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Sep 22, 2013
09/13

by
A. Armoni; M. Shifman

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We discuss k-strings in the large-N Yang-Mills theory and its supersymmetric extension. Whereas the tension of the bona fide (stable) QCD string is expected to depend only on the N-ality of the representation, tensions that depend on specific representation R are often reported in the lattice literature. In particular, adjoint strings are discussed and found in certain simulations. We clarify this issue by systematically exploiting the notion of the quasi-stable strings which becomes...

Source: http://arxiv.org/abs/hep-th/0307020v2

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Sep 19, 2013
09/13

by
A. Armoni; J. Sonnenschein

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The screening nature of the potential between external quarks in massless $SU(N_c)$ $QCD_2$ is derived using an expansion in $N_f$- the number of flavors. Applying the same method to the massive model, we find a confining potential. We consider the N=1 super Yang Mills theory, reveal certain problematic aspects of its bosonized version and show the associated screening behavior by applying a point splitting method to the scalar current.

Source: http://arxiv.org/abs/hep-th/9703114v1

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Sep 19, 2013
09/13

by
A. Armoni; M. Shifman

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We discuss domain walls and vacuum energy density (cosmological constant) in N=1 gluodynamics and in non-supersymmetric large N orientifold field theories which have been recently shown to be planar equivalent (in the boson sector) to N=1 gluodynamics. A relation between the vanishing force between two parallel walls and vanishing cosmological constant is pointed out. This relation may explain why the cosmological constant vanishes in the orientifold field theory at leading order although the...

Source: http://arxiv.org/abs/hep-th/0303109v2

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Sep 21, 2013
09/13

by
A. Armoni; J. Sonnenschein

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We discuss bosonized two-dimensional QCD with massless fermions in the adjoint and multi-flavor fundamental representations. We evaluate the massive mesonic spectra of several models by using the light-front quantization and diagonalizing the mass operator $M^2=2P^+P^- $. We recover previous results in the case of one flavor adjoint fermions and we find the exact massive spectrum of multi flavor QCD in the limit of large number of flavors.

Source: http://arxiv.org/abs/hep-th/9508006v1

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Sep 19, 2013
09/13

by
A. Armoni; M. Shifman

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We discuss the k dependence of the k-string tension sigma_k in SU(N) supersymmetric gluodynamics. As well known, at large N the k-string consists, to leading order, of k noninteracting fundamental strings, so that sigma_k=k sigma_1. We argue, both from field-theory and string-theory side, that subleading corrections to this formula run in powers of 1/N^2 rather than 1/N, thus excluding the Casimir scaling. We suggest a heuristic model allowing one to relate the k-string tension in...

Source: http://arxiv.org/abs/hep-th/0304127v2

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Sep 23, 2013
09/13

by
A. Armoni; M. Shifman

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We consider the dynamics of a strongly coupled SU(N) chiral gauge theory. By using its large-N equivalence with N=1 super-Yang-Mills theory we find the vacuum structure of the former. We also consider its finite-N dynamics.

Source: http://arxiv.org/abs/1202.1657v1

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Sep 18, 2013
09/13

by
A. Armoni; A. Brandhuber

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We use type IIB brane configurations which were recently suggested by Hanany and Zaffaroni to study four dimensional N=1 supersymmetric gauge theories. We calculate the one loop beta function and realize Seiberg's duality using a particular configuration. We also comment on the anomaly cancelation condition in the case of chiral theories and the beta function in the case of chiral and SO/Sp theories.

Source: http://arxiv.org/abs/hep-th/9803186v2

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Sep 18, 2013
09/13

by
A. Armoni; A. Gorsky; M. Shifman

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We discuss the fate of the Z2 symmetry and the vacuum structure in an SU(N)xSU(N) gauge theory with one bifundamental Dirac fermion. This theory can be obtained from SU(2N) supersymmetric Yang--Mills (SYM) theory by virtue of Z2 orbifolding. We analyze dynamics of domain walls and argue that the Z2 symmetry is spontaneously broken. Since unbroken Z2 is a necessary condition for nonperturbative planar equivalence we conclude that the orbifold daughter is nonperturbatively nonequivalent to its...

