12,633 research outputs found
The magnon kinematics of the AdS/CFT correspondence
The planar dilatation operator of N=4 supersymmetric Yang-Mills is the
hamiltonian of an integrable spin chain whose length is allowed to fluctuate.
We will identify the dynamics of length fluctuations of planar N=4 Yang-Mills
with the existence of an abelian Hopf algebra Z symmetry with non-trivial
co-multiplication and antipode. The intertwiner conditions for this Hopf
algebra will restrict the allowed magnon irreps to those leading to the magnon
dispersion relation. We will discuss magnon kinematics and crossing symmetry on
the spectrum of Z. We also consider general features of the underlying Hopf
algebra with Z as central Hopf subalgebra, and discuss the giant magnon
semiclassical regime.Comment: 21 pages, Latex. v2: Minor changes and additional reference
Integrability and non-perturbative effects in the AdS/CFT correspondence
We present a non-perturbative resummation of the asymptotic strong-coupling
expansion for the dressing phase factor of the AdS_5xS^5 string S-matrix. The
non-perturbative resummation provides a general form for the coefficients in
the weak-coupling expansion, in agreement with crossing symmetry and
transcendentality. The ambiguities of the non-perturbative prescription are
discussed together with the similarities with the non-perturbative definition
of the c=1 matrix model.Comment: 8 pages. Late
M-Theory, Torons and Confinement
We study the decompactification limit of M-theory superpotentials for N=1
four dimensional supersymmetric gauge theories. These superpotentials can be
interpreted as generated by toron configurations. The connection with the
confinement picture in the maximal abelian gauge is discussed.Comment: Latex file. 9 pages. Lecture given by C. G. at the XXXIII Karpacz
School: "Duality, Strings and Fields". February 1997. Improved version, with
a clarifying exposition on the dynamical role of torons in M-theory include
M and F-Theory Instantons, N=1 Supersymmetry and Fractional Topological Charges
We analize instanton generated superpotentials for three dimensional N=2
supersymmetric gauge theories obtained by compactifying on S^1 N=1 four
dimensional theories. In the N_f=1 case, we find that the vacua in the
decompactification limit is given by the singular points of the Coulomb branch
of the N=2 four dimensional theory (we also consider the massive case). The
decompactification limit of the superpotential for pure gauge theories without
chiral matter is interpreted in terms of `t Hooft's fractional instanton
amplitudes.Comment: Latex file. 11 pages. Typos corrected. Section on QCD has been
rewritten, clarifying some points, and a reference has been added. Final
version to appear at Int. Jour. Mod. Phys.
Child health in rural Colombia: determinants and policy interventions
In this paper we study the determinants of child anthropometrics on a sample of poor Colombian
children living in small municipalities. We focus on the influence of household consumption, and
public infrastructure. We take into account the endogeneity of household consumption using two
different sets of instruments: household assets and municipality average wage. We find that household
consumption is an important determinant of child health. The importance of the effect is confirmed by
the two different sets of instruments. We find that using ordinary least squares would lead to conclude
that the importance of household consumption is much smaller than the instrumental variable
estimates suggest. The presence of a public hospital in the municipality positively influences child
health. The extent of the piped water network positively influences the health of children if their
parents have at least some education. The number of hours of growth and development check-ups is
also an important determinant of child health. We find that some of these results only show up once
squared and interaction terms have been included in the regression. Overall, our estimates suggest that
both public and private investments are important to improve child health in poor environments
Magnons and BFKL
We extract from the double logarithmic contributions to DGLAP anomalous
dimensions for twist-two operators up to three-loops the magnon dispersion
relation for planar N=4 supersymmetric Yang-Mills. Perturbatively the magnon
dispersion relation agrees with the expansion of the anomalous dimension for
spin-one as well as with the non-collinear double logarithmic contributions to
the BFKL anomalous dimensions analytically extended to negative spin. The
all-loop expression for the magnon dispersion relation is determined by the
double logarithmic resummation of the corresponding Bethe-Salpeter equation. A
potential map relating the spin chain magnon to BFKL eigenfunctions in the
double logarithm approximation is suggested.Comment: 21 pages. Latex. v2: Reference added and minor change
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