2,666 research outputs found
An improved model of vector mesons in holographic QCD
We analyze the sector of dimension-three vector meson operators in the "hard
wall" model of holographic QCD, including the vector and axial currents, dual
to gauge fields in the bulk, and the tensor operator
, dual to a two-form field satisfying a complex
self-duality condition. The model includes the effect of chiral symmetry
breaking on vector mesons, that involves a coupling between the dual gauge
field and the two-form field. We compute the leading logarithmic terms in the
operator product expansion of two-point functions and the leading
non-perturbative contribution to the tensor-vector correlator. The result is
consistent with the operator product expansion of QCD. We also study the
spectrum of vector mesons numerically.Comment: 19 page
The star-formation histories of elliptical galaxies across the fundamental plane
We present the first results from a study designed to test whether, given
high-quality spectrophotometry spanning the mid-UV--optical wavelength regime,
it is possible to distinguish the metal content (Z) and star-formation history
(sfh) of individual elliptical galaxies with sufficient accuracy to establish
whether their formation history is linked to their detailed morphology and
position on the Fundamental Plane. From a detailed analysis of UV-optical
spectrophotometry of the `cuspy' elliptical galaxy NGC 3605 and the giant
elliptical NGC 5018 we find that: 1) optical spectra with l > 3500 A may not
contain sufficient data to robustly uncover all the stellar populations present
in individual galaxies, even in such relatively passive objects as ellipticals,
2) the addition of the UV data approaching l = 2500 A holds the key to
establishing well-constrained sfhs, from which we can infer a formation and
evolution history which is consistent with their photometric properties, 3)
despite the superficial similarity of their spectra, the two galaxies have very
different `recent' sfhs -- the smaller, cuspy elliptical NGC 3605 contains a
high-Z population of age ~= 1 Gyr, and has a position on the fundamental plane
typical of the product of a low-z gas-rich merger (most likely at z ~ 0.08),
while the giant elliptical NGC 5018, with a sub-solar secondary population,
appears to have gained its more recent stars via mass transfer / accretion of
gas from its spiral companion, 4) despite these differences in detailed
history, more than 85% of the stellar mass of both galaxies is associated with
an old (9-12 Gyr) stellar population of near-solar Z. This pilot study provides
strong motivation for the construction and analysis of high-quality UV-optical
spectra for a substantial sample of ellipticals spanning the Fundamental Plane.Comment: 11 pages, 10 figures, submitted to MNRAS, revised versio
Non-universal results induced by diversity distribution in coupled excitable systems
We consider a system of globally coupled active rotators near the excitable
regime. The system displays a transition to a state of collective firing
induced by disorder. We show that this transition is found generically for any
diversity distribution with well defined moments. Singularly, for the
Lorentzian distribution (widely used in Kuramoto-like systems) the transition
is not present. This warns about the use of Lorentzian distributions to
understand the generic properties of coupled oscillators
Alignment tests for low CMB multipoles
We investigate the large scale anomalies in the angular distribution of the
cosmic microwave background radiation as measured by WMAP using several tests.
These tests, based on the multipole vector expansion, measure correlations
between the phases of the multipoles as expressed by the directions of the
multipole vectors and their associated normal planes. We have computed the
probability distribution functions for 46 such tests, for the multipoles l=2-5.
We confirm earlier findings that point to a high level of alignment between l=2
(quadrupole) and l=3 (octopole), but with our tests we do not find significant
planarity in the octopole. In addition, we have found other possible anomalies
in the alignment between the octopole and the l=4 (hexadecupole) components, as
well as in the planarity of l=4 and l=5. We introduce the notion of a total
likelihood to estimate the relevance of the low-multipoles tests of
non-gaussianity. We show that, as a result of these tests, the CMB maps which
are most widely used for cosmological analysis lie within the ~ 10% of randomly
generated maps with lowest likelihoods.Comment: References added, updated discussion on alignment with Ecliptic
Plane. 12 Pages, 6 Figures. Results for additional maps, the normalized
frequencies for the tests and a Mathematica Notebook that computes the tests
can be found on http://fma.if.usp.br/~abramo/MVA.htm
Results from EDGES High-Band: II. Constraints on Parameters of Early Galaxies
We use the sky-average spectrum measured by EDGES High-Band ( MHz) to
constrain parameters of early galaxies independent of the absorption feature at
~MHz reported by Bowman et al. (2018). These parameters represent
traditional models of cosmic dawn and the epoch of reionization produced with
the 21cmFAST simulation code (Mesinger & Furlanetto 2007, Mesinger et al.
