897 research outputs found
Deficits in Beam-Walking After Neonatal Motor Cortical Lesions are not Spared by Fetal Cortical Transplants in Rats
Adult rats that sustained unilateral motor cortical lesions at birth demonstrated deficits in traversing an elevated narrow beam. These deficits, manifested by hindlimb slips off the edge of the beam, were not spared in animals that received fetal cortical transplants into the lesion cavity immediately after lesion placement
Conformal Symmetry and the Three Point Function for the Gravitational Axial Anomaly
This work presents a first study of a radiative calculation for the
gravitational axial anomaly in the massless Abelian Higgs model. The two loop
contribution to the anomalous correlation function of one axial current and two
energy-momentum tensors, , is computed
at an order that involves only internal matter fields. Conformal properties of
massless field theories are used in order to perform the Feynman diagram
calculations in the coordinate space representation. The two loop contribution
is found not to vanish, due to the presence of two independent tensor
structures in the anomalous correlator.Comment: 34 pages, 5 figures, RevTex, Minor changes, Final version for Phys.
Rev.
Exploring Holographic General Gauge Mediation
We study models of gauge mediation with strongly coupled hidden sectors,
employing a hard wall background as an holographic dual description. The
structure of the soft spectrum depends crucially on the boundary conditions one
imposes on bulk fields at the IR wall. Generically, vector and fermion
correlators have poles at zero momentum, leading to gauge mediation by massive
vector messengers and/or generating Dirac gaugino masses. Instead, non-generic
choices of boundary conditions let one cover all of GGM parameter space.
Enriching the background with R-symmetry breaking scalars, the SSM soft term
structure becomes more constrained and similar to previously studied top-down
models, while retaining the more analytic control the present bottom-up
approach offers.Comment: 28 pages, 4 figures; v2: typos corrected and refs adde
In-medium hadronic spectral functions through the soft-wall holographic model of QCD
We study the scalar glueball and vector meson spectral functions in a hot and
dense medium by means of the soft-wall holographic model of QCD. Finite
temperature and density effects are implemented through the AdS/RN metric. We
analyse the behaviour of the hadron masses and widths in the plane,
and compare our results with the experimental ones and with other theoretical
determinations.Comment: 16 pages, 6 figures. matching the published versio
Sensitivity and Insensitivity of Galaxy Cluster Surveys to New Physics
We study the implications and limitations of galaxy cluster surveys for
constraining models of particle physics and gravity beyond the Standard Model.
Flux limited cluster counts probe the history of large scale structure
formation in the universe, and as such provide useful constraints on
cosmological parameters. As a result of uncertainties in some aspects of
cluster dynamics, cluster surveys are currently more useful for analyzing
physics that would affect the formation of structure than physics that would
modify the appearance of clusters. As an example we consider the Lambda-CDM
cosmology and dimming mechanisms, such as photon-axion mixing.Comment: 24 pages, 8 eps figures. References added, discussion of scatter in
relations between cluster observables lengthene
Holographic two dimensional QCD and Chern-Simons term
We present a holographic realization of large Nc massless QCD in two
dimensions using a D2/D8 brane construction. The flavor axial anomaly is dual
to a three dimensional Chern-Simons term which turns out to be of leading
order, and it affects the meson spectrum and holographic renormalization in
crucial ways. The massless flavor bosons that exist in the spectrum are found
to decouple from the heavier mesons, in agreement with the general lore of
non-Abelian bosonization. We also show that an external dynamical photon
acquires a mass through the three dimensional Chern-Simons term as expected
from the Schwinger mechanism. Massless two dimensional QCD at large Nc exhibits
anti-vector-meson dominance due to the axial anomaly.Comment: 22 page
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
AdS/QCD: The Relevance of the Geometry
We investigate the relevance of the metric and of the geometry in
five-dimensional models of hadrons. Generically, the metric does not affect
strongly the results and even flat space agrees reasonably well with the data.
Nevertheless, we observe a preference for a decreasing warp factor, for example
AdS space. The Sakai-Sugimoto model reduces to one of these models and the
level of agreement is similar to the one of flat space. We also consider the
discrete version of the five-dimensional models, obtained by dimensional
deconstruction. We find that essentially all the relevant features of
"holographic" models of QCD can be reproduced with a simple 3-site model
describing only the states below the cut-off of the theory.Comment: 25 pages + appendix. v2 minor changes and Refs. adde
4D Constructions of Supersymmetric Extra Dimensions and Gaugino Mediation
We present 4D gauge theories which at low energies coincide with higher
dimensional supersymmetric (SUSY) gauge theories on a transverse lattice. We
show that in the simplest case of pure 5D SUSY Yang-Mills there is an
enhancement of SUSY in the continuum limit without fine-tuning. This result no
longer holds in the presence of matter fields, in which case fine-tuning is
necessary to ensure higher dimensional Lorentz invariance and supersymmetry. We
use this construction to generate 4D models which mimic gaugino mediation of
SUSY breaking. The way supersymmetry breaking is mediated in these models to
the MSSM is by assuming that the physical gauginos are a mixture of a number of
gauge eigenstate gauginos: one of these couples to the SUSY breaking sector,
while another couples to the MSSM matter fields. The lattice can be as coarse
as just two gauge groups while still obtaining the characteristic
gaugino-mediated soft breaking terms.Comment: 32 pages LaTeX; missing factor in two-loop gauge-mediated scalar mass
estimate fixed, comments on unification revise
It is a Graviton! or maybe not
The discovery of Kaluza-Klein (KK) gravitons is a smoking gun of extra
dimensions. Other scenarios, however, could give rise to spin-two resonances of
a new strongly-coupled sector and act as impostors. In this paper we prove that
a spin-two resonance does not couple to the Standard Model through
dimension-four operators. We then show that the massive graviton and its
impostor both couple to the Standard Model through the same dimension-five
operators. Therefore the spin determination is identical. Nevertheless, we also
show that one can use the ratio of branching ratios to photons and to jets for
distinguishing between KK gravitons and their impostors. The capacity to
distinguish between KK gravitons and impostors is a manifestation of the
breakdown of the duality between AdS and strongly-coupled theories.Comment: 14 pages, 3 figures, 1 table. References added, typos correcte
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