654 research outputs found
Towards a direct transition energy measurement of the lowest nuclear excitation in 229Th
The isomeric first excited state of the isotope 229Th exhibits the lowest
nuclear excitation energy in the whole landscape of known atomic nuclei. For a
long time this energy was reported in the literature as 3.5(5) eV, however, a
new experiment corrected this energy to 7.6(5) eV, corresponding to a UV
transition wavelength of 163(11) nm. The expected isomeric lifetime is
3-5 hours, leading to an extremely sharp relative linewidth of Delta E/E ~
10^-20, 5-6 orders of magnitude smaller than typical atomic relative
linewidths. For an adequately chosen electronic state the frequency of the
nuclear ground-state transition will be independent from influences of external
fields in the framework of the linear Zeeman and quadratic Stark effect,
rendering 229mTh a candidate for a reference of an optical clock with very high
accuracy. Moreover, in the literature speculations about a potentially enhanced
sensitivity of the ground-state transition of Th for eventual
time-dependent variations of fundamental constants (e.g. fine structure
constant alpha) can be found. We report on our experimental activities that aim
at a direct identification of the UV fluorescence of the ground-state
transition energy of 229mTh. A further goal is to improve the accuracy of the
ground-state transition energy as a prerequisite for a laser-based optical
control of this nuclear excited state, allowing to build a bridge between
atomic and nuclear physics and open new perspectives for metrological as well
as fundamental studies
BlogForever D3.2: Interoperability Prospects
This report evaluates the interoperability prospects of the BlogForever platform. Therefore, existing interoperability models are reviewed, a Delphi study to identify crucial aspects for the interoperability of web archives and digital libraries is conducted, technical interoperability standards and protocols are reviewed regarding their relevance for BlogForever, a simple approach to consider interoperability in specific usage scenarios is proposed, and a tangible approach to develop a succession plan that would allow a reliable transfer of content from the current digital archive to other digital repositories is presented
The finiteness of the four dimensional antisymmetric tensor field model in a curved background
A renormalizable rigid supersymmetry for the four dimensional antisymmetric
tensor field model in a curved space-time background is constructed. A closed
algebra between the BRS and the supersymmetry operators is only realizable if
the vector parameter of the supersymmetry is a covariantly constant vector
field. This also guarantees that the corresponding transformations lead to a
genuine symmetry of the model. The proof of the ultraviolet finiteness to all
orders of perturbation theory is performed in a pure algebraic manner by using
the rigid supersymmetry.Comment: 23 page
Vacuum polarisation induced coupling between Maxwell and Kalb-Ramond Fields
We present here a manifestly gauge invariant calculation of vacuum
polarization to fermions in the presence of a constant Maxwell and a constant
Kalb-Ramond field in four dimensions. The formalism is a generalisation of the
one used by Schwinger in his famous paper on gauge invariance and vacuum
polarization. We get an explicit expression for the vacuum polarization induced
effective Lagrangian for a constant Maxwell field interacting with a constant
Kalb-Ramond field. In the weak field limit we get the coupling between the
Maxwell field and the Kalb-Ramond field to be , where
and is
the dual of .Comment: 16 pages, Revte
Geometric Laws of Vortex Quantum Tunneling
In the semiclassical domain the exponent of vortex quantum tunneling is
dominated by a volume which is associated with the path the vortex line traces
out during its escape from the metastable well. We explicitly show the
influence of geometrical quantities on this volume by describing point vortex
motion in the presence of an ellipse. It is argued that for the semiclassical
description to hold the introduction of an additional geometric constraint, the
distance of closest approach, is required. This constraint implies that the
semiclassical description of vortex nucleation by tunneling at a boundary is in
general not possible. Geometry dependence of the tunneling volume provides a
means to verify experimental observation of vortex quantum tunneling in the
superfluid Helium II.Comment: 4 pages, 2 figures, revised version to appear in Phys. Rev.
