41 research outputs found
Cross-correlation of the Polarizations of the 21-cm and Cosmic Microwave Backgrounds
The polarization of the 21-cm radiation from the epoch of reionization arises
from Thomson scattering of 21-cm photons from free electrons and provides
information that complements that from the intensity fluctuation. Previous work
showed that a direct detection of this signal will be difficult, and hinted
that the signal might be enhanced via correlation with other tracers. Here, we
discuss the cross-correlation between the cosmic microwave background (CMB)
polarization and the 21-cm polarization. We treat reionization using an
analytical model with parameters calibrated by semi-numerical simulations. We
then derive the cross-correlation angular power spectrum using the
total-angular-momentum formalism. We also provide a noise analysis to test
against two closely related, but subtly different, null hypotheses. First, we
assume no reionization as a null hypothesis, and determine how well this null
hypothesis could be ruled out by an observed 21cm-CMB polarization correlation.
Second, we determine how well the null hypothesis of no 21-cm polarization can
be ruled out by seeking the cross-correlation, assuming reionization is
established from the CMB. We find that the first question could be answered by
a synergy of ambitious next-generation 21-cm and CMB missions, whereas the
second question will still remain out of reach.Comment: 9 pages, 3 figure
Transverse velocities and matter gradient correlations: a new signal and a new challenge to moving-lens analyses
An observer that is moving towards a high-density region sees, on average, a
higher matter density and more foreground-emitting sources ahead than behind
themself. Consequently, the average abundance and luminosity of objects
producing cosmological signals around an in-falling dark matter halo is larger
in the direction of the halo's motion. In this Letter, we demonstrate this
effect from simulated cosmological maps of the thermal Sunyaev Zel'dovich
effect and the cosmic infrared background. We find that, for a wide range of
halo masses and redshifts, oriented stacked profiles of these foregrounds show
significant, potentially detectable gradients aligned with the transverse
velocity of halos. The signal depends on the halo's mass and redshift, as well
as the physical properties of the cosmic web surrounding the halos. We show
that this signal is sufficiently prominent to be detected in future Cosmic
Microwave Background experiments, therefore offering a new window into the
study of cosmological structures. We argue that the dipolar morphological
structure of this signal, its orientation, as well as its overall large
amplitude, constitute a challenge for the detection of the transverse velocity
through the study of the moving lens effect for stacked halos.Comment: 8 pages, 4 figures, comments welcom
Uncorrelated Compensated Isocurvature Perturbations from kSZ Tomography
Compensated isocurvature perturbations (CIPs) are relative density
perturbations in which a baryon-density fluctuation is accompanied by a dark
matter density fluctuation such that the total-matter density is unperturbed.
These fluctuations can be produced primordially if multiple fields are present
during inflation, and therefore they can be used to differentiate between
different models for the early Universe. Kinetic Sunyaev-Zeldovich (kSZ)
tomography allows for the reconstruction of the radial-velocity field of matter
as a function of redshift. This technique can be used to reconstruct the
total-matter-overdensity field, independent of the galaxy-density field
obtained from large-scale galaxy surveys. We leverage the ability to measure
the galaxy- and matter-overdensity fields independently to construct a
minimum-variance estimator for the primordial CIP amplitude, based on a
mode-by-mode comparison of the two measurements. We forecast that a
configuration corresponding to CMB-S4 and VRO will be able to detect (at
) a CIP amplitude (for a scale-invariant power spectrum) as small
as . Similarly, a configuration corresponding to SO
and DESI will be sensitive to a CIP amplitude . These
values are to be compared to current constraints .Comment: 9 pages, 2 figures. All comments are welcome
Effect of reheating on predictions following multiple-field inflation
We study the sensitivity of cosmological observables to the reheating phase
following inflation driven by many scalar fields. We describe a method which
allows semi-analytic treatment of the impact of perturbative reheating on
cosmological perturbations using the sudden decay approximation. Focusing on
-quadratic inflation, we show how the scalar spectral index and
tensor-to-scalar ratio are affected by the rates at which the scalar fields
decay into radiation. We find that for certain choices of decay rates,
reheating following multiple-field inflation can have a significant impact on
the prediction of cosmological observables.Comment: Published in PRD. 4 figures, 10 page
Probing helium reionization with kinetic Sunyaev Zel'dovich tomography
Reionization of helium is expected to occur at redshifts and have
important consequences for quasar populations, galaxy formation, and the
morphology of the intergalactic medium, but there is little known empirically
about the process. Here we show that kinetic Sunyaev-Zeldovich (kSZ)
tomography, based on the combination of CMB measurements and galaxy surveys,
can be used to infer the primordial helium abundance as well as the time and
duration of helium reionization. We find a high-significance detection at
can be expected from Vera Rubin Observatory and CMB-S4 in the
near future. A more robust characterization of helium reionization will require
next-generation experiments like MegaMapper (a proposed successor to DESI) and
CMB-HD.Comment: 4+2 pages, 2 figures, comments welcom