633 research outputs found
Towards the lattice study of M-theory
We propose the Wilson discretization of the supersymmetric Yang-Mills Quantum
Mechanics as a lattice version of the matrix model of M-theory. An SU(2) model
is studied numerically in the quenched approximation for D=4. A clear signal
for the existence of two different phases is found and the continuum
pseudocritical temperature is determined. We have also extracted the continuum
limit of the total size of the system in both phases and for different
temperatures.Comment: Lattice 2000 (Gravity and Matrix Models
Towards a diagrammatic derivation of the Veneziano-Yankielowicz-Taylor superpotential
We show how it is possible to integrate out chiral matter fields in N=1
supersymmetric theories and in this way derive in a simple diagrammatic way the
part of the Veneziano-Yankielowicz-Taylor
superpotential.Comment: 8 pages, 2 figure
Reggeon exchange from AdS/CFT
Using the AdS/CFT correspondence in a confining backgroundand the worldline
formalism of gauge field theories,we compute scattering amplitudes with an
exchange of quark andantiquark in the -channel corresponding to Reggeon
exchange. Itrequires going beyond the eikonal approximation, which was used
when studying Pomeron exchange. The wordline path integral is evaluated through
the determination of minimal surfaces and their boundaries by the saddle-point
method at large gauge coupling g^2N_c. We find a Regge behaviour with linear
Regge trajectories. The slope is related to the static potential and
is four times the Pomeronslope obtained in the same framework. A contribution
to the intercept, related to the L\"uscher term, comes from the fluctuations
around the minimal surface.Comment: 11 pages, 1 eps figur
Factorization of Seiberg-Witten Curves with Fundamental Matter
We present an explicit construction of the factorization of Seiberg-Witten
curves for N=2 theory with fundamental flavors. We first rederive the exact
results for the case of complete factorization, and subsequently derive new
results for the case with breaking of gauge symmetry U(Nc) to U(N1)xU(N2). We
also show that integrality of periods is necessary and sufficient for
factorization in the case of general gauge symmetry breaking. Finally, we
briefly comment on the relevance of these results for the structure of N=1
vacua.Comment: 24 pages, 2 figure
On the Couplings of Vector Mesons in AdS/QCD
We address, in the AdS/CFT context, the issue of the universality of the
couplings of the rho meson to other hadrons. Exploring some models, we find
that generically the rho-dominance prediction f_\rho g_{\rho H H}=m_\rho^2 does
not hold, and that g_{\rho H H} is not independent of the hadron H. However, we
prove that, in any model within the AdS/QCD context, there are two limiting
regimes where the g_{\rho H H}, along with the couplings of all excited vector
mesons as well, become H-independent: (1) when H is created by an operator of
large dimension, and (2) when H is a highly-excited hadron. We also find a
sector of a particular model where universality for the rho coupling is exact.
Still, in none of these cases need it be true that f_\rho g_\rho=m_\rho^2,
although we find empirically that the relation does hold approximately (up to a
factor of order two) within the models we have studied.Comment: 28 pages, 3 figures. ver 2: Comments about the commutability of two
universal limits in the D3/D7 case corrected. Typos corrected. ver 3:
Substantive revisions of certain calculations, with improved conventions,
correction of typos, clarifications, new formulas, new figures; no changes in
essential results or conclusion
Lectures on Chiral Disorder in QCD
I explain the concept that light quarks diffuse in the QCD vacuum following
the spontaneous breakdown of chiral symmetry. I exploit the striking analogy to
disordered electrons in metals, identifying, among others, the universal regime
described by random matrix theory, diffusive regime described by chiral
perturbation theory and the crossover between these two domains.Comment: Lectures given at the Cargese Summer School, August 6-18, 200
Minimal surfaces and Reggeization in the AdS/CFT correspondence
We address the problem of computing scattering amplitudes related to the
correlation function of two Wilson lines and/or loops elongated along
light-cone directions in strongly coupled gauge theories. Using the AdS/CFT
correspondence in the classical approximation, the amplitudes are shown to be
related to minimal surfaces generalizing the {\em helicoid} in various
backgrounds. Infra-red divergences appearing for Wilson lines can be factorized
out or can be cured by considering the IR finite case of correlation functions
of two Wilson loops. In non-conformal cases related to confining theories,
reggeized amplitudes with linear trajectories and unit intercept are obtained
and shown to come from the approximately flat metrics near the horizon, which
sets the scale for the Regge slope. In the conformal case the absence of
confinement leads to a different solution. A transition between both regimes
appears, in a confining theory, when varying impact parameter.Comment: 22 pages, 2 eps figures, expanded discussion, conclusions unchanged,
version to be published in Nuclear Physics
Eigenvalue density of Wilson loops in 2D SU(N) YM
In 1981 Durhuus and Olesen (DO) showed that at infinite N the eigenvalue
density of a Wilson loop matrix W associated with a simple loop in
two-dimensional Euclidean SU(N) Yang-Mills theory undergoes a phase transition
at a critical size. The averages of det(z-W), 1/det(z-W), and det(1+uW)/(1-vW)
at finite N lead to three different smoothed out expressions, all tending to
the DO singular result at infinite N. These smooth extensions are obtained and
compared to each other.Comment: 35 pages, 8 figure
Conformal invariance and QCD Pomeron vertices in the limit
Using the dipole framework for QCD at small x in the 1/N_c limit, we derive
the expression of the 1 -> p dipole multiplicity density in momentum space.
This gives an analytical expression for the 1 -> p QCD Pomeron amplitudes in
terms of one-loop integration of effective vertices in transverse momentum.
Conformal invariance and a Hilbert space construction for dipole correlation
functions are the main tools of the derivation. Relations with conformal field
theories in the classical limit are discussed.Comment: 16 pages, LATEX file, 1 .eps figur
High energy scattering and the AdS/CFT correspondence
We consider small angle and large impact parameter high energy scattering of
colourless states in SYM using the AdS/CFT correspondence. The gauge theory
scattering amplitude is linked with a correlation function of tilted Wilson
loops, which can be calculated by the exchange of bulk supergravity fields
between the two corresponding string worldsheets. We identify the dominant
contributions, which all correspond to real phase shifts. In particular, we
find a contribution of the bulk graviton which gives an unexpected
`gravity-like' behaviour of the gauge theory phase shift in a specific
range of energies and (large) impact parameters.Comment: 22p, 2 figure
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