531,575 research outputs found
Pygmy dipole resonance as a constraint on the neutron skin of heavy nuclei
The isotopic dependence of the isovector Pygmy dipole response in tin is
studied within the framework of the relativistic random phase approximation.
Regarded as an oscillation of the neutron skin against the isospin-symmetric
core, the pygmy dipole resonance may place important constraints on the neutron
skin of heavy nuclei and, as a result, on the equation of state of neutron-rich
matter. The present study centers around two questions. First, is there a
strong correlation between the development of a neutron skin and the emergence
of low-energy isovector dipole strength? Second, could one use the recently
measured Pygmy dipole resonance in 130Sn and 132Sn to discriminate among
theoretical models? For the first question we found that while a strong
correlation between the neutron skin and the Pygmy dipole resonance exists, a
mild anti-correlation develops beyond 120Sn. The answer to the second question
suggests that models with overly large neutron skins--and thus stiff symmetry
energies--are in conflict with experiment.Comment: 16 pages with 6 figure
Multi-Agent Complex Systems and Many-Body Physics
Multi-agent complex systems comprising populations of decision-making
particles, have many potential applications across the biological,
informational and social sciences. We show that the time-averaged dynamics in
such systems bear a striking resemblance to conventional many-body physics. For
the specific example of the Minority Game, this analogy enables us to obtain
analytic expressions which are in excellent agreement with numerical
simulations.Comment: Accepted for publication in Europhysics Letter
Flux Tube Zero-Point Motion, Hadronic Charge Radii, and Hybrid Meson Production Cross Sections
Flux tube zero-point motion produces quark displacements transverse to the
flux tube which make significant contributions to hadronic charge radii. In
heavy quark systems, these contributions can be related by Bjorken's sum rule
to the rates for semileptonic decay to hybrid mesons. This connection can be
generalized to other leptoproduction processes, where transverse contributions
to elastic form factor slopes are related to the cross sections for the
production of the associated hybrid states. I identify the flux tube overlap
integral responsible for these effects as the strong QCD analogue of the
Sudakov form factor of perturbative QCD.Comment: 16 pages, revised to clarify some points and to improve and correct
the notation for the flux tube wave function
Measurement of the electron's electric dipole moment using YbF molecules: methods and data analysis
We recently reported a new measurement of the electron's electric dipole
moment using YbF molecules [Nature 473, 493 (2011)]. Here, we give a more
detailed description of the methods used to make this measurement, along with a
fuller analysis of the data. We show how our methods isolate the electric
dipole moment from imperfections in the experiment that might mimic it. We
describe the systematic errors that we discovered, and the small corrections
that we made to account for these. By making a set of additional measurements
with greatly exaggerated experimental imperfections, we find upper bounds on
possible uncorrected systematic errors which we use to determine the systematic
uncertainty in the measurement. We also calculate the size of some systematic
effects that have been important in previous electric dipole moment
measurements, such as the motional magnetic field effect and the geometric
phase, and show them to be negligibly small in the present experiment. Our
result is consistent with an electric dipole moment of zero, so we provide
upper bounds to its size at various confidence levels. Finally, we review the
prospects for future improvements in the precision of the experiment.Comment: 35 pages, 15 figure
Effect of phase noise on useful quantum correlations in Bose Josephson junctions
In a two-mode Bose Josephson junction the dynamics induced by a sudden quench
of the tunnel amplitude leads to the periodic formation of entangled states.
For instance, squeezed states are formed at short times and macroscopic
superpositions of phase states at later times. The two modes of the junction
can be viewed as the two arms of an interferometer; use of entangled states
allows to perform atom interferometry beyond the classical limit. Decoherence
due to the presence of noise degrades the quantum correlations between the
atoms, thus reducing phase sensitivity of the interferometer. We consider the
noise induced by stochastic fluctuations of the energies of the two modes of
the junction. We analyze its effect on squeezed states and macroscopic
superpositions and study quantitatively the amount of quantum correlations
which can be used to enhance the phase sensitivity with respect to the
classical limit. To this aim we compute the squeezing parameter and the quantum
Fisher information during the quenched dynamics. For moderate noise intensities
we show that these useful quantum correlations increase on time scales beyond
the squeezing regime. This suggests multicomponent superpositions as
interesting candidates for high-precision atom interferometry
Noise in Bose Josephson junctions: Decoherence and phase relaxation
Squeezed states and macroscopic superpositions of coherent states have been
predicted to be generated dynamically in Bose Josephson junctions. We solve
exactly the quantum dynamics of such a junction in the presence of a classical
noise coupled to the population-imbalance number operator (phase noise),
accounting for, for example, the experimentally relevant fluctuations of the
magnetic field. We calculate the correction to the decay of the visibility
induced by the noise in the non-Markovian regime. Furthermore, we predict that
such a noise induces an anomalous rate of decoherence among the components of
the macroscopic superpositions, which is independent of the total number of
atoms, leading to potential interferometric applications.Comment: Fig 2 added; version accepted for publicatio
Major Substructure in the M31 Outer Halo: the South-West Cloud
We undertake the first detailed analysis of the stellar population and
spatial properties of a diffuse substructure in the outer halo of M31. The
South-West Cloud lies at a projected distance of ~100 kpc from the centre of
M31, and extends for at least ~50 kpc in projection. We use Pan-Andromeda
Archaeological Survey photometry of red giant branch stars to determine a
distance to the South-West Cloud of 793 +/- 45 kpc. The metallicity of the
cloud is found to be [Fe/H] = -1.3 +/- 0.1. This is consistent with the
coincident globular clusters PAndAS-7 and PAndAS-8, which have metallicities
determined using an independent technique of [Fe/H] = -1.35 +/- 0.15. We
measure a brightness for the Cloud of M_V = -12.1 mag; this is ~75 per cent of
the luminosity implied by the luminosity-metallicity relation. Under the
assumption that the South-West Cloud is the visible remnant of an accreted
dwarf satellite, this suggests that the progenitor object was amongst M31's
brightest dwarf galaxies prior to disruption.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Vortex annihilation in the ordering kinetics of the O(2) model
The vortex-vortex and vortex-antivortex correlation functions are determined
for the two-dimensional O(2) model undergoing phase ordering. We find
reasonably good agreement with simulation results for the vortex-vortex
correlation function where there is a short-scaled distance depletion zone due
to the repulsion of like-signed vortices. The vortex-antivortex correlation
function agrees well with simulation results for intermediate and long-scaled
distances. At short-scaled distances the simulations show a depletion zone not
seen in the theory.Comment: 28 pages, REVTeX, submitted to Phys. Rev.
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