1,531 research outputs found
Instantons of Type IIB Supergravity in Ten Dimensions
A family of SO(10) symmetric instanton solutions in Type IIB supergravity is
developed. The instanton of least action is a candidate for the low-energy,
semiclassical approximation to the {D=--1} brane. Unlike a previously published
solution,[GGP] this admits an interpretation as a tunneling amplitude between
perturbatively degenerate asymptotic states, but with action twice that found
previously. A number of associated issues are discussed such as the relation
between the magnetic and electric pictures, an inversion symmetry of the
dilaton and the metric, the topology of the background, and some
properties of the solution in an "instanton frame" corresponding to a
Lagrangian in which the dilaton's kinetic energy vanishes.Comment: 15 pages, no figures; Version 2 has revised sections IV and V.
Earlier equations are essentially unchanged, but interpretation changed, on
advice of counse
Non-renormalisation Conditions in Type II String Theory and Maximal Supergravity
This paper considers general features of the derivative expansion of Feynman
diagram contributions to the four-graviton scattering amplitude in
eleven-dimensional supergravity compactified on a two-torus. These are
translated into statements about interactions of the form D^2k R^4 in type II
superstring theories, assuming the standard M-theory/string theory duality
relationships, which provide powerful constraints on the effective
interactions. In the ten-dimensional IIA limit we find that there can be no
perturbative contributions beyond k string loops (for k>0). Furthermore, the
genus h=k contributions are determined exactly by the one-loop
eleven-dimensional supergravity amplitude for all values of k. A plausible
interpretation of these observations is that the sum of h-loop Feynman diagrams
of maximally extended supergravity is less divergent than might be expected and
could be ultraviolet finite in dimensions d < 4 + 6/h -- the same bound as for
N=4 Yang--Mills.Comment: 30 pages, 4 figures. v3 Some rewording, typos corrected and some
references added. v4: Abstract rephrased. More typos corrected. Version to be
publishe
Superstrings in AdS in light cone gauge
We discuss light-cone gauge description of type IIB Green-Schwarz superstring
in AdS_5 x S^5 with a hope to make progress towards understanding spectrum of
this theory. As in flat space, fixing light cone gauge consists of two steps:
(i) fixing kappa symmetry in such a way that the fermionic part of the action
does not depend on x^-; (ii) fixing 2-d reparametrizations by x^+ = tau and a
condition on 2-d metric. In curved AdS space the latter cannot be the standard
conformal gauge and breaks manifest 2-d Lorentz invariance. It is natural,
therefore, to work in phase-space framework, imposing the GGRT gauge conditions
x^+= tau, P^+ =const. We obtain the resulting light cone superstring
Hamiltonian. This is a review of hep-th/0007036 and hep-th/0009171.Comment: 10 pages, latex. Contribution to the Proceedings of Strings 2000, Ann
Arbo
Exactly solvable model of superstring in Ramond-Ramond plane wave background
We describe in detail the solution of type IIB superstring theory in the
maximally supersymmetric plane-wave background with constant null Ramond-Ramond
5-form field strength. The corresponding light-cone Green-Schwarz action found
in hep-th/0112044 is quadratic in both bosonic and fermionic coordinates. We
find the spectrum of the light-cone Hamiltonian and the string representation
of the supersymmetry algebra. The superstring Hamiltonian has a
``harmonic-oscillator'' form in both the string-oscillator and the zero-mode
parts and thus has discrete spectrum in all 8 transverse directions. We analyze
the structure of the zero-mode sector of the theory, establishing the precise
correspondence between the lowest-lying ``massless'' string states and the type
IIB supergravity fluctuation modes in the plane-wave background. The zero-mode
spectrum has certain similarity to the supergravity spectrum in AdS_5 x S^5 of
which the plane-wave background is a special limit. We also compare the
plane-wave string spectrum with expected form of the light-cone gauge spectrum
of superstring in AdS_5 x S^5.Comment: 33 pages, latex. v4: minor sign corrections in (1.5) and (3.62), to
appear in PR
Instantons and SL(2,R) Symmetry in Type IIB Supergravity
We discuss the relation between the dual formulations of Type IIB
supergravity emphasizing the differences between Lorentz and Euclidean
signature. We demonstrate how the SL(2,R) symmetry of the usual action is
