175 research outputs found
D-brane charges on non-simply connected groups
The maximally symmetric D-branes of string theory on the non-simply connected
Lie group SU(n)/Z_d are analysed using conformal field theory methods, and
their charges are determined. Unlike the well understood case for simply
connected groups, the charge equations do not determine the charges uniquely,
and the charge group associated to these D-branes is therefore in general not
cyclic. The precise structure of the charge group depends on some number
theoretic properties of n, d, and the level of the underlying affine algebra k.
The examples of SO(3)=SU(2)/Z_2 and SU(3)/Z_3 are worked out in detail, and the
charge groups for SU(n)/Z_d at most levels k are determined explicitly.Comment: 31 pages, 1 figure. 2 refs added. Added the observation: the charge
group for each su(2) theory equals the centre of corresponding A-D-E grou
D-brane charges on SO(3)
In this letter we discuss charges of D-branes on the group manifold SO(3).
Our discussion will be based on a conformal field theory analysis of boundary
states in a Z_2-orbifold of SU(2). This orbifold differs from the one recently
discussed by Gaberdiel and Gannon in its action on the fermions and leads to a
drastically different charge group. We shall consider maximally symmetric
branes as well as branes with less symmetry, and find perfect agreement with a
recent computation of the corresponding K-theory groups.Comment: 11 pages, 1 figure. Some comments adde
Probing Orientifold Behavior Near NS Branes
The effect of NS 5 branes on an orientifold is studied. The orientifold is
allowed to pass through a pile of k NS branes forming a regularized CHS
geometry. Its effect on open strings in its vicinity is used to study the
change in the orientifold charge induced by the NS branes.Comment: Important references added, 30 pages, 8 figure
Liouville Field Theory on an Unoriented Surface
Liouville field theory on an unoriented surface is investigated, in
particular, the one point function on a RP^2 is calculated. The constraint of
the one point function is obtained by using the crossing symmetry of the two
point function. There are many solutions of the constraint and we can choose
one of them by considering the modular bootstrap.Comment: 13 pages, no figures, LaTeX, minor changes, equations in section 4
are correcte
Crosscap States for Orientifolds of Euclidean AdS_3
Crosscap states for orientifolds of Euclidean AdS_3 are constructed. We show
that our crosscap states describe the same orientifolds which were obtained by
the classical analysis. The spectral density of open strings in the system with
orientifold can be read from the M"obius strip amplitudes and it is compared to
that of the open strings stretched between branes and their mirrors. We also
compute the Klein bottle amplitudes.Comment: 17 pages, LaTeX2e, v2: clarification and discussion added, v3: minor
changes, to appear in JHE
Supersymmetric D-branes in the D1-D5 background
We construct supersymmetric D-brane probe solutions in the background of the
2-charge D1-D5 system on M, where M is either K3 or T^4. We focus on
`near-horizon bound states' that preserve supersymmetries of the near-horizon
AdS_3 x S^3 x M geometry and are static with respect to the global time
coordinate. We find a variety of half-BPS solutions that span an AdS_2 subspace
in AdS_3, carry worldvolume flux and can wrap an S^2 within S^3 and/or
supersymmetric cycles in M.Comment: Latex, 24 pages. v2: references added, modified Discussion, published
versio
Open String Attractors
We present a simple example of a supersymmetric attractor mechanism in the
purely open string context of D-branes embedded in curved space-time. Our
example involves a class of D3-branes embedded in the 2-charge D1-D5 background
of type IIB whose worldvolume contains a 2-sphere. Turning on worldvolume
fluxes, these branes carry induced (p,q) string charges. Supersymmetric
configurations display a flow of the open string moduli towards an attractor
solution independent of their asymptotics. The equations governing this
mechanism closely resemble the attractor flow equations for supersymmetric
black holes in closed string theory. The BPS equations take the form of a
gradient flow and describe worldvolume solitons interpolating between an AdS_2
geometry where the two-sphere has collapsed, and an attractor solution with
AdS_2 x S^2 geometry. In these limiting solutions, the preserved supersymmetry
is enhanced from 4 to 8 supercharges. We also discuss the interpretation of our
solutions as intersecting brane configurations placed in the D1-D5 background,
as well as the S-duality transformation to the F1-NS5 background.Comment: 37 pages, 6 figures. v2: small corrections, figure and references
adde
Predictive validity of the CriSTAL tool for short-term mortality in older people presenting at Emergency Departments: a prospective study
