111 research outputs found
D-Branes on K3-Fibrations
B-type D-branes are constructed on two different K3-fibrations over IP_1
using boundary conformal field theory at the rational Gepner points of these
models. The microscopic CFT charges are compared with the Ramond charges of
D-branes wrapped on holomorphic cycles of the corresponding Calabi-Yau
manifold. We study in particular D4-branes and bundles localized on the K3
fibers, and find from CFT that each irreducible component of a bundle on K3
gains one modulus upon fibration over IP_1. This is in agreement with
expectations and so provides a further test of the boundary CFT.Comment: 16p, harvmac, tables.tex; typos corrected, refs added, discussion
about moduli spaces improve
Triangle-generation in topological D-brane categories
Tachyon condensation in topological Landau-Ginzburg models can generally be
studied using methods of commutative algebra and properties of triangulated
categories. The efficiency of this approach is demonstrated by explicitly
proving that every D-brane system in all minimal models of type ADE can be
generated from only one or two fundamental branes.Comment: 34 page
The Generalized Green-Schwarz Mechanism for Type IIB Orientifolds with D3- and D7-Branes
In this paper, we work out in detail the tadpole cancellation conditions as
well as the generalized Green-Schwarz mechanism for type IIB orientifold
compactifications with D3- and D7-branes. We find that not only the well-known
D3- and D7-tadpole conditions have to be satisfied, but in general also the
vanishing of the induced D5-brane charges leads to a non-trivial constraint. In
fact, for the case the latter condition is important for
the cancellation of chiral anomalies. We also extend our analysis by including
D9- as well as D5-branes and determine the rules for computing the chiral
spectrum of the combined system.Comment: 33+7 pages; 2 figures; v2: references added; v3: published versio
Boundary Fixed Points, Enhanced Gauge Symmetry and Singular Bundles on K3
We investigate certain fixed points in the boundary conformal field theory
representation of type IIA D-branes on Gepner points of K3. They correspond
geometrically to degenerate brane configurations, and physically lead to
enhanced gauge symmetries on the world-volume. Non-abelian gauge groups arise
if the stabilizer group of the fixed points is realized projectively, which is
similar to D-branes on orbifolds with discrete torsion. Moreover, the fixed
point boundary states can be resolved into several irreducible components.
These correspond to bound states at threshold and can be viewed as (non-locally
free) sub-sheaves of semi-stable sheaves. Thus, the BCFT fixed points appear to
carry two-fold geometrical information: on the one hand they probe the boundary
of the instanton moduli space on K3, on the other hand they probe discrete
torsion in D-geometry.Comment: harvmac, 20
Obstructions and lines of marginal stability from the world-sheet
The behaviour of supersymmetric D-branes under deformations of the closed
string background is studied using world-sheet methods. We explain how lines of
marginal stability and obstructions arise from this point of view. We also show
why N=2 B-type branes may be obstructed against (cc) perturbations, but why
such obstructions do not occur for N=4 superconformal branes at c=6, i.e. for
half-supersymmetric D-branes on K3. Our analysis is based on a field theory
approach in superspace, as well as on techniques from perturbed conformal field
theory.Comment: 32 page
Defects and Bulk Perturbations of Boundary Landau-Ginzburg Orbifolds
We propose defect lines as a useful tool to study bulk perturbations of
conformal field theories, in particular to analyse the induced renormalisation
group flows of boundary conditions. As a concrete example we investigate bulk
perturbations of N=2 supersymmetric minimal models. To these perturbations we
associate a special class of defects between the respective UV and IR theories,
whose fusion with boundary conditions indeed reproduces the behaviour of the
latter under the corresponding RG flows. v2: Some explanations added in section
4, minor changes.Comment: 37 pages, 6 figure
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
Measurement of the CP-Violating Asymmetry Amplitude sin2
We present results on time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates. The measurements use a data sample of about 88 million Y(4S) --> B Bbar decays collected between 1999 and 2002 with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We study events in which one neutral B meson is fully reconstructed in a final state containing a charmonium meson and the other B meson is determined to be either a B0 or B0bar from its decay products. The amplitude of the CP-violating asymmetry, which in the Standard Model is proportional to sin2beta, is derived from the decay-time distributions in such events. We measure sin2beta = 0.741 +/- 0.067 (stat) +/- 0.033 (syst) and |lambda| = 0.948 +/- 0.051 (stat) +/- 0.017 (syst). The magnitude of lambda is consistent with unity, in agreement with the Standard Model expectation of no direct CP violation in these modes
TRY plant trait database â enhanced coverage and open access
Plant traitsâthe morphological, anatomical, physiological, biochemical and phenological characteristics of plantsâdetermine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of traitâbased plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traitsâalmost complete coverage for âplant growth formâ. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and traitâenvironmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives
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