6,265 research outputs found
On Locality, Holography and Unfolding
We study the functional class and locality problems in the context of
higher-spin theories and Vasiliev's equations. A locality criterion that is
sufficient to make higher-spin theories well-defined as field theories on
Anti-de-Sitter space is proposed. This criterion identifies admissible
pseudo-local field redefinitions which preserve AdS/CFT correlation functions
as we check in the 3d example. Implications of this analysis for known
higher-spin theories are discussed. We also check that the cubic coupling
coefficients previously fixed in 3d at the action level give the correct CFT
correlation functions upon computing the corresponding Witten diagrams.Comment: 36 pages, LaTex. References added, typos corrected. Final version to
appear in JHE
Higher Spin Interactions in Four Dimensions: Vasiliev vs. Fronsdal
We consider four-dimensional Higher-Spin Theory at the first nontrivial order
corresponding to the cubic action. All Higher-Spin interaction vertices are
explicitly obtained from Vasiliev's equations. In particular, we obtain the
vertices that are not determined solely by the Higher-Spin algebra structure
constants. The dictionary between the Fronsdal fields and Higher-Spin
connections is found and the corrections to the Fronsdal equations are derived.
These corrections turn out to involve derivatives of arbitrary order. We
observe that the vertices not determined by the Higher-Spin algebra produce
naked infinities, when decomposed into the minimal derivative vertices and
improvements. Therefore, standard methods can only be used to check a rather
limited number of correlation functions within the HS AdS/CFT duality. A
possible resolution of the puzzle is discussed.Comment: 56 pages=40+Appendices; 1 figure; typos fixed, one ref adde
On the uniqueness of higher-spin symmetries in AdS and CFT
We study the uniqueness of higher-spin algebras which are at the core of
higher-spin theories in AdS and of CFTs with exact higher-spin symmetry, i.e.
conserved tensors of rank greater than two. The Jacobi identity for the gauge
algebra is the simplest consistency test that appears at the quartic order for
a gauge theory. Similarly, the algebra of charges in a CFT must also obey the
Jacobi identity. These algebras are essentially the same. Solving the Jacobi
identity under some simplifying assumptions spelled out, we obtain that the
Eastwood-Vasiliev algebra is the unique solution for d=4 and d>6. In 5d there
is a one-parameter family of algebras that was known before. In particular, we
show that the introduction of a single higher-spin gauge field/current
automatically requires the infinite tower of higher-spin gauge fields/currents.
The result implies that from all the admissible non-Abelian cubic vertices in
AdS(d), that have been recently classified for totally symmetric higher-spin
gauge fields, only one vertex can pass the Jacobi consistency test. This cubic
vertex is associated with a gauge deformation that is the germ of the
Eastwood-Vasiliev's higher-spin algebra.Comment: 37 pages; refs added, proof of uniquiness was improve
Higher Spins and Matter Interacting in Dimension Three
The spectrum of Prokushkin--Vasiliev Theory is puzzling in light of the
Gaberdiel--Gopakumar conjecture because it generically contains an additional
sector besides higher-spin gauge and scalar fields. We find the unique
truncation of the theory avoiding this problem to order 2 in perturbations
around AdS. The second-order backreaction on the physical gauge sector
induced by the scalars is computed explicitly. The cubic action for the
physical fields is determined completely. We comment on a different higher-spin
theory without such additional fields at .Comment: 55 pages + appendices, LaTex. Final version to appear in JHE
The Fate of the First Galaxies. I. Self-Consistent Cosmological Simulations with Radiative Transfer
In cold dark matter (CDM) cosmogonies, low-mass objects play an important
role in the evolution of the universe. Not only are they the first luminous
objects to shed light in a previously dark universe, but, if their formation is
not inhibited by their own feedback, they dominate the galaxy mass function
until redshift z \sim 5. In this paper we present and discuss the
implementation of a 3D cosmological code that includes most of the needed
physics to simulate the formation and evolution of the first galaxies with a
self-consistent treatment of radiative feedback. The simulation includes
continuum radiative transfer using the ``Optically Thin Variable Eddington
Tensor'' (OTVET) approximation and line-radiative transfer in the H_2
Lyman-Werner bands of the background radiation. We include detailed chemistry
for H_2 formation/destruction, molecular and atomic cooling/heating processes,
ionization by secondary electrons, and heating by Ly\alpha resonant scattering.
We find that the first galaxies ("small-halos") are characterized by a
bursting star formation, self-regulated by a feedback process that acts on
cosmological scales. Their formation is not suppressed by feedback processes;
therefore, their impact on cosmic evolution cannot be neglected. The main focus
of this paper is on the methodology of the simulations, and we only briefly
introduce some of the results. An extensive discussion of the results and the
nature of the feedback mechanism are the focus of a companion paper.Comment: Accepted for publication on ApJ, 33 pages, including 14 figures and 2
tables. Movies and a higher quality version of the paper (figures) are
available at: http://casa.colorado.edu/~ricotti/MOVIES.htm
Permutation sampling in Path Integral Monte Carlo
A simple algorithm is described to sample permutations of identical particles
in Path Integral Monte Carlo (PIMC) simulations of continuum many-body systems.
The sampling strategy illustrated here is fairly general, and can be easily
incorporated in any PIMC implementation based on the staging algorithm.
