arXiv subjects

Robert de Mello Koch

Publications and source records attributed to Robert de Mello Koch.

At least 127 records · Page 7Linked to original sources

arXiv2006

Unstable Giants

We find giant graviton solutions in Frolov's three parameter generalization of the Lunin-Maldacena background. The background we study has $\tildeγ_1=0$ and $\tildeγ_2=\tildeγ_3=\tildeγ$. This class of backgrounds provide a non-superymmetric example of the gauge theory/gravity correspondence that can be tested quantitatively, as recently shown by Frolov, Roiban and Tseytlin. The giant graviton solutions we find have a greater energy than the point gravitons, making them unstable states. Despite this, we find striking quantitative agreement between the gauge theory and gravity descriptions of open strings attached to the giant.

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arXiv2005

Fluctuating Fuzzy Funnels

It is well known that a D-string ending on a D3, D5 or D7 brane is described in terms of a non-commutative fuzzy funnel geometry. In this article, we give a numerical study of the fluctuations about this leading geometry. This allows us to investigate issues related to the stability and moduli space of these solutions. We comment on the comparison to the linearized fluctuations in supergravity.

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arXiv2005

Deformed PP-waves from the Lunin-Maldacena Background

In this article we study a pp-wave limit of the Lunin-Maldacena background. We show that the relevant string theory background is a homogeneous pp-wave. We obtain the string spectrum. The dual field theory is a deformation of N=4 super Yang-Mills theory. We have shown that, for a class of operators, at O(g_{YM}^2) and at leading order in N, all contributions to the anomalous dimension come from F-terms. We are able to identify the operator in the deformed super Yang-Mills which is dual to the lowest string mode. By studying the undeformed theory we are able to provide some evidence, directly in the field theory, that a small set of nearly protected operators decouple. We make some comments on operators in the Yang-Mills theory that are dual to excited string modes.

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arXiv2005

On Exponential corrections to the 1/N expansion in two-dimensional Yang Mills theory

We compute $e^{-AN}$ corrections to the Gross-Taylor 1/N expansion of the paritition function of two-dimensional SU(N) and U(N) Yang Mills theory. We find a very similar structure of mixing between holomorphic and anti-holomorphic sectors as that described by Vafa for the 1/N expansion. Some of the non-perturbative terms are suggestive of D-strings wrapping the $T^2$ of the 2dYM but blowing up into a fuzzy geometry by the Myers effect in the directions transverse to the $T^2$.

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arXiv2005

Instantons in c=0 CSFT

Following the recent work of hep-th/0405076 we discuss the emergence of D-brane instanton solutions in c=0 noncritical string theory. Our emphasis is on finding the D-instanton effects in a field theoretic setting. Using the framework of single matrix collective field theory (CSFT) we exhibit the appearance of such solutions. Some subtle issues regarding the form of the field theory equations, the comparison with string equations and the importance of a finite N exclusion principle are also discussed.

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arXiv2004

Giant Graviton Correlators from Dual SU(N) super Yang-Mills Theory

Certain correlation functions are computed exactly in the zero coupling limit of N=4 super Yang-Mills theory with gauge group SU(N). A set of linearly independent operators that are in one-to-one correspondence with the half-BPS representations of the SU(N) gauge theory is given. These results are used to study giant gravitons in the dual AdS5xS5 string theory. In addition, for the U(N) gauge theory, we explain how to systematically identify contributions coming from the boundary degrees of freedom.

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arXiv2003

Non-Abelian BIonic Brane Intersections

We study "fuzzy funnel" solutions to the non-Abelian equations of motion of the D-string. Our funnel describes n^6/360 coincident D-strings ending on n^3/6 D7-branes, in terms of a fuzzy six-sphere which expands along the string. We also provide a dual description of this configuration in terms of the world volume theory of the D7-branes. Our work makes use of an interesting non-linear higher dimensional generalization of the instanton equations.

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arXiv2003

Derivation of String Field Theory from the Large N BMN Limit

We continue the development of a systematic procedure for deriving closed string pp wave string field theory from the large N Berenstein-Maldacena-Nastase limit. In the present paper the effects of the Yang-Mills interaction are considered in detail for general BMN states. The SFT interaction with the appropriate operator insertion at the interaction point is demonstrated.

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arXiv2003

Collective String Field Theory of Matrix Models in the BMN Limit

We develop a systematic procedure for deriving canonical string field theory from large N matrix models in the Berenstein-Maldacena-Nastase limit. The approach, based on collective field theory, provides a generalization of standard string field theory.

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arXiv2000

Lumps in level truncated open string field theory

The ratios of the masses of D(p-d) branes to the masses of Dp in open bosonic string field theory are computed within the modified level truncation approximation of Moeller, Sen and Zweibach. At the lowest non-trivial truncation requiring the addition of new primary states, we find evidence of rapid convergence to the expected result for 1<d<7 providing additional evidence for the consistency of this approximation.

