61 research outputs found
Nonassociative Star Product Deformations for D-brane Worldvolumes in Curved Backgrounds
We investigate the deformation of D-brane world-volumes in curved
backgrounds. We calculate the leading corrections to the boundary conformal
field theory involving the background fields, and in particular we study the
correlation functions of the resulting system. This allows us to obtain the
world-volume deformation, identifying the open string metric and the
noncommutative deformation parameter. The picture that unfolds is the
following: when the gauge invariant combination \omega = B + F is constant one
obtains the standard Moyal deformation of the brane world-volume. Similarly,
when d\omega = 0 one obtains the noncommutative Kontsevich deformation,
physically corresponding to a curved brane in a flat background. When the
background is curved, H = d\omega \not= 0, we find that the relevant algebraic
structure is still based on the Kontsevich expansion, which now defines a
nonassociative star product with an A_\infty homotopy associative algebraic
structure. We then recover, within this formalism, some known results of Matrix
theory in curved backgrounds. In particular, we show how the effective action
obtained in this framework describes, as expected, the dielectric effect of
D-branes. The polarized branes are interpreted as a soliton, associated to the
condensation of the brane gauge field.Comment: Latex, 50 pages; v2: added 2 references and corrected typos; v3: new
section on the homotopy associative algebraic structure, final version for
CM
Eikonal Approximation in AdS/CFT: From Shock Waves to Four-Point Functions
We initiate a program to generalize the standard eikonal approximation to compute amplitudes in Anti-de Sitter spacetimes. Inspired by the shock wave derivation of the eikonal amplitude in flat space, we study the two-point function E ~ _{shock} in the presence of a shock wave in Anti-de Sitter, where O_1 is a scalar primary operator in the dual conformal field theory. At tree level in the gravitational coupling, we relate the shock two-point function E to the discontinuity across a kinematical branch cut of the conformal field theory four-point function A ~ , where O_2 creates the shock geometry in Anti-de Sitter. Finally, we extend the above results by computing E in the presence of shock waves along the horizon of Schwarzschild BTZ black holes. This work gives new tools for the study of Planckian physics in Anti-de Sitter spacetimes
Eikonal Approximation in AdS/CFT: Conformal Partial Waves and Finite N Four-Point Functions
We introduce the impact-parameter representation for conformal field theory
correlators of the form A ~ . This representation is
appropriate in the eikonal kinematical regime, and approximates the conformal
partial-wave decomposition in the limit of large spin and dimension of the
exchanged primary. Using recent results on the two-point function < O_1 O_1
>_{shock} in the presence of a shock wave in Anti-de Sitter, and its relation
to the discontinuity of the four-point amplitude A across a kinematical
branch-cut, we find the high spin and dimension conformal partial- wave
decomposition of all tree-level Anti-de Sitter Witten diagrams. We show that,
as in flat space, the eikonal kinematical regime is dominated by the T-channel
exchange of the massless particle with highest spin (graviton dominance). We
also compute the anomalous dimensions of the high-spin O_1 O_2 composites.
Finally, we conjecture a formula re-summing crossed-ladder Witten diagrams to
all orders in the gravitational coupling.Comment: JHEP3.cls, 27 pages, 8 figure
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