Cosmic Ruler: Inflection Point Instead of Peak ⚡ экспресс
The linear point — a purely geometric feature in the monopole component of the two-point correlation function of galaxies — is considered an alternative standard ruler, more robust against late-time nonlinear effects (at the percent level) than the BAO peak. Using improved simulations and data from the first and second data releases of the DESI survey (DR1, DR2), measurements of the linear point were performed, converted into the dimensionless parameter α_iso,LP, analogous to the isotropic BAO parameter. Based on second-generation AbacusSummit mock catalogs, it was found that after density reconstruction, measurement precision increases by 15–60% compared to pre-reconstruction. A systematic shift relative to BAO measurements was discovered, caused by an isotropic damping parameter that blurs the linear point in the nonlinear regime. A sample-dependent correction was proposed to compensate for this effect; although it introduces a cosmological dependency into the otherwise model-independent measurement, it is necessary to achieve sub-percent precision in modern surveys. Comparison of α_iso,LP with BAO measurements after correction shows excellent agreement, especially in the post-reconstruction regime.
There's no tool to measure distances to faraway galaxies, but nature left a clue: after the Big Bang, sound waves created rhythmic clumps of matter. Today, this is noticeable as a slight preference for galaxies to be at a certain distance from each other — a built-in ruler. Over cosmic time, the pattern blurs, like a sand dune in the wind: the sharp peak on the distance graph becomes a gentle slope, but its steepest part barely moves. This inflection point — the linear point — more reliably preserves the imprint of the early universe.
Data from the DESI project, mapping millions of galaxies, confirmed its advantages. After reconstruction, which partially cleans the signal from late-time distortions, measurement precision improved by 15–60%. A small correction for the galaxy sample composition, accounting for dark matter and gravity, yielded perfect agreement with traditional measurements. Thus, the linear point becomes a new tool for hunting dark energy and understanding the future of the universe's expansion.
🎯 The theoretical idea has been around since the 2010s, but only DESI's unprecedented maps allowed it to be used with sub-percent precision — and it turned out that the inflection point is more informative than the blurred peak.