5,816 research outputs found
A Unified Scheme for Modular Invariant Partition Functions of WZW Models
We introuduce a unified method which can be applied to any WZW model at
arbitrary level to search systematically for modular invariant physical
partition functions. Our method is based essentially on modding out a known
theory on group manifold by a discrete group .
We apply our method to with , and to
models, and obtain all the known partition functions and some
new ones, and give explicit expressions for all of them.Comment: 30 page ,SUTDP/11/93/72 Department of Physics, Sharif University of
Technolog
A Class of N=1 Dual String Pairs and its Modular Superpotential
We compare the N=1 F-theory compactification of Donagi, Grassi and Witten
with modular superpotential - and some closely related models - to dual
heterotic models. We read of the F-theory spectrum from the cohomology of the
fourfold and discuss on the heterotic side the gauge bundle moduli sector
(including the spectral surface) and the necessary fivebranes. Then we consider
the N=1 superpotential and show how a heterotic superpotential matching the
F-theory computation is built up by worldsheet instantons. Finally we discuss
how the original modular superpotential should be corrected by an additional
modular correction factor, which on the F-theory side matches nicely with a
`curve counting function' for the del Pezzo surface. On the heterotic side we
derive the same factor demanding correct T-duality transformation properties of
the superpotential.Comment: 18 pages, Late
Comments on D-Brane and Enhanced Symmetry in Type II String
We propose a configuration of D-branes welded by analogous orbifold operation
to be responsible for the enhancement of gauge symmetry in type II
string compactified on the -type singular limit of K3. Evidences are
discussed from the -type ALE and D-manifold point of view. A subtlety
regarding the ability of seeing the enhanced gauge symmetry
perturbatively is briefly addressed.Comment: LaTex, one figure, 10 page
BPS D-branes on Non-supersymmetric Cycles
In certain regions of the moduli space of K3 and Calabi-Yau manifolds,
D-branes wrapped on non-supersymmetric cycles may give rise to stable
configurations. We show that in the orbifold limit, some of these stable
configurations can be described by solvable boundary conformal field theories.
The world-volume theory of N coincident branes of this type is described by a
non-supersymmetric U(N) gauge theory. At the boundary of the region of
stability, there are marginal deformations connecting the non-supersymmetric
brane to a pair of D-branes wrapped on supersymmetric cycles. We also discuss
various relationships between BPS and non-BPS D-branes of type II string
theories.Comment: LaTeX file, epsf.sty, 26 pages, 2 figures, minor change
Prosuming, or when customers turn collaborators: coordination and motivation of customer contribution
This article investigates the phenomenon of increasing integration of customers and users into the organizational creation of value, focusing primarily on the dissolving boundaries between production and consumption. Concepts such as "prosuming", the "working customer", "produsing" and "interactive value creation" have been used to describe this phenomenon. Within the framework of a research project at the Goethe-University Frankfurt/Main, this debate was investigated theoretically as well as empirically in three case studies. The research question is as follows: Why do customers participate in "new types of prosuming" or "interactive value creation" and how are these processes coordinated by the firms? The results show a considerable range of motives and forms of coordination: The customers’ primary motives to voluntarily assume tasks and activities were both intrinsic and extrinsic in nature. The organizational models identified range from strategies of rationalization to prosuming as a basic business model to the collaborative and interactive value creation between the company and the web-community
Crystallographic Orbifolds: Towards a Classification of Unitary Conformal Field Theories with Central Charge c = 2
We study the moduli space C^2 of unitary two-dimensional conformal field
theories with central charge c=2. We construct all the 28 nonexceptional
nonisolated irreducible components of C^2 that may be obtained by an orbifold
procedure from toroidal theories. The parameter spaces and partition functions
are calculated explicitly, and all multicritical points and lines are
determined. We show that all but four of the 28 irreducible components of C^2
corresponding to nonexceptional orbifolds are directly or indirectly connected
to the moduli space of toroidal theories in C^2. We relate our results to those
by Dixon, Ginsparg, Harvey on the classification of c=3/2 superconformal field
theories and thereby give geometric interpretations to all nonisolated
orbifolds discussed there.Comment: 47 pages, spelling mistakes corrected; final version for JHE
Spacetime-Filling Branes and Strings with Sixteen Supercharges
We discuss branes whose worldvolume dimension equals the target spacetime
dimension, i.e. ``spacetime-filling branes''. In addition to the D9-branes,
there are 9-branes in the NS-NS sectors of both the IIA and IIB strings. The
worldvolume actions of these branes are constructed, via duality, from the
known actions of branes with codimension larger than zero. Each of these types
of branes is used in the construction of a string theory with sixteen
supercharges by modding out a type II string by an appropriate discrete
symmetry and adding 32 9-branes. These constructions are related by a web of
dualities and each arises as a different limit of the Horava-Witten
construction.Comment: 43 pages, LaTeX, 8 figures, uses html.sty, version to appear in Nucl.
Phys.
N=1 Dual String Pairs and their Massless Spectra
We construct two chains of fourdimensional F-theory/heterotic dual string
pairs with N=1 supersymmetry. On the F-theory side as well as on the heterotic
side the geometry of the involved manifolds relies on del Pezzo surfaces. We
match the massless spectra by using, for one chain of models, an index formula
to count the heterotic bundle moduli and determine the dual F-theory spectra
from the Hodge numbers of the fourfolds and of the type IIB base spaces.Comment: 22 pages, latex, some references correcte
On Susy Standard-like models from orbifolds of D=6 Gepner orientifolds
As a further elaboration of the proposal of Ref. [1] we address the
construction of Standard-like models from configurations of stacks of
orientifold planes and D-branes on an internal space with the structure
. As a first step, the construction of
D=6 Type II B orientifolds on Gepner points, in the diagonal invariant case and
for both, odd and even, affine levels is discussed. We build up the explicit
expressions for B-type boundary states and crosscaps and obtain the amplitudes
among them. From such amplitudes we read the corresponding spectra and the
tadpole cancellation equations. Further compactification on a T^2 torus, by
simultaneously orbifolding the Gepner and the torus internal sectors, is
performed. The embedding of the orbifold action in the brane sector breaks the
original gauge groups and leads to N=1 supersymmetric chiral spectra. Whenever
even orbifold action on the torus is considered, new branes, with worldvolume
transverse to torus coordinates, must be included. The detailed rules for
obtaining the D=4 model spectra and tadpole equations are shown. As an
illustration we present a 3 generations Left-Right symmetric model that can be
further broken to a MSSM model.Comment: 40 pages, 2 figures, added references, table 3 correcte
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