5 research outputs found
Measures of non-Gaussianity in axion-string-induced CMB birefringence
The presence of axion strings in the Universe after recombination can leave
an imprint on the polarization pattern of the cosmic microwave background
radiation through the phenomenon of axion-string-induced birefringence via the
hyperlight axion-like particle's coupling to electromagnetism. Across the sky,
the polarization rotation angle is expected to display a patchwork of uniform
regions with sharp boundaries that arise as the `shadow' of axion string loops.
The statistics of such a birefringence sky map are therefore necessarily
non-Gaussian. In this article we quantify the non-Gaussianity in
axion-string-induced birefringence using two techniques, kurtosis and
bispectrum, which correspond to - and -point correlation functions. If
anisotropic birefringence were detected in the future, a measurement of its
non-Gaussian properties would facilitate a discrimination across different new
physics sources generally, and in the context of axion strings specifically, it
would help to break degeneracies between the axion-photon coupling and
properties of the string network.Comment: 12 pages, plus appendix, 6 figure
Symmetries of CMB Temperature Correlation at Large Angular Separations
A new analysis is presented of the angular correlation function
of cosmic microwave background (CMB) temperature at large angular separation,
based on published maps derived from {\sl WMAP} and {\sl Planck} satellite
data, using different models of astrophysical foregrounds. It is found that
using a common analysis, the results from the two satellites are very similar.
In particular, it is found that previously published differences between
measured values of near arise mainly from
different choices of masks in regions of largest Galactic emissions, and that
demonstrated measurement biases are reduced by eliminating masks altogether.
Maps from both satellites are shown to agree with to within
estimated statistical and systematic errors, consistent with an exact symmetry
predicted in a new holographic quantum model of inflation.Comment: resubmitted to ApJ Letters, with revisions in response to referee
comment
Searching for axion-like particles through CMB birefringence from string-wall networks
Axion-like particles (ALPs) can form a network of cosmic strings and domain
walls that survives after recombination and leads to anisotropic birefringence
of the cosmic microwave background (CMB). In addition to studying cosmic
strings, we clarify and emphasize how the formation of ALP-field domain walls
impacts the cosmic birefringence signal; these observations provide a unique
way of probing ALPs with masses in the range . Using measurements of CMB birefringence from several telescopes,
we find no evidence for axion-defect-induced anisotropic birefringence of the
CMB. We extract constraints on the model parameters that include the ALP mass
, ALP-photon coupling , the
domain wall number , and parameters characterizing the abundance
and size of defects in the string-wall network. Considering also recent
evidence for isotropic CMB birefringence, we find it difficult to accommodate
this with the non-detection of anisotropic birefringence under the assumption
that the signal is generated by an ALP defect network.Comment: 20 pages + 3 appendices, 14 figures, 3 table