Exploring the origin of the fine structures in the CMB temperature angular power spectrum

TL;DR

This paper investigates the fine oscillatory features in the CMB temperature power spectrum, confirming their rarity and exploring their potential origins through regional and frequency analyses of WMAP data.

Contribution

It provides a detailed analysis of the fine structures in the CMB power spectrum, assessing their statistical significance and regional dependencies, which was not thoroughly examined before.

Findings

Fine structures are rare, about 2.5-3 sigma significance.

Structures around l=120 show no frequency or directional dependence.

An anomaly at l~140 is localized to the South East region.

Abstract

The angular power spectrum of the cosmic microwave background (CMB) temperature anisotropies is a good probe to look into the primordial density fluctuations at large scales in the universe. Here we re-examine the angular power spectrum of the Wilkinson Microwave Anisotropy Probe data, paying particular attention to the fine structures (oscillations) at $\ell=100 \sim 150$ reported by several authors. Using Monte-Carlo simulations, we confirm that the gap from the simple power law spectrum is a rare event, about 2.5--3$\sigma$, if these fine structures are generated by experimental noise and the cosmic variance. Next, in order to investigate the origin of the structures, we examine frequency and direction dependencies of the fine structures by dividing the observed QUV frequency maps into four sky regions. We find that the structures around $\ell \sim 120$ do not have significant dependences either on frequencies or directions. For the structure around $\ell \sim 140$, however, we find that the characteristic signature found in the all sky power spectrum is attributed to the anomaly only in the South East region.