Application of Genetic Algorithm to Estimate the Large Angular Scale Features of Cosmic Microwave Background

Abstract

Genetic Algorithm (GA) -- motivated by natural evolution -- is a robust method to estimate the global optimal solutions of problems involving multiple objective functions. In this article, for the first time, we apply GA to reconstruct the CMB temperature anisotropy map over large angular scales of the sky using (internal) linear combination (ILC) of the final-year WMAP and Planck satellite observations. To avoid getting trapped into a local minimum, we implement the GA with generous diversity in the populations by selecting pairs with diverse fitness coefficients and by introducing a small but significant amount of mutation of genes. We find that the new GA-ILC method produces a clean map which agrees very well with that obtained using the exact analytical expression of weights in ILC. By performing extensive Monte Carlo simulations of the CMB reconstruction using the GA-ILC algorithm, we find that residual foregrounds in the cleaned map are minimal and tend to occupy localized regions along the galactic plane. The CMB angular power spectrum shows no indication of any bias in the entire multipole range $2 \leq \ell \leq 32$ studied in this work. The error in the CMB angular power spectrum is also minimal and given entirely by the cosmic-variance-induced error. Our results agree well with those obtained by various other reconstruction methods by different research groups. This problem-independent robust GA-ILC method provides a flexible way towards the complex and challenging task of CMB component reconstruction in cosmology.