599 research outputs found
Decaying Dark Matter from Dark Instantons
We construct an explicit, TeV-scale model of decaying dark matter in which
the approximate stability of the dark matter candidate is a consequence of a
global symmetry that is broken only by instanton-induced operators generated by
a non-Abelian dark gauge group. The dominant dark matter decay channels are to
standard model leptons. Annihilation of the dark matter to standard model
states occurs primarily through the Higgs portal. We show that the mass and
lifetime of the dark matter candidate in this model can be chosen to be
consistent with the values favored by fits to data from the PAMELA and Fermi
LAT experiments.Comment: 19 pages LaTeX, 3 eps figures. v2,v3: references adde
Form Factors and Wave Functions of Vector Mesons in Holographic QCD
Within the framework of a holographic dual model of QCD, we develop a
formalism for calculating form factors of vector mesons. We show that the
holographic bound states can be described not only in terms of eigenfunctions
of the equation of motion, but also in terms of conjugate wave functions that
are close analogues of quantum-mechanical bound state wave functions. We derive
a generalized VMD representation for form factors, and find a very specific VMD
pattern, in which form factors are essentially given by contributions due to
the first two bound states in the Q^2-channel. We calculate electric radius of
the rho-meson, finding the value _C = 0.53 fm^2.Comment: 7 pages, RevTex. References were added, some modifications in the
text were mad
Measuring human rights abuse from access to information requests
Existing measures of human rights abuses are often only available at the country-year level. Several more fine-grained measures exhibit spatio-temporal inaccuracies or reporting biases due to the primary sources upon which they rely. To address these challenges, and to increase the diversity of available human rights measures more generally, this study provides the first quantitative effort to measure human rights abuses from textual records of citizen-government interactions. Using a dataset encompassing over 1.5 million access-to-information (ATI) requests made to the Mexican federal government from June 2003 onward, supervised classification is used to identify the subset of these requests that pertain to human rights abuses of various types. The results from this supervised machine learning exercise are validated against (i) gold standard ATI requests pertaining to past human rights abuses in Mexico and (ii) several accepted external measures of sub-national and sub-annual human rights abuses. In doing so, we demonstrate that the measurement of human rights abuses from citizen-submitted ATI request texts can provide measures of human rights abuse that exhibit both high validity and notable spatio-temporal specificity, relative to existent human rights datasets and variables
Gravitational collapse and thermalization in the hard wall model
We study a simple example of holographic thermalization in a confining field
theory: the homogeneous injection of energy in the hard wall model. Working in
an amplitude expansion, we find black brane formation for sufficiently fast
energy injection and a scattering wave solution for sufficiently slow
injection. We comment on our expectations for more sophisticated holographic
QCD models.Comment: 33 pages, 5 figure
Pion and Vector Meson Form Factors in the Kuperstein-Sonnenschein holographic model
We study phenomenological aspects of the holographic model of chiral symmetry
breaking recently introduced by Kuperstein and Sonnenschein (KS). As a first
step, we calculate the spectrum of vector and axial-vector mesons in the KS
model. We numerically compute various coupling constants of the mesons and
pions. Our analysis indicates that vector meson dominance is realized in this
model. The pion, vector meson and axial-vector meson form factors are obtained
and studied in detail. We find good agreement with QCD results. In particular,
the pion form factor closely matches available experimental data.Comment: v1: 27 pages, 9 figures, 4 tables; v2: minor changes, added more
general discussion of vector meson dominance; v3: minor changes and
additions, version accepted for publication in JHE
Effective AdS/renormalized CFT
For an effective AdS theory, we present a simple prescription to compute the
renormalization of its dual boundary field theory. In particular, we define
anomalous dimension holographically as the dependence of the wave-function
renormalization factor on the radial cutoff in the Poincare patch of AdS. With
this definition, the anomalous dimensions of both single- and double- trace
operators are calculated. Three different dualities are considered with the
field theory being CFT, CFT with a double-trace deformation and spontaneously
broken CFT. For the second dual pair, we compute scaling corrections at the UV
and IR fixed points of the RG flow triggered by the double-trace deformation.
For the last case, we discuss whether our prescription is sensitive to the AdS
interior or equivalently, the IR physics of the dual field theory.Comment: 20 pages, 3 figure
Positivity Constraints on Anomalies in Supersymmetric Gauge Theories
The relation between the trace and R-current anomalies in supersymmetric
theories implies that the U, U and U anomalies which
are matched in studies of N=1 Seiberg duality satisfy positivity constraints.
Some constraints are rigorous and others conjectured as four-dimensional
generalizations of the Zamolodchikov -theorem. These constraints are tested
in a large number of N=1 supersymmetric gauge theories in the non-Abelian
Coulomb phase, and they are satisfied in all renormalizable models with unique
anomaly-free R-current, including those with accidental symmetry. Most striking
is the fact that the flow of the Euler anomaly coefficient, , is
always positive, as conjectured by Cardy.Comment: latex, 36 page
Long-Range Rapidity Correlations in Heavy Ion Collisions at Strong Coupling from AdS/CFT
We use AdS/CFT correspondence to study two-particle correlations in heavy ion
collisions at strong coupling. Modeling the colliding heavy ions by shock waves
on the gravity side, we observe that at early times after the collision there
are long-range rapidity correlations present in the two-point functions for the
glueball and the energy-momentum tensor operators. We estimate rapidity
correlations at later times by assuming that the evolution of the system is
governed by ideal Bjorken hydrodynamics, and find that glueball correlations in
this state are suppressed at large rapidity intervals, suggesting that
late-time medium dynamics can not "wash out" the long-range rapidity
correlations that were formed at early times. These results may provide an
insight on the nature of the "ridge" correlations observed in heavy ion
collision experiments at RHIC and LHC, and in proton-proton collisions at LHC.Comment: 32 pages, 2 figures; v2: typos corrected, references adde
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