arXiv subjects

Adi Armoni

Publications and source records attributed to Adi Armoni.

At least 37 records · Page 2Linked to original sources

arXiv2016

Large-N QCD and the Veneziano Amplitude

We consider four scalar mesons scattering in large-Nc QCD. Using the worldline formalism we show that the scattering amplitude can be written as a formal sum over Wilson loops. The AdS/CFT correspondence maps this sum into a sum over string worldsheets in a confining background. We then argue that for well separated mesons the sum is dominated by flat space configurations. Under additional assumptions about the dual string path integral we obtain the Veneziano amplitude.

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arXiv2015

Defects in Chern-Simons theory, gauged WZW models on the brane, and level-rank duality

We consider Hanany-Witten setups of 3- and 5-branes in type IIB string theory that realize N=(1,0),(2,0) and (1,1) gauged WZW models in 1+1 dimensions. The gauged WZW models arise as theories residing on the boundary of D3 branes ending on D5 branes. From the point of view of low energy dynamics the D5 branes play the role of half-BPS co-dimension-1 defects (domain walls) in 3d N=1 or N=2 Chern-Simons theories. Extending the analysis of previous works on the subject of boundary conditions in (supersymmetric) Chern-Simons theory, we discuss in detail the field theory construction of a large class of Chern-Simons domain wall theories and its embedding in open string dynamics. Finally, we exhibit how standard brane moves that result to 3d Seiberg duality, translate in our setup to a generalized level-rank duality in gauged-WZW models.

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arXiv2015

Center symmetry and Hagedorn spectrum

This paper explores the conjecture that large Nc gauge theories have a Hagedorn spectrum, if, and only if, they are confining and posses an explicit or emergent center symmetry. Evidence in support of this conjecture is presented. Many classes of large Nc gauge theories are considered. In all cases, we find that theories for which there exists a strong plausibility argument for a Hagedorn spectrum at large Nc are also believed to be confining and possess either an explicit center symmetric or have a strong plausibility argument for the existence of an emergent center symmetry at large Nc . Conversely, all theories we considered which are believed not to have a Hagedorn spectrum at large Nc, either were known not to be confining or else were believed to lack an emergent center symmetry. This is consistent with expectations based on the conjecture.

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arXiv2014

The Quark Condensate in Multi-Flavour QCD - Planar Equivalence Confronting Lattice Simulations

Planar equivalence between the large $N$ limits of ${\cal N}=1$ Super Yang-Mills (SYM) theory and a variant of QCD with fermions in the antisymmetric representation is a powerful tool to obtain analytic non-perturbative results in QCD itself. In particular, it allows the quark condensate for $N=3$ QCD with quarks in the fundamental representation to be inferred from exact calculations of the gluino condensate in ${\cal N}=1$ SYM. In this paper, we review and refine our earlier predictions for the quark condensate in QCD with a general number $n_f$ of flavours and confront these with lattice results.

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arXiv2014

Level-Rank Duality in Chern-Simons Theory from a Non-Supersymmetric Brane Configuration

We derive level-rank duality in pure Chern-Simons gauge theories from a non-supersymmetric Seiberg duality by using a non-supersymmetric brane configuration in type IIB string theory. The brane configuration consists of fivebranes, N D3 antibranes and an O3 plane. By swapping the fivebranes we derive a 3d non-supersymmetric Seiberg duality. After level shifts from loop effects, this identifies the IR of Sp(2N)_{2k-2N+2} and Sp(2k-2N+2)_{-2N} pure Chern-Simons theories, which is a level-rank pair. We also derive level-rank duality in a Chern-Simons theory based on a unitary group.

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arXiv2014

Non-Supersymmetric Brane Configurations, Seiberg Duality and Dynamical Symmetry Breaking

We consider type IIA brane configurations, similar to those that realize SO(2N) supersymmetric QCD, that include orientifold planes and anti-branes. Such brane configurations lead to Sp(2N) field theories that become supersymmetric in the large-N limit and break supersymmetry upon the inclusion of 1/N corrections. We argue that this class of field theories admit Seiberg duality and interpret the potential between branes and orientifolds as field theory phenomena. In particular we find in the magnetic theory a meson potential that leads to dynamical symmetry breaking and a meson condensate similar to the anticipated quark condensate in QCD.

