135 research outputs found
K-theory and Ramond-Ramond charge
We discuss the relation between the Ramond-Ramond charges of D-branes and the
topology of Chan-Paton vector bundles. We show that a topologically nontrivial
normal bundle induces RR charge and that the result fits in perfectly with the
proposal that D-brane charge is the topology of the Chan-Paton bundle, regarded
as an element of K-theory.Comment: 8 pages, harvmac. Partial retraction of the partial retraction, as
explained in note adde
N=2 higher-derivative couplings from strings
We consider the Calabi-Yau reduction of the Type IIA eight derivative
one-loop stringy corrections focusing on the couplings of the four dimensional
gravity multiplet with vector multiplets and a tensor multiplet containing the
NS two-form. We obtain a variety of higher derivative invariants generalising
the one-loop topological string coupling, , controlled by the lowest order
Kahler potential and two new non-topological quantities built out of the
Calabi-Yau Riemann curvature.Comment: 43 page
Mirror symmetry & supersymmetry on SU(4)-structure backgrounds
We revisit the backgrounds of type IIB on manifolds with -structure
and discuss two sets of solutions arising from internal geometries that are
complex and symplectic respectively. Both can be realized in terms of
generalized complex geometry. We identify a map which relates the complex and
symplectic supersymmetric systems. In the semi-flat torus bundle setting this
map corresponds to T-duality and suggest a way of extending the mirror
transform to non-K\"ahler geometries.Comment: 40 page
Computing 1/N^2 corrections in AdS/CFT
Stringy corrections in AdS/CFT generally fall into the category of either
\alpha' effects or string loop effects, corresponding to 1/\lambda and 1/N
corrections, respectively, in the dual field theory. While \alpha'^3R^4
corrections have been well studied, at least in the context of N=4
super-Yang-Mills, less is known about the 1/N^2 corrections arising from closed
string loops. In this paper, we consider AdS_5 x SE_5 compactifications of the
IIB string, and compute the closed string loop correction to the anomaly
coefficients a and c in the dual field theory. For T^{1,1} reductions, we find
the string loop correction to yield c-a=1/24, which is the contribution to c-a
of a free N=2 hypermultiplet. We also comment on reductions to lower
dimensional AdS theories as well as the nature of T-duality with higher
derivatives.Comment: 24 pages, LaTe
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