2,550,067 research outputs found
Cooper-pair qubit and Cooper-pair electrometer in one device
An all-superconductor charge qubit enabling a radio-frequency readout of its
quantum state is described. The core element of the setup is a superconducting
loop which includes the single-Cooper-pair (Bloch) transistor. This circuit has
two functions: First, it operates as a charge qubit with magnetic control of
Josephson coupling and electrostatic control of the charge on the transistor
island. Secondly, it acts as the transducer of the rf electrometer, which
probes the qubit state by measuring the Josephson inductance of the transistor.
The evaluation of the basic parameters of this device shows its superiority
over the rf-SET-based qubit setup.Comment: 4 pages incl. 3 figues; the SQUID'2001 paper, to be published in
Physica
Higgs Boson pair production merged to one jet
We develop a Monte Carlo event generator for Higgs Boson pair production
merged to exact one-jet matrix elements. The matrix elements are generated with
OpenLoops and event generation is performed with the HERWIG++ general-purpose
event generator. This allows us to simulate fully-exclusive hadronic final
states with accurate description of the kinematics of the leading jet in
conjunction with a parton shower. We use the implementation to examine in
detail the systematic uncertainties which result from the merging procedure. We
assess the magnitude of the impact of the merging on experimental searches of
Standard Model di-Higgs production that aim to constrain the Higgs boson
self-coupling. We find that the use of a merged sample can reduce theoretical
systematic uncertainties in the efficiencies of cuts on certain observables.
This constitutes the most accurate simulation of the process available to date.
The Monte Carlo event generator developed for this project is available as an
add-on to the HERWIG++ event generator at http://www.itp.uzh.ch/~andreasp/hhComment: 19 pages, 10 figures, updated UR
Soft two-meson-exchange nucleon-nucleon potentials. II. One-pair and two-pair diagrams
Two-meson-exchange nucleon-nucleon potentials are derived where either one or
both nucleons contains a pair vertex. Physically, the meson-pair vertices are
meant to describe in an effective way (part of) the effects of heavy-meson
exchange and meson-nucleon resonances. {}From the point of view of ``duality,''
these two kinds of contribution are roughly equivalent. The various
possibilities for meson pairs coupling to the nucleon are inspired by the
chiral-invariant phenomenological Lagrangians that have appeared in the
literature. The coupling constants are fixed using the linear model.
We show that the inclusion of these two-meson exchanges gives a significant
improvement over a potential model including only the standard one-boson
exchanges.Comment: 21 pages RevTeX, 7 postscript figures; revised version as to appear
in Phys. Rev.
One-dimensional pair cascade emission in gamma-ray binaries
In gamma-ray binaries such as LS 5039 a large number of electron-positron
pairs are created by the annihilation of primary very high energy (VHE)
gamma-rays with photons from the massive star. The radiation from these
particles contributes to the total high energy gamma-ray flux and can initiate
a cascade, decreasing the effective gamma-ray opacity in the system. The aim of
this paper is to model the cascade emission and investigate if it can account
for the VHE gamma-ray flux detected by HESS from LS 5039 at superior
conjunction, where the primary gamma-rays are expected to be fully absorbed. A
one-dimensional cascade develops along the line-of-sight if the deflections of
pairs induced by the surrounding magnetic field can be neglected. A
semi-analytical approach can then be adopted, including the effects of the
anisotropic seed radiation field from the companion star. Cascade equations are
numerically solved, yielding the density of pairs and photons. In LS 5039, the
cascade contribution to the total flux is large and anti-correlated with the
orbital modulation of the primary VHE gamma-rays. The cascade emission
dominates close to superior conjunction but is too strong to be compatible with
HESS measurements. Positron annihilation does not produce detectable 511 keV
emission. This study provides an upper limit to cascade emission in gamma-ray
binaries at orbital phases where absorption is strong. The pairs are likely to
be deflected or isotropized by the ambient magnetic field, which will reduce
the resulting emission seen by the observer. Cascade emission remains a viable
explanation for the detected gamma-rays at superior conjunction in LS 5039.Comment: 8 pages, 7 figures, 1 table, accepted for publication in Astronomy
and Astrophysic
Pair correlation functions in one-dimensional correlated-hopping models
We investigate ground-state properties of two correlated-hopping electron
models, the Hirsch and the Bariev model. Both models are of recent interest in
the context of hole superconductivity. Applying the Lanczos technique to small
clusters, we numerically determine the binding energy, the spin gaps,
correlation functions, and other properties for various values of the
bond-charge interaction parameter. Our results for small systems indicate that
pairing is favoured in a certain parameter range. However, in contrast to the
Bariev model, superconducting correlations are suppressed in the Hirsch model,
for a bond-charge repulsion larger than a critical value.Comment: 7 pages (LaTeX) + 6 postcript figures in a separate uuencoded fil
Enhancement of pair correlation in a one-dimensional hybridization model
We propose an integrable model of one-dimensional (1D) interacting electrons
coupled with the local orbitals arrayed periodically in the chain. Since the
local orbitals are introduced in a way that double occupation is forbidden, the
model keeps the main feature of the periodic Anderson model with an interacting
host. For the attractive interaction, it is found that the local orbitals
enhance the effective mass of the Cooper-pair-like singlets and also the pair
correlation in the ground state. However, the persistent current is depressed
in this case. For the repulsive interaction case, the Hamiltonian is
non-Hermitian but allows Cooper pair solutions with small momenta, which are
induced by the hybridization between the extended state and the local orbitals.Comment: 11 page revtex, no figur
Relic density at one-loop with gauge boson pair production
We have computed the full one-loop corrections (electroweak as well as QCD)
to processes contributing to the relic density of dark matter in the MSSM where
the LSP is the lightest neutralino. We cover scenarios where the most important
channels are those with gauge boson pair production. This includes the case of
a bino with some wino admixture, a higgsino and a wino. In this paper we
specialise to the case of light dark matter much below the TeV scale. The
corrections can have a non-negligible impact on the predictions and should be
taken into account in view of the present and forthcoming increasing precision
on the relic density measurements. Our calculations are made with the help of
\SloopS, an automatic tool for the calculation of one-loop processes in the
MSSM. The renormalisation scheme dependence of the results as concerns \tgb
is studied.Comment: 25 pages, 10 figures, Citations adde
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