Tail Dependence among Agricultural Insurance Indices: The Case of Iowa County-Level Rainfalls

Index insurance has been promoted as a cost-effective risk management alternative for agricultural producers in developing countries. In this paper, we ask whether spatially separated weather variables commonly used in index insurance design, such as rainfall at different weather stations within a defined geographical area, are more highly correlated at the tails. As a case study, we assess the degree of tail dependence exhibited by Iowa June county-level rainfalls using copulas. We search among various candidate bivariate copulas and, using goodness-of-fit for copulas, attempt to identify the copula structures that best explain the nature of dependence among rainfalls in adjacent counties. Our results provide strong evidence that lower tail dependence exists in most of adjacent county-level rainfalls in Iowa. The results also suggest that patterns of tail dependence differ across counties.tail dependence, copulas, index insurance, weather indices, Risk and Uncertainty,

Itinerant chiral ferromagnetism in a trapped Rashba spin-orbit coupled Fermi gas

How ferromagnetic phases emerge in itinerant systems is an outstanding problem in quantum magnetism. Here we consider a repulsive two-component Fermi gas confined in a two dimensional isotropic harmonic potential and subject to a large Rashba spin-orbit (SO) coupling, whose single-particle dispersion can be tailored by adjusting the SO coupling strength. We show that the interplay among SO coupling, correlation effects and mean-field repulsion leads to a competition between ferromagnetic and non-magnetic phases. At intermediate interaction strengths, ferromagnetic phase emerges which can be well described by the mean-field Hartree-Fock theory; whereas at strong interaction strengths, a strongly correlated non-magnetic phase is favored due to the beyond-mean-field quantum correlation effects. Furthermore, the ferromagnetic phase of this system possesses a chiral current density induced by the Rashba spin-orbit coupling, whose experimental signature is investigated.Comment: Main text: 5 pages, 6 figures; Supplement: 4 pages, 2 figure