2,088 research outputs found
B-mode CMB Polarization from Patchy Screening during Reionization
B-modes in CMB polarization from patchy reionization arise from two effects:
generation of polarization from scattering of quadrupole moments by
reionization bubbles, and fluctuations in the screening of E-modes from
recombination. The scattering contribution has been studied previously, but the
screening contribution has not yet been calculated. We show that on scales
smaller than the acoustic scale (l>300), the B-mode power from screening is
larger than the B-mode power from scattering. The ratio approaches a constant
~2.5 below the damping scale (l>2000). On degree scales relevant for
gravitational waves (l<100), screening B-modes have a white noise tail and are
subdominant to the scattering effect. These results are robust to uncertainties
in the modeling of patchy reionization.Comment: 4 pages, 1 figure; minor changes matching PRD published versio
Supersonic baryon-CDM velocities and CMB B-mode polarization
It has recently been shown that supersonic relative velocities between dark
matter and baryonic matter can have a significant effect on formation of the
first structures in the universe. If this effect is still non-negligible during
the epoch of hydrogen reionization, it generates large-scale anisotropy in the
free electron density, which gives rise to a CMB B-mode. We compute the B-mode
power spectrum and find a characteristic shape with acoustic peaks at l ~ 200,
400, ... The amplitude of this signal is a free parameter which is related to
the dependence of the ionization fraction on the relative baryon-CDM velocity
during the epoch of reionization. However, we find that the B-mode signal is
undetectably small for currently favored reionization models in which hydrogen
is reionized promptly at z ~ 10, although constraints on this signal by future
experiments may help constrain models in which partial reionization occurs at
higher redshift, e.g. by accretion onto primordial black holes.Comment: 5 pages, 3 figure
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