6,588 research outputs found
A GAS OF D-INSTANTONS
A D-instanton is a space-time event associated with world-sheet boundaries
that contributes non-perturbative effects of order to
closed-string amplitudes. Some properties of a gas of D-instantons are
discussed in this paper.Comment: 11 Pages and 3 figures in uuencoded fil
Boundary Effects in String Theory
Some of the properties of string theory defined on world-sheets with
boundaries are reviewed. Particular emphasis is put on the possibility of
identifying string configurations (\lq D-instantons' and \lq D-branes') that
give rise to stringy non-perturbative effects.Comment: Talk presented at the Strings '95 Conference, USC (March 1995).
Latex, 10 page
D-instanton induced interactions on a D3-brane
Non-perturbative features of the derivative expansion of the effective action
of a single D3-brane are obtained by considering scattering amplitudes of open
and closed strings. This motivates expressions for the coupling constant
dependence of world-volume interactions of the form (where F
is the Born-Infeld field strength), (where are the
normal coordinates of the D3-brane) and other interactions related by \calN=4
supersymmetry. These include terms that transform with non-trivial modular
weight under Montonen-Olive duality. The leading D-instanton contributions that
enter into these effective interactions are also shown to follow from an
explicit stringy construction of the moduli space action for the
D-instanton/D3-brane system in the presence of D3-brane open-string sources
(but in the absence of a background antisymmetric tensor potential). Extending
this action to include closed-string sources leads to a unified description of
non-perturbative terms in the effective action of the form (embedding
curvature) together with open-string interactions that describe
contributions of the second fundamental form.Comment: 40 pages, harvmac (b), some typos corrected and references adde
D-instantons, Strings and M-theory
The R^4 terms in the effective action for M-theory compactified on a
two-torus are motivated by combining one-loop results in type II superstring
theories with the Sl(2,Z) duality symmetry. The conjectured expression
reproduces precisely the tree-level and one-loop R^4 terms in the effective
action of the type II string theories compactified on a circle, together with
the expected infinite sum of instanton corrections. This conjecture implies
that the R^4 terms in ten-dimensional string type II theories receive no
perturbative corrections beyond one loop and there are also no non-perturbative
corrections in the ten-dimensional IIA theory. Furthermore, the
eleven-dimensional M-theory limit exists, in which there is an R^4 term that
originates entirely from the one-loop contribution in the type IIA theory and
is related by supersymmetry to the eleven-form C^{(3)}R^4. The generalization
to compactification on T^3 as well as implications for non-renormalization
theorems in D-string and D-particle interactions are briefly discussed.Comment: harvmac (b) 17 pages. v4: Some formulae corrected. Dimensions
corrected for eleven-dimensional expression
Instantons and Non-renormalisation in AdS/CFT
The series of perturbative fluctuations around a multi-instanton contribution
to a specific class of correlation functions of supercurrents in
supersymmetric SU(N) Yang-Mills theory is examined in the light of the AdS/CFT
correspondence. Subject to certain plausible assumptions, we argue that a given
term in the 1/N expansion in such a background receives only a finite number of
perturbative corrections in the 't Hooft limit. Such instanton
non-renormalisation theorems would explain, for example, the exact agreement of
certain weak coupling Yang-Mills instanton calculations with the strong
coupling predictions arising from D-instanton effects in string theory
amplitudes. These non-renormalisation theorems essentially follow from the
assumption of a well defined derivative expansion in the
string theory dual of the Yang-Mills theory.Comment: 11 pages, harvmac, minor typo correcte
Summing Over World-Sheet Boundaries
The moduli associated with boundaries in a Riemann surface are parametrized
by the positions and strengths of electric charges. This suggests a method for
summing over orientable Riemann surfaces with Dirichlet boundary conditions on
the embedding coordinates. A light-cone parameterization of such boundaries is
also discussed.Comment: 10 page
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