2011). The parameters considered are: (1) the UV ionizing efficiency (),
(2) minimum halo virial temperature hosting efficient star-forming galaxies
(), (3) integrated soft-band X-ray luminosity (), and (4) minimum X-ray energy escaping the first
galaxies (), corresponding to a typical H column
density for attenuation through the interstellar medium. The High-Band spectrum
disfavors high values of and , which correspond
to signals with late absorption troughs and sharp reionization transitions. It
also disfavors intermediate values of , which
produce relatively deep and narrow troughs within the band. Specifically, we
rule out
( C.L.). We then combine the EDGES High-Band data with constraints on the
electron scattering optical depth from Planck and the hydrogen neutral fraction
from high- quasars. This produces a lower degeneracy between and
than that reported in Greig & Mesinger (2017a) using
the Planck and quasar constraints alone. Our main result in this combined
analysis is the estimate ~~ ( C.L.). We leave for future work the evaluation of
~cm models using simultaneously data from EDGES Low- and High-Band.Comment: Accepted in Ap
The Cosmic Neutrino Background and the Age of the Universe
We discuss the cosmological degeneracy between the age of the Universe, the
Hubble parameter and the effective number of relativistic particles N_eff. We
show that independent determinations of the Hubble parameter H(z) as those
recently provided by Simon,Verde, Jimenez (2006), combined with other
cosmological data sets can provide the most stringent constraint on N_eff,
yielding N_eff=3.7 (-1.2) (+1.1) at 95% confidence level. A neutrino background
is detected with high significance: N_eff >1.8 at better than 99% confidence
level. Constraints on the age of the universe in the framework of an extra
background of relativistic particles are improved by a factor 3.Comment: JCAP, in pres
Buckling strength of adhesively-bonded single and double-strap repairs on carbon-epoxy structures
This work reports on an experimental and finite element method (FEM) parametric study of adhesively-bonded single and double-strap repairs on carbon-epoxy structures under buckling unrestrained compression. The influence of the overlap length and patch thickness was evaluated. This loading gains a particular significance from the additional characteristic mechanisms of structures under compression, such as fibres microbuckling, for buckling restrained structures, or global buckling of the assembly, if no transverse restriction exists. The FEM analysis is based on the use of cohesive elements including mixed-mode criteria to simulate a cohesive fracture of the adhesive layer. Trapezoidal laws in pure modes I and II were used to account for the ductility of most structural adhesives. These laws were estimated for the adhesive used from double cantilever beam (DCB) and end-notched flexure (ENF) tests, respectively, using an inverse technique. The pure mode III cohesive law was equalled to the pure mode II one. Compression failure in the laminates was predicted using a stress-based criterion. The accurate FEM predictions open a good prospect for the reduction of the extensive experimentation in the design of carbon-epoxy repairs. Design principles were also established for these repairs under buckling
Monte Carlo Simulation Calculation of Critical Coupling Constant for Continuum \phi^4_2
We perform a Monte Carlo simulation calculation of the critical coupling
constant for the continuum {\lambda \over 4} \phi^4_2 theory. The critical
coupling constant we obtain is [{\lambda \over \mu^2}]_crit=10.24(3).Comment: 11 pages, 4 figures, LaTe
Intergroup Contact and White Racial Apathy: Findings from the National Study of Youth and Religion (NSYR)
Scholars theorize racial apathy is one form contemporary white racial prejudice takes. Racial apathy signals not caring about racial inequality. Invoking intergroup contact theory, we hypothesize interracial contact would predict less racial apathy among whites. To test our hypothesis, we analyze survey data from white teenagers participating in the 2003 National Study of Youth and Religion (NSYR). We find interracial contact matters and its inclusion improves model fit over and above previously specified correlates. Specifically, interracial friendship and dating, and having a different race mentor predict the tendency to care about racial equality. Furthermore, any interracial contact and a count of interracial contact experiences across five settings, respectively, predict less racial apathy. We encourage scholars to investigate further the sociological significance of racial apathy and its correlates, including interracial contact
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