154 research outputs found
Searching for primordial magnetism with multi-frequency CMB experiments
Bounds on the amplitude of a scale-invariant stochastic primordial magnetic
field (PMF) can be significantly improved by measurements of the Faraday
Rotation (FR) of CMB polarization. The mode-coupling correlations induced by FR
make it possible to extract it from cross-correlations of the B-mode
polarization with the E-mode and the temperature anisotropy. In this paper, we
construct an estimator of the rotation measure that appropriately combines
measurements of the FR from multiple frequency channels. We study the
dependence of the signal-to-noise in the PMF detection on the resolution and
the noise of the detectors, as well as the removal of the weak lensing
contribution and the galactic FR. We show that a recently proposed space-based
experiment PRISM can detect magnetic fields of 0.1 nano-Gauss strength at a 2
sigma level. Higher detection levels can be achieved by reducing the detector
noise and improving the resolution or increasing the number of channels in the
30-70 GHz frequency range.Comment: 6 pages, 1 figure, 1 table; references added, Figure and the caption
improved; matches the version accepted to MNRA
Did BICEP2 see vector modes? First B-mode constraints on cosmic defects
Scaling networks of cosmic defects, such as strings and textures, actively
generate scalar, vector and tensor metric perturbations throughout the history
of the universe. In particular, {\em vector} modes sourced by defects are an
efficient source of the CMB B-mode polarization. We use the recently released
BICEP2 and POLARBEAR B-mode polarization spectra to constrain properties of a
wide range of different types of cosmic strings networks. We find that in order
for strings to provide a satisfactory fit on their own, the effective
inter-string distance needs to be extremely large -- spectra that fit the data
best are more representative of global strings and textures. When a local
string contribution is considered together with the inflationary B-mode
spectrum, the fit is improved. We discuss implications of these results for
theories that predict cosmic defects.Comment: 5 pages, 3 figures; a reference added; matches the version published
in Phys Rev Let
Interaction of Magnetic Monopoles and Domain Walls
We study the interaction of magnetic monopoles and domain walls in a model
with SU(5)\times Z_2 symmetry by numerically evolving the field equations. We
find that the monopoles unwind and dissipate their magnetic energy on collision
with domain walls within which the full SU(5) symmetry is restored.Comment: 4 pages; included additional degree of freedom in ansatz (eq. 4),
discussed time and distance scales; version to be published in PR
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