923 research outputs found
Casimir self-energy of a \delta-\delta' sphere
We extend previous work on the vacuum energy of a massless scalar field in
the presence of singular potentials. We consider a single sphere denoted by the
so-called "delta-delta prime" interaction. Contrary to the Dirac delta
potential, we find a nontrivial one-parameter family of potentials such that
the regularization procedure gives an unambiguous result for the Casimir
self-energy. The procedure employed is based on the zeta function
regularization and the cancellation of the heat kernel coefficient a_2. The
results obtained are in agreement with particular cases, such as the Dirac
delta or Robin and Dirichlet boundary conditions
MeV measurements of gamma-ray bursts by CGRO-COMPTEL
Since the launch of the Compton Gamma-Ray Observatory in April 1991, the imaging COMPTEL telescope has accumulated positions and 0.75–30 MeV spectra of more than thirty gamma-ray bursts within its ∼π sr field of view. In an ongoing collaboration with BACODINE/GCN, COMPTEL positions are relayed to a global network of multiwavelength observers in near real time (∼10 minutes). Here we summarize the MeV properties, and present spatial, spectral, and temporal data for the latest of these events, GRB 970807. In concurrence with earlier SMM and current BATSE, OSSE, and EGRET measurements, COMPTEL data add to the accumulating evidence that GRB spectra do seem to have a characteristic shape: a peak (inE2F(E) ) around several hundred keV; and a power law above (spectral index 1.5–3.5) extending beyond the COMPTEL energy range
Casimir interaction between plane and spherical metallic surfaces
We give an exact series expansion of the Casimir force between plane and
spherical metallic surfaces in the non trivial situation where the sphere
radius , the plane-sphere distance and the plasma wavelength
have arbitrary relative values. We then present numerical
evaluation of this expansion for not too small values of . For metallic
nanospheres where and have comparable values, we interpret
our results in terms of a correlation between the effects of geometry beyond
the proximity force approximation (PFA) and of finite reflectivity due to
material properties. We also discuss the interest of our results for the
current Casimir experiments performed with spheres of large radius .Comment: 4 pages, new presentation (highlighting the novelty of the results)
and added references. To appear in Physical Review Letter
Light Meson Dynamics Workshop. Mini proceedings
The mini-proceedings of the Light Meson Dynamics Workshop held in Mainz from
February 10th to 12th, 2014, are presented. The web page of the conference,
which contains all talks, can be found at
https://indico.cern.ch/event/287442/overview .Comment: 46 pages, 17 contributions. Editors: W. Gradl, P. Masjuan, M.
Ostrick, and S. Schere
Three-Body Dynamics and Self-Powering of an Electrodynamic Tether in a Plasmasphere
The dynamics of an electrodynamic tether in a three-body gravitational environment are investigated. In the classical two-body scenario the extraction of power is at the expense of orbital kinetic energy. As a result of power extraction, an electrodynamic tether satellite system loses altitude and deorbits. This concept has been proposed and well investigated in the past, for example for orbital debris mitigation and spent stages reentry. On the other hand, in the three-body scenario an electrodynamic tether can be placed in an equilibrium position fixed with respect to the two primary bodies without deorbiting, and at the same time generate power for onboard use. The appearance of new equilibrium positions in the perturbed three-body problem allow this to happen as the electrical power is extracted at the expenses of the plasma corotating with the primary body. Fundamental differences between the classical twobody dynamics and the new phenomena appearing in the circular restricted three-body problem perturbed by the electrodynamic force of the electrodynamic tether are shown in the paper. An interesting application of an electrodynamic tether placed in the Jupiter plasma torus is then considered, in which the electrodynamic tether generates useful electrical power of about 1 kW with a 20-km-long electrodynamic tether from the environmental plasma without losing orbital energy
Dynamical study of the light scalar mesons below 1 GeV in a flux-tube model
The light scalar mesons below 1 GeV as tetraquark states are studied in the
framework of the flux-tube model, the multi-body confinement instead of the
additive two-body confinement is used. From the calculated results, we find
that the light scalar mesons, , could be well accommodated in
the diquark-antidiquark tetraquark picture in the flux-tube model and they
could be color confinement resonances. The mass of the first radial excited
state of is 1019 MeV, which is close to the mass of
. Whereas can not be fitted in this interpretation.Comment: 11 pages, 1 figur
The K^*_0(800) scalar resonance from Roy-Steiner representations of pi K scattering
We discuss the existence of the light scalar meson K^*_0(800) (also called
kappa) in a rigorous way, by showing the presence of a pole in the pi K --> pi
K amplitude on the second Riemann sheet. For this purpose, we study the domain
of validity of two classes of Roy-Steiner representations in the complex energy
plane. We prove that one of them is valid in a region sufficiently broad in the
imaginary direction. From this representation, we compute the l=0 partial wave
in the complex plane with neither additional approximation nor model
dependence, relying only on experimental data. A scalar resonance with
strangeness S=1 is found with the following mass and width: E_kappa = 658 \pm
13 MeV and Gamma_kappa = 557 \pm 24 MeV.Comment: 16 pages, 8 figures. Domain of validity of a Roy-Steiner
representation corrected and enlarged, and features of the K^*_0(800) pole
discussed in more details. Conclusions unchange
The preliminary lattice QCD calculation of meson decay width
We present a direct lattice QCD calculation of the meson decay width
with the s-wave scattering phase shift for the isospin pion-kaon () system. We employ a special finite size formula, which is the extension of
the Rummukainen-Gottlieb formula for the system in the moving frame, to
calculate the scattering phase, which indicates a resonance around
meson mass. Through the effective range formula, we extract the effective
coupling constant GeV and
decay width MeV. Our simulations are done with the MILC
gauge configurations with flavors of the "Asqtad" improved staggered
dynamical sea quarks on a lattice at and lattice spacing fm.Comment: To make it concise. arXiv admin note: text overlap with
arXiv:1110.1422, but much of v1 text overlap with articles by same and other
authors remove
Evaluating chiral symmetry restoration through the use of sum rules
We pursue the idea of assessing chiral restoration via in-medium
modifications of hadronic spectral functions of chiral partners. The usefulness
of sum rules in this endeavor is illustrated, focusing on the vector and
axial-vector channels. We first present an update on constructing quantitative
results for pertinent vacuum spectral functions. These spectral functions serve
as a basis upon which the in-medium spectral functions can be constructed. A
striking feature of our analysis of the vacuum spectral functions is the need
to include excited resonances, dictated by satisfying the Weinberg-type sum
rules. This includes excited states in both the vector and axial-vector
channels. Preliminary results for the finite temperature vector spectral
function are presented. Based on a rho spectral function tested in dilepton
data which develops a shoulder at low energies, we find that the rho' peak
flattens off. The flattening may be a sign of chiral restoration, though a
study of the finite temperature axial-vector spectral function remains to be
carried out.Comment: 9 pages, conference proceedings from Resonance Workshop at UT Austin,
March 5-7 201
- …