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

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 ℓ = 100 ∼ 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 2.5-3σ, 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 ℓ ∼ 120 do not have significant dependences either on frequencies or directions. For the structure around ℓ ∼ 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.

Reconstruction of the primordial power spectrum of curvature perturbations using multiple data sets

“…Although the octupole moment was higher in the 3-year data release, the quadrupole is still unexpectedly low in the WMAP 9-year data and outliers or 'glitches' (exceeding the cosmic variance) persist around the = 22 and = 40 multipoles, despite the improved control of experimental systematics and the additional integration time. In addition, a possible anomaly around = 120 has been identified [73,74]. The overall χ 2 assuming a power-law spectrum equals 3336.4 for 3115 degrees of freedom, the probability to exceed this being only 0.3% (stated to be mainly due to the polarized likelihood [75]).…”