22,343 research outputs found
Atomic screening of nuclear transitions
In the analysis of time-reversal and Mössbauer absorption experiments, it is important to consider atomic processes which interfere with the direct nuclear transition. Interaction of the photon with the atomic electrons causes the radiation to acquire a phase shift, specified by the interference parameter ξ(L_π). We present theoretical expressions for ξ and compare our calculated values with experiment. Satisfactory agreement is obtained. In particular, an apparent violation of time-reversal invariance in the 129-keV transition of ^(191)Ir is fully explained by these effects
Hot entanglement in a simple dynamical model
How mixed can one component of a bi-partite system be initially and still
become entangled through interaction with a thermalized partner? We address
this question here. In particular, we consider the question of how mixed a
two-level system and a field mode may be such that free entanglement arises in
the course of the time evolution according to a Jaynes-Cummings type
interaction. We investigate the situation for which the two-level system is
initially in mixed state taken from a one-parameter set, whereas the field has
been prepared in an arbitrary thermal state. Depending on the particular choice
for the initial state and the initial temperature of the quantised field mode,
three cases can be distinguished: (i) free entanglement will be created
immediately, (ii) free entanglement will be generated, but only at a later time
different from zero, (iii) the partial transpose of the joint state remains
positive at all times. It will be demonstrated that increasing the initial
temperature of the field mode may cause the joint state to become distillable
during the time evolution, in contrast to a non-distillable state at lower
initial temperatures. We further assess the generated entanglement
quantitatively, by evaluating the logarithmic negativity numerically, and by
providing an analytical upper bound.Comment: 5 pages, 2 figures. Contribution to the proceedings of the
'International Conference on Quantum Information', Oviedo, July 13-18, 2002.
Discusses sudden changes of entanglement properties in a dynamical quantum
mode
On continuum modeling of sputter erosion under normal incidence: interplay between nonlocality and nonlinearity
Under specific experimental circumstances, sputter erosion on semiconductor
materials exhibits highly ordered hexagonal dot-like nanostructures. In a
recent attempt to theoretically understand this pattern forming process, Facsko
et al. [Phys. Rev. B 69, 153412 (2004)] suggested a nonlocal, damped
Kuramoto-Sivashinsky equation as a potential candidate for an adequate
continuum model of this self-organizing process. In this study we theoretically
investigate this proposal by (i) formally deriving such a nonlocal equation as
minimal model from balance considerations, (ii) showing that it can be exactly
mapped to a local, damped Kuramoto-Sivashinsky equation, and (iii) inspecting
the consequences of the resulting non-stationary erosion dynamics.Comment: 7 pages, 2 Postscript figures, accepted by Phys. Rev. B corrected
typos, few minor change
Lepton Flavor Violation without Supersymmetry
We study the lepton flavor violating (LFV) processes mu -> e gamma, mu -> 3e,
and mu -> e conversion in nuclei in the left-right symmetric model without
supersymmetry and perform the first complete computation of the LFV branching
ratios B(mu -> f) to leading non-trivial order in the ratio of left- and
right-handed symmetry breaking scales. To this order, B(mu -> e gamma) and B(mu
-> e) are governed by the same combination of LFV violating couplings, and
their ratio is naturally of order unity. We also find B(mu -> 3 e)/B(mu -> e)
\sim 100 under slightly stronger assumptions. Existing limits on the branching
ratios already substantially constrain mass splittings and/or mixings in the
heavy neutrino sector. When combined with future collider studies and precision
electroweak measurements, improved limits on LFV processes will test the
viability of low-scale, non-supersymmetric LFV scenarios.Comment: 24 pages, 7 figures, 2 table
Muonium-Antimuonium Oscillations in an extended Minimal Supersymmetric Standard Model with right-handed neutrinos
The electron and muon number violating muonium-antimuonium oscillation
process in an extended Minimal Supersymmetric Standard Model is investigated.