Source: http://arxiv.org/abs/hep-th/0505022v2

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Sep 19, 2013
09/13

by
A. Armoni; Y. Frishman; J. Sonnenschein

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We compute the string tension in massive $QCD_2$. It is shown that the string tension vanishes when the mass of the dynamical quark is zero, with no dependence on the representations of the dynamical or of the external charges. When a small mass ($m\ll e$) is added, a tension appears and we calculate its value as a function of the representations.

Source: http://arxiv.org/abs/hep-th/9709097v1

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Sep 22, 2013
09/13

by
A. Armoni; M. Shifman; G. Veneziano

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We review and extend our recent work on the planar (large N) equivalence between gauge theories with varying degree of supersymmetry. The main emphasis is made on the planar equivalence between N=1 gluodynamics (super-Yang-Mills theory) and a non-supersymmetric "orientifold field theory." We outline an "orientifold" large N expansion, analyze its possible phenomenological consequences in one-flavor massless QCD, and make a first attempt at extending the correspondence to...

Source: http://arxiv.org/abs/hep-th/0403071v2

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Sep 24, 2013
09/13

by
A. Armoni; M. Shifman; G. Veneziano

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We outline a full non-perturbative proof of planar (large-N) equivalence between bosonic correlators in a theory with Majorana fermions in the adjoint representation and one with Dirac fermions in the two-index (anti)symmetric representation. In a particular case (one flavor), this reduces to our previous result - planar equivalence between super-Yang--Mills theory and a non-supersymmetric ``orientifold field theory.'' The latter theory becomes one-flavor massless QCD at N=3.

Source: http://arxiv.org/abs/hep-th/0412203v3

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Sep 18, 2013
09/13

by
A. Armoni; Y. Frishman; J. Sonnenschein

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We review and elaborate on properties of the string tension in two-dimensional gauge theories. The first model we consider is massive QED in the $m\ll e$ limit. We evaluate the leading string tension both in the fermionic and bosonized descriptions. We discuss the next to leading corrections in $m/e$. The next-to-leading terms in the long distance behavior of the quark-antiquark potential, are evaluated in a certain region of external versus dynamical charges. The finite temperature behavior is...

Source: http://arxiv.org/abs/hep-th/9903153v2

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Sep 19, 2013
09/13

by
A. Armoni; M. Shifman; G. Veneziano

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We consider non-supersymmetric large N orientifold field theories. Specifically, we discuss a gauge theory with a Dirac fermion in the anti-symmetric tensor representation. We argue that, at large N and in a large part of its bosonic sector, this theory is non-perturbatively equivalent to N=1 SYM, so that exact results established in the latter (parent) theory also hold in the daughter orientifold theory. In particular, the non-supersymmetric theory has an exactly calculable bifermion...

Source: http://arxiv.org/abs/hep-th/0302163v3

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Sep 22, 2013
09/13

by
A. Armoni; M. Shifman; G. Veneziano

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We estimate the quark condensate in one-flavor massless QCD from the known value of the gluino condensate in SUSY Yang-Mills theory using our newly proposed "orientifold" large-N expansion. The numerical result for the quark condensate renormalized at the scale 2 GeV is then given as a function of alpha_s(2 GeV) and of possible corrections from sub-leading terms. Our value can be compared with the quark condensate in (quenched) lattice QCD or with the one extracted from the...

Source: http://arxiv.org/abs/hep-th/0309013v1

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Sep 22, 2013
09/13

by
A. Armoni; Y. Frishman; J. Sonnenschein

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We show that the string tension in N=1 two-dimensional super Yang-Mills theory vanishes independently of the representation of the quark anti-quark external source. We argue that this result persists in SQCD_2 and in two-dimensional gauge theories with extended supersymmetry or in chiral invariant models with at least one massless dynamical fermion. We also compute the string tension for the massive Schwinger model, as a demonstration of the method of the calculation.

