8,518 research outputs found
Vacuum Properties of Mesons in a Linear Sigma Model with Vector Mesons and Global Chiral Invariance
We present a two-flavour linear sigma model with global chiral symmetry and
vector and axial-vector mesons. We calculate pion-pion scattering lengths and
the decay widths of scalar, vector, and axial-vector mesons. It is demonstrated
that vector and axial-vector meson degrees of freedom play an important role in
these low-energy processes and that a reasonable theoretical description
requires globally chirally invariant terms other than the vector meson mass
term. An important question for meson vacuum phenomenology is the quark content
of the physical scalar f0(600) and a0(980) mesons. We investigate this question
by assigning the quark-antiquark sigma and a0 states of our model with these
physical mesons. We show via a detailed comparison with experimental data that
this scenario can describe all vacuum properties studied here except for the
decay width of the sigma, which turns out to be too small. We also study the
alternative assignment f0(1370) and a0(1450) for the scalar mesons. In this
case the decay width agrees with the experimental value, but the pion-pion
scattering length is too small. This indicates the necessity to
extend our model by additional scalar degrees of freedom.Comment: 22 pages, 6 figure
Beyond convergence rates: Exact recovery with Tikhonov regularization with sparsity constraints
The Tikhonov regularization of linear ill-posed problems with an
penalty is considered. We recall results for linear convergence rates and
results on exact recovery of the support. Moreover, we derive conditions for
exact support recovery which are especially applicable in the case of ill-posed
problems, where other conditions, e.g. based on the so-called coherence or the
restricted isometry property are usually not applicable. The obtained results
also show that the regularized solutions do not only converge in the
-norm but also in the vector space (when considered as the
strict inductive limit of the spaces as tends to infinity).
Additionally, the relations between different conditions for exact support
recovery and linear convergence rates are investigated.
With an imaging example from digital holography the applicability of the
obtained results is illustrated, i.e. that one may check a priori if the
experimental setup guarantees exact recovery with Tikhonov regularization with
sparsity constraints
Adapting SAM for CDF
The CDF and D0 experiments probe the high-energy frontier and as they do so
have accumulated hundreds of Terabytes of data on the way to petabytes of data
over the next two years. The experiments have made a commitment to use the
developing Grid based on the SAM system to handle these data. The D0 SAM has
been extended for use in CDF as common patterns of design emerged to meet the
similar requirements of these experiments. The process by which the merger was
achieved is explained with particular emphasis on lessons learned concerning
the database design patterns plus realization of the use cases.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 4 pages, pdf format, TUAT00
Asymptotic behaviour of the spectrum of a waveguide with distant perturbations
We consider the waveguide modelled by a -dimensional infinite tube. The
operator we study is the Dirichlet Laplacian perturbed by two distant
perturbations. The perturbations are described by arbitrary abstract operators
''localized'' in a certain sense, and the distance between their ''supports''
tends to infinity. We study the asymptotic behaviour of the discrete spectrum
of such system. The main results are a convergence theorem and the asymptotics
expansions for the eigenvalues. The asymptotic behaviour of the associated
eigenfunctions is described as well. We also provide some particular examples
of the distant perturbations. The examples are the potential, second order
differential operator, magnetic Schroedinger operator, curved and deformed
waveguide, delta interaction, and integral operator
Bloch-Nordsieck violating electroweak corrections to inclusive TeV scale hard processes
We point out that, since the colliders initial states (e+ e-,p p, p pbar, ...
