skies generated in universes with compact spatial topologies. The analysis is based on the Komatsu–Spergel–Wandelt (KSW) estimator for local-type non-Gaussianity and on topological simulations produced with the CMBtopology code developed within the COMPACT collaboration.
The estimator pipeline was first validated on Gaussian and non-Gaussian statistically isotropic simulations through a series of consistency tests and benchmark comparisons. We then applied the same isotropic estimator, without modification, to Gaussian topological realizations, where any reconstructed non-zero value of the non-linearity parameter $f_{\rm NL}$ must be interpreted as an effective response of the estimator to topology-induced anisotropic correlations rather than as genuine primordial non-Gaussianity.
As a first case study, we analyzed the E1 compact flat topology. Ongoing work includes extending the analysis to the more anisotropic E3 quarter-turn topology, which provides a promising test case for investigating the impact of potentially stronger topology-induced anisotropies on standard primordial non-Gaussianity estimators.
| Parallel session | Astrophysical Probes of Dark Matter and Dark Energy |
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