Although it is similar in spirit to an existing prescription, it differs from
it in some key aspects. It allows one to sample permutations efficiently, even
if long paths (e.g., hundreds, or thousands of slices) are needed. We
illustrate its effectiveness by presenting results of a PIMC calculation of
thermodynamic properties of superfluid Helium-four, in which a very simple
approximation for the high-temperature density matrix was utilized
Gradient expansion, curvature perturbations and magnetized plasmas
The properties of magnetized plasmas are always investigated under the
hypothesis that the relativistic inhomogeneities stemming from the fluid
sources and from the geometry itself are sufficiently small to allow for a
perturbative description prior to photon decoupling. The latter assumption is
hereby relaxed and pre-decoupling plasmas are described within a suitable
expansion where the inhomogeneities are treated to a given order in the spatial
gradients. It is argued that the (general relativistic) gradient expansion
shares the same features of the drift approximation, customarily employed in
the description of cold plasmas, so that the two schemes are physically
complementary in the large-scale limit and for the low-frequency branch of the
spectrum of plasma modes. The two-fluid description, as well as the
magnetohydrodynamical reduction, are derived and studied in the presence of the
spatial gradients of the geometry. Various solutions of the coupled system of
evolution equations in the anti-Newtonian regime and in the quasi-isotropic
approximation are presented. The relation of this analysis to the so-called
separate Universe paradigm is outlined. The evolution of the magnetized
curvature perturbations in the nonlinear regime is addressed for the magnetized
adiabatic mode in the plasma frame.Comment: 40 pages, no figure
Intense terahertz pulses from SPARC-LAB coherent radiation source
The linac-based Terahertz source at the SPARC_LAB test facility is able to gene
rate highly intense Terahertz broadband
pulses
via
coherent transition radiation (CTR) from high brightness electron beams. The THz pulse duration is typically
down to 100 fs RMS and can be tuned through the electron bunch duration and shaping. The measured stored energy in a
single THz pulse has reached 40
ÎĽ
J, which corresponds to a peak
electric field of 1.6 MV/cm at the THz focus. Here we
present the main features, in particular spatial and sp
ectral distributions and energy
characterizations of the
SPARC_LAB THz source, which is very competitive for investigations in Condensed Matter, as well as a valid tool for
electron beam longitudinal diagnostics
Genetic Features of Metachronous Esophageal Cancer Developed in Hodgkin's Lymphoma or Breast Cancer Long-Term Survivors: An Exploratory Study.
Background
Development of novel therapeutic drugs and regimens for cancer treatment has led to improvements in patient long-term survival. This success has, however, been accompanied by the increased occurrence of second primary cancers. Indeed, patients who received regional radiotherapy for Hodgkin's Lymphoma (HL) or breast cancer may develop, many years later, a solid metachronous tumor in the irradiated field. Despite extensive epidemiological studies, little information is available on the genetic changes involved in the pathogenesis of these solid therapy-related neoplasms.
Methods
Using microsatellite markers located in 7 chromosomal regions frequently deleted in sporadic esophageal cancer, we investigated loss of heterozygosity (LOH) and microsatellite instability (MSI) in 46 paired (normal and tumor) samples. Twenty samples were of esophageal carcinoma developed in HL or breast cancer long-term survivors: 14 squamous cell carcinomas (ESCC) and 6 adenocarcinomas (EADC), while 26 samples, used as control, were of sporadic esophageal cancer (15 ESCC and 11 EADC).
Results
We found that, though the overall LOH frequency at the studied chromosomal regions was similar among metachronous and sporadic tumors, the latter exhibited a statistically different higher LOH frequency at 17q21.31 (p = 0.018). By stratifying for tumor histotype we observed that LOH at 3p24.1, 5q11.2 and 9p21.3 were more frequent in ESCC than in EADC suggesting a different role of the genetic determinants located nearby these regions in the development of the two esophageal cancer histotypes.
Conclusions
Altogether, our results strengthen the genetic diversity among ESCC and EADC whether they occurred spontaneously or after therapeutic treatments. The presence of histotype-specific alterations in esophageal carcinoma arisen in HL or breast cancer long-term survivors suggests that their transformation process, though the putative different etiological origin, may retrace sporadic ESCC and EADC carcinogenesis
Theoretical Limb Darkening for Classical Cepheids: II. Corrections for the Geometric Baade-Wesselink Method
The geometric Baade-Wesselink method is one of the most promising techniques
for obtaining a better calibration of the Cepheid period-luminosity relation by
means of interferometric measurements of accurate diameters. In this paper we
present new wavelength- and phase-dependent limb darkening corrections based on
our time-dependent hydrodynamic models of the classical Cepheid zeta Gem. We
show that a model simulation of a Cepheid atmosphere, taking into account the
hydrodynamic effects associated with the pulsation, shows strong departures
from the limb darkening otherwise predicted by a static model. For most of its
pulsational cycle the hydrodynamic model predicts a larger limb darkening then
the equivalent static model. The hydrodynamics affects the limb darkening
mainly at UV and optical wavelengths. Most of these effects evolve slowly as
the star pulsates, but there are phases, associated with shocks propagating
into the photosphere, in which significant changes in the limb darkening take
place on time-scales of the order of less than a day. We assess the implication
of our model LD corrections fitting the geometric Baade-Wesselink distance of
zeta Gem for the available near-IR PTI data. We discuss the effects of our
model limb darkening on the best fit result, and analyze the requirements
needed to test the time-dependence of the limb darkening with future
interferometric measurements.Comment: 22 pages, 5 figures, to be published on the Astrophysical Journal,
June 1 2003 issu
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