129 research outputs found
Geometric Aspects of D-branes and T-duality
We explore the differential geometry of T-duality and D-branes. Because
D-branes and RR-fields are properly described via K-theory, we discuss the
(differential) K-theoretic generalization of T-duality and its application to
the coupling of D-branes to RR-fields. This leads to a puzzle involving the
transformation of the A-roof genera in the coupling.Comment: 26 pages, JHEP format, uses dcpic.sty; v2: references added, v3:
minor change
Relating branes and matrices
We construct a general map between a Dp-brane with magnetic flux and a matrix
configuration of D0-branes, by showing how one can rewrite the boundary state
of the Dp-brane in terms of its D0-brane constituents. This map gives a simple
prescription for constructing the matrices of fuzzy spaces corresponding to
branes of arbitrary shape and topology. Since we explicitly identify the
D0-brane degrees of freedom on the brane, we also derive the D0-brane charge of
the brane in a very direct way including the A-genus term. As a check on our
formalism, we use our map to derive the abelian-Born-Infeld equations of motion
from the action of the D0-brane matrices.Comment: 28 pages, Late
A Class of Topological Actions
We review definitions of generalized parallel transports in terms of
Cheeger-Simons differential characters. Integration formulae are given in terms
of Deligne-Beilinson cohomology classes. These representations of parallel
transport can be extended to situations involving distributions as is
appropriate in the context of quantized fields.Comment: 41 pages, no figure
Geometric K-Homology of Flat D-Branes
We use the Baum-Douglas construction of K-homology to explicitly describe
various aspects of D-branes in Type II superstring theory in the absence of
background supergravity form fields. We rigorously derive various stability
criteria for states of D-branes and show how standard bound state constructions
are naturally realized directly in terms of topological K-cycles. We formulate
the mechanism of flux stabilization in terms of the K-homology of non-trivial
fibre bundles. Along the way we derive a number of new mathematical results in
topological K-homology of independent interest.Comment: 45 pages; v2: References added; v3: Some substantial revision and
corrections, main results unchanged but presentation improved, references
added; to be published in Communications in Mathematical Physic
D-branes, Matrix Theory and K-homology
In this paper, we study a new matrix theory based on non-BPS D-instantons in
type IIA string theory and D-instanton - anti D-instanton system in type IIB
string theory, which we call K-matrix theory. The theory correctly incorporates
the creation and annihilation processes of D-branes. The configurations of the
theory are identified with spectral triples, which are the noncommutative
generalization of Riemannian geometry a la Connes, and they represent the
geometry on the world-volume of higher dimensional D-branes. Remarkably, the
configurations of D-branes in the K-matrix theory are naturally classified by a
K-theoretical version of homology group, called K-homology. Furthermore, we
argue that the K-homology correctly classifies the D-brane configurations from
a geometrical point of view. We also construct the boundary states
corresponding to the configurations of the K-matrix theory, and explicitly show
that they represent the higher dimensional D-branes.Comment: 53 pages, corrected a few typos, version published in JHE
D6-branes and torsion
The D6-brane spectrum of type IIA vacua based on twisted tori and RR
background fluxes is analyzed. In particular, we compute the torsion factors of
the (co)homology groups H_n and describe the effect that they have on D6-brane
physics. For instance, the fact that H_3 contains Z_N subgroups explains why RR
tadpole conditions are affected by geometric fluxes. In addition, the presence
of torsional (co)homology shows why some D6-brane moduli are lifted, and it
suggests how the D-brane discretum appears in type IIA flux compactifications.
Finally, we give a clear, geometrical understanding of the Freed-Witten anomaly
in the present type IIA setup, and discuss its consequences for the
construction of semi-realistic flux vacua.Comment: 35 pages, 1 figure. One reference adde
Branes on Generalized Calibrated Submanifolds
We extend previous results on generalized calibrations to describe
supersymmetric branes in supergravity backgrounds with diverse fields turned
on, and provide several new classes of examples. As an important application,
we show that supersymmetric D-branes in compactifications with field strength
fluxes, and on SU(3)-structure spaces, wrap generalized calibrated
submanifolds, defined by simple conditions in terms of the underlying globally
defined, but non-closed, 2- and 3-forms. We provide examples where the
geometric moduli of D-branes (for instance D7-branes in 3-form flux
configurations) are lifted by the generalized calibration condition. In
addition, we describe supersymmetric D6-branes on generalized calibrated
3-submanifolds of half-flat manifolds, which provide the mirror of B-type
D-branes in IIB CY compactifications with 3-form fluxes. Supersymmetric sets of
such D-branes carrying no homology charges are mirror to supersymmetric sets of
D-branes which are homologically non-trivial, but trivial in K-theory. As an
additional application, we describe models with chiral gauge sectors, realized
in terms of generalized calibrated brane box configurations of NS- and
D5-branes, which are supersymmetric but carry no charges, so that no
orientifold planes are required in the compactification.Comment: 40 pages, 3 figures, references adde
Search for Gravitational Waves Associated with Gamma-Ray Bursts Detected by Fermi and Swift during the LIGO-Virgo Run O3b
We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC-2020 March 27 17:00 UTC). We conduct two independent searches: A generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate. © 2022. The Author(s). Published by the American Astronomical Society
Narrowband Searches for Continuous and Long-duration Transient Gravitational Waves from Known Pulsars in the LIGO-Virgo Third Observing Run
Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectable continuous gravitational waves. This paper presents a fully coherent search for such signals from eighteen pulsars in data from LIGO and Virgo's third observing run (O3). For known pulsars, efficient and sensitive matched-filter searches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagnetic emission. In the search presented here, we relax this assumption and allow both the frequency and the time derivative of the frequency of the gravitational waves to vary in a small range around those inferred from electromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on the strain amplitude for each target. These limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation. In an additional search, we look in O3 data for long-duration (hours-months) transient gravitational waves in the aftermath of pulsar glitches for six targets with a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for such emission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints for any of these targets. © 2022. The Author(s). Published by the American Astronomical Society
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