Searching for local features in primordial power spectrum using genetic algorithms

TL;DR

This paper introduces a genetic algorithm-based method to detect local features in the primordial power spectrum from CMB data, improving fit quality and addressing anomalies without relying on specific models.

Contribution

It presents a novel, model-independent pipeline combining genetic algorithms and a Boltzmann solver to reconstruct primordial power spectra from CMB data.

Findings

Significant fit improvements with Δχ² ≈ -21.

Addresses low-ell TT anomaly and high-ell oscillations.

Provides an adaptable, model-independent feature exploration tool.

Abstract

We present a novel methodology for exploring local features directly in the primordial power spectrum using a genetic algorithm (GA) pipeline coupled with a Boltzmann solver and Cosmic Microwave Background data (CMB). After testing the robustness of our pipeline using mock data, we apply it to the latest CMB data, including Planck 2018 and CamSpec PR4. Our model-independent approach provides an analytical reconstruction of the power spectra that best fits the data, with the unsupervised machine learning algorithm exploring a functional space built off simple ``grammar'' functions. We find significant improvements upon the simple power-law behaviour, by $\Delta \chi^2 \lesssim -21$, consistently with more traditional model-based approaches. These best-fits always address both the low$\ell$ anomaly in the TT spectrum and the residual high$\ell$ oscillations in the TT, TE and EE spectra. The proposed pipeline provides an adaptable tool for exploring features in the primordial power spectrum in a model-independent way, providing valuable hints to theorists for constructing viable inflationary models that are consistent with the current and upcoming CMB surveys.