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Nathan Seiberg

Publications and source records attributed to Nathan Seiberg.

At least 127 records · Page 7Linked to original sources
arXiv1999

Noncommutative Perturbative Dynamics

We study the perturbative dynamics of noncommutative field theories on R^d, and find an intriguing mixing of the UV and the IR. High energies of virtual particles in loops produce non-analyticity at low momentum. Consequently, the low energy effective action is singular at zero momentum even when the original noncommutative field theory is massive. Some of the nonplanar diagrams of these theories are divergent, but we interpret these divergences as IR divergences and deal with them accordingly. We explain how this UV/IR mixing arises from the underlying noncommutativity. This phenomenon is reminiscent of the channel duality of the double twist diagram in open string theory.

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arXiv1999

String Theory and Noncommutative Geometry

We extend earlier ideas about the appearance of noncommutative geometry in string theory with a nonzero B-field. We identify a limit in which the entire string dynamics is described by a minimally coupled (supersymmetric) gauge theory on a noncommutative space, and discuss the corrections away from this limit. Our analysis leads us to an equivalence between ordinary gauge fields and noncommutative gauge fields, which is realized by a change of variables that can be described explicitly. This change of variables is checked by comparing the ordinary Dirac-Born-Infeld theory with its noncommutative counterpart. We obtain a new perspective on noncommutative gauge theory on a torus, its T-duality, and Morita equivalence. We also discuss the D0/D4 system, the relation to M-theory in DLCQ, and a possible noncommutative version of the six-dimensional (2,0) theory.

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arXiv1999

The D1/D5 System And Singular CFT

We study the conformal field theory of the D1/D5 system compactified on X (X is T^4 or K3). It is described by a sigma model whose target space is the moduli space of instantons on X. For values of the parameters where the branes can separate, the spectrum of dimensions in the conformal field theory exhibits a continuum above a gap. This continuum leads to a pathology of the conformal field theory, which explains a variety of problems in various systems. In particular, we explain the apparent discrepancy between different methods of finding the spectrum of chiral fields at certain points in the moduli space of the system.

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arXiv1999

Comments on the IIA NS5-brane

We study $N$ coincident IIA NS5-branes at large $N$ using supergravity. We show that the absorption cross section for gravitons in this background does not vanish at zero string coupling for energies larger than $m_s/\sqrt{N}$ ($m_s$ is the string scale). Using a holographic description of the intrinsic theory of the IIA NS5-branes, we find an expression for the two point function of the stress energy tensor, and comment on its structure.

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arXiv1998

Linear Dilatons, NS5-branes and Holography

We argue that vacua of string theory which asymptote at weak coupling to linear dilaton backgrounds are holographic. The full string theory in such vacua is ``dual'' to a theory without gravity in fewer dimensions. The dual theory is generically not a local quantum field theory. Excitations of the string vacuum, which can be studied in the weak coupling region using worldsheet methods, give rise to observables in the dual theory. An interesting example is string theory in the near-horizon background of parallel NS5-branes, the CHS model, which is dual to the decoupled NS5-brane theory (``little string theory''). This duality can be used to study some of the observables in this theory and some of their correlation functions. Another interesting example is the ``old'' matrix model, which gives a holographic description of two dimensional string theory.

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arXiv1998

Three-Point Functions of Chiral Operators in D=4, $\mathcal{N}=4$ SYM at Large N

We study all three-point functions of normalized chiral operators in D=4, $\mathcal{N}=4$, U(N) supersymmetric Yang-Mills theory in the large $N$ limit. We compute them for small 't Hooft coupling $λ=g_{YM}^2N<<1$ using free field theory and at strong coupling $λ=g_{YM}^2>>1$ using the $AdS$/CFT correspondence. Surprisingly, we find the same answers in the two limits. We conjecture that at least for large $N$ the exact answers are independent of $λ$ .

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arXiv1998

String Theory, Supersymmetry, Unification, and All That

String theory and supersymmetry are theoretical ideas that go beyond the standard model of particle physics and show promise for unifying all forces. After a brief introduction to supersymmetry, we discuss the prospects for its experimental discovery in the near future. We then show how the magic of supersymmetry allows us to solve certain quantum field theories exactly, thus leading to new insights about field theory dynamics related to electric-magnetic duality. The discussion of superstring theory starts with its perturbation expansion, which exhibits new features including ``stringy geometry.'' We then turn to more recent non-perturbative developments. Using new dualities, all known superstring theories are unified, and their strong coupling behavior is clarified. A central ingredient is the existence of extended objects called branes.

hep-th↗
arXiv1998

The Superworld

An overview of supersymmetry and its different applications is presented. We motivate supersymmetry in particle physics. We then explain how supersymmetry helps us analyze field theories exactly, and what dynamical lessons these solutions teach us. Finally, we describe how supersymmetry is used to derive exact results in string theory. These results have led to a revolution in our understanding of the theory.