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arXiv2014

Silver Blaze Puzzle in 1/Nc Expansions of Cold and Dense QCD Matter

We consider quantum chromodynamics (QCD) with Nc colors and Nf quark flavors at finite quark chemical potential mu_q or isospin chemical potential mu_I. We specifically address the nature of the ``Silver Blaze'' behavior in the framework of 1/Nc expansion. Starting with the QCD partition function, we implement Veneziano's Nf/Nc expansion to identify the density onset. We find the baryon mass M_B and the pion mass m_pi appearing from different order of Veneziano's expansion. We argue that the confining properties are responsible for the Silver Blaze in the region of m_pi/2 < mu_q < M_B/Nc. We point out, however, that Veneziano's expansion brings about a puzzling subtlety along the same line as the baryon problem in finite-density quenched simulations. We emphasize that the large-Nc limit can allow for the physical ordering of M_B and m_pi thanks to the similarity to the quenched approximation, while the unphysical ghost quarks contaminate the baryon sector if Nc is finite. We also discuss the ``orientifold'' large-Nc limit that does not quench quark loops.

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arXiv2013

A Note on Seiberg Duality and Chiral Symmetry Breaking

Following arXiv:1310.2027 and arXiv:0801.0762, we consider a non-supersymmetric Seiberg duality between electric and magnetic "orientifold field theories". These theories live on brane configurations of type 0' string theory. In the electric theory side the scalars acquire a mass and decouple, resulting in an SU(Nc) gauge theory coupled to Nf massless quarks and an additional massless fermion that transforms in the two-index antisymmetric representation. In the magnetic theory side there exists a fundamental meson field that develops a Coleman-Weinberg potential. At the one-loop approximation the potential admits a minimum with chiral symmetry breaking of the form SU(Nf)L x SU(Nf)R --> SU(Nf)V and an additional breaking of an axial U(1) symmetry. The resulting theory admits a spectrum whose massless degrees of freedom are Nf^2 Nambu-Goldstone bosons.

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arXiv2013

Correlators of Circular Wilson Loops from Holography

We study the correlators of two circular Wilson loops of different radii at strong coupling. In our setup one Wilson loop is located inside the other. We use holography to calculate the connected two-point function. Both an AdS background and a confining background are considered. As the computation for the confining case cannot be carried out analytically we solve the problem numerically. In the AdS case our results agree with similar holographic calculations. In the case of a confining background we find an asymptotic area law, in agreement with the result of the lattice strong coupling expansion. We also elaborate on the subtle issue of the interplay between connected and disconnected string worldsheets.

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arXiv2012

QCD With A Chemical Potential, Topology, And The 't Hooft 1/N Expansion

We discuss the dependence of observables on the chemical potential in 't Hooft's large-N QCD. To this end we use the worldline formalism to expand the fermionic determinant in powers of 1/N. We consider the hadronic as well as the deconfining phase of the theory. We discuss the origin of the sign problem in the worldline approach and elaborate on the planar equivalence between QCD with a baryon chemical potential and QCD with an isospin chemical potential. We show that for C-even observables the sign problem occurs at a subleading order in the 1/N expansion of the fermionic determinant. Finally, we comment on the finite N theory.

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arXiv2011

k-String Tension from Eguchi-Kawai Reduction

We consider three-dimensional SU(N) gauge theories with massless Dirac or Majorana fermions in the adjoint representation. We use the Eguchi-Kawai volume reduction to two-dimensions to calculate the tension sigma_k of the k-string in such theories. Under some assumptions whose validity we discuss, we derive the previously conjectured sine formula, sigma_k ~ N sin pi k/N.

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arXiv2011

Noncommutative Two-Dimensional Gauge Theories

We elaborate on the dynamics of noncommutative two-dimensional gauge field theories. We consider U(N) gauge theories with fermions in either the fundamental or the adjoint representation. Noncommutativity leads to a rather non-trivial dependence on theta (the noncommutativity parameter) and to a rich dynamics. In particular the mass spectrum of the noncommutative U(1) theory with adjoint matter is similar to that of ordinary (commutative) two-dimensional large-N SU(N) gauge theory with adjoint matter. The noncommutative version of the 't Hooft model receives a non-trivial contribution to the vacuum polarization starting from three-loops order. As a result the mass spectrum of the noncommutative theory is expected to be different from that of the commutative theory.