The Minimal Supersymmetric Standard Model is modified by the inclusion of three
right-handed neutrino superfields. While the model allows the neutrino mass
terms to mix among the different generations, the sneutrino and slepton mass
terms have only intra-generation lepton number violation but not
inter-generation lepton number mixing. So doing, the muonium-antimuonium
conversion can then be used to constrain those model parameters which avoid
further constraint from the decay bounds. For a wide range of
parameter values, the contributions to the muonium-antimuonium oscillation time
scale are at least two orders of magnitude below the sensivity of current
experiments. However, if the ratio of the two Higgs field VEVs, , is
very small, there is a limited possibility that the contributions are large
enough for the present experimental limit to provide an inequality relating
with the light neutrino mass scale which is generated by
see-saw mechanism. The resultant lower bound on as a function of
is more stringent than the analogous bounds arising from the muon and
electron anomalous magnetic moments as computed using this model.Comment: 29 pages, 7 figures, 3 tables, Late
Search for Majorana neutrinos with the first two years of EXO-200 data
Many extensions of the standard model of particle physics suggest that neutrinos should be Majorana-type fermions—that is, that neutrinos are their own anti-particles—but this assumption is difficult to confirm. Observation of neutrinoless double-β decay (0νββ), a spontaneous transition that may occur in several candidate nuclei, would verify the Majorana nature of the neutrino and constrain the absolute scale of the neutrino mass spectrum. Recent searches carried out with ^(76)Ge (the GERDA experiment) and ^(136)Xe (the KamLAND-Zen and EXO (Enriched Xenon Observatory)-200 experiments) have established the lifetime of this decay to be longer than 10^(25) years, corresponding to a limit on the neutrino mass of 0.2–0.4 electronvolts. Here we report new results from EXO-200 based on a large ^(136)Xe exposure that represents an almost fourfold increase from our earlier published data sets. We have improved the detector resolution and revised the data analysis. The half-life sensitivity we obtain is 1.9 × 10^(25) years, an improvement by a factor of 2.7 on previous EXO-200 results. We find no statistically significant evidence for 0νββ decay and set a half-life limit of 1.1 × 10^(25) years at the 90 per cent confidence level. The high sensitivity holds promise for further running of the EXO-200 detector and future 0νββ decay searches with an improved Xe-based experiment, nEXO
Jet propulsion without inertia
A body immersed in a highly viscous fluid can locomote by drawing in and
expelling fluid through pores at its surface. We consider this mechanism of jet
propulsion without inertia in the case of spheroidal bodies, and derive both
the swimming velocity and the hydrodynamic efficiency. Elementary examples are
presented, and exact axisymmetric solutions for spherical, prolate spheroidal,
and oblate spheroidal body shapes are provided. In each case, entirely and
partially porous (i.e. jetting) surfaces are considered, and the optimal
jetting flow profiles at the surface for maximizing the hydrodynamic efficiency
are determined computationally. The maximal efficiency which may be achieved by
a sphere using such jet propulsion is 12.5%, a significant improvement upon
traditional flagella-based means of locomotion at zero Reynolds number. Unlike
other swimming mechanisms which rely on the presentation of a small cross
section in the direction of motion, the efficiency of a jetting body at low
Reynolds number increases as the body becomes more oblate, and limits to
approximately 162% in the case of a flat plate swimming along its axis of
symmetry. Our results are discussed in the light of slime extrusion mechanisms
occurring in many cyanobacteria
A multi-centennial record of past floods and earthquakes in Valle d'Aosta, Mediterranean Italian Alps
Mediterranean Alpine populations are particularly exposed to
natural hazards like floods and earthquakes because of both the close
Mediterranean humidity source and the seismically active Alpine region.
Knowledge of long-term variability in flood and earthquake occurrences is of
high value since it can be useful to improve risk assessment and mitigation.
In this context, we explore the potential of a lake-sediment sequence from
Lago Inferiore de Laures in Valle d'Aosta (Northern Italy) as a long-term
record of past floods and earthquakes. The high-resolution sedimentological
study revealed 76 event layers over the last ca. 270 years; 8 are interpreted
as most probably induced by earthquakes and 68 by flood events. Comparison to
historical seismic data suggests that the recorded earthquakes are strong
(epicentral Medvedev–Sponheuer–Kárník (MSK) intensity of VI–IX) and/or close to the lake (distance of
25–120 km). Compared to other lake-sediment sequences, Lago Inferiore de
Laures sediments appear to be regionally the most sensitive to earthquake
shaking, offering a great potential to reconstruct the past regional
seismicity further back in time. Comparison to historical and palaeoflood
records suggests that the flood signal reconstructed from Lago Inferiore de
Laures sediments represents the regional and (multi-)decadal variability
of summer–autumn floods well, in connection to Mediterranean mesoscale
precipitation events. Overall, our results reveal the high potential of Lago
Inferiore de Laures sediments to extend the regional earthquake and flood
catalogues far back in time
- …