Low-energy p-d scattering and He-3 in pionless EFT

We calculate low-energy proton--deuteron scattering in the framework of pionless effective field theory. In the quartet channel, we calculate the elastic scattering phase shift up to next-to-next-to-leading order in the power counting. In the doublet channel, we perform a next-to-leading order calculation. We obtain good agreement with the available phase shift analyses down to the scattering threshold. The phase shifts in the region of non-perturbative Coulomb interactions are calculated by using an optimised integration mesh. Moreover, the Coulomb contribution to the 3He-3H binding energy difference is evaluated in first order perturbation theory. We comment on the implications of our results for the power counting of subleading three-body forces.Comment: 27 pages, 13 figures, typos corrected in Sec. V.A (trinucleon wave functions

Non--Heisenberg Spin Dynamics of Double-Exchange Ferromagnets with Coulomb Repulsion

With a variational three--body calculation we study the role of the interplay between the onsite Coulomb, Hund's rule, and superexchange interactions on the spinwave excitation spectrum of itinerant ferromagnets. We show that correlations between a Fermi sea electron--hole pair and a magnon result in a very pronounced zone boundary softening and strong deviations from the Heisenberg spinwave dispersion. We show that this spin dynamics depends sensitively on the Coulomb and exchange interactions and discuss its possible relevance to experiments in the manganites.Comment: 4 pages, 4 figures, published in Physical Review B as rapid communication

Cotunneling at resonance for the single-electron transistor

We study electron transport through a small metallic island in the perturbative regime. Using a recently developed diagrammatic technique, we calculate the occupation of the island as well as the conductance through the transistor in forth order in the tunneling matrix elements, a process referred to as cotunneling. Our formulation does not require the introduction of a cut-off. At resonance we find significant modifications of previous theories and good agreement with recent experiments.Comment: 5 pages, Revtex, 5 eps-figure

Influence of spin waves on transport through a quantum-dot spin valve

We study the influence of spin waves on transport through a single-level quantum dot weakly coupled to ferromagnetic electrodes with noncollinear magnetizations. Side peaks appear in the differential conductance due to emission and absorption of spin waves. We, furthermore, investigate the nonequilibrium magnon distributions generated in the source and drain lead. In addition, we show how magnon-assisted tunneling can generate a fullly spin-polarized current without an applied transport voltage. We discuss the influence of spin waves on the current noise. Finally, we show how the magnonic contributions to the exchange field can be detected in the finite-frequency Fano factor.Comment: published version, 15 pages, 10 figure

Hanle Effect in Transport through Quantum Dots Coupled to Ferromagnetic Leads

We suggest a series of transport experiments on spin precession in quantum dots coupled to one or two ferromagnetic leads. Dot spin states are created by spin injection and analyzed via the linear conductance through the dot, while an applied magnetic field gives rise to the Hanle effect. Such a Hanle experiment can be used to determine the spin lifetime in the quantum dot, to measure the spin injection efficiency into the dot, as well as proving the existence of intrinsic spin precession which is driven by the Coulomb interaction.Comment: 7 pages, 4 figures, minor changes, added reference

How the Eurosceptics brought down David Cameron: a serious case of supplier lock-in

David Cameron’s decision to call a referendum on the EU was the result of intense Eurosceptic pressures from both within and outside his party. He found himself with little scope for manoeuvre as Ukip gained support and his backbenchers threatened rebellion. Pascal D König looks at what a competition theory usually applied to business can reveal about his misjudgment and eventual replacement as PM

efficiency and evolution of R&D Networks.

This work introduces a new model to investigate the efficiency and evolution of networks of firms exchanging knowledge in R&D partnerships. We first examine the efficiency of a given network structure from the point of view of maximizing total profits in the industry. We show that the efficient network structure depends on the marginal cost of collaboration. When the marginal cost is low, the complete graph is efficient. However, a high marginal cost implies that the efficient network is sparser and has a core-periphery structure. Next, we examine the evolution of the network structure when the decision on collaborating partners is decentralized. We show the existence of multiple equilibrium structures which are in general inefficient. This is due to (i) the path dependent character of the partner selection process, (ii) the presence of knowledge externalities and (iii) the presence of severance costs involved in link deletion. Finally, we study the properties of the emerging equilibrium networks and we show that they are coherent with the stylized facts on R&D networks.R&D networks;technology spillovers;network efficiency;network formation;