24,076 research outputs found
A study of Schwinger-Dyson Equations for Yukawa and Wess-Zumino Models
We study Schwinger-Dyson equation for fermions in Yukawa and Wess-Zumino
models, in terms of dynamical mass generation and the wavefunction
renormalization function. In the Yukawa model with -type interaction
between scalars and fermions, we find a critical coupling in the quenched
approximation above which fermions acquire dynamical mass. This is shown to be
true beyond the bare 3-point vertex approximation. In the Wess-Zumino model,
there is a neat cancellation of terms leading to no dynamical mass for
fermions. We comment on the conditions under which these results are general
beyond the rainbow approximation and also on the ones under which supersymmetry
is preserved and the scalars as well do not acquire mass. The results are in
accordance with the non-renormalization theorem at least to order in
perturbation theory. In both the models, we also evaluate the wavefunction
renormalization function, analytically in the neighbourhood of the critical
coupling and numerically, away from it.Comment: 12 pages and 7 Postscript figures, accepted for publication in
Journal of Physics G: Nuclear and Particle Physic
Internal kinematic and physical properties in a BCD galaxy: Haro 15 in detail
We present a detailed study of the kinematic and physical properties of the
ionized gas in multiple knots of the blue compact dwarf galaxy Haro 15. Using
echelle and long slit spectroscopy data, obtained with different instruments at
Las Campanas Observatory, we study the internal kinematic and physical
conditions (electron density and temperature), ionic and total chemical
abundances of several atoms, reddening and ionization structure. Applying
direct and empirical methods for abundance determination, we perform a
comparative analysis between these regions and in their different components.
On the other hand, our echelle spectra show complex kinematics in several
conspicuous knots within the galaxy. To perform an in-depth 2D spectroscopic
study we complete this work with high spatial and spectral resolution
spectroscopy using the Integral Field Unit mode on the Gemini Multi-Object
Spectrograph instrument at the Gemini South telescope. With these data we are
able to resolve the complex kinematical structure within star forming knots in
Haro 15 galaxy.Comment: 6 pages, 2 figures, IX Scientific Meeting of the Spanish Astronomical
Society held on September 13-17, 2010, in Madrid, Spai
The Nature of Deeply Buried Ultraluminous Infrared Galaxies: A Unified Model for Highly Obscured Dusty Galaxy Emission
We present models of deeply buried ultraluminous infrared galaxy (ULIRG)
spectral energy distributions (SEDs) and use them to construct a
three-dimensional diagram for diagnosing the nature of observed ULIRGs. Our
goal is to construct a suite of SEDs for a very simple model ULIRG structure,
and to explore how well this simple model can (by itself) explain the full
range of observed ULIRG properties. We use our diagnostic to analyze archival
Spitzer Space Telescope IRS spectra of ULIRGs and find that: (1) In general,
our model does provide a comprehensive explanation of the distribution of
mid-IR ULIRG properties; (2) >75% (in some cases 100%) of the bolometric
luminosities of the most deeply buried ULIRGs must be powered by a
dust-enshrouded active galactic nucleus; (3) an unobscured "keyhole" view
through <~10% of the obscuring medium surrounding a deeply buried ULIRG is
sufficient to make it appear nearly unobscured in the mid-IR; and (4) the
observed absence of deeply buried ULIRGs with large PAH equivalent widths is
naturally explained by our models showing that deep absorption features are
"filled-in" by small quantities of foreground unobscured PAH emission (e.g.,
from the host galaxy disk) at the level of ~1% the bolometric nuclear
luminosity. The modeling and analysis we present will also serve as a powerful
tool for interpreting the high angular resolution spectra of high-redshift
sources to be obtained with the James Webb Space Telescope.Comment: 20 pages, 14 figures. Accepted for publication in the Ap
Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub
Accepted versio
Multi-photon signal in supersymmetry comprising non-pointing photon(s) at the LHC
We study a distinct supersymmetric signal of multi-photons in association
with jets and missing transverse energy. At least one of these photons has the
origin in displaced vertex, thus delayed and non-pointing. We consider a
supersymmetric scenario in which the gravitino is the lightest supersymmetric
particle (LSP) (with a mass ) and the lightest neutralino is the
next-to-lightest supersymmetric particle (NLSP). The NLSP decays dominantly
into a photon and a gravitino within the detector with a decay length ranging
from 50-100 cm. In addition, we assume that the
second lightest neutralino and the lightest neutralino are nearly degenerate
and this leads to a prompt radiative decay of the next-to-lightest neutralino
into a photon and a lightest neutralino with a large branching ratio. Such
degenerate neutralinos can be realised in various representations of the
, , and Grand Unified Theories (GUTs). The non-pointing
photons can be reconstructed at the electromagnetic calorimeter of the ATLAS
inner-detector, which have been designed with good timing and directional
resolution. We find that with a centre-of-mass energy at an
integrated luminosity of 100 one may see evidence of hundreds of
tri-photon events and a few four-photons events at the LHC, in addition to
several thousands di-photon events. We also predict the event rates even at the
early phase of LHC run.Comment: 10 pages; 6 figure
Magnetic properties of Co doped Nb clusters
From magnetic deflection experiments on isolated Co doped Nb clusters we made
the interesting observation of some clusters being magnetic, while others
appear to be non-magnetic. There are in principle two explanations for this
behavior. Either the local moment at the Co site is completely quenched or it
is screened by the delocalized electrons of the cluster, i.e. the Kondo effect.
In order to reveal the physical origin, we conducted a combined theoretical and
experimental investigation. First, we established the ground state geometry of
the clusters by comparing the experimental vibrational spectra with those
obtained from a density functional theory study. Then, we performed an analyses
based on the Anderson impurity model. It appears that the non-magnetic clusters
are due to a complete quenching of the local Co moment and not due to the Kondo
effect. In addition, the magnetic behavior of the clusters can be understood
from an inspection of their electronic structure. Here magnetism is favored
when the effective hybridization around the chemical potential is small, while
the absence of magnetism is signalled by a large effective hybridization around
the chemical potential.Comment: 14 pages, 8 figure
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