382 research outputs found
D-Branes on Noncompact Calabi-Yau Manifolds: K-Theory and Monodromy
We study D-branes on smooth noncompact toric Calabi-Yau manifolds that are
resolutions of abelian orbifold singularities. Such a space has a distinguished
basis {S_i} for the compactly supported K-theory. Using local mirror symmetry
we demonstrate that the S_i have simple transformation properties under
monodromy; in particular, they are the objects that generate monodromy around
the principal component of the discriminant locus. One of our examples, the
toric resolution of C^3/(Z_2 x Z_2), is a three parameter model for which we
are able to give an explicit solution of the GKZ system.Comment: 40 pp, substantial revision
The Elliptic curves in gauge theory, string theory, and cohomology
Elliptic curves play a natural and important role in elliptic cohomology. In
earlier work with I. Kriz, thes elliptic curves were interpreted physically in
two ways: as corresponding to the intersection of M2 and M5 in the context of
(the reduction of M-theory to) type IIA and as the elliptic fiber leading to
F-theory for type IIB. In this paper we elaborate on the physical setting for
various generalized cohomology theories, including elliptic cohomology, and we
note that the above two seemingly unrelated descriptions can be unified using
Sen's picture of the orientifold limit of F-theory compactification on K3,
which unifies the Seiberg-Witten curve with the F-theory curve, and through
which we naturally explain the constancy of the modulus that emerges from
elliptic cohomology. This also clarifies the orbifolding performed in the
previous work and justifies the appearance of the w_4 condition in the elliptic
refinement of the mod 2 part of the partition function. We comment on the
cohomology theory needed for the case when the modular parameter varies in the
base of the elliptic fibration.Comment: 23 pages, typos corrected, minor clarification
Duality Between String Junctions and D-Branes on Del Pezzo Surfaces
We revisit local mirror symmetry associated with del Pezzo surfaces in
Calabi-Yau threefolds in view of five-dimensional N=1 E_N theories compactified
on a circle. The mirror partner of singular Calabi-Yau with a shrinking del
Pezzo four-cycle is described as the affine 7-brane backgrounds probed by a
D3-brane. Evaluating the mirror map and the BPS central charge we relate
junction charges to RR charges of D-branes wrapped on del Pezzo surfaces. This
enables us to determine how the string junctions are mapped to D-branes on del
Pezzo surfaces.Comment: 35 pages, Latex, 1 figure; typos corrected, references update
N=8 supersymmetric mechanics on special K\"ahler manifolds
We propose the Hamiltonian model of supersymmetric mechanics on
dimensional special K\"ahler manifolds (of the rigid type).Comment: 4 page
Nilpotent Marsh and SUSY QM
We consider the nilpotent additions to classical trajectories in
supersymmetric and nonsupersymmetric theories. The condition of anilpotence of
action on some generalized solutions leads to the Witten supersymmetric
Lagrangian. The condition of anilpotence of topological charge is the same as
one of superpotential with spontaneous broken supersymmetry. We should vanish
half of Grassmann constants of integration, because in this case only we obtain
the same number of normalized bosonic and fermionic zero modes.Comment: 8 pages, Latex 2.09. Talk given at the conference in memory of V.I.
Ogievetski, Dubna, July, 1997. To be published in the Proceeding
On D0-branes in Gepner models
We show why and when D0-branes at the Gepner point of Calabi-Yau manifolds
given as Fermat hypersurfaces exist.Comment: 22 pages, substantial improvements in sections 2 and 3, references
added, version to be publishe
The fate of the type I non-BPS D7-brane
We describe the fate of the Type I non-BPS D7-brane, which is tachyonic but
carries a non-trivial K-theory \IZ_2 charge. It decays to topologically
non-trivial gauge field configurations on the background D9-branes. In the
uncompactified theory the decay proceeds to infinity, while with a transverse
torus the decay reaches a final state, a toron gauge configuration with
vanishing Chern classes but non-trivial \IZ_2 charge. A similar behaviour is
obtained for the type I non-BPS D8-brane, and other related systems. We
construct explicit examples of type IIB orientifolds with non-BPS D7-branes,
which are hence non-supersymmetric, but for which supersymmetry is restored
upon condensation of the tachyon. We also report on the interesting structure
of non-BPS states of type IIA theory in the presence of an O6-plane, their
M-theory lifts, the relation between string theory K-theory and M-theory
cohomology, and its interplay with NS-NS charged objects. We discuss several
new effects, including: i) transmutation between NS-NS and RR torsion charges,
ii) non-BPS states classified by K-theory but not by cohomology in string
theory, but whose lift to M-theory is cohomological.Comment: 26 pages, latex, 4 eps figures. v2. Footnote concerning the
non-existence of certain 1-brane charges in Section
Parity Violation with Electrons and Hadrons
A key question in understanding the structure of nucleons involves the role
of sea quarks in their ground state electromagnetic properties such as charge
and magnetism. Parity-violating electron scattering, when combined with
determination of nucleon electromagnetic form factors from parity-conserving
e-N scattering, provides another degree of freedom to separately determine the
up, down and strange quark contributions to nucleon electromagnetic structure.
Strange quarks are unique in that they are exclusively in the nucleon's sea. A
program of experiments using parity violating electron scattering has been
underway for approximately a decade, and results are beginning to emerge. This
paper is a brief overview of the various experiments and their results to date
along with a short-term outlook of what can be anticipated from experiments in
the next few years.Comment: Invited talk at the 17th International IUPAP Conference on Few-Body
Problems in Physic
Dispersive contributions to cross section ratio in forward regime
Two-photon exchange (TPE) contributions to elastic electron-proton scattering
in the forward regime are considered. The imaginary part of TPE amplitude in
these kinematics is related to the DIS nucleon structure functions. The real
part of the TPE amplitude is obtained from the imaginary part by means of
dispersion relations. We demonstrate that the dispersion integrals for the
relevant elastic -scattering amplitude converge and do not need
subtraction. This allows us to make clean prediction for the real part of the
TPE amplitude at forward angles. We furthermore compare and cross
sections which depends on the real part of TPE amplitude, and predict the
positron cross section to exceed the electron one by a few per cent, with the
difference ranging from 1.4% to 2.8% for electron energies in the range
from 3 to 45 GeV. We furthermore predict that the absolute value of this
asymmetry grows with energy, which makes it promising for experimental tests.Comment: 10 pages, 6 figure
Twisted K-Theory from Monodromies
RR fluxes representing different cohomology classes may correspond to the
same twisted K-theory class. We argue that such fluxes are related by
monodromies, generalizing and sometimes T-dual to the familiar monodromies of a
D7-brane. A generalized theta angle is also transformed, but changes by a
multiple of 2pi. As an application, NS5-brane monodromies modify the twisted
K-theory classification of fluxes. Furthermore, in the noncompact case K-theory
does not distinguish flux configurations in which dG is nontrivial in compactly
supported cohomology. Such fluxes are realized as the decay products of
unstable D-branes that wrapped nontrivial cycles. This is interpreted using the
E8 bundle formalism.Comment: 24 Pages, 6 eps figure
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