73 research outputs found
Cosmic-Ray Bounds on Lepton-Flavor-Violating Dark-Matter Decays *
Abstract We consider possible leptonic three-body decays of spin-1/2 charge-asymmetric dark matter. Assuming a general Dirac structure for the four-fermion contact interactions of interest, we study the cosmic-ray electron and positron spectra and show that good fits to the current data can be obtained for both charged-lepton-flavor-conserving and flavor-violating decay channels. We find that different choices for the Dirac structure of the underlying decay operator can be significantly compensated by different choices for the dark-matter mass and lifetime. The decay modes we consider provide differing predictions for the cosmic-ray positron fraction at energies higher than those currently probed at the PAMELA experiment; these predictions might be tested at cosmic-ray detectors like AMS-02. Additionally, we consider the constraints imposed on these decays by neutrino and gamma-ray observatories
Magnetic Misalignment of Interstellar Dust Filaments
We present evidence for scale-independent misalignment of interstellar dust
filaments and magnetic fields. We estimate the misalignment by comparing
millimeter-wave dust-polarization measurements from Planck with filamentary
structures identified in neutral-hydrogen (HI) measurements from HI4PI. We find
that the misalignment angle displays a scale independence (harmonic coherence)
for features larger than the HI4PI beam width (). We additionally find a
spatial coherence on angular scales of . We present
several misalignment estimators formed from the auto- and cross-spectra of
dust-polarization and HI-based maps, and we also introduce a map-space
estimator. Applied to large regions of the high-Galactic-latitude sky, we find
a global misalignment angle of , which is robust to a variety of
masking choices. By dividing the sky into small regions, we show that the
misalignment angle correlates with the parity-violating cross-spectrum
measured in the Planck dust maps. The misalignment paradigm also predicts a
dust signal, which is of relevance in the search for cosmic birefringence
but as yet undetected; the measurements of are noisier than of , and
our correlations of with misalignment angle are found to be weaker and
less robust to masking choices. We also introduce an HI-based dust-polarization
template constructed from the Hessian matrix of the HI intensity, which is
found to correlate more strongly than previous templates with Planck dust
modes.Comment: 30 pages, 17 figure
Filamentary Dust Polarization and the Morphology of Neutral Hydrogen Structures
Filamentary structures in neutral hydrogen (H I) emission are well-aligned
with the interstellar magnetic field, so H I emission morphology can be used to
construct templates that strongly correlate with measurements of polarized
thermal dust emission. We explore how the quantification of filament morphology
affects this correlation. We introduce a new implementation of the Rolling
Hough Transform (RHT) using spherical harmonic convolutions, which enables
efficient quantification of filamentary structure on the sphere. We use this
spherical RHT algorithm along with a Hessian-based method to construct H
I-based polarization templates. We discuss improvements to each algorithm
relative to similar implementations in the literature and compare their
outputs. By exploring the parameter space of filament morphologies with the
spherical RHT, we find that the most informative H I structures for modeling
the magnetic field structure are the thinnest resolved filaments. For this
reason, we find a enhancement in the -mode correlation with dust
polarization with higher-resolution H I observations. We demonstrate that
certain interstellar morphologies can produce parity-violating signatures,
i.e., nonzero and , even under the assumption that filaments are
locally aligned with the magnetic field. Finally, we demonstrate that modes
from interstellar dust filaments are mostly affected by the topology of the
filaments with respect to one another and their relative polarized intensities,
whereas modes are mostly sensitive to the shapes of individual filaments.Comment: 22 pages, 17 figure
On the Cosmic-Ray Spectra of Three-Body Lepton-Flavor-Violating Dark Matter Decays
We consider possible leptonic three-body decays of spin-1/2,
charge-asymmetric dark matter. Assuming a general Dirac structure for the
four-fermion contact interactions of interest, we study the cosmic-ray electron
and positron spectra and show that good fits to the current data can be
obtained for both charged-lepton-flavor-conserving and flavor-violating decay
channels. We find that different choices for the Dirac structure of the
underlying decay operator can be significantly compensated by different choices
for the dark matter mass and lifetime. The decay modes we consider provide
differing predictions for the cosmic-ray positron fraction at energies higher
than those currently probed at the PAMELA experiment; these predictions might
be tested at cosmic-ray detectors like AMS-02.Comment: 14 pages LaTeX, 3 figures (8 eps files). v2 and v3: clarifications
and references adde
Making maps of cosmic microwave background polarization for B-mode studies: The POLARBEAR example
Analysis of cosmic microwave background (CMB) datasets typically requires some filtering of the raw time-ordered data. For instance, in the context of ground-based observations, filtering is frequently used to minimize the impact of low frequency noise, atmospheric contributions and/or scan synchronous signals on the resulting maps. In this work we have explicitly constructed a general filtering operator, which can unambiguously remove any set of unwanted modes in the data, and then amend the map-making procedure in order to incorporate and correct for it. We show that such an approach is mathematically equivalent to the solution of a problem in which the sky signal and unwanted modes are estimated simultaneously and the latter are marginalized over. We investigated the conditions under which this amended map-making procedure can render an unbiased estimate of the sky signal in realistic circumstances. We then discuss the potential implications of these observations on the choice of map-making and power spectrum estimation approaches in the context of B-mode polarization studies. Specifically, we have studied the effects of time-domain filtering on the noise correlation structure in the map domain, as well as impact it may haveon the performance of the popular pseudo-spectrum estimators. We conclude that although maps produced by the proposed estimators arguably provide the most faithful representation of the sky possible given the data, they may not straightforwardly lead to the best constraints on the power spectra of the underlying sky signal and special care may need to be taken to ensure this is the case. By contrast, simplified map-makers which do not explicitly correct for time-domain filtering, but leave it to subsequent steps in the data analysis, may perform equally well and be easier and faster to implement. We focused on polarization-sensitive measurements targeting the B-mode component of the CMB signal and apply the proposed methods to realistic simulations based on characteristics of an actual CMB polarization experiment, POLARBEAR. Our analysis and conclusions are however more generally applicable. \ua9 ESO, 2017
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