Litmus Test for Cosmic Hemispherical Asymmetry in the Cosmic Microwave Background B-Mode Polarization

Area of Science:

• Cosmology
• Astrophysics
• Cosmic Microwave Background Radiation

Background:

• Statistical isotropy (SI) is a fundamental assumption in cosmology.
• Recent CMB temperature measurements (WMAP, Planck) show a 7% departure from SI at large angular scales.
• Future CMB temperature measurements may not significantly improve the detection of SI violation due to cosmic variance.

Purpose of the Study:

• To investigate whether weak lensing of the CMB by scalar perturbations can lead to observable SI violations.
• To explore a new window for detecting SI violation in CMB polarization B modes.
• To establish independent bounds on the spatial range of hemispherical asymmetry in the scalar sector.

Main Methods:

• Theoretical analysis of weak gravitational lensing effects on CMB polarization.
• Investigating the relationship between power asymmetry in temperature and polarization data.
• Assessing the measurability of SI violation in B modes based on angular scales (l range).

Main Results:

• Weak lensing of CMB by scalar perturbations induces SI violation in B modes at smaller angular scales.
• The measurability of this effect is dependent on the angular scales where power asymmetry is present.
• Power asymmetry restricted to l<64 in the temperature field limits the observable effect in this new window.

Conclusions:

• Weak lensing of CMB polarization provides a novel, complementary method to probe SI violation.
• This effect can constrain the spatial extent of hemispherical asymmetry in the early universe's scalar sector.
• Future studies should focus on the specific angular scales relevant for detecting lensing-induced SI violation in CMB B modes.