3,768 research outputs found
Realistic calculations of nuclear disappearance lifetimes induced by neutron-antineutron oscillations
Realistic calculations of nuclear disappearance lifetimes induced by
neutron-antineutron oscillations are reported for oxygen and iron, using
antineutron nuclear potentials derived from a recent comprehensive analysis of
antiproton atomic X-ray and radiochemical data. A lower limit of 3.3 x 10E8 s
on the neutron-antineutron oscillation time is derived from the
Super-Kamiokande I new lower limit of 1.77 x 10E32 yr on the neutron lifetime
in oxygen. Antineutron scattering lengths in carbon and nickel, needed in trap
experiments using ultracold neutrons, are calculated from updated antinucleon
optical potentials at threshold, with results shown to be largely model
independent.Comment: version matching PRD publication, typos and references correcte
Limits on nu_e and anti-nu_e disappearance from Gallium and reactor experiments
The deficit observed in the Gallium radioactive source experiments is
interpreted as a possible indication of the disappearance of electron
neutrinos. In the effective framework of two-neutrino mixing we obtain
and . The compatibility of this result with the data of the Bugey and
Chooz reactor short-baseline antineutrino disappearance experiments is studied.
It is found that the Bugey data present a hint of neutrino oscillations with
and , which is compatible with the Gallium allowed region of the
mixing parameters. This hint persists in the combined analyses of Bugey and
Chooz data, of Gallium and Bugey data, and of Gallium, Bugey, and Chooz data.Comment: 21 pages. Final version to be published in Phys. Rev.
Towards single-electron metrology
We review the status of the understanding of single-electron transport (SET)
devices with respect to their applicability in metrology. Their envisioned role
as the basis of a high-precision electrical standard is outlined and is
discussed in the context of other standards. The operation principles of single
electron transistors, turnstiles and pumps are explained and the fundamental
limits of these devices are discussed in detail. We describe the various
physical mechanisms that influence the device uncertainty and review the
analytical and numerical methods needed to calculate the intrinsic uncertainty
and to optimise the fabrication and operation parameters. Recent experimental
results are evaluated and compared with theoretical predictions. Although there
are discrepancies between theory and experiments, the intrinsic uncertainty is
already small enough to start preparing for the first SET-based metrological
applications.Comment: 39 pages, 14 figures. Review paper to be published in International
Journal of Modern Physics
Dark Matter from Baryon Asymmetry
The measured densities of dark and baryonic matter are surprisingly close to
each other, even though the baryon asymmetry and the dark matter are usually
explained by unrelated mechanisms. We consider a scenario where the dark matter
S is produced non-thermally from the decay of a messenger particle X, which
carries the baryon number and compensates for the baryon asymmetry in the
Universe, thereby establishing a connection between the baryonic and dark
matter densities. We propose a simple model to realize this scenario, adding
only a light singlet fermion S and a colored particle X which has a mass in the
O(TeV) range and a lifetime to appear long-lived in collider detector.
Therefore in hadron colliders the signal is similar to that of a stable or
long-lived gluino in supersymmetric models.Comment: 12 pages; v2: bounds on the mass of the messenger particle are
relaxed; conclusions unchanged. additional minor modification
The Supersymmetric Stueckelberg Mass and Overcoming the Fayet-Iliopoulos Mechanism for Breaking Symmetry
Gauge invariant generation of mass for supersymmetric U(1) vector field
through use of a chiral Stueckelberg superfield is considered. When a
Fayet-Iliopoulos D term is also present, no breaking of supersymmetry ever
occurs so long as the Stueckelberg mass is not zero. A moduli space in which
gauge symmetry is spontaneously broken arises in this case
Sensitivity of depth of maximum and absorption depth of EAS to hadron production mechanism
Comparison of experimental data on depth of extensive air showers (EAS) development maximum in the atmosphere, T sub M and path of absorption, lambda, in the lower atmosphere of EAS with fixed particle number in the energy region eV with the results of calculation show that these parameters are sensitive mainly to the inelastic interaction cross section and scaling violation in the fragmentation and pionization region. The data are explained in a unified manner within the framework of a model in which scaling is violated slightly in the fragmentation region and strongly in the pionization region at primary cosmic rays composition close to the normal one and a permanent increase of inelastic interaction cross section. It is shown that, while interpreting the experimental data, disregard of two methodical points causes a systematic shift in T sub M: (1) shower selection system; and (2) EAS electron lateral distribution when performing the calculations on basis of which the transfer is made from the Cerenkov pulse FWHM to the depth of shower maximum, T sub M
Chandra detection of extended X-ray emission from the recurrent nova RS Ophiuchi
Radio, infrared, and optical observations of the 2006 eruption of the
symbiotic recurrent nova RS Ophiuchi (RS Oph) showed that the explosion
produced non-spherical ejecta. Some of this ejected material was in the form of
bipolar jets to the east and west of the central source. Here we describe Xray
observations taken with the Chandra X-ray Observatory one and a half years
after the beginning of the outburst that reveal narrow, extended structure with
a position angle of approximately 300 degrees (east of north). Although the
orientation of the extended feature in the X-ray image is consistent with the
readout direction of the CCD detector, extensive testing suggests that the
feature is not an artifact. Assuming it is not an instrumental effect, the
extended X-ray structure shows hot plasma stretching more than 1,900 AU from
the central binary (taking a distance of 1.6 kpc). The X-ray emission is
elongated in the northwest direction - in line with the extended infrared
emission and some minor features in the published radio image. It is less
consistent with the orientation of the radio jets and the main bipolar optical
structure. Most of the photons in the extended X-ray structure have energies of
less than 0.8 keV. If the extended X-ray feature was produced when the nova
explosion occurred, then its 1".2 length as of 2007 August implies that it
expanded at an average rate of more than 2 mas/d, which corresponds to a flow
speed of greater than 6,000 km/s (d/1.6 kpc) in the plane of the sky. This
expansion rate is similar to the earliest measured expansion rates for the
radio jets.Comment: accepted in Ap
Spatially-resolved probing of a non-equilibrium superconductor
Spatially resolved relaxation of non-equilibrium quasiparticles in a
superconductor at ultra-low temperatures was experimentally studied. It was
found that the quasiparticle injection through a tunnel junction results in
modification of the shape of I-V characteristic of a remote `detector'
junction. The effect depends on temperature, injection current and proximity to
the injector. The phenomena can be understood in terms of creation of
quasiparticle charge and energy disequilibrium characterized by two different
length scales m and
m. The findings are in good agreement with existing phenomenological
models, while more elaborated microscopic theory is mandatory for detailed
quantitative comparison with experiment. The results are of fundamental
importance for understanding electron transport phenomena in various
nanoelectronic circuits.Comment: 7 pages, 5 figure
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