arXiv subjects

Changhyun Ahn

Publications and source records attributed to Changhyun Ahn.

140 records · Page 8Linked to original sources

arXiv1997

M Theory Fivebrane Interpretation for Strong Coupling Dynamics of SO(N_c) Gauge Theories

We study M theory fivebranes to understand the moduli space of vacua of N=1 supersymmetric SO(N_c) gauge theory with N_f flavors in four dimensions. We discuss how the various branches of this theory arise in the string/M theory brane configurations and compare our results with the ones obtained earlier by Intriligator and Seiberg in the context of field theory. In the M theory approach, we explain the various branches from the asymptotic position of semi-infinite D4 branes in the $w=x^8+i x^9$ direction, which is closely related to the eigenvalues of the meson matrix $M^{ij} = Q^{i}_a Q^{j}_a$ where $Q^{i}_a$ is a squark multiplet ( $i=1, \cdots, 2N_f$ and $ a=1, \cdots, N_c$).In M theory, these branches are explained by observing a new phenomena which did not occur for the gauge groups SU(N_c) or Sp(N_c).

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arXiv1997

Quantum N=2 super $W_3^{(2)}$ Algebra In Superspace

We discuss the N=2 extension of Polyakov-Bershadsky $W_3^{(2)}$ algebra with the generic central charge, $c$, at the quantum level in superspace. It contains, in addition to the spin 1 N=2 stress tensor, the spins $1/2, 2$ bosonic and spins $1/2, 2$ fermionic supercurrents satisfying the first class nonlinear chiral constraints. In the $c \to \infty $ limit, the ``classical'' N=2 $W_3^{(2)}$ algebra is recovered.

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arXiv1997

N=2 Affine Superalgebras and Hamiltonian Reduction in N=2 Superspace

We construct N=2 affine current algebras for the superalgebras sl(n|n-1)^{(1)} in terms of N=2 supercurrents subjected to nonlinear constraints and discuss the general procedure of the hamiltonian reduction in N=2 superspace at the classical level. We consider in detail the simplest case of N=2 sl(2|1)^{(1)} and show how N=2 superconformal algebra in N=2 superspace follows via the hamiltonian reduction. Applying the hamiltonian reduction to the case of N=2 sl(3|2)^{(1)}, we find two new extended N=2 superconformal algebras in a manifestly supersymmetric N=2 superfield form. Decoupling of four component currents of dimension 1/2 in them yields, respectively, u(2|1) and u(3) Knizhnik-Bershadsky superconformal algebras. We also discuss how the N=2 superfield formulations of N=2 W_{3} and N=2 W_{3}^{(2)} superconformal algebras come out in this framework, as well as some unusual extended N=2 superconformal algebras containing constrained N=2 stress tensor and/or spin 0 supercurrents.

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arXiv1997

Geometry, D-branes and N=1 Duality in Four Dimensions with Product Gauge Group

We study N=1 dualities in four dimensional supersymmetric gauge theories by D 6-branes wrapping around 3-cycles of Calabi-Yau threefolds in the type IIA string theory. We consider the models involving $SU(N_{c1})\times SU(N_{c2})$ product gauge group without or with adjoint matter in terms of geometrical realisation of the configuration of D 6-branes wrapped 3-cycles. We also find simple geometric description for the triple product gauge group $SU(N_{c1})\times SU(N_{c2})\times SU(N_{c3})$ interpreted recently by Brodie and Hanany in the context of D brane configurations together with NS 5-branes. Their introduction of semi-infinite D 4-branes appears naturally by looking at the flavor group in the dual theory. We generalize to product of arbitrary number of gauge groups.

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arXiv1997

Geometry, D-Branes and N=1 Duality in Four Dimensions II

We study N=1 dualities in four dimensional supersymmetric gauge theories in terms of wrapping D 6-branes around 3-cycles of Calabi-Yau threefolds in type IIA string theory. We generalize the recent work of geometrical realization for the models which have the superpotential corresponding to an $A_k$ type singularity, to various models presented by Brodie and Strassler, consisting of $D_{k+2}$ superpotential of the form $W=Tr X^{k+1} + Tr XY^2$. We discuss a large number of representations for the field $Y$, but with $X$ always in the adjoint (symmetric) [antisymmetric] representation for $SU (SO) [Sp]$ gauge groups.

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arXiv1997

Geometry, D-Branes and N=1 Duality in Four Dimensions I

We consider N=1 dualities in four dimensional supersymmetric gauge theories as a geometrical realization of wrapping D 6-branes around 3-cycles of Calabi-Yau threefolds in type IIA string theory. By extending the recent work of Ooguri and Vafa to the case of $SU, SO and Sp$ gauge groups with additional fields together with defining fields, we give simple geometrical descriptions of the interrelation between the electric theory and its magnetic dual in terms of the configuration of D 6-branes wrapped 3-cycles.

