Cosmic microwave background power asymmetry from non-Gaussian modulation

Area of Science:

• Cosmology
• Inflationary Theory
• Cosmic Microwave Background

Background:

• Cosmic Microwave Background (CMB) power spectrum anomalies, like power asymmetry, are often attributed to a breakdown of statistical isotropy.
• Non-Gaussianity in primordial perturbations can naturally lead to large-angle modulations of the CMB power spectrum.

Purpose of the Study:

• To investigate non-Gaussianity as an alternative explanation for observed power asymmetry in the CMB.
• To explore the implications of infrared-divergent bispectra in inflationary models for CMB power asymmetry.

Main Methods:

• Analyzing the coupling between observable and superhorizon modes due to non-Gaussianity.
• Investigating the squeezed limit of the bispectrum for infrared divergence in non-Bunch-Davies initial state models.
• Constraining inflationary model parameters using upper limits on CMB power asymmetry.

Main Results:

• Non-Gaussianity can induce a significant large-angle modulation of the CMB power spectrum, mimicking power asymmetry.
• This effect is possible even for typical perturbation amplitudes (~10^-5) if the bispectrum is sufficiently infrared divergent.
• Models with non-Bunch-Davies initial states can exhibit such infrared-divergent bispectra.

Conclusions:

• Non-Gaussianity provides a viable alternative origin for CMB power asymmetry, distinct from a violation of statistical isotropy.
• Stringent constraints on the duration of inflation arise from CMB power asymmetry limits in models with infrared-divergent bispectra.