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Adi Armoni

Publications and source records attributed to Adi Armoni.

At least 55 records · Page 3Linked to original sources
arXiv2008

Orientifold Planar Equivalence: The Chiral Condensate

The recently introduced orientifold planar equivalence is a promising tool for solving non-perturbative problems in QCD. One of the predictions of orientifold planar equivalence is that the chiral condensates of a theory with $N_f$ flavours of Dirac fermions in the symmetric (or antisymmetric) representation and $N_f$ flavours of Majorana fermions in the adjoint representation have the same large $N$ value for any value of the mass of the (degenerate) fermions. Assuming the invariance of the theory under charge conjugation, we prove this statement on the lattice for staggered quenched condensates in SU($N$) Yang-Mills in the large $N$ limit. Then, we compute numerically those quenched condensates for $N$ up to 8. After separating the even from the odd corrections in $1/N$, we are able to show that our data support the equivalence; however, unlike other quenched observables, subleading terms in $1/N$ are needed for describing the data for the symmetric and antisymmetric representation at $N$=3. Possible lessons for the unquenched case are discussed.

hep-lat↗
arXiv2008

A Non-Supersymmetric Large-N 3D CFT And Its Gravity Dual

We propose a three dimensional non-supersymmetric theory that is conformal in the large N limit. In a certain well defined bosonic sub-sector of gauge invariant operators, this theory is planar equivalent to the theory recently proposed by Aharony, Bergman, Jafferis and Maldacena as the theory on multiple M2 branes at an orbifold singularity. We discuss the realization of the theory on a brane configuration of type 0B string theory. Moreover, we propose an 11D gravity dual, obtained by a projection of M-theory on AdS4 x S7 / Z_k.

hep-th↗
arXiv2008

Lattice Study of Planar Equivalence: The Quark Condensate

We study quenched SU(N) gauge theories with fermions in the two-index symmetric, antisymmetric and the adjoint representations. Our main motivation is to check whether at large number of colours those theories become non-perturbatively equivalent. We prove the equivalence assuming that the charge-conjugation symmetry is not broken in pure Yang-Mills theory. We then carry out a quenched lattice simulation of the quark condensate in the symmetric, antisymmetric and the adjoint representations for SU(2), SU(3), SU(4), SU(6) and SU(8). We show that the data support the equivalence and discuss the size of subleading corrections.

hep-th↗
arXiv2008

Quantum Broadening of k-Strings from the AdS/CFT Correspondence

We study the quantum broadening (width) of k-strings. We generalise an old result by Luscher, Munster and Weisz to the case of a k-string, by using the gauge/gravity correspondence. When the fundamental QCD-string is replaced by a bound state of k strings, the bound state is better described by a wrapped D-brane. We calculate the width of the k-string (the wrapped D-brane) in several AdS/CFT backgrounds by using a D-brane probe and find universally that omega_k ^2 = 1 / (2πσ_k) log R/r .

hep-th↗
arXiv2008

The Hagedorn Temperature and Open QCD-String Tachyons in Pure N=1 Super Yang-Mills

We consider large-N confining gauge theories with a Hagedorn density of states. In such theories the potential between a pair of colour-singlet sources may diverge at a critical distance r_c = 1/ T_H. We consider, in particular, pure N=1 super Yang-Mills theory and argue that when a domain-wall and an anti domain-wall are brought to a distance near r_c the interaction potential is better described by an ``open QCD-string channel''. We interpret the divergence of the potential in terms of a tachyonic mode and relate its mass to the Hagedorn temperature. Finally we relate our result to a theorem of Kutasov and Seiberg and argue that the presence of an open string tachyonic mode in the annulus amplitude implies an exponential density of states in the UV of the closed string channel.

hep-th↗
arXiv2008

Non-Supersymmetric Seiberg Duality, Orientifold QCD and Non-Critical Strings

We propose an electric-magnetic duality and conjecture an exact conformal window for a class of non-supersymmetric U(N_c) gauge theories with fermions in the (anti)symmetric representation of the gauge group and N_f additional scalar and fermion flavors. The duality exchanges N_c with N_f -N_c \mp 4 leaving N_f invariant, and has common features with Seiberg duality in N=1 SQCD with SU or SO/Sp gauge group. At large N the duality holds due to planar equivalence with N=1 SQCD. At finite N we embed these gauge theories in a setup with D-branes and orientifolds in a non-supersymmetric, but tachyon-free, non-critical type 0B string theory and argue in favor of the duality in terms of boundary and crosscap state monodromies as in analogous supersymmetric situations. One can verify explicitly that the resulting duals have matching global anomalies. Finally, we comment on the moduli space of these gauge theories and discuss other potential non-supersymmetric examples that could exhibit similar dualities.

