The Topology of Double Field Theory

We describe the doubled space of Double Field Theory as a group manifold $G$ with an arbitrary generalized metric. Local information from the latter is not relevant to our discussion and so $G$ only captures the topology of the doubled space. Strong Constraint solutions are maximal isotropic submanifold $M$ in $G$. We construct them and their Generalized Geometry in Double Field Theory on Group Manifolds. In general, $G$ admits different physical subspace $M$ which are Poisson-Lie T-dual to each other. By studying two examples, we reproduce the topology changes induced by T-duality with non-trivial $H$-flux which were discussed by Bouwknegt, Evslin and Mathai [hep-th/0306062].Comment: 37 pages, 1 figure, published versio

Regime Shifts and Volatility Spillovers on International Stock Markets

A standard capital asset pricing model is extended to allow for stochastic shifts in the volatility of the news process. This model is then estimated on bivariate stock market data to separate two exogenous news processes – a world and a domestic. The results indicate that the influence of the world news process on the Swedish stock market has increased significantly over the period 1970-1995. I also find that the foreign influence is much stronger when the volatility of the world news process is high. Furthermore, when the world state shifts to high risk, the Swedish stock market immediately reacts by a large fall, estimated to 7.0%. The bivariate model is also estimated on a set of other national stock markets.capital asset pricing model; stochastic shifts; news process; Swedish stock market

The Effect of Linear Time Trends on Cointegration Testing in Single Equations

This paper surveys the asymptotic distributions of three widely used single equation cointegration tests. Particular attention is paid to the case where the regressors are integrated with drift, i.e. at least one of the regressors follows a linear trend. Even if the regressions are not detrended, the asymptotic critical values are affected by the presence of linear trends in the regressors. Not taking into account this effect leads to tests that are biased towards establishing cointegration too often. The correct limiting distribution theory of regressions without detrending in the presence of integrated regressors with drift is described. Appropriate critical values are readily available from the literature and are simple to use following the tables included here.

Majorana fermions coupled to electromagnetic radiation

We consider a voltage-biased Josephson junction between two nanowires hosting Majorana zero modes which occur as topological protected zero-energy excitations at the junction. We show that two Majorana fermions localized at the junction, even though being neutral particles, interact with the electromagnetic field and generate coherent radiation similar to the conventional Josephson radiation. Within a semiclassical analysis of the radiation field, we find that the optical phase gets locked to the superconducting phase difference and that the radiation is emitted at half the Josephson frequency. In order to confirm the coherence of the radiation, we study correlations of the radiation emitted by two spatially-separated junctions in a d.c.-SQUID geometry taking into account decoherence due to spontaneous state-switches as well as due to quasi-particle poisoning.Comment: 18 pages, 4 figure

Charge response of the Majorana toric code

At zero temperature, a two dimensional lattice of Majorana zero modes on mesoscopic superconducting islands has a topologically ordered toric code phase. Recently, a Landau field theory has been proposed for the system that captures its different phases and the associated phase-transitions. It was shown that with the increase of Josephson tunneling between the islands, a continuous symmetry-breaking 3D-XY transition gets transformed into a discrete symmetry-breaking 3D-Ising transition through a couple of tricritical points and first order transitions. Using the proposed field theory, we analyze the charge-response of the system at the different continuous phase-transitions. We calculate the universal conductivity at the 3D-XY transitions and the change in the superconducting density at the Ising transition using 1/N expansion. Furthermore, by computing a one-loop correction to the field theory, we show that an additional tricritical point is likely to be present in the phase-diagram. Finally, we provide a mean-field calculation that supports the earlier proposed field theory.Comment: Published versio

The Corn and Climate Report

Summarizes research on climate change and its impact on Midwestern agriculture, how to mitigate its effects, and other issues discussed among weather and climate service providers, agribusiness providers, producers, and state advisors at a 2008 workshop

Majorana-assisted nonlocal electron transport through a floating topological superconductor

The nonlocal nature of the fermionic mode spanned by a pair of Majorana bound states in a one-dimensional topological superconductor has inspired many proposals aiming at demonstrating this property in transport. In particular, transport through the mode from a lead attached to the left bound state to a lead attached to the right will result in current cross-correlations. For ideal zero modes on a grounded superconductor, the cross-correlations are however completely suppressed in favor of purely local Andreev reflection. In order to obtain a non-vanishing cross-correlation, previous studies have required the presence of an additional global charging energy. Adding nonlocal terms in the form of a global charging energy to the Hamiltonian when testing the intrinsic nonlocality of the Majorana modes seems to be conceptually troublesome. Here, we show that a floating superconductor allows to observe nonlocal current correlations in the absence of charging energy. We show that the non-interacting and the Coulomb-blockade regime have the same peak conductance $e^2/h$ but different shot-noise power; while the shot noise is sub-Poissonian in the Coulomb-blockade regime in the large bias limit, Poissonian shot noise is generically obtained in the non-interacting case