58,592 research outputs found
D-branes in a plane-wave background
The D-branes of the maximally supersymmetric plane-wave background are
described.Comment: 6 pages; contribution to the proceedings of the 35th Symposium
Ahrenshoop, 2002; v2: minor correction
An SL(2,Z) anomaly in IIB supergravity and its F-theory interpretation
The SL(2,Z) duality transformations of type IIB supergravity are shown to be
anomalous in generic F-theory backgrounds due to the anomalous transformation
of the phase of the chiral fermion determinant. The anomaly is partially
cancelled provided the ten-dimensional type IIB theory lagrangian contains a
term that is a ten-form made out of the composite U(1) field strength and four
powers of the curvature. A residual anomaly remains uncancelled, and this
implies a certain topological restriction on consistent backgrounds of the
euclidean theory. A similar, but slightly stronger, restriction is also derived
from an explicit F-theory compactification on K3 x M8 (where M8 is an
eight-manifold with a nowhere vanishing chiral spinor) where the cancellation
of tadpoles for Ramond--Ramond fields is only possible if M8 has an Euler
character that is a positive multiple of 24. The interpretation of this
restriction in the dual heterotic theory on T2 x M8 is also given.Comment: Argument has been streamlined and references have been added. 18
pages, harvmac (b
The mechanisms of temporal inference
The properties of a temporal language are determined by its constituent elements: the temporal objects which it can represent, the attributes of those objects, the relationships between them, the axioms which define the default relationships, and the rules which define the statements that can be formulated. The methods of inference which can be applied to a temporal language are derived in part from a small number of axioms which define the meaning of equality and order and how those relationships can be propagated. More complex inferences involve detailed analysis of the stated relationships. Perhaps the most challenging area of temporal inference is reasoning over disjunctive temporal constraints. Simple forms of disjunction do not sufficiently increase the expressive power of a language while unrestricted use of disjunction makes the analysis NP-hard. In many cases a set of disjunctive constraints can be converted to disjunctive normal form and familiar methods of inference can be applied to the conjunctive sub-expressions. This process itself is NP-hard but it is made more tractable by careful expansion of a tree-structured search space
Multiparticle one-loop amplitudes and S-duality in closed superstring theory
Explicit expressions for one-loop five supergraviton scattering amplitudes in
both type II superstring theories are determined by making use of the pure
spinor formalism. The type IIB amplitude can be expressed in terms of a
doubling of ten-dimensional super Yang--Mills tree amplitude, while the type
IIA amplitude has additional pieces that cannot be expressed in that manner. We
evaluate the coefficients of terms in the analytic part of the low energy
expansion of the amplitude, which correspond to a series of terms in an
effective action of the schematic form D^{2k}R^5 for 0\le k \le 5 (where R is
the Riemann curvature). Comparison with earlier analyses of the tree amplitudes
and of the four-particle one-loop amplitude leads to an interesting extension
of the action of SL(2,Z) S-duality on the moduli-dependent coefficients in the
type IIB theory. We also investigate closed-string five-particle amplitudes
that violate conservation of the U(1) R-symmetry charge -- processes that are
forbidden in supergravity. The coefficients of their low energy expansion are
shown to agree with S-duality systematics. A less detailed analysis is also
given of the six-point function, resulting in the vanishing of the analytic
parts of the R^6 and D^4 R^6 interactions in the ten-dimensional effective
action, but not in lower dimensions.Comment: 62 pages, Mathematica notebook on integral expansion included in
submission. v2: minor modifications, references added, matches published
versio
String Bit Models for Superstring
We extend the model of string as a polymer of string bits to the case of
superstring. We mainly concentrate on type II-B superstring, with some
discussion of the obstacles presented by not II-B superstring, together with
possible strategies for surmounting them. As with previous work on bosonic
string we work within the light-cone gauge. The bit model possesses a good deal
less symmetry than the continuous string theory. For one thing, the bit model
is formulated as a Galilei invariant theory in dimensional
space-time. This means that Poincar\'e invariance is reduced to the Galilei
subgroup in space dimensions. Naturally the supersymmetry present in the
bit model is likewise dramatically reduced. Continuous string can arise in the
bit models with the formation of infinitely long polymers of string bits. Under
the right circumstances (at the critical dimension) these polymers can behave
as string moving in dimensional space-time enjoying the full
Poincar\'e supersymmetric dynamics of type II-B superstring.Comment: 43 pages, phyzzx require
Matching the (DR4)-R-6 interaction at two-loops
The coefficient of the interaction in the low energy
expansion of the two-loop four-graviton amplitude in type II superstring theory
is known to be proportional to the integral of the Zhang-Kawazumi (ZK)
invariant over the moduli space of genus-two Riemann surfaces. We demonstrate
that the ZK invariant is an eigenfunction with eigenvalue 5 of the
Laplace-Beltrami operator in the interior of moduli space. Exploiting this
result, we evaluate the integral of the ZK invariant explicitly, finding
agreement with the value of the two-loop interaction predicted
on the basis of S-duality and supersymmetry. A review of the current
understanding of the interactions in type II superstring
theory compactified on a torus with and is
included.Comment: 40 pages, various typos and coefficients corrected in version
Anomalous Creation of Branes
In certain circumstances when two branes pass through each other a third
brane is produced stretching between them. We explain this phenomenon by the
use of chains of dualities and the inflow of charge that is required for the
absence of chiral gauge anomalies when pairs of D-branes intersect.Comment: 7 pages, two figure
Remarks on the Classical Size of D-Branes
We discuss different criteria for `classical size' of extremal Dirichlet
p-branes in type-II supergravity. Using strong-weak coupling duality, we find
that the size of the strong-coupling region at the core of the (p<3)-branes, is
always given by the asymptotic string scale, if measured in the weakly coupled
dual string metric. We also point out how the eleven-dimensional Planck scale
arises in the classical 0-brane solution, as well as the ten-dimensional Planck
scale in the D-instanton solution.Comment: 8 pp, harvma
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