60 research outputs found
Nearly degenerate heavy sterile neutrinos in cascade decay: mixing and oscillations
Some extensions beyond the Standard Model propose the existence of nearly
degenerate heavy sterile neutrinos. If kinematically allowed these can be
resonantly produced and decay in a cascade to common final states. The common
decay channels lead to mixing of the heavy sterile neutrino states and
interference effects. We implement non-perturbative methods to study the
dynamics of the cascade decay to common final states, which features
similarities but also noteworthy differences with the case of neutral meson
mixing. We show that mixing and oscillations among the nearly degenerate
sterile neutrinos can be detected as \emph{quantum beats} in the distribution
of final states produced from their decay. These oscillations would be a
telltale signal of mixing between heavy sterile neutrinos. We study in detail
the case of two nearly degenerate sterile neutrinos produced in the decay of
pseudoscalar mesons and decaying into a purely leptonic "visible" channel:
. Possible cosmological implications for the
effective number of neutrinos are discussed.Comment: updated references, more comments, same results, published version.
arXiv admin note: text overlap with arXiv:1406.573
Dual-Mode Deformable Models for Free-Viewpoint Video of Sports Events
Generating free-viewpoint video in outdoor sports environ-ments is currently an unsolved problem due to difficulties in obtaining accurate background segmentation and cam-era calibration. This paper introduces a technique for the reconstruction of a scene in the presence of these errors. We tackle the issues of reconstruction completeness, and accuracy of surface shape and appearance. We introduce the concept of the conservative visual hull as a technique to improve reconstruction completeness. We then present a view-dependent surface optimisation technique using de-formable models to improve surface shape and appearance. We contribute a novel dual-mode snake algorithm that is robust to noise and demonstrates reduced dependence on parameterisation by separating the search of the solution space from the data fitting. We conclude by presenting re-sults of this technique along with a quantitative evaluation against other reconstruction techniques using a leave-one-out data set. 1
Toward understanding rich superclusters
We present a morphological study of the two richest superclusters from the
2dF Galaxy Redshift Survey (SCL126, the Sloan Great Wall, and SCL9, the
Sculptor supercluster). We use Minkowski functionals, shapefinders, and galaxy
group information to study the substructure of these superclusters as formed by
different populations of galaxies. We compare the properties of grouped and
isolated galaxies in the core region and in the outskirts of superclusters. The
fourth Minkowski functional and the morphological signature -
show a crossover from low-density morphology (outskirts of supercluster) to
high-density morphology (core of supercluster) at mass fraction . The galaxy content and the morphology of the galaxy populations in
supercluster cores and outskirts is different. The core regions contain a
larger fraction of early type, red galaxies, and richer groups than the
outskirts of superclusters. In the core and outskirt regions the fine structure
of the two prominent superclusters as delineated by galaxies from different
populations also differs. Our results suggest that both local (group/cluster)
and global (supercluster) environments are important in forming galaxy
morphologies and colors (and determining the star formation activity). The
differences between the superclusters indicate that these superclusters have
different evolutional histories (Abridged).Comment: 23 pages, accepted for publication in The Astrophysical Journa
The effect of environment on star forming galaxies at redshift 1 - First insight from PACS
We use deep 70, 100 and 160 um observations taken with PACS, the
Photodetector Array Camera and Spectrometer on board of Herschel, as part of
the PACS Evolutionary Probe (PEP) guaranteed time, to study the relation
between star formation rate and environment at redshift ~ 1 in the GOODS-S and
GOODS-N fields. We use the SDSS spectroscopic catalog to build the local analog
and study the evolution of the star formation activity dependence on the
environment. At z ~ 1 we observe a reversal of the relation between star
formation rate and local density, confirming the results based on Spitzer 24 um
data. However, due to the high accuracy provided by PACS in measuring the star
formation rate also for AGN hosts, we identify in this class of objects the
cause for the reversal of the density-SFR relation. Indeed, AGN hosts favor
high stellar masses, dense regions and high star formation rates. Without the
AGN contribution the relation flattens consistently with respect to the local
analog in the same range of star formation rates. As in the local universe, the
specific star formation rate anti-correlates with the density. This is due to
mass segregation both at high and low redshift. The contribution of AGN hosts
does not affect this anti-correlation, since AGN hosts exhibit the same
specific star formation rate as star forming galaxies at the same mass. The
same global trends and AGN contribution is observed once the relations are
studied per morphological type. We study the specific star formation rate vs
stellar mass relation in three density regimes. Our data provides an indication
that at M/M_{\odot} > 10^{11} the mean specific star formation rate tends to be
higher at higher density, while the opposite trend is observed in the local
SDSS star forming sample.Comment: 10 pages, 16 figures, accepted for publication on A&
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