manifested in the solution of the equations of motion with Euclidean signature
for the dual theory.Comment: 4 pages, no figure
String Creation, D-branes and Effective Field Theory
This paper addresses several unsettled issues associated with string creation
in systems of orthogonal Dp-D(8-p) branes. The interaction between the branes
can be understood either from the closed string or open string picture. In the
closed string picture it has been noted that the DBI action fails to capture an
extra RR exchange between the branes. We demonstrate how this problem persists
upon lifting to M-theory. These D-brane systems are analysed in the closed
string picture by using gauge-fixed boundary states in a non-standard lightcone
gauge, in which RR exchange can be analysed precisely. The missing piece in the
DBI action also manifests itself in the open string picture as a mismatch
between the Coleman-Weinberg potential obtained from the effective field theory
and the corresponding open string calculation. We show that this difference can
be reconciled by taking into account the superghosts in the (0+1)effective
theory of the chiral fermion, that arises from gauge fixing the spontaneously
broken world-line local supersymmetries.Comment: 33 page
D3-branes on the Coulomb branch and instantons
The relative coefficients of higher derivative interactions of the IIB
effective action of the form C^4, (D F_5)^4, F_5^8, ... (where C is the Weyl
tensor and F_5 is the five-form field strength) are motivated by supersymmetry
arguments. It is shown that the classical supergravity solution for N parallel
D3-branes is unaltered by this combination of terms. The non-vanishing of
\zeroC^2 in this background (where \zero C is the background value of the Weyl
tensor) leads to effective O(1/alpha') interactions, such as C^2 and Lambda^8
(where Lambda is the dilatino). These contain D-instanton contributions in
addition to tree and one-loop terms. The near horizon limit of the N D3-brane
system describes a multi-AdS_5xS^5 geometry that is dual to \calN=4 SU(N)
Yang-Mills theory spontaneously broken to S(U(M_1)x...xU(M_r)). Here, the N
D3-branes are grouped into r coincident bunches with M_r in each group, with
M_r/N = m_r fixed as N goes to infinity. The boundary correlation function of
eight Lambda's is constructed explicitly. The second part of the paper
considers effects of a constrained instanton in this large-N Yang-Mills theory
by an extension of the analysis of Dorey, Hollowood and Khoze of the
one-instanton measure at finite N. This makes precise the correspondence with
the supergravity D-instanton measure at leading order in the 1/N expansion.
However, the duality between instanton-induced correlation functions in
Yang-Mills theory and the dual supergravity is somewhat obscured by
complications relating to the structure of constrained instantons.Comment: 30 pages, JHEP style. Typos corrected and minor clarifications adde
Dispersion Relations in String Theory
We analyze the analytic continuation of the formally divergent one-loop
amplitude for scattering of the graviton multiplet in the Type II Superstring.
In particular we obtain explicit double and single dispersion relations,
formulas for all the successive branch cuts extending out to plus infinity, as
well as for the decay rate of a massive string state of arbitrary mass 2N into
two string states of lower mass. We compare our results with the box diagram in
a superposition of -like field theories. The stringy effects are traced
to a convergence problem in this superposition.Comment: 17 pages, COLUMBIA-YITP-UCLA/93/TEP/45 (figures fixed up
The principle of least action and the geometric basis of D-branes
We analyze thoroughly the boundary conditions allowed in classical non-linear
sigma models and derive from first principle the corresponding geometric
objects, i.e. D-branes. In addition to giving classical D-branes an intrinsic
and geometric foundation, D-branes in nontrivial H flux and D-branes embedded
within D-branes are precisely defined. A well known topological condition on
D-branes is replaced
Light-Cone Gauge String Field Theory in Noncritical Dimensions
We study light-cone gauge string field theory in noncritical space-time
dimensions. Such a theory corresponds to a string theory in a Lorentz
noninvariant background. We identify the worldsheet theory for the longitudinal
coordinate variables and study its properties. It is a CFT with the
right value of Virasoro central charge, using which we propose a BRST invariant
formulation of the worldsheet theory.Comment: 27 pages, 2 figure
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