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arXiv1997

Compactifications of F-Theory on Calabi-Yau Threefolds at Constant Coupli ng

Generalizing the work of Sen, we analyze special points in the moduli space of the compactification of the F-theory on elliptically fibered Calabi-Yau threefolds where the coupling remains constant. These contain points where they can be realized as orbifolds of six torus $T^6$ by $Z_m \times Z_n (m, n=2, 3, 4, 6)$. At various types of intersection points of singularities, we find that the enhancement of gauge symmetries arises from the intersection of two kinds of singularities. We also argue that when we take the Hirzebruch surface as a base for the Calabi- Yau threefold, the condition for constant coupling corresponds to the case where the point like instantons coalesce, giving rise to enhanced gauge group of $Sp(k)$.

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arXiv1996

Integrable structure in supersymmetric gauge theories with massive hypermultiplets

We study the quantum moduli space of vacua of $N=2$ supersymmetric $SU(N_c)$ gauge theories coupled to $N_f$ flavors of quarks in the fundamental representation. We identify the moduli space of the $N_c = 3$ and $N_f=2$ massless case with the full spectral curve obtained from the Lax representation of the Goryachev-Chaplygin top. For the case with {\it massive} quarks, we present an integrable system where the corresponding hyperelliptic curve parametrizing the Laurent solution coincides with that of the moduli space of $N_{c}=3$ with $N_{f}=0, 1, 2$. We discuss possible generalizations of the integrable systems relevant to gauge theories with $N_c \neq 3 $ and general $N_f$.

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arXiv1995

Yangian Symmetries in the $SU(N)_1$ WZW Model and the Calogero-Sutherland Model

We study the $SU(N)$, level $1$ Wess-Zumino-Witten model, with affine primary fields as spinon fields of fundamental representation. By evaluating the action of the Yangian generators $Q_{0}^{a}, Q_{1}^{a}$ and the Hamiltonian $H_2$ on two spinon states we get a new connection between this conformal field theory and the Calogero-Sutherland model with $SU(N)$ spin. This connection clearly confirms the need for the $W_3$ generator in $H_2$ and an additional term in the $Q^{a}_{1}$. We also evaluate some energy spectra of $H_2$, by acting it on multi-spinon states.

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arXiv1994

Explicit Construction of $N=2$ $W_3$ Current in the $N=2$ Coset $\frac{SU(3)}{SU(2) \times U(1)}$ Model

We discuss the nonlinear extension of $N=2$ superconformal algebra by generalizing Sugawara construction and coset construction built from $N=2$ currents based on Kazama-Suzuki $N=2$ coset model $\frac{SU(3)}{SU(2) \times U(1)}$ in $N=2$ superspace. For the generic unitary minimal series $c = 6(1-\frac{3}{k+3})$ where $k$ is the level of $SU(3)$ supersymmetric Wess-Zumino-Witten model, this algebra reproduces exactly $N=2$ $W_3$ algebra which has been worked out by Romans in component formalism.

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arXiv1993

Free Superfield Realization of N=2 Quantum Super W_{3} Algebra

We rewrite $ N=2$ quantum super $W_{3}$ algebra, a nonlinear extended $N=2$ super Virasoro algebra, containing one additional primary superfield of dimension $2$ which has no $U(1)$ charge, besides the super stress energy tensor of dimension $1$ in $N=2$ superspace. The free superfield realization of this algebra is obtained by two $N=2$ chiral fermionic superfields of dimension $1/2$ satisfying $N=2$ complex $ U(1)$ Kac-Moody algebras.

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arXiv1992

Explicit Construction of Spin 4 Casimir Operator in the Coset Model $ \hat{SO} (5)_{1} \times \hat{SO} (5)_{m} / \hat{SO} (5)_{1+m} $

We generalize the Goddard-Kent-Olive (GKO) coset construction to the dimension 5/2 operator for $ \hat{so} (5) $ and compute the fourth order Casimir invariant in the coset model $\hat{SO} (5)_{1} \times \hat{SO} (5)_{m} / \hat{SO} (5)_{1+m} $ with the generic unitary minimal $ c < 5/2 $ series that can be viewed as perturbations of the $ m \rightarrow \infty $ limit, which has been investigated previously in the realization of $ c= 5/2 $ free fermion model.

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arXiv1991

c=5/2 Free Fermion Model of WB_{2} Algebra

We investigate the explicit construction of the $WB_{2}$ algebra, which is closed and associative for all values of the central charge $c$, using the Jacobi identity and show the agreement with the results studied previously. Then we illustrate a realization of $c=\frac{5}{2}$ free fermion model, which is $m \rightarrow \infty$ limit of unitary minimal series, $c ( WB_{2} )=\frac{5}{2} (1-\frac{12}{ (m+3)(m+4) })$ based on the cosets $( \hat{B_{2}} \oplus \hat{B_{2}}, \hat{B_{2} })$ at level $(1,m).$ We confirm by explicit computations that the bosonic currents in the $ WB_{2}$ algebra are indeed given by the Casimir operators of $\hat{B_{2}}$ .

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arXiv1991

Superspace WZW Models and Black Holes

We show how to write an off-shell action for the $SU(2)\times U(1)$ supersymmetric WZW model in terms of $N=2$ chiral and twisted chiral multiplets. We discuss the $N=4$ supersymmetry of this model and exhibit the $N=4$ superconformal current algebra. Finally, we show that the off-shell formulation makes it possible to perform a duality transformation, which leads to a supersymmetric sigma model on a manifold with a black hole type singularity.

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