187 research outputs found
Constraining dark matter decays with cosmic microwave background and weak lensing shear observations
From observations at low and high redshifts, it is well known that the bulk
of dark matter (DM) has to be stable or at least very long-lived. However, the
possibility that a small fraction of DM is unstable or that all DM decays with
a half-life time () significantly longer than the age of the Universe is
not ruled out. One-body decaying dark matter (DDM) consists of a minimal
extension to the CDM model. It causes a modification of the cosmic
growth history as well as a suppression of the small-scale clustering signal,
providing interesting consequences regarding the tension, which is the
observed difference in the clustering amplitude between weak-lensing (WL) and
cosmic microwave background (CMB) observations. In this paper, we investigate
models in which a fraction or all DM decays into radiation, focusing on the
long-lived regime, that is, ( being the
Hubble time). We used WL data from the Kilo-Degree Survey (KiDS) and CMB data
from Planck. First, we confirm that this DDM model cannot alleviate the
difference. We then show that the most constraining power for DM decay does not
come from the nonlinear WL data, but from CMB via the integrated Sachs-Wolfe
effect. From the CMB data alone, we obtain constraints of ~Gyr
if all DM is assumed to be unstable, and we show that a maximum fraction of
is allowed to decay assuming the half-life time to be comparable to
(or shorter than) one Hubble time. The constraints from the KiDS-1000 WL data
are significantly weaker, ~Gyr and . Combining the CMB
and WL data does not yield tighter constraints than the CMB alone, except for
short half-life times, for which the maximum allowed fraction becomes .
All limits are provided at the 95% confidence level
Probing the two-body decaying dark matter scenario with weak lensing and the cosmic microwave background
Decaying dark matter (DDM) scenarios have recently re-gained attention due to
their potential ability to resolve the well-known clustering (or ) tension
between weak lensing (WL) and cosmic microwave background (CMB) measurements.
In this paper, we investigate a well-established model, where the original dark
matter (DM) particle decays into a massless and a massive daughter particles.
The latter obtains a velocity kick during the decay process resulting in a
suppression of the matter power spectrum at scales that are observable with WL
shear observations. We perform the first fully nonlinear WL analysis of this
two-body decaying dark matter (DDM) scenario including intrinsic
alignment and baryonic feedback processes. We thereby use the cosmic shear band
power spectra from the KiDS-1000 data combining it with temperature and
polarization data from Planck to constrain the DDM model. We report
new limits on the decay rate and mass splitting parameters that are
significantly stronger than previous results, especially for the case of low
mass splittings. We also investigate the tension only finding a marginal
improvement of 0.3 for DDM compared to the CDM case.
The improvement is not caused by a shift but a slight bloating of the posterior
contours caused by the additional free model parameters. We therefore conclude
that the two-body DDM model does not provide a convincing solution to
the tension. Our emulator to model the nonlinear DDM power
spectrum is published as part of the publicly available code DMemu at
https://github.com/jbucko/DMemu.Comment: 16 pages, 13 figure
A mitotic kinase scaffold depleted in testicular seminomas impacts spindle orientation in germ line stem cells.
Correct orientation of the mitotic spindle in stem cells underlies organogenesis. Spindle abnormalities correlate with cancer progression in germ line-derived tumors. We discover a macromolecular complex between the scaffolding protein Gravin/AKAP12 and the mitotic kinases, Aurora A and Plk1, that is down regulated in human seminoma. Depletion of Gravin correlates with an increased mitotic index and disorganization of seminiferous tubules. Biochemical, super-resolution imaging, and enzymology approaches establish that this Gravin scaffold accumulates at the mother spindle pole during metaphase. Manipulating elements of the Gravin-Aurora A-Plk1 axis prompts mitotic delay and prevents appropriate assembly of astral microtubules to promote spindle misorientation. These pathological responses are conserved in seminiferous tubules from Gravin(-/-) mice where an overabundance of Oct3/4 positive germ line stem cells displays randomized orientation of mitotic spindles. Thus, we propose that Gravin-mediated recruitment of Aurora A and Plk1 to the mother (oldest) spindle pole contributes to the fidelity of symmetric cell division
Quasiparticle bandgap engineering of graphene and graphone on hexagonal boron nitride substrate
Graphene holds great promise for post-silicon electronics, however, it faces
two main challenges: opening up a bandgap and finding a suitable substrate
material. In principle, graphene on hexagonal boron nitride (hBN) substrate
provides potential system to overcome these challenges. Recent theoretical and
experimental studies have provided conflicting results: while theoretical
studies suggested a possibility of a finite bandgap of graphene on hBN, recent
experimental studies find no bandgap. Using the first-principles density
functional method and the many-body perturbation theory, we have studied
graphene on hBN substrate. A Bernal stacked graphene on hBN has a bandgap on
the order of 0.1 eV, which disappears when graphene is misaligned with respect
to hBN. The latter is the likely scenario in realistic devices. In contrast, if
graphene supported on hBN is hydrogenated, the resulting system (graphone)
exhibits bandgaps larger than 2.5 eV. While the bandgap opening in graphene/hBN
is due to symmetry breaking and is vulnerable to slight perturbation such as
misalignment, the graphone bandgap is due to chemical functionalization and is
robust in the presence of misalignment. The bandgap of graphone reduces by
about 1 eV when it is supported on hBN due to the polarization effects at the
graphone/hBN interface. The band offsets at graphone/hBN interface indicate
that hBN can be used not only as a substrate but also as a dielectric in the
field effect devices employing graphone as a channel material. Our study could
open up new way of bandgap engineering in graphene based nanostructures.Comment: 8 pages, 4 figures; Nano Letters, Publication Date (Web): Oct. 25
2011, http://pubs.acs.org/doi/abs/10.1021/nl202725
Effect of Layer-Stacking on the Electronic Structure of Graphene Nanoribbons
The evolution of electronic structure of graphene nanoribbons (GNRs) as a
function of the number of layers stacked together is investigated using
\textit{ab initio} density functional theory (DFT) including interlayer van der
Waals interactions. Multilayer armchair GNRs (AGNRs), similar to single-layer
AGNRs, exhibit three classes of band gaps depending on their width. In zigzag
GNRs (ZGNRs), the geometry relaxation resulting from interlayer interactions
plays a crucial role in determining the magnetic polarization and the band
structure. The antiferromagnetic (AF) interlayer coupling is more stable
compared to the ferromagnetic (FM) interlayer coupling. ZGNRs with the AF
in-layer and AF interlayer coupling have a finite band gap while ZGNRs with the
FM in-layer and AF interlayer coupling do not have a band gap. The ground state
of the bi-layer ZGNR is non-magnetic with a small but finite band gap. The
magnetic ordering is less stable in multilayer ZGNRs compared to single-layer
ZGNRs. The quasipartcle GW corrections are smaller for bilayer GNRs compared to
single-layer GNRs because of the reduced Coulomb effects in bilayer GNRs
compared to single-layer GNRs.Comment: 10 pages, 5 figure
Contribution to the understanding of tribological properties of graphite intercalation compounds with metal chloride
Intrinsic tribological properties of lamellar compounds are usually attributed to the presence of van der Waals gaps in their structure through which interlayer interactions are weak. The controlled variation of the distances and interactions between graphene layers by intercalation of electrophilic species in graphite is used in order to explore more deeply the friction reduction properties of low-dimensional compounds. Three graphite intercalation compounds with antimony pentachloride, iron trichloride and aluminium trichloride are studied. Their tribological properties are correlated to their structural parameters, and the interlayer interactions are deduced from ab initio bands structure calculations
- …