) carry a definite nonabelian flavor, electroweak radiative corrections to
inclusive hard cross sections at the TeV scale are affected by peculiar
Bloch-Nordsieck violating double logs. We recall the setup of soft cancellation
theorems, and we analyze the magnitude of the noncancelling terms in the
example of electron - positron annihilation into hadrons.Comment: Minor typos corrected, references added. Final version to appear on
Phys. Rev. Let
Electron Quasiparticles Drive the Superconductor-to-Insulator Transition in Homogeneously Disordered Thin Films
Transport data on Bi, MoGe, and PbBi/Ge homogeneously-disordered thin films
demonstrate that the critical resistivity, , at the nominal
insulator-superconductor transition is linearly proportional to the normal
sheet resistance, . In addition, the critical magnetic field scales
linearly with the superconducting energy gap and is well-approximated by
. Because is determined at high temperatures and is the
pair-breaking field, the two immediate consequences are: 1)
electron-quasiparticles populate the insulating side of the transition and 2)
standard phase-only models are incapable of describing the destruction of the
superconducting state. As gapless electronic excitations populate the
insulating state, the universality class is no longer the 3D XY model. The lack
of a unique critical resistance in homogeneously disordered films can be
understood in this context. In light of the recent experiments which observe an
intervening metallic state separating the insulator from the superconductor in
homogeneously disordered MoGe thin films, we argue that the two transitions
that accompany the destruction of superconductivity are 1) superconductor to
Bose metal in which phase coherence is lost and 2) Bose metal to localized
electron insulator via pair-breaking.Comment: This article is included in the Festschrift for Prof. Michael Pollak
on occasion of his 75th birthda
Radioelectric Field Features of Extensive Air Showers Observed with CODALEMA
Based on a new approach to the detection of radio transients associated with
extensive air showers induced by ultra high energy cosmic rays, the
experimental apparatus CODALEMA is in operation, measuring about 1 event per
day corresponding to an energy threshold ~ 5. 10^16 eV. Its performance makes
possible for the first time the study of radio-signal features on an
event-by-event basis. The sampling of the magnitude of the electric field along
a 600 meters axis is analyzed. It shows that the electric field lateral spread
is around 250 m (FWHM). The possibility to determine with radio both arrival
directions and shower core positions is discussed.Comment: Accepted for publication in Astroparticle Physic
The vulnerability of public spaces: challenges for UK hospitals under the 'new' terrorist threat
This article considers the challenges for hospitals in the United Kingdom that arise from the threats of mass-casualty terrorism. Whilst much has been written about the role of health care as a rescuer in terrorist attacks and other mass-casualty crises, little has been written about health care as a victim within a mass-emergency setting. Yet, health care is a key component of any nation's contingency planning and an erosion of its capabilities would have a significant impact on the generation of a wider crisis following a mass-casualty event. This article seeks to highlight the nature of the challenges facing elements of UK health care, with a focus on hospitals both as essential contingency responders under the United Kingdom's civil contingencies legislation and as potential victims of terrorism. It seeks to explore the potential gaps that exist between the task demands facing hospitals and the vulnerabilities that exist within them
Mechanical properties of Graphene Nanoribbons
Herein, we investigate the structural, electronic and mechanical properties
of zigzag graphene nanoribbons upon the presence of stress applying Density
Functional Theory within the GGA-PBE approximation. The uniaxial stress is
applied along the periodic direction, allowing a unitary deformation in the
range of +/- 0.02%. The mechanical properties show a linear-response within
that range while the non-linear dependence is found for higher strain. The most
relevant results indicate that Young's modulus is considerable higher than
those determined for graphene and carbon nanotubes. The geometrical
reconstruction of the C-C bonds at the edges hardness the nanostructure.
Electronic structure features are not sensitive to strain in this linear
elastic regime, being an additional promise for the using of carbon
nanostructures in nano-electronic devices in the near future.Comment: 30 pages. J. Phys.: Condens. Matter (accepted
New Pulsating DB White Dwarf Stars from the Sloan Digital Sky Survey
We are searching for new He atmosphere white dwarf pulsators (DBVs) based on
the newly found white dwarf stars from the spectra obtained by the Sloan
Digital Sky Survey. DBVs pulsate at hotter temperature ranges than their better
known cousins, the H atmosphere white dwarf pulsators (DAVs or ZZ Ceti stars).
Since the evolution of white dwarf stars is characterized by cooling,
asteroseismological studies of DBVs give us opportunities to study white dwarf
structure at a different evolutionary stage than the DAVs. The hottest DBVs are
thought to have neutrino luminosities exceeding their photon luminosities
(Winget et al. 2004), a quantity measurable through asteroseismology.
Therefore, they can also be used to study neutrino physics in the stellar
interior. So far we have discovered nine new DBVs, doubling the number of
previously known DBVs. Here we report the new pulsators' lightcurves and power
spectra.Comment: 15 pages, 2 figures, 3 tables, ApJ accepte
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