139 research outputs found
The gauge algebra of double field theory and Courant brackets
We investigate the symmetry algebra of the recently proposed field theory on
a doubled torus that describes closed string modes on a torus with both
momentum and winding. The gauge parameters are constrained fields on the
doubled space and transform as vectors under T-duality. The gauge algebra
defines a T-duality covariant bracket. For the case in which the parameters and
fields are T-dual to ones that have momentum but no winding, we find the gauge
transformations to all orders and show that the gauge algebra reduces to one
obtained by Siegel. We show that the bracket for such restricted parameters is
the Courant bracket. We explain how these algebras are realised as symmetries
despite the failure of the Jacobi identity.Comment: 25 pages, LaTe
Service development success: a contingent approach by knowledge strategy
Purpose
â Contingency theory suggests that effective strategies and structures are not universal but dependant upon situational factors. The purpose of this paper is to explore how the way service firms compete acts as a strategic contingency, moderating the effect of a new service development (NSD) system on innovation performance. Two knowledgeâbased strategies are tested as contingency factors. One strategy adds value for customers via the delivery of personalized knowledgeâbased services; the other strategy adds value by services exploiting codified knowledge.
Design/methodology/approach
â A sample of 70 large service enterprises is used to test a contingency model of service innovation. The NSD system is a synergistic meld of basic building blocks of NSD systems: people organized crossâfunctionally, the discipline of formal processes for guiding development activities, and the deployment of enabling tools/technologies. Regression analysis is used to test the relative impact of these three elements on innovation performance contingent on the type of knowledge strategy employed.
Findings
â While each element of the NSD system has an effect on performance, the optimal design is contingent on the strategy the firm employs. If firms enact a personalization strategy, NSD systems that score high in the deployment of crossâfunctional organization and disciplined processes are higher performers. If firms emphasize a codification strategy, NSD systems that score high in the deployment of tools/technologies are higher performers. Combinations of the two kinds of strategy permit the construction of a fourâcell classification of service firms. This typology is used to further explore the implications for how managers design NSD systems to optimize performance.
Originality/value
â This paper uses a contingency approach to demonstrate that an optimal NSD system is dependent upon the type of knowledge strategy firms deploy. The impact on performance of three components of NSD depends on the degree of either codification and/or personalization in the service offering. A novel approach based on the knowledge management literature is employed creating a typology of service firm strategies. This is the first time such a typology has been postulated
Worldvolume Theories, Holography, Duality and Time
Duality transformations involving compactifications on timelike as well as
spacelike circles link M-theory, the 10+1-dimensional strong coupling limit of
IIA string theory, to other 11-dimensional theories in signatures 9+2 and 6+5
and to type II string theories in all 10-dimensional signatures. These theories
have BPS branes of various world-volume signatures, and here we construct the
world-volume theories for these branes, which in each case have 16
supersymmetries. For the generalised D-branes of the various type II string
theories, these are always supersymmetric Yang-Mills theories with 16
supersymmetries, and we show that these all arise from compactifications of the
supersymmetric Yang-Mills theories in 9+1 or 5+5 dimensions. We discuss the
geometry of the brane solutions and, for the cases in which the world-volume
theories are superconformally invariant, we propose holographically dual string
or M theories in constant curvature backgrounds. For product space solutions
, there is in general a conformal field theory associated with the
boundary of and another with the boundary of .Comment: 35 pages, harvma
Branes, Times and Dualities
Dualities link M-theory, the 10+1 dimensional strong coupling limit of the
IIA string, to other 11-dimensional theories in signatures 9+2 and 6+5, and to
type II string theories in all 10-dimensional signatures. We study the
Freund-Rubin-type compactifications and brane-type solutions of these theories,
and find that branes with various world-volume signatures are possible. For
example, the 9+2 dimensional M* theory has membrane-type solutions with
world-volumes of signature (3,0) and (1,2), and a solitonic solution with
world-volume signature (5,1).Comment: 36 pages, 4 Postscript figures, uses harvmac macr
Generalized Kahler geometry and gerbes
We introduce and study the notion of a biholomorphic gerbe with connection.
The biholomorphic gerbe provides a natural geometrical framework for
generalized Kahler geometry in a manner analogous to the way a holomorphic line
bundle is related to Kahler geometry. The relation between the gerbe and the
generalized Kahler potential is discussed.Comment: 28 page
Double Field Theory
The zero modes of closed strings on a torus --the torus coordinates plus dual
coordinates conjugate to winding number-- parameterize a doubled torus. In
closed string field theory, the string field depends on all zero-modes and so
can be expanded to give an infinite set of fields on the doubled torus. We use
the string field theory to construct a theory of massless fields on the doubled
torus. Key to the consistency is a constraint on fields and gauge parameters
that arises from the L_0 - \bar L_0=0 condition in closed string theory. The
symmetry of this double field theory includes usual and 'dual diffeomorphisms',
together with a T-duality acting on fields that have explicit dependence on the
torus coordinates and the dual coordinates. We find that, along with gravity, a
Kalb-Ramond field and a dilaton must be added to support both usual and dual
diffeomorphisms. We construct a fully consistent and gauge invariant action on
the doubled torus to cubic order in the fields. We discuss the challenges
involved in the construction of the full nonlinear theory. We emphasize that
the doubled geometry is physical and the dual dimensions should not be viewed
as an auxiliary structure or a gauge artifact.Comment: 51 pages. v2: Corrected typo in eqn. (2.48) and very minor typos
elsewhere. Added ref. [9] to M. Van Raamsdon
Duality Twists, Orbifolds, and Fluxes
We investigate compactifications with duality twists and their relation to
orbifolds and compactifications with fluxes. Inequivalent compactifications are
classified by conjugacy classes of the U-duality group and result in gauged
supergravities in lower dimensions with nontrivial Scherk-Schwarz potentials on
the moduli space. For certain twists, this mechanism is equivalent to
introducing internal fluxes but is more general and can be used to stabilize
some of the moduli. We show that the potential has stable minima with zero
energy precisely at the fixed points of the twist group. In string theory, when
the twist belongs to the T-duality group, the theory at the minimum has an
exact CFT description as an orbifold. We also discuss more general twists by
nonperturbative U-duality transformations.Comment: 30 pages, harvmac, references and brief comments on gauged
supergravity adde
Null Brane Intersections
We study pairs of planar D-branes intersecting on null hypersurfaces, and
other related configurations. These are supersymmetric and have finite energy
density. They provide open-string analogues of the parabolic orbifold and
null-fluxbrane backgrounds for closed superstrings. We derive the spectrum of
open strings, showing in particular that if the D-branes are shifted in a
spectator dimension so that they do not intersect, the open strings joining
them have no asymptotic states. As a result, a single non-BPS excitation can in
this case catalyze a condensation of massless modes, changing significantly the
underlying supersymmetric vacuum state. We argue that a similar phenomenon can
modify the null cosmological singularity of the time-dependent orbifolds. This
is a stringy mechanism, distinct from black-hole formation and other strong
gravitational instabilities, and one that should dominate at weak string
coupling. A by-product of our analysis is a new understanding of the appearance
of 1/4 BPS threshold bound states, at special points in the moduli space of
toroidally-compactified type-II string theory.Comment: Tex file, uses harvmac, 24 pages with 5 figures. Corrected typos and
added references. Final version to appear in JHE
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