The Cosmic Score is Silent: Dark Matter and Neutrinos Don't Play a Duet ✛ ✎ ✦
Light from distant quasars, breaking through billions of years, leaves a pattern of dark absorption lines on the cosmic film — the spectroscopic Lyman-alpha forest. Each line is like a note in a grand score, written by the hydrogen of the intergalactic medium. But instead of violins and cellos, here the sounds are made by clumps of matter, and we're trying to catch the barely audible duet of two invisible instruments: dark matter and neutrinos.
The hypothesis of their interaction was born from a slight dissonance in the cosmic microwave background and large-scale structure. Barely perceptible hints promised a hidden harmony that could resolve modern cosmological tensions. But to hear the true melody, we needed the finest ear: full hydrodynamic simulations (48 runs with varying strength) and a neural network emulator that reproduces spectra with better than 1.5% accuracy.
Bayesian analysis compared model notes with real data from 15 quasars observed by Keck and VLT in three redshift ranges. The result: an unprecedented limit, a hundred times stronger than anything before. No duet is heard: the signal hinted at by previous works is completely ruled out. The score of the ΛCDM model remains pure, without the slightest hint of alien harmonies.
This is not a disappointment, but a triumph of precision. We silenced one of the most exciting hypothetical processes — and thus strengthened the foundations of standard cosmology. Ahead, with next-generation telescopes like ELT and data from 21-cm tomography, we will either finally hear the whisper of interaction or confirm that dark matter and neutrinos are doomed to eternal cosmic loneliness. For now, the silence of the score sounds louder than any notes.
The Lyman-alpha forest is a score where each line is like a note, and their chorus tells the story of invisible matter's distribution with a precision unattainable by direct observations.