Cosmic Discordance: Detection of a modulation in the primordial fluctuation spectrum

TL;DR

This paper reports the detection of an oscillatory modulation in the primordial fluctuation spectrum using CMB data, challenging the simple scale-invariant assumption of standard inflation.

Contribution

It introduces a method to identify localized oscillatory features in the primordial power spectrum and finds evidence for such a feature at a specific scale.

Findings

Detected a localized oscillatory modulation at k ≈ 0.009 Mpc^{-1}

Improved the fit to CMB data significantly with the modulation

Feature detectable through temperature and polarization cross-correlation

Abstract

As a test of the standard inflationary cosmology, which generically predicts nearly scale-invariant spectrum of primordial curvature fluctuations, we perform Markov-Chain Monte-Carlo analysis to search for possible modulations in the power spectrum and determine its shape together with the cosmological parameters using cosmic microwave background radiation data. By incorporating various three-parameter features on the simple power-law spectrum, we find an oscillatory modulation localized around the comoving wavenumber $k\simeq 0.009\mathrm{Mpc}^{-1}$ at 99.995% confidence level which improves the log-likelihood as much as $-\Delta 2\ln {\cal L}\equiv \Delta \chi^2_{\rm eff}=-22$. This feature can be detected even if we use only the cross correlation between the temperature and the E-mode polarization anisotropies.