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arXiv2011

Comments on Mesonic Correlators in the Worldline Formalism

We elaborate on how to incorporate mesonic correlators into the worldline formalism. We consider possible applications to QCD-like theories in various dimensions. We focus on large-N_c two dimensional QCD (the 't Hooft model) and relate it to a single harmonic oscillator. We also discuss the dependence of the Peskin S-parameter on the number of massless flavors and their representation and compare our expression to the corresponding expression obtained at weak coupling. Finally, we use the worldline formalism to discuss how the Veneziano limit of QCD is realized in holography in the limit of small N_f/N_c.

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arXiv2010

Domain Walls and Metastable Vacua in Hot Orientifold Field Theories

We consider "Orientifold field theories", namely SU(N) gauge theories with Dirac fermions in the two-index representation at high temperature. When N is even these theories exhibit a spontaneously broken Z2 centre symmetry. We study aspects of the domain wall that interpolates between the two vacua of the theory. In particular we calculate its tension to two-loop order. We compare its tension to the corresponding domain wall in a SU(N) gauge theory with adjoint fermions and find an agreement at large-N, as expected from planar equivalence between the two theories. Moreover, we provide a non-perturbative proof for the coincidence of the tensions at large-N. We also discuss the vacuum structure of the theory when the fermion is given a large mass and argue that there exist N-2 metastable vacua. We calculate the lifetime of those vacua in the thin wall approximation.

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arXiv2009

The Conformal Window from the Worldline Formalism

We use the worldline formalism to derive a universal relation for the lower boundary of the conformal window in non-supersymmetric QCD-like theories. The derivation relies on the convergence of the expansion of the fermionic determinant in terms of Wilson loops. The expansion shares a similarity with the lattice strong coupling expansion and the genus expansion in string theory. Our result relates the lower boundary of the conformal window in theories with different representations and different gauge groups. Finally, we use SQCD to estimate the boundary of the conformal window in QCD-like theories and compare it with other approaches.

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arXiv2009

Brane Dynamics and 3D Seiberg Duality on the Domain Walls of 4D N=1 SYM

We study a three-dimensional U(k) Yang-Mills Chern-Simons theory with adjoint matter preserving two supersymmetries. According to Acharya and Vafa, this theory describes the low-energy worldvolume dynamics of BPS domain walls in four-dimensional N=1 SYM theory. We demonstrate how to obtain the same theory in a brane configuration of type IIB string theory that contains threebranes and fivebranes. A combination of string and field theory techniques allows us to re-formulate some of the well-known properties of N=1 SYM domain walls in a geometric language and to postulate a Seiberg-like duality for the Acharya-Vafa theory. In the process, we obtain new information about the dynamics of branes in setups that preserve two supersymmetries. Using similar methods we also study other N=1 CS theories with extra matter in the adjoint and fundamental representations of the gauge group.

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arXiv2009

Degeneracy Between the Regge Slope of Mesons and Baryons from Supersymmetry

We consider the degeneracy between the Regge slope of mesons and baryons in QCD. We argue that within the "orientifold large-N approximation" asymptotically massive mesons and baryons become supersymmetric partners and hence degenerate. To this end, we generalize QCD by a SU(N) theory with a quark in the two-index antisymmetric representation. We show that in this framework the meson is represented by an oriented bosonic QCD-string and the baryon is represented by an un-oriented fermionic QCD-string. At large-N, due to an equivalence with super Yang-Mills, the tensions of the bosonic and the fermionic strings coincide. Our description of mesons and baryons as oriented and un-oriented bosonic and fermionic QCD-strings is in full agreement with the spectra of open strings in the dual type 0' string theory.

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arXiv2009

Z(N) Domain walls in hot N=4 SYM at weak and strong coupling

We study the tensions of domain walls in the deconfined phase of N=4 SUSY Yang-Mills theory on R^3 x S^1, at weak and strong coupling. We calculate the k-wall tension at one-loop order and find that it is proportional to k(N-k) (Casimir scaling). The two-loops analysis suggests that Casimir scaling persists to this order. The strong coupling calculation is performed by using the AdS/CFT correspondence. We argue that the k-wall should be identified with an NS5-brane wrapping an S^4 inside S^5 in the AdS-Schwarzschild x S^5 background in Type IIB string theory. The tension at strong coupling is compared with the weak coupling result. We also compare our results with those from lattice simulations in pure Yang-Mills theory.

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