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A new analysis of data from the upcoming Euclid telescope will help peer into the first moments after the Big Bang.
Abstract
The pipeline for joint analysis of the power spectrum (one-loop) and bispectrum (tree-level) in redshift space was validated on mock catalogs simulating the spectroscopic sample of Euclid. N-body simulations Abacus-PNG with Gaussian and locally non-Gaussian initial conditions were used, with galaxies populated via HOD calibrated on Euclid Flagship 2. We tested bias parameterization, priors, and scale cuts. Without prior information on b_φ, the dominant PNG contribution ∝ f_NL b_φ is poorly detected in individual redshift bins, but the bispectrum constrains other combinations, breaking degeneracies. A physically motivated prior on b_φ is proposed for unbiased estimates of f_NL, accounting for theoretical uncertainty; scale cuts for unbiased ΛCDM and f_NL are determined. With an effective volume of 16 h⁻³ Gpc³ (four slices, 0.8 ≤ z ≤ 1.7), the likelihood analysis yields a bias of less than 1σ. The bispectrum reduces σ(f_NL) by 29–46% relative to the power spectrum; joint analysis adds another 8–13%. The quadrupole of the bispectrum is critically important. Best results at z=1.7: 1.9σ for f_NL b_φ (without prior) and 2.35σ for f_NL (with prior).
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The Universe was born in the Big Bang and immediately underwent an ultrafast expansion — inflation. Quantum jitters imprinted themselves on the fabric of space like ripples on water from a tossed stone. These ripples became the seeds of galaxies. Usually the waves are random, but if inflation was complex, some crests are slightly higher — the shape isn't a perfect circle. Catching such a skew means reading the story of the first moments.
The European Euclid telescope will be able to check this. In their model, scientists combined two approaches: one measures the overall height of the ripples, the other catches triangular patterns from neighboring crests. Together they reduce noise and double the accuracy. The cleanest signal comes from distant galaxies half the age of the Universe. To avoid being fooled, the galaxy data is correlated with a dark matter map — the invisible scaffolding of the cosmos. This way, we can tell whether inflation was simple or multi-field, much like figuring out if one stone or several made the ripples.
🎯 If the cosmic ripples were perfectly symmetric, the Universe would have remained featureless, like white noise in headphones, and complex structures would never have formed.
🎬 In Carl Sagan's 'Contact,' a message hides in the noise of the cosmic microwave background. Astrophysicists with Euclid are also searching for a hidden signal in the cosmic ripples, but its author is not an extraterrestrial intelligence, but the quantum laws of the early Universe.
