117 research outputs found
Spherically symmetric ADM gravity with variable G and Lambda(c)
This paper investigates the Arnowitt--Deser--Misner (hereafter ADM) form of
spherically symmetric gravity with variable Newton parameter G and cosmological
term Lambda(c). The Newton parameter is here treated as a dynamical variable,
rather than being merely an external parameter as in previous work on closely
related topics. The resulting Hamilton equations are obtained; interestingly, a
static solution exists, that reduces to Schwarzschild geometry in the limit of
constant G, describing a Newton parameter ruled by a nonlinear differential
equation in the radial variable r. A remarkable limiting case is the one for
which the Newton parameter obeys an almost linear growth law at large r. An
exact solution for G as a function of r is also obtained in the case of
vanishing cosmological constant. Some observational implications of these
solutions are obtained and briefly discussed.Comment: 16 pages, 2 figures. The presentation has been improved in all
section
Direct WIMP identification: Physics performance of a segmented noble-liquid target immersed in a Gd-doped water veto
We evaluate background rejection capabilities and physics performance of a
detector composed of two diverse elements: a sensitive target (filled with one
or two species of liquefied noble gasses) and an active veto (made of Gd-doped
ultra-pure water). A GEANT4 simulation shows that for a direct WIMP search,
this device can reduce the neutron background to O(1) event per year per tonne
of material. Our calculation shows that an exposure of one tonne year
will suffice to exclude spin-independent WIMP-nucleon cross sections ranging
from pb to pb.Comment: 17 pages, 5 figures. Version accepted for publication in JCA
Submillimeter galaxies behind the Bullet Cluster (1E 0657-56)
Clusters of galaxies are effective gravitational lenses able to magnify
background galaxies and making it possible to probe the fainter part of the
galaxy population. Submillimeter galaxies, which are believed to be
star-forming galaxies at typical redshifts of 2 to 3, are a major contaminant
to the extended Sunyaev-Zeldovich (SZ) signal of galaxy clusters. For a proper
quantification of the SZ signal the contribution of submillimeter galaxies
needs to be quantified. The aims of this study are to identify submillimeter
sources in the field of the Bullet Cluster (1E 0657-56), a massive cluster of
galaxies at z~0.3, measure their flux densities at 870 micron, and search for
counterparts at other wavelengths to constrain their properties. We carried out
deep observations of the submillimeter continuum emission at 870 micron using
the Large APEX BOlometer CAmera (LABOCA) on the Atacama Pathfinder EXperiment
(APEX) telescope. Several numerical techniques were used to quantify the noise
properties of the data and extract sources. In total, seventeen sources were
found. Thirteen of them lie in the central 10 arcminutes of the map, which has
a pixel sensitivity of 1.2 mJy per 22 arcsec beam. After correction for flux
boosting and gravitational lensing, the number counts are consistent with
published submm measurements. Nine of the sources have infrared counterparts in
Spitzer maps. The strongest submm detection coincides with a source previously
reported at other wavelengths, at an estimated redshift z~2.7. If the submm
flux arises from two images of a galaxy magnified by a total factor of 75, as
models have suggested, its intrinsic flux would be around 0.6 mJy, consistent
with an intrinsic luminosity below 10^12 L_sun.Comment: Accepted by A&A, 15 pages, 11 figure
Photodynamics and quantum efficiency of germanium vacancy color centers in diamond
Color centers in diamond-especially group IV defects-have been advanced as a viable solid-state platform for quantum photonics and information technologies. We investigate the photodynamics and characteristics of germanium-vacancy (GeV) centers hosted in high-pressure high-temperature diamond nanocrystals. Through back-focal plane imaging, we analyze the far-field radiation pattern of the investigated emitters and derive a crossed-dipole emission, which is strongly aligned along one axis. We use this information in combination with lifetime measurements to extract the decay rate statistics of the GeV emitters and determine their quantum efficiency, which we estimated to be ∼ (22 ± 2) %. Our results offer further insight into the photodynamic properties of the GeV center in nanodiamonds and confirm its suitability as a desirable system for quantum technologies
SN 2016coi/ASASSN-16fp: An example of residual helium in a type Ic supernova?
