1,873 research outputs found
Status of CMB observations in 2015
The 2.725 K cosmic microwave background has played a key role in the
development of modern cosmology by providing a solid observational foundation
for constraining possible theories of what happened at very large redshifts and
theoretical speculation reaching back almost to the would-be big bang initial
singularity. After recounting some of the lesser known history of this area, I
summarize the current observational situation and also discuss some exciting
challenges that lie ahead: the search for B modes, the precision mapping of the
CMB gravitational lensing potential, and the ultra-precise characterization of
the CMB frequency spectrum, which would allow the exploitation of spectral
distortions to probe new physics.Comment: 17 pages, 3 figures, Latex, conference proceeding based on talk at
CosPA 2015 in Daejeon, South Korea in October 2015, minor typos correcte
The binned bispectrum estimator: template-based and non-parametric CMB non-Gaussianity searches
We describe the details of the binned bispectrum estimator as used for the
official 2013 and 2015 analyses of the temperature and polarization CMB maps
from the ESA Planck satellite. The defining aspect of this estimator is the
determination of a map bispectrum (3-point correlator) that has been binned in
harmonic space. For a parametric determination of the non-Gaussianity in the
map (the so-called fNL parameters), one takes the inner product of this binned
bispectrum with theoretically motivated templates. However, as a complementary
approach one can also smooth the binned bispectrum using a variable smoothing
scale in order to suppress noise and make coherent features stand out above the
noise. This allows one to look in a model-independent way for any statistically
significant bispectral signal. This approach is useful for characterizing the
bispectral shape of the galactic foreground emission, for which a theoretical
prediction of the bispectral anisotropy is lacking, and for detecting a
serendipitous primordial signal, for which a theoretical template has not yet
been put forth. Both the template-based and the non-parametric approaches are
described in this paper.Comment: Latex 42 pages with 10 figures and JCAP macros. v2: corrected small
mistake in section 5.3, changed colour scale of slice figures, other minor
changes and additions, matches published versio
On Detecting Discrete Cheshire Charge
We analyze the charges carried by loops of string in models with non-abelian
local discrete symmetry. The charge on a loop has no localized source, but can
be detected by means of the Aharonov--Bohm interaction of the loop with another
string. We describe the process of charge detection, and the transfer of charge
between point particles and string loops, in terms of gauge--invariant
correlation functions.Comment: (17 pp
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