The cosmic microwave background is the petrified light of the first moments. Shortly after the Big Bang, microscopic quantum fluctuations were stretched by inflation to the scales of galactic superclusters. Today, this ripple appears in the cosmic microwave background as a pattern of temperature spots. But what if, during the rapid expansion, supermassive particles were occasionally born and then instantly vanished, leaving gravitational 'imprints'? Like a dinosaur's footprint in instantly hardening clay, such an event freezes into the fabric of spacetime and manifests as a tiny feature in the spectrum of primordial perturbations. It was precisely these fossil traces that the authors sought, combining data from Planck and ACT.

Inflation, predicted by Alan Guth and inextricably linked with the names of George Gamow (who predicted the background) and Arno Penzias (who discovered it), is described by a model where quantum fluctuations of the inflaton field produce a nearly scale-invariant spectrum. The production of massive particles, however, introduces a characteristic ripple — petrified 'tree rings' with a period determined by the conformal moment η*. This modification depends on the amplitude and probability of pair production. The number of produced particles is given by an exponentially sensitive formula: P∗ ∼ (gφ̇₀)³/² exp(–π(m₀² – 2HI²)/(g|φ̇₀|)). Here, mass m₀ and the expansion rate HI set the threshold: only very heavy particles (m₀ ≳ 100 HI, about 10¹³ GeV) can leave a measurable trace. The spectral correction: P(k) = $P_{std}$(k) [1 + 2g² P∗ (Si(kη∗) – sin(kη∗))²/(kη∗)³ (1 + …)]. This resembles a sine wave frozen into the power spectrum. A Bayesian MCMC analysis with radio observation data imposed the strongest constraints on the amplitude, especially for light particles: the spectral method proved an order of magnitude more sensitive than the previous matched filter.

The noticed faint signal (~2σ) at η* ≈ 3–10 Mpc with amplitude 2g²P∗ = 0.26 ± 0.11 doesn’t yet qualify as a discovery. However, it lies in the region where Planck and ACT diverge in the spectral index ns — perhaps it’s not a mere fluctuation. If the Simons Observatory confirms it at the 3–5σ level, we would for the first time obtain direct evidence of physics at energies near Planckian. The cosmic microwave background would become a natural accelerator with energies unattainable in laboratories. Imagine: each such particle would require an energy billions of times greater than that of LHC protons, and this happened in the first 10⁻³⁵ second of the universe’s existence. Further steps (polarization analysis, accounting for gravitational lensing, and searching for periodic patterns) will help separate the sought signal from secondary distortions in the expanding Universe with its redshift. Thus, by gazing into the ancient 'petrified light,' we reconstruct the first moments of existence.