441 research outputs found
U-duality and D-brane Combinatorics
We investigate D-brane instanton contributions to R^4 couplings in any
toroidal compactification of type II theories. Starting from the 11D
supergravity one-loop four-graviton amplitude computed by Green, Gutperle and
Vanhove, we derive the non-perturbative O(e^{-1/\lambda}) corrections to R^4
couplings by a sequence of T-dualities, and interpret them as precise
configurations of bound states of D-branes wrapping cycles of the
compactification torus. Dp-branes explicitely appear as fluxes on
D(p+2)-branes, and as gauge instantons on D(p+4)-branes. Specific rules for
weighting these contributions are obtained, which should carry over to more
general situations. Furthermore, it is shown that U-duality in D<=6 relates
these D-brane configurations to O(e^{-1/\lambda^2}) instantons for which a
geometric interpretation is still lacking.Comment: 17 pages, LaTeX2e, intro. shortened and minor typos corrected, final
versio
4D gravity on a brane from bulk higher-curvature terms
We study a gravity model where a tensionful codimension-one three-brane is
embedded on a bulk with infinite transverse length. We find that 4D gravity is
induced on the brane already at the classical level if we include
higher-curvature (Gauss-Bonnet) terms in the bulk. Consistency conditions
appear to require a negative brane tension as well as a negative coupling for
the higher-curvature terms.Comment: 10 pages, no figures; a minor change in wording (to appear in MPLA
Heterotic/Type II Triality and Instantons on
A detailed understanding of instanton effects for half-BPS couplings is
pursued in theories with 16 supersymmetries. In particular, we investigate the
duality between heterotic string on and type IIA on at the
orbifold point, as well as their higher and lower dimensional
versions. We present a remarkably clean quantitative test of the duality at the
level of couplings, by completely matching a purely one-loop heterotic
amplitude to a purely tree-level type II result. The triality of SO(4,4) and
several other miracles are shown to be crucial for the duality to hold. Exact
non-perturbative new results for type I', F on , M on , and IIB on
are found, and the general form of D-instanton contributions in type IIA
or B on is obtained. We also analyze the NS5-brane contributions in
type II on , and predict the value
for the bulk contribution to the index of the NS5-brane world-volume theory on
.Comment: 52 pages, uses JHEP.cls; v2: minor corrections and 2 refs added.
Final version for JHE
The Lie h-Invariant Conformal Field Theories and the Lie h-Invariant Graphs
We use the Virasoro master equation to study the space of Lie h-invariant
conformal field theories, which includes the standard rational conformal field
theories as a small subspace. In a detailed example, we apply the general
theory to characterize and study the Lie h-invariant graphs, which classify the
Lie h-invariant conformal field theories of the diagonal ansatz on SO(n). The
Lie characterization of these graphs is another aspect of the recently observed
Lie group-theoretic structure of graph theory.Comment: 38p
Higher order corrections to the Newtonian potential in the Randall-Sundrum model
The general formalism for calculating the Newtonian potential in fine-tuned
or critical Randall-Sundrum braneworlds is outlined. It is based on using the
full tensor structure of the graviton propagator. This approach avoids the
brane-bending effect arising from calculating the potential for a point source.
For a single brane, this gives a clear understanding of the disputed overall
factor 4/3 entering the correction. The result can be written on a compact form
which is evaluated to high accuracy for both short and large distances.Comment: 12 pages, LaTeX2e with RevTeX4, 3 postscript figures; Minor
corrections, references update
Eisenstein Series in String Theory
We discuss the relevance of Eisenstein series for representing certain
G(Z)-invariant string theory amplitudes which receive corrections from BPS
states only. The Eisenstein series are constructed using G(Z)-invariant mass
formulae and are manifestly invariant modular functions on the symmetric space
K\G(R) of non-compact type, with K the maximal compact subgroup of G(R). In
particular, we show how Eisenstein series of the T-duality group SO(d,d,Z) can
be used to represent one- and g-loop amplitudes in compactified string theory.
We also obtain their non-perturbative extensions in terms of the Eisenstein
series of the U-duality group E_{d+1(d+1)}(Z).Comment: 11 pages, Latex, submitted to Proceedings of Strings '99, published
versio
R^2 Corrections and Non-perturbative Dualities of N=4 String ground states
We compute and analyse a variety of four-derivative gravitational terms in
the effective action of six- and four-dimensional type II string ground states
with N=4 supersymmetry. In six dimensions, we compute the relevant perturbative
corrections for the type II string compactified on K3. In four dimensions we do
analogous computations for several models with (4,0) and (2,2) supersymmetry.
Such ground states are related by heterotic-type II duality or type II-type II
U-duality. Perturbative computations in one member of a dual pair give a
non-perturbative result in the other member. In particular, the exact CP-even
R^2 coupling on the (2,2) side reproduces the tree-level term plus NS 5-brane
instanton contributions on the (4,0) side. On the other hand, the exact CP-odd
coupling yields the one-loop axionic interaction a.R\wedge R together with a
similar instanton sum. In a subset of models, the expected breaking of the
SL(2,Z)_S S-duality symmetry to a \Gamma(2)_S subgroup is observed on the
non-perturbative thresholds. Moreover, we present a duality chain that provides
evidence for the existence of heterotic N=4 models in which N=8 supersymmetry
appears at strong coupling.Comment: Latex2e, 51 pages, 1 figur
Correlators of N=1 Superconformal Currents
We give an explicit expression for the M-point correlator of the
superconformal current in two dimensional N=1 superconformal field theories.Comment: 8 pages. Some typos fixed. Unfortunately, these typos exist in the
published version in J Phys
Unoriented D-brane Instantons vs Heterotic worldsheet Instantons
We discuss Fermi interactions of four hyperini generated by ``stringy''
instantons in a Type I / Heterotic dual pair on T^4/Z_2.Comment: Minor corrections and clarifications. Added reference
Closed Bosonic String Partition Function in Time Independent Exact PP-Wave Background
The modular invariance of the one-loop partition function of the closed
bosonic string in four dimensions in the presence of certain homogeneous exact
pp-wave backgrounds is studied. In the absence of an axion field the partition
function is found to be modular invariant. In the presence of an axion field
modular invariace is broken. This can be attributed to the light-cone gauge
which breaks the symmetry in the -, -directions. Recovery of this
broken modular invariance suggests the introduction of twists in the
world-sheet directions. However, one needs to go beyond the light-cone gauge to
introduce such twists.Comment: 17 pages, added reference
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