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arXiv1997

Why is the Matrix Model Correct?

We consider the compactification of M theory on a light-like circle as a limit of a compactification on a small spatial circle boosted by a large amount. Assuming that the compactification on a small spatial circle is weakly coupled type IIA theory, we derive Susskind's conjecture that M theory compactified on a light-like circle is given by the finite $N$ version of the Matrix model of Banks, Fischler, Shenker and Susskind. This point of view provides a uniform derivation of the Matrix model for M theory compactified on a transverse torus $T^p$ for $p=0,...,5$ and clarifies the difficulties for larger values of $p$.

hep-th↗
arXiv1997

Comments on Neveu-Schwarz Five-Branes

We study the theory of NS five-branes in string theory with a smooth non-trivial transverse space. We show that in the limit that the bulk physics decouples, these theories become equivalent to theories with a flat and non-compact transverse space. We present a matrix model description of the type IIA theory on $\IR^9\times S^1$ with NS five-branes located at points on the circle. Consequently, we obtain a description of the dual configuration of Kaluza-Klein monopoles in the type IIB theory.

hep-th↗
arXiv1997

Matrix Description of M-theory on $T^5$ and $T^5/Z_2$

We present four infinite series of new quantum theories with super-Poincare symmetry in six dimensions, which are not local quantum field theories. They have string like excitations but the string coupling is of order one. Compactifying these theories on $T^5$ we find a Matrix theory description of M theory on $T^5$ and on $T^5/\IZ_2$, which is well defined and is manifestly U-duality invariant.

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arXiv1997

Notes on Theories with 16 Supercharges

We survey the various field theories with 16 real supercharges. The most widely known theory in this class is the N=4 theory in four dimensions. The moduli space of vacua of these theories are described and the physics at the singularities of the moduli spaces are studied.

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arXiv1997

Comments on Higher Derivative Operators in Some SUSY Field Theories

We study the leading irrelevant operators along the flat directions of certain supersymmetric theories. In particular, we focus on finite N=2 (including N=4) supersymmetric field theories in four dimensions and show that these operators are completely determined by the symmetries of the problem. This shows that they are generated only at one loop and are not renormalized beyond this order. An instanton computation in similar three dimensional theories shows that these terms are renormalized. Hence, the four dimensional non-renormalization theorem of these terms is not valid in three dimensions.

hep-th↗
arXiv1997

Matrix Description of M-theory on $T^4$ and $T^5$

We study the Matrix theory description of M-theory compactified on $T^4$ and $T^5$. M-theory on $T^4$ is described by the six dimensional (2,0) fixed point field theory compactified on a five torus, $\widetilde T^5$. For M-theory on $T^5$ we suggest the existence of a new theory which is compactified on a $\widetilde T^5$. The IR description of this theory is given by the (2,0) theory with a compactified moduli space. This new theory appears to be a new kind of a non-critical string theory. Clearly, these two descriptions differ from the ``standard'' Super-Yang-Mills on the dual torus prescription.

hep-th↗
arXiv1997

Zero and One-dimensional Probes with N=8 Supersymmetry

We study the symmetry structure of N=8 quantum mechanics, and apply it to the physics of D0-brane probes in type I' string theory. We focus on the theory with a global $Spin(8)$ R symmetry which arises upon dimensional reduction from $2d$ field theory with $(0,8)$ supersymmetry. There are several puzzles involving supersymmetry which we resolve. In particular, by taking into account the gauge constraint and central charge we explain how the system preserves supersymmetry despite having different numbers of bosonic and fermionic variables. The resulting zero-point energy leads to a linear potential consistent with supersymmetry, and the metric is largely unconstrained. We discuss implications for type I' string theory and the matrix model proposal for M theory.

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arXiv1997

Strings from Matrices

We identify Type IIA and IIB strings, as excitations in the matrix model of M theory.

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arXiv1997

Branes from Matrices

Various aspects of branes in the recently proposed matrix model for M theory are discussed. A careful analysis of the supersymmetry algebra of the matrix model uncovers some central charges which can be activated only in the large $N$ limit. We identify the states with non-zero charges as branes of different dimensions.

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