Cosmic microwave background polarization signals from tangled magnetic fields

Area of Science:

• Cosmology
• Astrophysics
• Cosmic Microwave Background Radiation (CMB)

Background:

• Tangled, primordial cosmic magnetic fields are hypothesized to exist in the early universe.
• These fields can induce rotational velocity perturbations on the last scattering surface.
• The cosmic microwave background (CMB) radiation carries imprints of these early universe conditions.

Purpose of the Study:

• To investigate the potential for primordial magnetic fields to generate detectable polarization anisotropies in the CMB.
• To quantify the expected signal strength of B-type polarization from these fields.
• To explore the characteristics of these signals and their implications for detection.

Main Methods:

• Modeling the generation of vector modes (rotational velocity perturbations) by cosmic magnetic fields.
• Calculating the resulting polarization anisotropies in the CMB for specific magnetic field strengths (B0 = 3 x 10^-9 G).
• Analyzing polarization signals for different spectral indices (n = -1 and n = 2) and angular scales (500 < l < 2000).

Main Results:

• Primordial magnetic fields are predicted to generate B-type polarization anisotropies in the CMB, ranging from 0.1-4 microK for n = -1 spectra.
• Significantly larger signals, approximately 200 times greater, are expected for n = 2 spectra.
• These B-mode signals are dominated by odd parity, distinguishing them from scalar mode contributions (e.g., from inflation).

Conclusions:

• The study demonstrates that primordial cosmic magnetic fields can produce observable B-type polarization signals in the CMB.
• The predicted signal strength and its unique polarization signature offer a promising avenue for future detection.
• Detecting these B-mode signals could provide crucial evidence for the existence and strength of primordial magnetic fields.