hep-th↗
arXiv2007

Planar Limit of Orientifold Field Theories and Emergent Center Symmetry

We consider orientifold field theories (i.e. SU(N) Yang--Mills theories with fermions in the two-index symmetric or antisymmetric representations) on R3xS1 where the compact dimension can be either temporal or spatial. These theories are planar equivalent to supersymmetric Yang--Mills. The latter has Z_N center symmetry. The famous Polyakov criterion establishing confinement-deconfinement phase transition as that from Z_N symmetric to Z_N broken phase applies. At the Lagrangian level the orientifold theories have at most a Z_2 center. We discuss how the full Z_N center symmetry dynamically emerges in the orientifold theories in the limit N-->infinity. In the confining phase the manifestation of this enhancement is the existence of stable k-strings in the large-N limit of the orientifold theories. These strings are identical to those of supersymmetric Yang--Mills theories. We argue that critical temperatures (and other features) of the confinement-deconfinement phase transition are the same in the orientifold daughters and their supersymmetric parent up to 1/N corrections. We also discuss the Abelian and non-Abelian confining regimes of four-dimensional QCD-like theories.

hep-th↗
arXiv2007

Non-Perturbative Planar Equivalence and the Absence of Closed String Tachyons

We consider 'orbifold' and 'orientifold' field theories from the dual closed string theory side. We argue that a necessary condition for planar equivalence to hold is the absence of a closed string tachyonic mode in the dual non-supersymmetric string. We analyze several gauge theories on R3xS1. In the specific case of U(N) theories with symmetric/anti-symmetric fermions ('orientifold field theories') the relevant closed string theory is tachyon-free at large compactification radius (due to winding modes), but it develops a tachyonic mode below a critical radius. Our finding is with agreement with field theory expectations of a phase transition from a C-parity violating phase to a C-parity preserving phase as the compactification radius increases. In the case of U(N)xU(N) theories with bi-fundamental matter ('orbifold field theories') a tachyon is always present in the string spectrum, at any compactification radius. We conclude that on R4 planar equivalence holds for 'orientfiold field theories', but fails for 'orbifold field theories' daughters of N=4 SYM and suggest the same for daughters of N=1 SYM. We also discuss examples of SO/Sp gauge theories with symmetric/anti-symmetric fermions. In this case planar equivalence holds at any compactification radius -in agreement with the absence of tachyons in the string dual.

hep-th↗
arXiv2007

A note on C-Parity Conservation and the Validity of Orientifold Planar Equivalence

We analyze the possibility of a spontaneous breaking of C-invariance in gauge theories with fermions in vector-like - but otherwise generic - representations of the gauge group. QCD, supersymmetric Yang-Mills theory, and orientifold field theories, all belong to this class. We argue that charge conjugation is not spontaneously broken as long as Lorentz invariance is maintained. Uniqueness of the vacuum state in pure Yang-Mills theory (without fermions) and convergence of the expansion in fermion loops are key ingredients. The fact that C-invariance is conserved has an interesting application to our proof of planar equivalence between supersymmetric Yang-Mills theory and orientifold field theory on R4, since it allows the use of charge conjugation to connect the large-N limit of Wilson loops in different representations.

hep-th↗
arXiv2007

Planar Equivalence 2006

Planar equivalence between supersymmetric Yang--Mills theory and its orientifold daughters is a promising tool for explorations of nonperturbative aspects of quantum chromodynamics. Taking our 2004 review as a starting point we summarize some recent developments in this issue.

hep-th↗
arXiv2006

Anomalous Dimensions from a Spinning D5-Brane

We consider the anomalous dimension of a certain twist two operator in N=4 super Yang-Mills theory. At strong coupling and large-N it is captured by the classical dynamics of a spinning D5-brane. The present calculation generalizes the result of Gubser, Klebanov and Polyakov (hep-th/0204051): in order to calculate the anomalous dimension of a bound state of k coincident strings, the spinning closed string is replaced by a spinning D5 brane that wraps an S4 inside the S5 part of the AdS5 times S5 metric.

