6,164 research outputs found
Self-interaction correction with Wannier functions
We describe the behavior of the Perdew-Zunger self-interaction-corrected
local density approximation (SIC-LDA) functional when implemented in a
plane-wave pseudopotential formalism with Wannier functions. Prototypical
semiconductors and wide-bandgap oxides show a large overcorrection of the LDA
bandgap. Application to transition-metal oxides and elements with d electrons
is hindered by a serious breaking of the spherical symmetry, which appears even
in a closed shell free atom. Our results indicate that, when all spherical
approximations are lifted, the general applicability of orbital-dependent
potentials is very limited and should be reconsidered in favor of rotationally
invariant functionals.Comment: 10 pages, 5 figure
Particle production and transplanckian problem on the non-commutative plane
We consider the coherent state approach to non-commutativity, and we derive
from it an effective quantum scalar field theory. We show how the
non-commutativity can be taken in account by a suitable modification of the
Klein-Gordon product, and of the equal-time commutation relations. We prove
that, in curved space, the Bogolubov coefficients are unchanged, hence the
number density of the produced particle is the same as for the commutative
case. What changes though is the associated energy density, and this offers a
simple solution to the transplanckian problem.Comment: Minor typos corrected, references added. Accepted for publication by
Modern Physics Letter
Efficiency fluctuations in quantum thermoelectric devices
We present a method, based on characterizing efficiency fluctuations, to
asses the performance of nanoscale thermoelectric junctions. This method
accounts for effects typically arising in small junctions, namely,
stochasticity in the junction's performance, quantum effects, and
nonequilibrium features preventing a linear response analysis. It is based on a
nonequilibrium Green's function (NEGF) approach, which we use to derive the
full counting statistics (FCS) for heat and work, and which in turn allows us
to calculate the statistical properties of efficiency fluctuations. We simulate
the latter for a variety of simple models where our method is exact. By
analyzing the discrepancies with the semi-classical prediction of a quantum
master equation (QME) approach, we emphasize the quantum nature of efficiency
fluctuations for realistic junction parameters. We finally propose an
approximate Gaussian method to express efficiency fluctuations in terms of
nonequilibrium currents and noises which are experimentally measurable in
molecular junctions.Comment: 11 pages, 6 figures, v2: version accepted in PR
Time-optimal trajectories to circumsolar space using solar electric propulsion
The aim of this paper is to explore the capabilities of a solar electric propelled spacecraft on a mission towards circumsolar space. Using an indirect approach, the paper investigates minimum time of transfer (direct) trajectories from an initial heliocentric parking orbit to a desired final heliocentric target orbit, with a low perihelion radius and a high orbital inclination. The simulation results are then collected into graphs and tables for a trade-off analysis of the main mission parameters. Finally, a comparison of the performance between a solar electric and a (photonic) solar sail based spacecraft is discussed
Connecting neutrino physics with dark matter
The origin of neutrino masses and the nature of dark matter are two of the
most pressing open questions of the modern astro-particle physics. We consider
here the possibility that these two problems are related, and review some
theoretical scenarios which offer common solutions. A simple possibility is
that the dark matter particle emerges in minimal realizations of the see-saw
mechanism, like in the majoron and sterile neutrino scenarios. We present the
theoretical motivation for both models and discuss their phenomenology,
confronting the predictions of these scenarios with cosmological and
astrophysical observations. Finally, we discuss the possibility that the
stability of dark matter originates from a flavour symmetry of the leptonic
sector. We review a proposal based on an A_4 flavour symmetry.Comment: 21 pages, 4 figures. Review prepared for the focus issue on "Neutrino
Physics". Matches published versio
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