70 research outputs found
A note on supersymmetric D-brane dynamics
We study the spin dependence of D-brane dynamics in the Green-Schwarz
formalism of boundary states. In particular we show how to interpret insertion
of supercharges on the boundary state as sources of non-universal spin effects
in D-brane potentials. In this way we find for a generic (D)p-brane, potentials
going like corresponding to interactions between the
different components of the D-brane supermultiplet. From the eleven dimensional
point of view, these potentials arise from the exchange of field strengths
corresponding to the graviton and the three form, coupled non-minimally to the
branes. We show how an annulus computation truncated to its massless
contribution is enough to reproduce these next-to-leading effects, meaning in
particular that the one-loop (M)atrix theory effective action should encode all
the spin dependence of low-energy supergravity interactions.Comment: LaTex file, 12 pages, no figures, some corrections in last section
and references added; version to appear in Physics Letters
Anomalous couplings for D-branes and O-planes
We study anomalous Wess-Zumino couplings of D-branes and O-planes in a
general background and derive them from a direct string computation by
factorizing in the RR channel various one-loop amplitudes. In particular, we
find that Op-planes present gravitational anomalous couplings involving the
Hirzebruch polynomial L, similarly to the roof genus A encoding Dp-brane
anomalous couplings. We determine, in each case, the precise dependence of
these couplings on the curvature of the tangent and normal bundles.Comment: 24 pages, LaTex, 5 figure
Heterotic compactifications and nearly-Kahler manifolds
We propose that under certain conditions heterotic string compactifications
on half-flat and nearly-Kahler manifolds are equivalent. Based on this
correspondence we argue that the moduli space of the nearly-Kahler manifolds
under discussion consists only of the Kahler deformations moduli space and
there is no correspondent for the complex structure deformations.Comment: 5 pages, references added, typos correcte
Higher Derivative F-terms in N=2 Strings
We study a special class of higher derivative F-terms of the form
where W is the N=2 gravitational superfield and
is the chiral projector applied to a non-holomorphic function of the
heterotic dilaton vector superfield. We analyze these couplings in the
heterotic theory on , where it is found they satisfy an anomaly
equation as the well studied terms. We recognize that, near a point
of SU(2) enhancement, a given generating function of the leading singularity of
the reproduces the free energy of a c=1 string at an arbitrary radius
R. According to the N=2 heterotic-type II duality in 4d, we then study these
couplings near a conifold singularity, using its local description in terms of
intersecting D-5-branes. In this context, it turns out that there exists, among
the other states involved, a vector gauge field reproducing the heterotic
leading singularity structure.Comment: 19 pages, latex file, no figure
Effective description of brane terms in extra dimensions
We study how theories defined in (extra-dimensional) spaces with localized
defects can be described perturbatively by effective field theories in which
the width of the defects vanishes. These effective theories must incorporate a
``classical'' renormalization, and we propose a renormalization prescription a
la dimensional regularization for codimension 1, which can be easily used in
phenomenological applications. As a check of the validity of this setting, we
compare some general predictions of the renormalized effective theory with
those obtained in a particular ultraviolet completion based on deconstruction.Comment: 28 page
Anomalies in orbifold field theories
We study the constraints on models with extra dimensions arising from local
anomaly cancellation. We consider a five-dimensional field theory with a U(1)
gauge field and a charged fermion, compactified on the orbifold S^1/(Z_2 x
Z_2'). We show that, even if the orbifold projections remove both fermionic
zero modes, there are gauge anomalies localized at the fixed points. Anomalies
naively cancel after integration over the fifth dimension, but gauge invariance
is broken, spoiling the consistency of the theory. We discuss the implications
for realistic supersymmetric models with a single Higgs hypermultiplet in the
bulk, and possible cancellation mechanisms in non-minimal models.Comment: 10 pages, 2 figures, LaTex; v2: final version to be published in
Phys. Lett.
Unitarity in Dirichlet Higgs Model
We show that a five dimensional Universal Extra Dimension model, compactified
on a line segment, is consistently formulated even when the gauge symmetry is
broken solely by non-zero Dirichlet boundary conditions on a bulk Higgs field,
without any quartic interaction. We find that the longitudinal W+W- elastic
scattering amplitude, under the absence of the Higgs zero-mode, is unitarized
by exchange of infinite towers of KK Higgs bosons. Resultant amplitude scales
linearly with the scattering energy, exhibiting five dimensional nature. A
tree-level partial-wave unitarity condition is satisfied up to 6.7 (5.7) TeV
for the KK scale 430 (500) GeV, favored by the electroweak data within 90% CL.Comment: 14pages, 2 figures (v1); References added (v2); Trivial error
corrected: u -> t and \cos\theta -> -\cos\theta, references added (v3);
comments added, a reference added, version to appear in Eur. Phys. J. C (v4);
Expressions matched to EPJC style, obsolete affiliation (on leave) has been
removed (v5
BPS states and supersymmetric index in N=2 type I string vacua
We study the moduli dependence of a class of couplings in
compactifications of type I string theory, for which one-loop amplitudes can be
written in terms of an N=2 supersymmetric index. This index is determined for
generic models as a function of the BPS spectrum. As an application we compute
the one-loop moduli dependence of the couplings, where W is the
N=2 gravitational superfield, for type I compactifications based on the
Gimon-Johnson K3 orientifolds, showing explicitly their dependence on the
aforementioned index.Comment: LaTex file, 26 pages, no figures, references added and typographical
errors correcte
The Matrix Theory S-Matrix
The technology required for eikonal scattering amplitude calculations in
Matrix theory is developed. Using the entire supersymmetric completion of the
v^4/r^7 Matrix theory potential we compute the graviton-graviton scattering
amplitude and find agreement with eleven dimensional supergravity at tree
level.Comment: 10 pages, RevTeX, no figure
Heterotic String Compactifications on Half-flat Manifolds II
In this paper, we continue the analysis of heterotic string compactifications
on half-flat mirror manifolds by including the 10-dimensional gauge fields. It
is argued, that the heterotic Bianchi identity is solved by a variant of the
standard embedding. Then, the resulting gauge group in four dimensions is still
E6 despite the fact that the Levi-Civita connection has SO(6) holonomy. We
derive the associated four-dimensional effective theories including matter
field terms for such compactifications. The results are also extended to more
general manifolds with SU(3) structure.Comment: 31 page
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