© 2018, The Author(s). Abstract: To determine the validity of the Australian clinical prediction tool Criteria for Screening and Triaging to Appropriate aLternative care (CRISTAL) based on objective clinical criteria to accurately identify risk of death within 3 months of admission among older patients. Methods: Prospective study of â„ 65 year-olds presenting at emergency departments in five Australian (Aus) and four Danish (DK) hospitals. Logistic regression analysis was used to model factors for death prediction; Sensitivity, specificity, area under the ROC curve and calibration with bootstrapping techniques were used to describe predictive accuracy. Results: 2493 patients, with median age 78â80 years (DKâAus). The deceased had significantly higher mean CriSTAL with Australian mean of 8.1 (95% CI 7.7â8.6 vs. 5.8 95% CI 5.6â5.9) and Danish mean 7.1 (95% CI 6.6â7.5 vs. 5.5 95% CI 5.4â5.6). The model with Fried Frailty score was optimal for the Australian cohort but prediction with the Clinical Frailty Scale (CFS) was also good (AUROC 0.825 and 0.81, respectively). Values for the Danish cohort were AUROC 0.764 with Fried and 0.794 using CFS. The most significant independent predictors of short-term death in both cohorts were advanced malignancy, frailty, male gender and advanced age. CriSTALâs accuracy was only modest for in-hospital death prediction in either setting. Conclusions: The modified CriSTAL tool (with CFS instead of Friedâs frailty instrument) has good discriminant power to improve prognostic certainty of short-term mortality for ED physicians in both health systems. This shows promise in enhancing clinicianâs confidence in initiating earlier end-of-life discussions
Orientifolds of SU(2)/U(1) WZW Models
The orientifolds of SU(2)/U(1) gauged WZW models are investigated. In
particular, we construct the new type orientifolds and identify their
geometries. We closely follow the analysis of D-branes in the SU(2)/U(1) WZW
models, which was given by Maldacena, Moore and Seiberg.Comment: 33 pages, 3 figures, the geometry of orientifolds corrected and the
spectral flow identification reconsidere
Partitioning of Mg, Sr, Ba and U into a subaqueous calcite speleothem
The trace-element geochemistry of speleothems is becoming increasingly used for reconstructing palaeoclimate, with a particular emphasis on elements whose concentrations vary according to hydrological conditions at the cave site (e.g. Mg, Sr, Ba and U). An important step in interpreting trace-element abundances is understanding the underlying processes of their incorporation. This includes quantifying the fractionation between the solution and speleothem carbonate via partition coefficients (where the partitioning (D) of element X (DX) is the molar ratio [X/Ca] in the calcite divided by the molar ratio [X/Ca] in the parent water) and evaluating the degree of spatial variability across time-constant speleothem layers. Previous studies of how these elements are incorporated into speleothems have focused primarily on stalagmites and their source waters in natural cave settings, or have used synthetic solutions under cave-analogue laboratory conditions to produce similar dripstones. However, dripstones are not the only speleothem types capable of yielding useful palaeoclimate information. In this study, we investigate the incorporation of Mg, Sr, Ba and U into a subaqueous calcite speleothem (CD3) growing in a natural cave pool in Italy. Pool-water measurements extending back 15 years reveal a remarkably stable geochemical environment owing to the deep cave setting, enabling the calculation of precise solution [X/Ca]. We determine the trace element variability of âmodernâ subaqueous calcite from a drill core taken through CD3 to derive DMg, DSr, DBa and DU then compare these with published cave, cave-analogue and seawater-analogue studies. The DMg for CD3 is anomalously high (0.042 ± 0.002) compared to previous estimates at similar temperatures (âŒ8 °C). The DSr (0.100 ± 0.007) is similar to previously reported values, but data from this study as well as those from Tremaine and Froelich (2013) and Day and Henderson (2013) suggest that [Na/Sr] might play an important role in Sr incorporation through the potential for Na to outcompete Sr for calcite non-lattice sites. DBa in CD3 (0.086 ± 0.008) is similar to values derived by Day and Henderson (2013) under cave-analogue conditions, whilst DU (0.013 ± 0.002) is almost an order of magnitude lower, possibly due to the unusually slow speleothem growth rates (<1 ÎŒm aâ1), which could expose the crystal surfaces to leaching of uranyl carbonate. Finally, laser-ablation ICP-MS analysis of the upper 7 ÎŒm of CD3, regarded as âmodernâ for the purposes of this study, reveals considerable heterogeneity, particularly for Sr, Ba and U, which is potentially indicative of compositional zoning. This reinforces the need to conduct 2D mapping and/or multiple laser passes to capture the range of time-equivalent elemental variations prior to palaeoclimate interpretation
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