The optical observations of Ic-4 supernova (SN) 2016coi/ASASSN-16fp, from
to days after explosion, are presented along with analysis
of its physical properties. The SN shows the broad lines associated with SNe
Ic-3/4 but with a key difference. The early spectra display a strong absorption
feature at \AA\ which is not seen in other SNe~Ic-3/4 at this
epoch. This feature has been attributed to He I in the literature. Spectral
modelling of the SN in the early photospheric phase suggests the presence of
residual He in a C/O dominated shell. However, the behaviour of the He I lines
are unusual when compared with He-rich SNe, showing relatively low velocities
and weakening rather than strengthening over time. The SN is found to rise to
peak d after core-collapse reaching a bolometric luminosity of Lp
\ergs. Spectral models, including the nebular epoch, show
that the SN ejected \msun\ of material, with \msun\ below
5000 \kms, and with a kinetic energy of erg. The
explosion synthesised \msun\ of 56Ni. There are significant
uncertainties in E(B-V)host and the distance however, which will affect Lp and
MNi. SN 2016coi exploded in a host similar to the Large Magellanic Cloud (LMC)
and away from star-forming regions. The properties of the SN and the
host-galaxy suggest that the progenitor had of \msun\
and was stripped almost entirely down to its C/O core at explosion.Comment: Accepted for publication in MNRAS. Updated to reflect the published
version, minor typographical changes onl
Effect of weekend admission on in-hospital mortality and functional outcomes for patients with acute subarachnoid haemorrhage (SAH)
BACKGROUND: Aneurysmal subarachnoid haemorrhage (aSAH) is an acute cerebrovascular event with high socioeconomic impact as it tends to affect younger patients. The recent NCEPOD study looking into management of aSAH has recommended that neurovascular units in the United Kingdom should aim to secure cerebral aneurysms within 48 h and that delays because of weekend admissions can increase the mortality and morbidity attributed to aSAH. METHOD: We used data from a prospective audit of aSAH patients admitted between January 2009 and December 2011. The baseline demographic and clinical features of the weekend and weekday groups were compared using the chi-squared test and T-test. Cox proportional hazards models (Proc Phreg in SAS) were used to calculate the adjusted overall hazard of in-hospital death associated with admission on weekend, adjusting for age, sex, baseline WFNS grade, type of treatment received and time from scan to treatment. Sliding dichotomy analysis was used to estimate the difference in outcomes after SAH at 3 months in weekend and weekday admissions. RESULTS: Those admitted on weekends had a significantly higher scan to treatment time (83.05 ± 83.4 h vs 40.4 ± 53.4 h, P < 0.0001) and admission to treatment (71.59 ± 79.8 h vs 27.5 ± 44.3 h, P < 0.0001) time. After adjustments for adjusted for relevant covariates weekend admission was statistically significantly associated with excess in-hospital mortality (HR = 2.1, CL [1.13–4.0], P = 0.01). After adjustments for all the baseline covariates, the sliding dichotomy analysis did not show effects of weekend admission on long-term outcomes on the good, intermediate and worst prognostic bands. CONCLUSIONS: This study provides important data showing excess in-hospital mortality of patients with SAH on weekend admissions served by the United Kingdom’s National Health Service.; However, there were no effects of weekend admission on long-term outcomes. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00701-016-2746-z) contains supplementary material, which is available to authorized users
Strong Gravitational Lensing as a Probe of Gravity, Dark-Matter and Super-Massive Black Holes
Whereas considerable effort has been afforded in understanding the properties
of galaxies, a full physical picture, connecting their baryonic and dark-matter
content, super-massive black holes, and (metric) theories of gravity, is still
ill-defined. Strong gravitational lensing furnishes a powerful method to probe
gravity in the central regions of galaxies. It can (1) provide a unique
detection-channel of dark-matter substructure beyond the local galaxy group,
(2) constrain dark-matter physics, complementary to direct-detection
experiments, as well as metric theories of gravity, (3) probe central
super-massive black holes, and (4) provide crucial insight into galaxy
formation processes from the dark matter point of view, independently of the
nature and state of dark matter. To seriously address the above questions, a
considerable increase in the number of strong gravitational-lens systems is
required. In the timeframe 2010-2020, a staged approach with radio (e.g. EVLA,
e-MERLIN, LOFAR, SKA phase-I) and optical (e.g. LSST and JDEM) instruments can
provide 10^(2-4) new lenses, and up to 10^(4-6) new lens systems from
SKA/LSST/JDEM all-sky surveys around ~2020. Follow-up imaging of (radio) lenses
is necessary with moderate ground/space-based optical-IR telescopes and with
30-50m telescopes for spectroscopy (e.g. TMT, GMT, ELT). To answer these
fundamental questions through strong gravitational lensing, a strong investment
in large radio and optical-IR facilities is therefore critical in the coming
decade. In particular, only large-scale radio lens surveys (e.g. with SKA)
provide the large numbers of high-resolution and high-fidelity images of lenses
needed for SMBH and flux-ratio anomaly studies.Comment: White paper submitted to the 2010 Astronomy & Astrophysics Decadal
Surve
Deja Vu All Over Again: The Reappearance of Supernova Refsdal
In Hubble Space Telescope (HST) imaging taken on 2014 November 10, four images of supernova (SN) "Refsdal" (redshift z = 1.49) appeared in an Einstein-cross-like configuration (images S1–S4) around an early-type galaxy in the cluster MACS J1149.5+2223 (z = 0.54). Almost all lens models of the cluster have predicted that the SN should reappear within a year in a second host-galaxy image created by the cluster's potential. In HST observations taken on 2015 December 11, we find a new source at the predicted position of the new image of SN Refsdal approximately from the previous images S1–S4. This marks the first time the appearance of a SN at a particular time and location in the sky was successfully predicted in advance! We use these data and the light curve from the first four observed images of SN Refsdal to place constraints on the relative time delay and magnification of the new image (SX) compared to images S1–S4. This enables us, for the first time, to test "blind" lens model predictions of both magnifications and time delays for a lensed SN. We find that the timing and brightness of the new image are consistent with the blind predictions of a fraction of the models. The reappearance illustrates the discriminatory power of this blind test and its utility to uncover sources of systematic uncertainty. From planned HST photometry, we expect to reach a precision of 1%–2% on the time delay between S1–S4 and SX
Multiple images of a highly magnified supernova formed by an early-type cluster galaxy lens
In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z = 0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z = 1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses
Dark Matter Candidates: A Ten-Point Test
An extraordinarily rich zoo of non-baryonic Dark Matter candidates has been
proposed over the last three decades. Here we present a 10-point test that a
new particle has to pass, in order to be considered a viable DM candidate: I.)
Does it match the appropriate relic density? II.) Is it {\it cold}? III.) Is it
neutral? IV.) Is it consistent with BBN? V.) Does it leave stellar evolution
unchanged? VI.) Is it compatible with constraints on self-interactions? VII.)
Is it consistent with {\it direct} DM searches? VIII.) Is it compatible with
gamma-ray constraints? IX.) Is it compatible with other astrophysical bounds?
X.) Can it be probed experimentally?Comment: 29 pages, 12 figure
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