Caregiver perspectives on the continued impact of the COVID-19 pandemic on children with intellectual/developmental disabilities
The COVID-19 pandemic has significantly impacted caregivers, especially those raising a child with an intellectual/developmental disability (IDD). While research has shown substantial disruption to the family, school, and occupational lives of the IDD community, little is known about the long-term impacts of COVID-19. To address this question, 249 caregivers were surveyed via an online questionnaire, between April and August of 2022 (more than 2 years into the pandemic) about potential impacts of the COVID-19 pandemic on their child\u27s access to health- and school-based therapeutic services, caregiver mental health, and family life. The majority of caregivers reported disruptions in access to and quality of school-based therapeutic services for their child as well as a reduction in educational accommodations in the 2021-2022 academic year. Nearly half of caregivers reported feeling anxious and almost a quarter reported feeling depressed for the majority of their days. More than half of respondents reported decreased social support, and one-fifth reported employment disruptions and decreased access to food. These findings suggest that families of children with IDD are still experiencing ongoing negative impacts of the pandemic, emphasizing the critical need for continued support in the wake of the initial and more obvious disruptions caused by the COVID-19 outbreak
Topological Landau-Ginzburg Theory for Vortices in Superfluid He
We propose a new Landau-Ginzburg theory for arbitrarily shaped vortex strings
in superfluid He. The theory contains a topological term and directly
describes vortex dynamics. We introduce gauge fields in order to remove
singularities from the Landau-Ginzburg order parameter of the superfluid, so
that two kinds of gauge symmetries appear, making the continuity equation and
conservation of the total vorticity manifest. The topological term gives rise
to the Berry phase term in the vortex mechanical actions.Comment: LATEX, 9 page
String Nature of Confinement in (Non-)Abelian Gauge Theories
Recent progress achieved in the solution of the problem of confinement in
various (non-)Abelian gauge theories by virtue of a derivation of their string
representation is reviewed. The theories under study include QCD within the
so-called Method of Field Correlators, QCD-inspired Abelian-projected theories,
and compact QED in three and four space-time dimensions. Various
nonperturbative properties of the vacua of the above mentioned theories are
discussed. The relevance of the Method of Field Correlators to the study of
confinement in Abelian models, allowing for an analytical description of this
phenomenon, is illustrated by an evaluation of field correlators in these
models.Comment: 100 pages, LaTeX2e, no figures, 1 table, based on the Ph.D. thesises
at the Humboldt University of Berlin (1999) (available under
http://dochost.rz.hu-berlin.de) and the Institute of Theoretical and
Experimental Physics, Moscow (2000), new results are included, extended with
respect to the journal versio
Neutral Particles in Light of the Majorana-Ahluwalia Ideas
The first part of this article (Sections I and II) presents oneself an
overview of theory and phenomenology of truly neutral particles based on the
papers of Majorana, Racah, Furry, McLennan and Case. The recent development of
the construct, undertaken by Ahluwalia [{\it Mod. Phys. Lett. A}{\bf 9} (1994)
439; {\it Acta Phys. Polon. B}{\bf 25} (1994) 1267; Preprints LANL
LA-UR-94-1252, LA-UR-94-3118], could be relevant for explanation of the present
experimental situation in neutrino physics and astrophysics.
In Section III the new fundamental wave equations for self/anti-self
conjugate type-II spinors, proposed by Ahluwalia, are re-casted to covariant
form. The connection with the Foldy-Nigam-Bargmann-Wightman- Wigner (FNBWW)
type quantum field theory is found. The possible applications to the problem of
neutrino oscillations are discussed.Comment: REVTEX file. 21pp. No figure
Finite, diffeomorphism invariant observables in quantum gravity
Two sets of spatially diffeomorphism invariant operators are constructed in
the loop representation formulation of quantum gravity. This is done by
coupling general relativity to an anti- symmetric tensor gauge field and using
that field to pick out sets of surfaces, with boundaries, in the spatial three
manifold. The two sets of observables then measure the areas of these surfaces
and the Wilson loops for the self-dual connection around their boundaries. The
operators that represent these observables are finite and background
independent when constructed through a proper regularization procedure.
Furthermore, the spectra of the area operators are discrete so that the
possible values that one can obtain by a measurement of the area of a physical
surface in quantum gravity are valued in a discrete set that includes integral
multiples of half the Planck area. These results make possible the construction
of a correspondence between any three geometry whose curvature is small in
Planck units and a diffeomorphism invariant state of the gravitational and
matter fields. This correspondence relies on the approximation of the classical
geometry by a piecewise flat Regge manifold, which is then put in
correspondence with a diffeomorphism invariant state of the gravity-matter
system in which the matter fields specify the faces of the triangulation and
the gravitational field is in an eigenstate of the operators that measure their
areas.Comment: Latex, no figures, 30 pages, SU-GP-93/1-
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