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