29,411 research outputs found
Dielectric-Branes
We extend the usual world-volume action for a Dp-brane to the case of N
coincident Dp-branes where the world-volume theory involves a U(N) gauge
theory. The guiding principle in our construction is that the action should be
consistent with the familiar rules of T-duality. The resulting action involves
a variety of potential terms, i.e., nonderivative interactions, for the
nonabelian scalar fields. This action also shows that Dp-branes naturally
couple to RR potentials of all form degrees, including both larger and smaller
than p+1. We consider the dynamics resulting from this action for Dp-branes
moving in nontrivial background fields, and illustrate how the Dp-branes are
``polarized'' by external fields. In a simple example, we show that a system of
D0-branes in an external RR four-form field expands into a noncommutative
two-sphere, which is interpreted as the formation of a spherical D2-D0 bound
state.Comment: 33 pages, Latex, 2 ref.'s added, few typo's fixe
The Free Energy of N=4 Super-Yang-Mills and the AdS/CFT Correspondence
We compute the high-temperature limit of the free energy for four-dimensional
N=4 supersymmetric SU(N_c) Yang-Mills theory. At weak coupling we do so for a
general ultrastatic background spacetime, and in the presence of slowly-varying
background gauge fields. Using Maldacena's conjectured duality, we calculate
the strong-coupling large-N_c expression for the special case that the
three-space has constant curvature. We compare the two results paying
particular attention to curvature corrections to the leading order expressions.Comment: 26 pages.Minor corrections to eqs.(19),(21). Results and conclusions
unchanged. References adde
Fractional Branes and the Entropy of 4D Black Holes
We reconsider the four dimensional extremal black hole constructed in type
IIB string theory as the bound state of D1-branes, D5-branes, momentum, and
Kaluza-Klein monopoles. Specifically, we examine the case of an arbitrary
number of monopoles. Consequently, the weak coupling calculation of the
microscopic entropy requires a study of the D1-D5 system on an ALE space. We
find that the complete expression for the Bekenstein-Hawking entropy is
obtained by taking into account the massless open strings stretched between the
fractional D-branes which arise in the orbifold limit of the ALE space. The
black hole sector therefore arises as a mixed Higgs-Coulomb branch of an
effective 1+1 dimensional gauge theory.Comment: 12 pages. 1 figure. v2: References adde
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