Source: http://arxiv.org/abs/hep-th/9807022v2

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Sep 20, 2013
09/13

by
A. Armoni; A. Gorsky; M. Shifman

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We discuss a nonperturbative relation for orientifold parent/daughter pairs of supersymmetric theories with an arbitrary tree-level superpotential. We show that super-Yang-Mills (SYM) theory with matter in the adjoint representation at N-->infinity, is equivalent to a SYM theory with matter in the antisymmetric representation and a related superpotential. The gauge symmetry breaking patterns match in these theories too. The moduli spaces in the limiting case of a vanishing superpotential are...

Source: http://arxiv.org/abs/hep-th/0404247v3

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Sep 22, 2013
09/13

by
A. Armoni; M. Shifman; G. Veneziano

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We suggest a new large-N_c limit for multi flavor QCD. Since fundamental and two-index antisymmetric representations are equivalent in SU(3), we have the option to define SU(N_c) QCD keeping quarks in the latter. We can then define a new 1/N_c expansion (at fixed number of flavors N_f) that shares appealing properties with the topological (fixed N_f/N_c) expansion while being more suitable for theoretical analysis. In particular, for N_f=1, our large-N_c limit gives a theory that we recently...

Source: http://arxiv.org/abs/hep-th/0307097v2

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Sep 22, 2013
09/13

by
A. Armoni; Y. Frishman; J. Sonnenschein

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We discuss the spectra of multi-flavor massless QCD_2. An approximation in which the Hilbert space is truncated to two currents states is used. We write down a 't Hooft like equation for the wave function of the two currents states. We solve this equation for the lowest massive state and find an excellent agreement with the DLCQ results. In addition, the 't Hooft model and the large N_f limit spectra are re-derived by using a description in terms of currents.

Source: http://arxiv.org/abs/hep-th/0011043v1

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Sep 22, 2013
09/13

by
A. Armoni; Y. Frishman; J. Sonnenschein; U. Trittmann

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Massless $QCD_2$ is dominated by classical configurations in the large $N_f$ limit. We use this observation to study the theory by finding solutions to equations of motion, which are the non-Abelian generalization of the Schwinger equation. We find that the spectrum consists of massive mesons with $M^2={e^2 N_f\over 2\pi}$ which correspond to Abelian solutions. We generalize previously discovered non-Abelian solutions and discuss their interpretation. We prove a no-go theorem ruling out the...

Source: http://arxiv.org/abs/hep-th/9805155v1

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Sep 19, 2013
09/13

by
A. Armoni; J. L. F. Barbon; A. C. Petkou

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We study semiclassical rotating strings in AdS/CFT backgrounds that exhibit both confinement and finite-size effects. The energy versus spin dispersion relation for short strings is the expected Regge trajectory behaviour, with the same string tension as is measured by the Wilson loop. Long strings probe the interplay between confinement and finite-size effects. In particular, the dispersion relation for long strings shows a characteristic dependence on the string tension and the finite-size...

Source: http://arxiv.org/abs/hep-th/0209224v2

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Sep 22, 2013
09/13

by
A. Armoni; J. L. F. Barbon; A. C. Petkou

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Following Gubser, Klebanov and Polyakov [hep-th/0204051], we study strings in AdS black hole backgrounds. With respect to the pure AdS case, rotating strings are replaced by orbiting strings. We interpret these orbiting strings as CFT states of large spin similar to glueballs propagating through a gluon plasma. The energy and the spin of the orbiting string configurations are associated with the energy and the spin of states in the dual finite temperature N=4 SYM theory. We analyse in...

Source: http://arxiv.org/abs/hep-th/0205280v3