660,227 research outputs found
Functionals and the Quantum Master Equation
The quantum master equation is usually formulated in terms of functionals of
the components of mappings from a space-time manifold M into a
finite-dimensional vector space. The master equation is the sum of two terms
one of which is the anti-bracket (odd Poisson bracket) of functionals and the
other is the Laplacian of a functional. Both of these terms seem to depend on
the fact that the mappings on which the functionals act are vector-valued. It
turns out that neither this Laplacian nor the anti-bracket is well-defined for
sections of an arbitrary vector bundle. We show that if the functionals are
permitted to have their values in an appropriate graded tensor algebra whose
factors are the dual of the space of smooth functions on M, then both the
anti-bracket and the Laplace operator can be invariantly defined. Additionally,
one obtains a new anti-bracket for ordinary functionals.Comment: 21 pages, Late
Evolution of the N=28 shell closure: a test bench for nuclear forces
The evolution of the N=28 shell closure is investigated far from stability.
Using the latest results obtained from various experimental techniques, we
discuss the main properties of the N=28 isotones, as well as those of the N=27
and N=29 isotones. Experimental results are confronted to various theoretical
predictions. These studies pinpoint the effects of several terms of the
nucleon-nucleon interaction, such as the central, the spin-orbit, the tensor
and the three-body force components, to account for the modification of the
N=28 shell gap and spin-orbit splittings. Analogies between the evolution of
the N=28 shell closure and other magic numbers originating from the spin-orbit
interaction are proposed (N=14,50, 82 and 90). More generally, questions
related to the evolution of nuclear forces towards the drip-line, in bubble
nuclei, and for nuclei involved in the r-process nucleosynthesis are proposed
and discussed.Comment: 40 pages,15 figures, Procceedings Nobel Symposium 2012, accepted for
publication in Physica Script
Preventing Multipartite Disentanglement by Local Modulations
An entangled multipartite system coupled to a zero-temperature bath undergoes
rapid disentanglement in many realistic scenarios, due to local,
symmetry-breaking, differences in the particle-bath couplings. We show that
locally controlled perturbations, addressing each particle individually, can
impose a symmetry, and thus allow the existence of decoherence-free
multipartite entangled systems in zero-temperature environments.Comment: 5 pages, 2 figure
Early Stage of Superradiance from Bose-Einstein Condensates
We investigate the dynamics of matter and optical waves at the early stage of
superradiant Rayleigh scattering from Bose-Einstein Condensates. Our analysis
is within a spatially dependent quantum model which is capable of providing
analytic solutions for the operators of interest. The predictions of the
present model are compared to the predictions of a closely related mean field
model, and we provide a procedure that allows one to calculate quantum
expectation values by averaging over semiclassical solutions. The coherence
properties of the outgoing scattered light are also analyzed, and it is shown
that the corresponding correlation functions may provide detailed information
about the internal dynamics of the system.Comment: 27 pages, 8 figure
X-ray emission from PSR J1809-1917 and its pulsar wind nebula, possibly associated with the TeV gamma-ray source HESS J1809-193
We detected X-ray emission from the 50-kyr-old pulsar J1809-1917 and resolved
its pulsar wind nebula (PWN) with Chandra. The pulsar spectrum fits PL+BB model
with the photon index of 1.2 and the BB temperature of 2 MK for n_{H}=0.7\times
10^{22} cm^{-2}. The luminosities are(4\pm 1)\times 10^{31} ergs s^{-1} for the
PL component (in the 0.5-8 keV band) and ~1\times 10^{32} ergs s^{-1} for the
BB component (bolometric) at a plausible distance of 3.5 kpc. The bright inner
PWN component of a 3''\times12'' size is elongated in the north-south
direction, with the pulsar close to its south end. This component is immersed
in a larger (20''\times40''), similarly elongated outer PWN component of lower
surface brightness. The elongated shape of the compact PWN can be explained by
the ram pressure confinement of the pulsar wind due to the supersonic motion of
the pulsar. The PWN spectrum fits a PL model with photon index of 1.4\pm0.1 and
0.5-8 keV luminosity of 4\times10^{32} ergs s^{-1}. The compact PWN appears to
be inside a large-scale (~4'\times4') emission more extended to the south of
the pulsar, i.e. in the direction of the alleged pulsar motion. To explain the
extended X-ray emission ahead of the moving pulsar, one has to invoke strong
intrinsic anisotropy of the pulsar wind or assume that this emission comes from
a relic PWN swept by the asymmetrical reverse SNR shock. The pulsar and its PWN
are located within the extent of the unidentified TeV source HESS J1809-193
whose brightest part is offset by ~8' to the south of the pulsar, i.e. in the
same direction as the large-scale X-ray emission. Although the association
between J1809-1917 and HESS J1809-193 is plausible, an alternative source of
relativistic electrons powering HESS J1809-193 might be the serendipitously
discovered X-ray source CXOU J180940.7-192544.Comment: 13 pages, 10 figures and 3 tables, submitted to ApJ. Version with the
high-resolution figures is available at
http://www.astro.psu.edu/users/green/J1809/ms_astroph.pd
Glass models on Bethe lattices
We consider ``lattice glass models'' in which each site can be occupied by at
most one particle, and any particle may have at most l occupied nearest
neighbors. Using the cavity method for locally tree-like lattices, we derive
the phase diagram, with a particular focus on the vitreous phase and the
highest packing limit. We also study the energy landscape via the
configurational entropy, and discuss different equilibrium glassy phases.
Finally, we show that a kinetic freezing, depending on the particular dynamical
rules chosen for the model, can prevent the equilibrium glass transitions.Comment: 24 pages, 11 figures; minor corrections + enlarged introduction and
conclusio
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