120 research outputs found
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.Comment: 14 pages. 4 eps figures. v2: refs. added. To appear in Nuclear
Physics
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.Comment: 14 pages, LaTex. 6 eps figures. v2: minor changes, typos fixed. To
appear in Nuclear Physics
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.Comment: Refs. added, discussion in sect. 3 improved, other minor changes; to
appear in JHE
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.Comment: 22 pages. LaTex. 5 eps figures. v2: minor changes, reference and a
comment about the GMOR relation added. To appear in Phys.Rev.
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.Comment: 10 pages, 3 figure
S-Dual of Maxwell Chern-Simons Theory
We discuss the dynamics of three dimensional Maxwell theory coupled to a
level Chern-Simons term. Motivated by S-duality in string theory we argue
that the theory admits an S-dual description. The S-dual theory contains a
non-gauge 1-form field, previously proposed by Deser and Jackiw and a level
Chern-Simons term, . The couplings to
external electric and magnetic currents and their string theory realisations
are also discussed.Comment: 11 pages,LaTex. 3 figures. v2: Few comments added, in particular how
to incorporate dynamical matter. Version to appear in PR
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 / (2\pi \sigma_k) log R/r .Comment: 13 pages, LaTex. v2: minor changes, references added. To appear in
Nucl.Phys.
Equivalence of meson scattering amplitudes in strong coupling lattice and flat space string theory
We consider meson scattering in the framework of the lattice strong coupling expansion. In particular we derive an expression for the 4-point function of meson operators in the planar limit of scalar Chromodynamics. Interestingly, in the naive continuum limit the expression coincides with an independently known result, that of the worldline formalism. Moreover, it was argued by Makeenko and Olesen that (assuming confinement) the resulting scattering amplitude in momentum space is the celebrated expression proposed by Veneziano several decades ago. This motivates us to also use holography in order to argue that the continuum expression for the scattering amplitude is related to the result obtained from flat space string theory. Our results hint that at strong coupling and large-Nc the naive continuum limit of the lattice formalism can be related to a flat space string theory
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