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arXiv1999

Monopole Dynamics in N=2 super Yang-Mills Theory From a Threebrane Probe

The BPS states of N=2 super Yang-Mills theory with gauge group SU(2) are constructed as non-trivial finite-energy solutions of the worldvolume theory of a threebrane probe in F theory. The solutions preserve 1/2 of N=2 supersymmetry and provide a worldvolume realization of strings stretching from the probe to a sevenbrane. The positions of the sevenbranes correspond to singularities in the field theory moduli space and to curvature singularities in the supergravity background. We explicitly show how the UV cut off of the effective field theory is mapped into an IR cut off in the supergravity. Finally, we discuss some features of the moduli spaces of these solutions.

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arXiv1999

Non-holomorphic Corrections from Threebranes in F Theory

We construct solutions of type IIB supergravity dual to N=2 super Yang-Mills theories. By considering a probe moving in a background with constant coupling and an AdS_{5} component in its geometry, we are able to reproduce the exact low energy effective action for the theory with gauge group SU(2) and N_{f}=4 massless flavors. After turning on a mass for the flavors we find corrections to the AdS_{5} geometry. In addition, the coupling shows a power law dependence on the energy scale of the theory. The origin of the power law behaviour of the coupling is traced back to instanton corrections. Instanton corrections to the four derivative terms in the low energy effective action are correctly obtained from a probe analysis. By considering a Wilson loop in this geometry we are also able to compute the instanton effects on the quark-antiquark potential. Finally we consider a solution corresponding to an asymptotically free field theory. Again, the leading form of the four derivative terms in the low energy effective action are in complete agreement with field theory expectations.

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arXiv1999

Moduli Space for Conifolds as Intersection of Orthogonal D6 branes

We show that a system of parallel D3 branes near a conifold singularity can be mapped onto an intersecting configuration of orthogonal branes in type IIA string theory. Using this brane configuration, we analyze the Higgs moduli space of the associated field theory. The dimension of the Higgs moduli space is computed from a geometrical analysis of the conifold singularity. Our results provide evidence for an extended s-rule. In addition, a discrepancy between the prediction of the brane configuration and the result obtained from a geometrical anaysis is noted. This discrepancy is traced back to worldsheet instanton effects.

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arXiv1998

Higher Derivative Terms from Threebranes in F Theory

The computation of higher derivative corrections to the low energy effective actions of ${\cal N}=2$ gauge theories is considered. In particular, higher derivative corrections are computed for four dimensional ${\cal N}=2$ super Yang-Mills theory with gauge group SU(2) and $N_f=4$ hypermultiplets in the fundamental representation. The four derivative terms computed in an approach which realizes the gauge theory as the world volume theory of three branes in F theory are in agreement with the field theory result.

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arXiv1998

Duality and Light Cone Symmetries of the Equations of Motion

The matrix theory description of the discrete light cone quantization of $M$ theory on a $T^{2}$ is studied. In terms of its super Yang- Mills description, we identify symmetries of the equations of motion corresponding to independent rescalings of one of the world sheet light cone coordinates, which show how the $S$ duality of Type IIB string theory is realized as a Nahm-type transformation. In the $M$ theory description this corresponds to a simple $9-11$ flip.

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arXiv1997

Twelve Dimensions and the D2-Brane Tension

In this letter we study $D$ particle quantum mechanics on a torus in the limit that one or more cycles of the torus have a zero length.

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arXiv1997

Classical integrability of chiral $QCD_{2}$ and classical curves

In this letter, classical chiral $QCD_{2}$ is studied in the lightcone gauge $A_{-}=0$. The once integrated equation of motion for the current is shown to be of the Lax form, which demonstrates an infinite number of conserved quantities. Specializing to gauge group SU(2), we show that solutions to the classical equations of motion can be identified with a very large class of curves. We demonstrate this correspondence explicitly for two solutions. The classical fermionic fields associated with these currents are then obtained.

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arXiv1997

The Dynamics of Classical Chiral $QCD_{2}$ Currents

In this paper the dynamics of the classical chiral $QCD_{2}$ currents is studied. We describe how the dynamics of the theory can be summarized in an equation of the Lax form, thereby demonstrating the existence of an infinite set of conserved quantities. Next, the $r$ matrix of a fundamental Poisson relation is obtained and used to demonstrate that the conserved charges Poisson commute. An underlying diffeomorphism symmetry of the equations of motion which is not a symmetry of the action is used to provide a geometric interpretation for the case of gauge group SU(2). This enables us to show that the solutions to the classical equations of motion can be identified with a large class of curves, to demonstrate an auto-Bäcklund transformation and to demonstrate a non linear superposition principle. A link between the spectral problem for $QCD_{2}$ and the solution to the closed curve problem is also demonstrated. We then go on to provide a systematic inverse scattering treatment. This formalism is used to obtain the reflectionless single boundstate eigenvalue soliton solution.

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