hep-th↗
arXiv2006

Universality of k-string Tensions from Holography and the Lattice

We consider large Wilson loops with quarks in higher representations in SU(N) Yang-Mills theories. We consider representations with common N-ality and check whether the expectation value of the Wilson loop depends on the specific representation or only on the N-ality. In the framework of AdS/CFT we show that = dim R exp -sigma_k A, namely that the string tension depends only on the N-ality k but the pre-exponent factor is representation dependent. The lattice strong coupling expansion yields an identical result at infinite N, but shows a representation dependence of the string tension at finite N, a result which we interpret as an artifact. In order to confirm the representation independence of the string tension we re-analyse results of lattice simulations involving operators with common N-ality in pure SU(N) Yang-Mills theory. We find that the picture of the representation-independence of the string tension is confirmed by the spectrum of excited states in the stringy sector, while the lowest-lying states seem to depend on the representation. We argue that this unexpected result is due to the insufficient distance of the static sources for the asymptotic behaviour to be visible and give an estimate of the distance above which a truly representation-independent spectrum should be observed.

hep-th↗
arXiv2006

Interactions of Domain Walls of SUSY Yang-Mills as D-Branes

Domain walls in supersymmetric Yang-Mills are BPS configurations which preserve two supercharges of the parent theory and so their tensions are known exactly. On the other hand, they have been described as D-branes for the confining string. This leads to a description of their collective dynamics in terms of a 2+1 -dimensional gauge theory with two supersymmetries and a Chern-Simons term. We show that this open string description can capture the qualitative behaviour of the forces between the domain walls for an arbitrary configuration of n walls at leading order in 1/N, extending earlier calculations for two walls. The potential admits a supersymmetric bound state when the n walls are all coincident and asymptotes to a constant at large separation with an n dependence which agrees perfectly with the exact tension formula.

hep-th↗
arXiv2005

Quark Condensate in Massless QCD from Planar Equivalence

A previous estimate of the quark condensate in one-flavour massless QCD from the known value of the gluino condensate in super Yang-Mills (SYM) theory is extended to Nf >1 by considering the large-N limit of an SU(N) gauge theory with one flavour in the antisymmetric representation and nf = Nf -1 extra flavours in the fundamental representation. We argue that, even at nf> 0, suitably chosen correlators in this theory can be mapped to those of SYM as N--> infinity. We give arguments why this correspondence should be particularly good for Nf =3 and compare our prediction with available (real and Monte Carlo) data.

hep-ph↗
arXiv2005

Predictions for orientifold field theories from type 0' string theory

Two predictions about finite-N non-supersymmetric "orientifold field theories" are made by using the dual type 0' string theory on C^3 / Z_2 x Z_2 orbifold singularity. First, the mass ratio between the lowest pseudoscalar and scalar color-singlets is estimated to be equal to the ratio between the axial anomaly and the scale anomaly at strong coupling, M_- / M_+ ~ C_- / C_+. Second, the ratio between the domain wall tension and the value of the quark condensate is computed.

hep-th↗
arXiv2005

Sitting on the Domain Walls of N=1 Super Yang-Mills

In pure N=1 supersymmetric Yang-Mills with gauge group SU(N), the domain walls which separate the N vacua have been argued, on the basis of string theory realizations, to be D-branes for the confining string. In a certain limit, this means that a configuration of k parallel domain walls is described by a 2+1-dimensional U(k) gauge theory. This theory has been identified by Acharya and Vafa as the U(k) gauge theory with 4 supercharges broken by a Chern-Simons term of level N in such a way that 2 supercharges are preserved. We argue further that the gauge coupling of the domain wall gauge theory goes like g^2 ~ Lambda/N, for large N. In the case of two domain walls, we show that the U(2) world-volume theory generates a quadratic potential on the Coulomb branch at two loops in perturbation theory which is consistent with there being a supersymmetric bound state of the two wall system. A mass gap of order Lambda/N is generated around the supersymmetric minimum and we estimate the size of the bound-state to be order Lambda/ \sqrt N. At large distance the potential reaches a constant that can qualitatively account for the binding energy of the two walls even though stringy effects are not, strictly speaking, decoupled.

hep-th↗
arXiv2004

Witten-Veneziano from Green-Schwarz

We consider the U(1) problem within the AdS/CFT framework. We explain how the Witten-Veneziano formula for the eta' mass is related to a generalized Green-Schwarz mechanism. The closed string mode, that cancels the anomaly of the gauged U(1) axial symmetry, is identified with the eta' meson. In a particular set-up of D3-branes on a C3/(Z3xZ3) orbifold singularity, the eta' meson is a twisted-sector R-R field.

hep-th↗