330 research outputs found
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.Comment: 8 pages, LaTex. v2: figure added. minor changes. To appear in JHE
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.Comment: v2: extended version. Appendices and references adde
Rotating Strings in Confining AdS/CFT Backgrounds
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 scale.Comment: 18 pages, 3 figures. v2: minor changes, refs. adde
On the spectrum of QCD(1+1) with large numbers of flavours N_F and colours N_C near N_F/N_C = 0
QCD(1+1) in the limit of a large number of flavours N_F and a large number of
colours N_C is examined in the small N_F/N_C regime. Using perturbation theory
in N_F/N_C, stringent results for the leading behaviour of the spectrum
departing from N_F/N_C = 0 are obtained. These results provide benchmarks in
the light of which previous truncated treatments of QCD(1+1) at large N_F and
N_C are critically reconsidered.Comment: 6 revtex page
Strings Inside Walls in N=1 Super Yang-Mills
We conjecture the existence of strings bounded inside walls in SU
Super Yang-Mills theory. These strings carry quantum number, where
is the greatest common divisor between , the charge of the wall, and
. We provide field-theoretical arguments and string-theoretical evidences,
both from MQCD and from gauge-gravity correspondence. We interpret this result
from the point of view of the low-energy effective action living on the
-wall.Comment: 25 pp. Major changes. In particular, following the recent work
arXiv:0807.1908 we have been able to give a field theoretical proof of the
statement. We have also corrected an important erroneous interpretation in
the previous version regarding the 2+1 effective action; Typo
Large N Field Theory and AdS Tachyons
In non-supersymmetric orbifolds of N =4 super Yang-Mills, conformal
invariance is broken by the logarithmic running of double-trace operators -- a
leading effect at large N. A tachyonic instability in AdS_5 has been proposed
as the bulk dual of double-trace running. In this paper we make this
correspondence more precise. By standard field theory methods, we show that the
double-trace beta function is quadratic in the coupling, to all orders in
planar perturbation theory. Tuning the double-trace coupling to its (complex)
fixed point, we find conformal dimensions of the form 2 + i b, as formally
expected for operators dual to bulk scalars that violate the stability bound.
We also show that conformal invariance is broken in perturbation theory if and
only if dynamical symmetry breaking occurs. Our analysis is applicable to a
general large N field theory with vanishing single-trace beta functions.Comment: 26 pages, 6 figures. v3: small changes, version published on JHEP
The Renormalization of Non-Commutative Field Theories in the Limit of Large Non-Commutativity
We show that renormalized non-commutative scalar field theories do not reduce
to their planar sector in the limit of large non-commutativity. This follows
from the fact that the RG equation of the Wilson-Polchinski type which
describes the genus zero sector of non-commutative field theories couples
generic planar amplitudes with non-planar amplitudes at exceptional values of
the external momenta. We prove that the renormalization problem can be
consistently restricted to this set of amplitudes. In the resulting
renormalized theory non-planar divergences are treated as UV divergences
requiring appropriate non-local counterterms. In 4 dimensions the model turns
out to have one more relevant (non-planar) coupling than its commutative
counterpart. This non-planar coupling is ``evanescent'': although in the
massive (but not in the massless) case its contribution to planar amplitudes
vanishes when the floating cut-off equals the renormalization scale, this
coupling is needed to make the Wilsonian effective action UV finite at all
values of the floating cut-off.Comment: 35 pages, 8 figures; typos correcte
A new lattice measurement for potentials between static SU(3) sources
In this article, a new calculation of static potentials between sources of
different representations in SU(3) gauge group is presented. The results of
author's previous study \cite{Deld00} at the smallest lattice spacing
~ fm are shown to have been affected by finite volume effects.
Within statistical errors, the new results obtained here are still in agreement
with both, Casimir scaling and flux tube counting. There is also no
contradiction to the results obtained in Ref.~ \cite{Bali00} which however
exclude flux counting.Comment: To be published in EPJ
The Skyrmion strikes back: baryons and a new large limit
In the large limit of QCD, baryons can be modeled as solitons, for
instance, as Skyrmions. This modeling has been justified by Witten's
demonstration that all properties of baryons and mesons scale with
in the same way as the analogous meson-based soliton model scales with a
generic meson-meson coupling constant . An alternative large limit
(the orientifold large limit) has recently been proposed in which quarks
transform in the two-index antisymmetric representation of . By
carrying out the analog of Witten's analysis for the new orientifold large
limit, we show that baryons and solitons can also be identified in the
orientifold large limit. However, in the orientifold large limit,
the interaction amplitudes and matrix elements scale with in the
same way as soliton models scale with the generic meson coupling constant
rather than as as in the traditional large limit.Comment: 10 pages, 26 figure
On the Spectrum of QCD(1+1) with SU(N_c) Currents
Extending previous work, we calculate in this note the fermionic spectrum of
two-dimensional QCD (QCD_2) in the formulation with SU(N_c) currents. Together
with the results in the bosonic sector this allows to address the as yet
unresolved task of finding the single-particle states of this theory as a
function of the ratio of the numbers of flavors and colors, \lambda=N_f/N_c,
anew. We construct the Hamiltonian matrix in DLCQ formulation as an algebraic
function of the harmonic resolution K and the continuous parameter \lambda.
Amongst the more surprising findings in the fermionic sector chiefly considered
here is that the fermion momentum is a function of \lambda. This dependence is
necessary in order to reproduce the well-known 't Hooft and large N_f spectra.
Remarkably, those spectra have the same single-particle content as the ones in
the bosonic sectors. The twist here is the dramatically different sizes of the
Fock bases in the two sectors, which makes it possible to interpret in
principle all states of the discrete approach. The hope is that some of this
insight carries over into the continuum. We also present some new findings
concerning the single-particle spectrum of the adjoint theory.Comment: 21 pp., 13 figures, version published in PR
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